Search

The lettuce downy mildew pathogen, Bremia lactucae, is an obligate oomycete that causes extensive produce losses. Initial chlorotic symptoms that severely reduce the market value of the produce are followed by the appearance of white, downy sporulation on the abaxial side of the leaves. These spores become airborne and disseminate the pathogen. Controlling lettuce downy mildew has relied on repeated fungicide applications to prevent outbreaks. However, in addition to direct economic costs, heterogeneity and rapid adaptation of this pathogen to repeatedly applied fungicides has led to the development of fungicide-insensitivity in the pathogen. We deployed a quantitative PCR assay-based detection method using a species-specific DNA target for B. lactucae coupled with a spore trap system to measure airborne B. lactucae spore loads within three commercial fields that each contained experimental plots, designated EXP1 to EXP3. Based upon these measurements, when the spore load in the air reached a critical level (8.548 sporangia per m3 air), we advised whether or not to apply fungicides on a weekly basis within EXP1 to EXP3. This approach saved three sprays in EXP1, and one spray each in EXP2 and EXP3 without a significant increase in disease incidence. The reduction in fungicide applications to manage downy mildew can decrease lettuce production costs while slowing the development of fungicide resistance in B. lactucae by eliminating unnecessary fungicide applications.

Isolates of the Fusarium oxysporum species complex have been characterized as plant pathogens that commonly cause vascular wilt, stunting, and yellowing of the leaves in a variety of hosts. F. oxysporum species complex isolates have been grouped into formae speciales based on their ability to cause disease on a specific host. F. oxysporum f. sp. fragariae is the causal agent of Fusarium wilt of strawberry and has become a threat to production as fumigation practices have changed in California. F. oxysporum f. sp. fragariae is polyphyletic and limited genetic markers are available for its detection. In this study, next-generation sequencing and comparative genomics were used to identify a unique genetic locus that can detect all of the somatic compatibility groups of F. oxysporum f. sp. fragariae identified in California. This locus was used to develop a TaqMan quantitative polymerase chain reaction assay and an isothermal recombinase polymerase amplification (RPA) assay that have very high sensitivity and specificity for more than 180 different isolates of the pathogen tested. RPA assay results from multiple field samples were validated with pathogenicity tests of recovered isolates.

Verticillium wilt, a disease caused by the fungus Verticillium dahliae, affects a vast range of crops, including strawberries. A field trial was established to evaluate the effect of broccoli in rotation prior to strawberries, anaerobic soil disinfestation (ASD), and mustard cake (MC) alone and in combination at suppressing V. dahliae. Broccoli, cauliflower and fallow plots were established in year 1, followed by strawberry, winter cover crop, and lettuce across all plots over the next two years. ASD and ASD + MC improved strawberry yields compared to the untreated control (UTC). At the end of the harvest season, V. dahliae infection rates in strawberry crowns were lower in the ASD and ASD + MC treatments compared to the UTC. After harvest of the lettuce crop, the number of V. dahliae microsclerotia in soil treated previously with ASD was lower than in the UTC. Broccoli residue incorporation had no effect and MC alone a limited effect on strawberry yields, V. dahliae in strawberry crowns, and soil microsclerotia levels at lettuce harvest. All rotations treated with ASD showed higher total net returns despite the higher cost of treatments. The ability of ASD to control V. dahliae and its persistent suppressive effect on soil microsclerotia levels have important economic implications for growers.

Alternatives to soil fumigation are needed for soil-borne disease control. Our goal was to test anaerobic soil disinfestation (ASD) as an alternative to soil fumigation for control of critical soil-borne pathogens in California strawberry production. Controlled environment experiments were conducted at 25°C and 15°C testing different materials as carbon sources for ASD using soil inoculated with Verticillium dahliae. Field trials were conducted in three locations comparing ASD with 20Mg ha−1 rice bran (RB) against fumigated and untreated controls, steam, mustard seed meal and fish emulsion. In ASD treated soils, temperature and anaerobicity were critical for control of V. dahliae, but multiple carbon inputs reduced inoculum by 80-100%. In field trials, ASD with RB provided control of a number of pathogens, and in three of four trials produced marketable fruit yields equivalent to fumigation. Little weed control benefit from ASD was found. ASD with RB also induced changes in the soil microbiome that persisted through the growing season. When equivalent yields were obtained, net returns above harvest and treatment costs with ASD RB were 92–96% of those with bed fumigation based on average prices over the previous 5 years. ASD can be a viable alternative for control of some soil-borne pathogens. Growers are adopting ASD in CA strawberry production, but research to determine optimal soil temperatures, anaerobicity thresholds and carbon sources for effective control of specific pathogens is needed. This article is protected by copyright. All rights reserved.

Since 1994, a fungal disease has been affecting celery (Apium graveolens) grown for seed in the central coast region of California. White, ectophytic mycelia and conidia, characteristic of a powdery mildew, were present on compound umbels, including the involucre, rays, raylets, flowers, and fruits. Celery with powdery mildew had twisted flower petals, and the disease possibly contributed to premature senescence and drying of the fruits. Powdery mildew was not observed on leaves. Mycelial growth was effused and amphigenous and had lobed appressoria. Conidiophores were straight, and cylindrical foot cells were followed by a longer cell and one or two shorter cells. Conidia were produced singly and were 36 to 44 × 11 to 16 μm. Fibrosin bodies were not observed. Germ tubes were located at the ends of conidia and formed lobed appressoria. Cleistothecia were not present. Based on these characteristics, the fungus was identified as Erysiphe heraclei (1). In California, parsley (Petroselinum crispum) is a host of E. heraclei (4), and parsley is grown in the same region as celery seed crops. To determine if parsley was an alternative host of the celery powdery mildew, infected celery umbels were gently pressed onto adaxial surfaces of leaves on 2-month-old greenhouse grown parsley cvs. Italian Plain and Triple Curled. Inoculated plants were incubated 48 h in a moist chamber at 22°C, then transferrred to a greenhouse at 22 ± 2°C / 16 ± 2°C day/night temperatures, 75% relative humidity, and natural light. After 12 to 14 days, powdery mildew was observed on both parsley cultivars. Uninoculated control plants did not develop the disease. This is the first report of powdery mildew on celery in North America. Previous reports list E. heraclei on celery in Chile, the former Czechoslovakia, France, Iraq, Italy, and the former USSR (Georgia region). In the U.S., E. heraclei is reported on carrot (Daucus carota) (2), parsley (4), meadow parsnip (Zizia aptera and Z. aurea) (3), and now celery. References: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN. (3) K. A. Hirata. Host Range and Geographic Distribution of the Powdery Mildew Fungi. Jpn. Scientif. Soc. Press, Tokyo. (4) S. T. Koike and G. S. Saenz. Plant Dis. 78:1219, 1994.

Three growth stages of each of 20 Sclerotinia minor isolates were tested for resistance to iprodione. Sclerotia and both vegetative and mature mycelium of each isolate were plated on potato-dextrose agar (PDA) amended with 0, 1, 5, 10, 25, and 100 µg of the fungicide per ml, and radial growth was measured. All wild-type field isolates were initially sensitive and did not grow in the presence of iprodione. However, fungicide resistance arose readily in vitro. All 20 isolates produced measurable growth (≥2 mm) on iprodione at 5 µg/ml after 2 weeks when started from mature mycelium, and 18 of 20 isolates produced measurable growth after 4 weeks when started from vegetative mycelium. In general, fungicide-resistant growth arose more frequently and mean colony diameters were significantly greater (P ≤ 0.05) with mature mycelium than with vegetative mycelium at all times and concentrations. In sclerotial germination tests, at least 1% of sclerotia germinated in 18 of 20 isolates after 2 weeks on iprodione at 5 µg/ml, and in 19 of 20 isolates after 5 weeks on 100 µg/ml. Of growth produced on 79 plates containing iprodione, 73 remained viable on PDA after 5 months, and 71 retained resistance to 5 µg/ml. Seventy of these also exhibited cross-resistance to vinclozolin, another dicarboximide fungicide. Pathogenicity of five fungicide-resistant strains was tested in greenhouse, microplot, and field experiments, with and without iprodione. Two months after in vitro production, one of the five resistant strains was avirulent, but disease incidence for the other four ranged from 40 to 75%, compared with 40% for the wild-type isolates. However, the virulence of the fungicide-resistant strains declined over time. Ten months after their production, two of the isolates were avirulent and disease incidence for the others ranged from 3 to 17%, compared with 40 to 90% for the wild-type isolates. The strains that remained virulent 5 and 7 months after in vitro production were not significantly controlled by iprodione sprayed according to labeled rates, although disease was significantly controlled by the fungicide in treatments inoculated with wild-type field isolates (P > 0.05). In experiments in commercial fields to determine the efficacy of fungicide sprays on the wild-type S. minor population, there was no evidence that fungicide resistance was the cause of lack of lettuce drop control observed in many coastal California fields. Application of fungicides at a less than optimal time may account for some incidents of control failure.

Pseudomonas syringae pv. apii, causal agent of bacterial leaf spot (BLS) of celery, was first identified in California in 1989. By 1991, BLS was apparent in all celery-growing areas of the state. Greenhouse-produced transplants were affected most severely, and disease incidence approached 100% in some greenhouses. In this study, sources of inoculum and factors contributing to disease development were investigated in three Salinas Valley greenhouse operations during the 1991, 1992, and 1993 celery transplant seasons (January to August). Epiphytic P. syringae pv. apii was not detected on celery transplants until April or May of each year. Increased epiphytic populations preceded BLS outbreaks, and high-pressure, overhead irrigation favored bacterial infiltration and disease development. In seed-wash assays, P. syringae pv. apii was recovered from 5 of 24 commercial celery seed lots. In field tests, epiphytic P. syringae pv. apii was found on umbels of inoculated celery plants, and seeds from these plants were heavily contaminated with P. syringae pv. apii. Contaminated seed produced seedlings with large epiphytic P. syringae pv. apii populations. Hot-water treatment (50°C for 25 min) eliminated >99.9% of seed contamination. Based on these results, disease management techniques are proposed.

In 1996, commercial plantings of sage (Salvia officinalis) in the Salinas Valley in Monterey County, CA, were affected by a root and crown disease. Roots were necrotic, and crowns and lower stems turned black. Affected plants withered and died. A Phytophthora sp. was consistently isolated from roots and stems of the symptomatic plants. The species was identified as Phytophthora cryptogea based upon the formation of hyphal swellings, morphology of sporangia and oospores, and growth at cardinal temperatures (1). Pathogenicity of representative isolates was confirmed by applying 2 ml of a zoospore suspension (2.0 × 105 zoospores per ml) to roots and crowns of 3-month-old potted sage plants. After treatment, plants were placed for 24 h in shallow trays of water to saturate the root zone, then were removed from trays and incubated in a greenhouse. After 4 days, foliage of all inoculated plants began to wilt. After 7 days, plant crowns and stems turned black and the plants collapsed. P. cryptogea was reisolated and recharacterized from all plants. Control plants, which were treated with water and then handled in the same way as inoculated plants, did not develop any symptoms. The tests were repeated and the results were similar. This is the first report of P. cryptogea attacking commercial plantings of sage. The authors also detected this disease in experimental plantings of sage in Stanislaus County in 1990. Reference: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

In the spring of 1997, commercial plantings of daikon or Chinese radish (Raphanus sativus L. cv. longipinnatus) in the San Joaquin Valley, Fresno County, were damaged by a disease previously undocumented in California. Symptoms consisted of small (2 to 5 mm diameter), circular to oblong, brown to light tan leaf spots that contained concentric rings. Following rains in January, leaf spots proliferated, coalesced, and resulted in significant necrosis of foliage. An Alternaria species with conidia with prominent beaks and spores produced singly or in chains of two was consistently observed on and isolated from the host. Conidia from naturally infected daikon leaves had mean dimensions of 190.1 × 23.1 μm, with a mean beak length of 60.0 μm. The isolates were identified as Alternaria brassicae (2). Pathogenicity was confirmed by culturing six representative isolates on sterilized 20% V8 juice solution for 14 days under a 12 h light/12 h dark cycle, filtering the suspensions through cheesecloth, adjusting spore concentrations to 25,000 conidia per ml, and spraying suspensions onto 4-week-old seedlings of daikon cvs. April and Summer. Plants were incubated in a humid chamber for 48 h and then maintained in a greenhouse. After 5 days, leaf spots similar to the original symptoms developed on all inoculated plants. The pathogen was reisolated and identified as A. brassicae. Control plants sprayed with distilled water remained symptomless. The inoculation test was repeated and results were the same. With the method described above, daikon isolates were also inoculated onto the following A. brassicae hosts (1): radish (Raphanus sativus L. cv. EXCO 517), broccoli (Brassica oleracea L. subsp. botrytis cv. Greenbelt), Chinese cabbage (Brassica campestris L. subsp. pekinensis cv. Cha-Cha), and broccoli raab (Brassica rapa L. subsp. rapa cv. Spring Raab). After 5 (radish) to 12 (other hosts) days, similar leaf spots developed on all inoculated plants and A. brassicae was reisolated and identified. Control plants sprayed with distilled water remained symptomless. These inoculations were repeated and results were the same. For California, this is the first report of black spot caused by A. brassicae on commercially grown daikon. References: (1) S. T. Koike. Plant Dis. 81:552, 1997. (2) E. G. Simmons. Mycotaxon 55:55, 1995.

Gaillardia grandiflora, or blanket flower, is a perennial, herbaceous composite used as an ornamental plant. Following a series of rains in January, 1997, landscape plantings of G. grandiflora in Monterey County, CA, exhibited symptoms of a previously undescribed disease. Affected stems turned gray to tan and became dry and brittle. Large branches often developed cracks. Attached leaves and flowers wilted and turned tan. Infections on the smaller stems and branches sometimes spread to the main stem and crown of the plant, resulting in plant death. White mycelia and large, irregular, black sclerotia (3 to 6 mm in diameter) were occasionally observed on external surfaces of infected stems and crowns. However, the internal pith cavity of diseased stems often contained abundant mycelia and sclerotia. Isolations from symptomatic stems, mycelia, and sclerotia produced colonies of Sclerotinia sclerotiorum. Pathogenicity was confirmed by culturing representative isolates on potato dextrose agar and allowing the fungus to colonize sterilized toothpicks placed on the surface of the agar (1). The pointed tips of the toothpicks were inserted approximately 3 mm deep into stems of potted G. grandiflora cv. Goblin plants, which were incubated in plastic bags for 48 h and then kept in a greenhouse. After 10 to 14 days, symptoms and mycelia similar to those originally observed developed on inoculated plants and S. sclerotiorum was reisolated. Stems on plants left for 21 or more days contained abundant sclerotia. Plants inoculated with sterile, uncolonized toothpicks did not develop disease. This pathogenicity test was repeated and the results were similar. This is the first report of G. grandiflora as a host of S. sclerotiorum. Reference: (1) Y. Yanar et al. Plant Dis. 80:342, 1996.

In 1997, greenhouse-produced transplants of watermelon (Citrullus lanatus) developed water-soaked lesions on leaf petioles and main stems. As disease progressed, petioles and stems became necrotic and shriveled, and exuded a sticky, translucent tan liquid. Symptoms spread to leaves, which wilted and collapsed. Affected transplants eventually died. Although fruiting bodies were not observed on diseased plants, a fungal agent was consistently isolated from symptomatic tissues. When incubated under lights (12 h light/12 h dark cycle), isolates on potato dextrose agar produced numerous pycnidia with hyaline, cylindrical, one-septate conidia with mean dimensions of 5.6 × 2.8 μm. Under the same incubation conditions, isolates on V8 juice agar produced sparse ostiolate pseudothecia with bitunicate asci and hyaline, oval, one-septate ascospores with mean dimensions of 12.0 × 4.0 μm. Based on these characters, the isolates were identified as Didymella bryoniae (anamorph Phoma cucurbitacearum) (1,2). Pathogenicity was tested by producing conidial inocula of representative isolates and inoculating wounded cotyledons, true leaves, and petioles of watermelon (cv. Sangria), and wounded true leaves and petioles of cucumber (Cucumis sativus cv. Premier Hybrid) (3). Sterile, distilled water was applied to corresponding wounded tissues of control plants. All plants were kept in a humid chamber for 4 days. After 6 (watermelon) to 10 (cucumber) days, inoculated plants exhibited water-soaked lesions followed by necrosis, petiole and leaf wilting, and shriveling of tissues. Pycnidia were observed on cucumber plants after 18 days. The pathogen was reisolated from all inoculated plants and identified as D. bryoniae. Control plants developed no disease symptoms. In addition, agar plugs colonized with the watermelon isolates were placed onto cucumber fruit that were wounded slightly with a sterile scalpel. Fruit were incubated at 22 to 24°C in humid chambers and after 2 days sunken, circular lesions developed. The same pathogen was reisolated from the margins of fruit lesions. Wounded control fruit received sterile agar plugs and did not develop any symptoms. This is the first documentation of gummy stem blight on watermelon transplants in California. References: (1) W. F. Chiu and J. C. Walker. J. Agric. Res. 78:81, 1949. (2) A. P. Keinath et al. Phytopathology 85:364, 1995. (3) A. J. Wyszogrodzka et al. Euphytica 35:603, 1986.

In 1997, greenhouse-produced transplants of tomato (Lycopersicon esculentum) exhibited stunting, yellowing of leaves, and lack of vigorous growth. Roots of affected plants had numerous small (2 to 10 mm long), brown lesions. Isolations from symptomatic roots onto acidified potato dextrose agar and TBM-V8 medium (1) consistently resulted in gray fungal colonies that formed catenulate, cylindrical, hyaline endoconidia and catenulate, subrectangular, thick-walled, dark aleuriospores. The fungus was identified as Thielaviopsis basicola (Berk. & Broome) Ferraris based on colony characteristics and conidial morphology. Pathogenicity was tested by producing endoconidial suspensions of representative isolates and applying them as root drenches to 2-month-old tomato (cv. Early Girl) plants in soil-less, peat-based potting mix. Sterile, distilled water was applied to control plants. After 14 days in a greenhouse, symptoms similar to those originally observed developed and the pathogen was reisolated from lesions on the roots. Control plants developed no disease symptoms. The test was repeated and the results were similar. This is the first documentation of black root rot caused by T. basicola on tomato transplants in California. Disease incidence reached as high as 50 to 60% in certain plantings. Reference: (1) J. N. C. Maduewesi et al. Phytopathology 66:526, 1976.

A foliar disease of commercially grown radicchio (Cichorium intybus) was observed in 1996 and 1997 in the Salinas Valley (Monterey County), California. Symptoms consisted of circular to oblong, necrotic spots ranging in diameter from 3 to 20 mm and having concentric zones of darker tissue. A fungus identified as Alternaria cichorii Nattrass (1) was observed fruiting on the spots and was consistently isolated from the margins of the spots. Conidia from leaves were obclavate in shape with slender, unbranched beaks extending from the narrow end of the spore body. Spore body dimensions measured 56 to 78 × 14 to 20 μm, and beaks measured 36 to 81 × 1 to 2 μm. Spore bodies had 7 to 9 transverse septa. Often there were no longitudinal septa, but occasionally there were 1 or 2 such septa. For pathogenicity tests, five isolates were grown for 4 weeks on potato dextrose agar under a combination of cool white and Vita-Lite fluorescent tubes on a 12 h light/dark cycle. Conidial suspensions (4.0 × 104 conidia per ml) were sprayed onto 8-week-old radicchio (cv. Rossana Rogers). Plants were incubated in a moist chamber for 48 h and then maintained in a greenhouse. After 12 days, leaf spots similar to the original symptoms developed on all plants inoculated with the five isolates, and the pathogen was reisolated. Control plants sprayed with distilled water remained symptomless. The experiment was repeated and the results were similar. When inoculated onto endive (Cichorium endivia cv. Tres Fine Maraicchere) and two lettuce (Lactuca sativa) cultivars, the isolates caused small (1 to 2 mm in diameter), necrotic, circular leaf spots on endive and Romaine lettuce cv. Green Towers, but did not cause symptoms on the iceberg lettuce cv. Alpha. This is the first report of A. cichorii on commercially grown radicchio in California. In addition, the same disease was confirmed on commercially produced greenhouse transplants of radicchio, indicating that primary inoculum can possibly be seed-borne. Reference: (1) J. C. David. Mycopathologia 129:41, 1995.

Over the past 5 years, commercial acreage of the leafy crucifer arugula (Eruca sativa) has increased greatly in the Salinas Valley (Monterey County), California, and the crop is an important component in packaged salad products. A foliar disease has affected this crop and at times reduced its quality to the extent that it could not be harvested. Symptoms consisted of small (1 to 4 mm in diameter), irregular, dark brown to black speckling on adaxial leaf surfaces. Speckling sometimes expanded into tan spots 3 to 8 mm in diameter. Corresponding abaxial surfaces usually supported white fungal growth typical of a downy mildew. Conidiophores had main trunks with dichotomous branches ending in slender curved tips. Conidia were ovoid in shape, measuring 22 to 25 μm long and 19 μm wide. The fungus was identified as Peronospora parasitica. Pathogenicity was established by gently pressing diseased leaves onto arugula test plants and incubating plants in a humidity chamber for 48 h. Downy mildew developed after 6 days and the same fungus was observed. Although this disease has occurred on this crop for several years, this is the first documentation of P. parasitica on arugula in California. A previously described foliar bacterial disease caused by Pseudomonas syringae (1) has similar symptoms, making field diagnoses difficult if fungal signs of the downy mildew are not present on the leaf. Reference: (1) S. T. Koike et al. Plant Dis. 80:464. 1996.

In 1997, commercially grown bell pepper in the Salinas Valley (Monterey County), California, developed a previously undescribed disease. Plant foliage became pale green and wilted. Crowns developed brown lesions that girdled the plants, resulting in plant death. White mycelia and small (2 to 3 mm), black, irregularly shaped sclerotia were observed on the outside of plant crowns and in the centers of stem cavities. Isolations consistently resulted in the recovery of Sclerotinia minor. Pathogenicity was tested by inoculating 2-month-old bell pepper plants (cv. California Wonder) with sclerotia from three pepper and three lettuce (Lactuca sativa) isolates of S. minor (seven plants per isolate). Six to 10 sclerotia were placed 1 cm below the soil line and adjacent to the plant crowns. After 8 days, plants inoculated with pepper and lettuce isolates developed symptoms similar to those found in commercial fields, and S. minor was recovered from all peppers. The uninoculated control plants developed no symptoms. This is the first report of bell pepper as a host of S. minor.

Bacterial blight is a new disease of broccoli raab or rappini (Brassica rapa subsp. rapa) that has developed on commercially grown crops in the Salinas Valley (Monterey County) in California. Symptoms consist of small, angular, water-soaked flecks on lower foliage that are visible from both adaxial and abaxial sides of the leaves. These flecks expand and become surrounded by bright yellow borders. With time, multiple leaf spots coalesce and result in large, irregular necrotic areas, extensive leaf yellowing, and eventual leaf death. If symptoms develop on the uppermost leaves attached to the inflorescence, the shoot loses market quality and will not be harvested. Pseudomonas syringae was consistently isolated from symptomatic plants, and selected strains caused similar symptoms when inoculated onto broccoli raab test plants. Broccoli raab strains caused leaf spot symptoms on nine other Cruciferous plants, as well as on three grass species (California brome, oat, and common timothy). Conversely, broccoli raab was not infected by P. syringae pathovars coronafaciens, maculicola, and tomato. Broccoli raab strains were positive for coronatine toxin production. Fatty acid analyses indicated that the P. syringae from broccoli raab was most closely related to P. syringae pvs. coronafaciens and maculicola, but its distinct host range suggests that it may be considered a separate pathovar.

In 1997, a foliar disease was detected on leek (Allium porrum) grown as transplants in California greenhouses. Initial symptoms consisted of small (less than 5 mm in diameter), circular, white leaf spots. Spots later enlarged, and became elliptical to oblong in shape and purple with tan borders in color. When spots coalesced, the leaf tips desiccated and wilted. Singly borne, brown conidia from leaves were obclavate in shape with slender, unbranched beaks extending from the narrow end of the spore body. Spore body dimensions measured 81 to 120 (96 mean) µm × 14 to 19 (16 mean) µm, and beaks measured 11 to 56 (30 mean) µm × 3 to 6 (4 mean) µm. Spore bodies had 6 to 9 transverse septa and occasionally 1 longitudinal septum. The fungus was identified as Alternaria porri (Ellis) Cif. (1). The same fungus was also consistently isolated from the margins of the spots. For pathogenicity tests, isolates were grown for 6 weeks on potato dextrose agar under a combination of one cool white and one Vita-Lite fluorescent tube on a 12 h light/dark cycle. Conidial suspensions (1.0 × 10 e 4 conidia/ml) were sprayed onto 2-month-old leek (cvs. Broad London and Gavilan). Plants were incubated in a moist chamber for 48 h and then kept in a greenhouse. After 14 days, leaf spots similar to the original symptoms developed on inoculated plants, and the pathogen was reisolated. Control plants sprayed with distilled water remained symptomless. The experiment was repeated and the results were similar. The isolates also caused leaf spots on onion (Allium cepa cv. Stockton Early Yellow) and chives (Allium schoenoprasum). This is the first report of purple blotch caused by A. porri on commercially grown leeks in California. The occurrence of this disease on leeks in enclosed greenhouses strongly suggested that the primary inoculum was seed-borne. Reference: (1) M. B. Ellis and P. Holliday. C.M.I. Descriptions No. 248, 1970.

In December 1996 and January 1997, powdery mildew was observed on potted poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants in Monterey County, CA. Mycelia were observed on stems, petioles, mature and immature leaves, and bracts. Severely diseased leaves became twisted and bent and senesced prematurely. The white mycelia were conspicuous, epiphytic, and amphigenous; hyphae measured 4.6 to 6.9 μm in diameter. Growth initially was in patches but eventually became effused. Appressoria were slightly lobed to lobed and sometimes opposite. Conidiophore foot cells were cylindrical, sometimes bent at the base, and slightly flexuous to flexuous. Foot cells measured 30.0 to 46.2 μm × 5.8 to 6.9 μm and were followed by one to two shorter cells. Conidia were cylindrical to slightly doliform and measured 25.4 to 32.3 μm × 11.6 to 18.5 μm. The length-to-width ratios of conidia generally were greater than 2.0. Conidia were produced singly, placing the fungus in the Pseudoidium-type powdery mildew group. Conidia germinated at the ends, and no fibrosin bodies were observed. Cleistothecia were not found. The fungus was identified as an Oidium species. Pathogenicity was demonstrated by gently pressing infected leaves having abundant sporulation onto leaves of potted poinsettia plants (cvs. Freedom Red, Peter Star Marble, and Nutcracker White), incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 12 to 14 days, powdery mildew colonies developed on the inoculated plants, and the pathogen was morphologically identical to the original isolates. Uninoculated control plants did not develop powdery mildew. This is the first report of powdery mildew on poinsettia in California. This fungus appears similar to Microsphaera euphorbiae but has longer, slightly flexuous foot cells that do not match the description for M. euphorbiae (1,2). An alternative identification would be Erysiphe euphorbiae; however, there are no available mitosporic descriptions for morphological comparisons (1,2). In the United States, powdery mildew of poinsettia previously has been reported in various states in the Pacific Northwest, Midwest, and Northeast. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

In 1997 and 1998, the white fungal growth of a powdery mildew was observed on leaves and stems of both nursery and landscape spearmint (Mentha spicata) growing in coastal California (Monterey County). Mycelia were conspicuous, amphigenous, and epiphytic with indistinct to nipple-shaped appressoria. Conidiophore foot cells were cylindrical, straight, nonconstricted at the base, 61 to 92 μm × 11 to 14 μm in size, and were followed by 1 to 3 cells. Doliiform conidia, which were borne in chains of at least 3 to 5 conidia, measured 28 to 33 μm × 17 to 22 μm. Catenate conidia had sinuate edge lines. Conidia lacked fibrosin bodies. Upon germination, conidia produced germ tubes that were mostly apically inserted and ended in club-shaped appressoria, which fit Braun's Cichoracearum-type of conidial germination (1). Cleistothecia were not observed. Based on these features, the pathogen was identified as Erysiphe orontii Cast. (1). Pathogenicity was demonstrated by gently pressing diseased leaves onto leaves of potted spearmint, incubating plants in a humidity chamber for 48 h, then maintaining plants in a greenhouse. The powdery mildew that later developed was morphologically identical to the original isolates. While powdery mildew on spearmint has been observed previously in the state, this is the first report of the disease and first characterization of the pathogen for California. Reference: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987.

In recent years a disease causing dieback and necrosis of Romaine and leaf lettuce has become increasingly important in California and incidence is becoming more widespread. This disease has been primarily found in areas where soil has been dredged from a river or in flooded land. Tomato bushy stunt virus (TBSV) isolates have been isolated from roots and leaves of symptomatic lettuce. The particles are isometric with a diameter of 30 nm. Double-stranded RNA (dsRNA) profiles are identical to the tomato and Prunus isolates of TBSV. However, spurs are formed in agar double diffusion tests when antisera to the tomato and Prunus isolates were used. A similar dieback disease of lettuce was observed in several counties of California during the mid-1980s. Symptoms of this disease are very similar to those described for the “brown blight” disease of lettuce reported in the 1920s (1), including severe stunting of plants and extensive chlorosis, mottling, and necrosis of older leaves. Plants infected early in their development may die. Although inoculation under greenhouse conditions has not reproduced the dieback disease in lettuce, TBSV has been consistently isolated from field-grown, symptomatic lettuce. The question of whether this new dieback disease of lettuce is caused only by lettuce isolates of TBSV or if some other viruses are also involved needs further studies. Reference: (1) I. C. Jagger. Phytopathology 30:53, 1940.

Saponaria (Saponaria vaccaria [= Vaccaria hispanica]) is a Caryophyllaceae plant that is grown commercially in California as a cut flower. In 1998, a leaf spot disease devastated the commercially grown saponaria in coastal California. The entire saponaria crop was completely unmarketable because of extensive leaf spotting. Symptoms consisted of circular, brown, necrotic leaf spots with diameters up to 8 mm and concentric zones of lighter and darker tissue. Chlorotic borders developed around the spots. Conidia from leaves were obclavate, usually had 7 transverse and 1 to 4 longitudinal septa, and narrowed gradually toward the apex into a blunt-tipped, unbranched beak cell. The spore body measured 69 to 90 (to 119) × 17 to 21 (to 25) μm, with the distinctive beak cell 17 to 53 μm long. Conidia formed short chains on host tissue. The fungus was identified as Alternaria saponariae (Peck) Neergaard (2). For pathogenicity tests, six representative isolates were grown on V8 juice agar under fluorescent tube lighting. Potted saponaria were sprayed with either conidial concentrations (1 × 10e5 conidia per ml) or water. Plants were incubated in a chamber with a humidifier for 48 h and then maintained in a greenhouse (23 to 25°C). After 14 days, leaf spots similar to the original symptoms developed on all inoculated plants, and the pathogen was reisolated. Plants sprayed with water were symptomless. The experiment was repeated and the results were similar. Using the same isolates and method, we inoculated carnation (Dianthus caryophyllus), sweet William (Dianthus barbatus), and saponaria. However, disease developed only on saponaria. While A. saponariae on saponaria was reported previously in California (1), this is the first report to characterize the pathogen and document that isolates are pathogenic on saponaria but not on other commercial Caryophyllaceae hosts. References: (1) K. F. Baker and L. H. Davis. Plant Dis. Rep. 34:403, 1950. (2) P. Neergaard. Aarsberet. J. E. Ohlsens Enkes Plantepat. Lab. No. 3, 1938.

Endive (Cichorium endivia) and escarole (broad-leaf type of C. endivia) are two of the many leafy vegetables produced commercially in coastal California. For several years, both crops have been affected by a disease that causes soft, watery, brown leaf decay. In the tightly appressed heads of endive and escarole plants, decay generally spreads in a concentric circle, resulting in circular whorls of brown, rotted leaves within diseased heads. Such symptoms make the heads unmarketable. In the Salinas Valley (Monterey County), the disease was much more prevalent during 1998, when weather was affected by “El Niño.” Rhizoctonia solani was isolated consistently from symptomatic leaves of both endive and escarole. Pathogenicity was tested by placing two agar plugs of representative isolates inside the leaf whorls of 15 potted plants each of endive (cv. Tres Fine Maraicchere) and escarole (cv. Full Heart). Watery, brown leaf decay, similar to symptoms observed in the field, occurred on all plants within 7 days after inoculation, and R. solani was reisolated. Control plants, treated with sterile agar plugs, did not develop disease. Tests were repeated, and results were similar. Anastomosis-group testing revealed that four endive isolates belonged to AG2-2 (1). This appears to be the first report of leaf blight of endive and escarole caused by R. solani in California. Reference: (1) Sneh et al. 1991. Identification of Rhizoctonia Species. The American Phytopathological Society, St. Paul, MN.

In California, arugula (Eruca sativa) is grown commercially as a component of specialty mixed green salads. In 1999, white rust was observed on arugula in the central coast county of Santa Barbara. Symptoms consisted of white, blisterlike sori beneath the raised host epidermis on the underside of leaves from the seedling stage onward. Secondary infection of flower heads led to staghead development. Affected plantings were severely diseased and were not harvested. The pathogen was confirmed to be Albugo candida (Pers.) Kunze (2). Sporangia diameters ranged from 19.5 to 22.2 μm. Inoculum for pathogenicity tests was prepared by scraping sporangia from infected leaves and incubating them in sterile, distilled water for 12 h at 5°C to induce zoospore formation (1). The following plants were then spray inoculated: arugula, cauliflower (Brassica oleracea subsp. botrytis), Chinese cabbage (Brassica campestris subsp. pekinensis), Japanese mustard (Brassica campestris subsp. nipposinica), red mustard (Brassica juncea subsp. rugosa), and tah tsai (Brassica campestris subsp. narinosa). Twelve plants of each species were inoculated with 1.5 × 104 spores per ml at the six- to eight-leaf stage. Plants were incubated in a dew chamber for 48 h at 18°C and then maintained in a greenhouse at 20 to 24°C. After 10 to 12 days, white rust pustules similar to the original symptoms observed in the field developed only on arugula. The experiment was conducted three times and the results were the same. Distinct biological races of A. candida have been described for some Brassicaceae hosts of white rust (1). This is the first report of white rust of arugula in California caused by A. candida. References: (1) R. S. Pidskalny and S. R. Rimmer. Can. J. Plant Pathol. 7:283, 1985. (2) G. S. Pound and P. H. Williams. Phytopathology 53:1146, 1963.

In 1998 and 1999, a new disease was detected in commercial broccoli (Brassica oleracea var. botrytis) grown in the Salinas Valley, Monterey County, CA. Initial symptoms consisted of large, water-soaked, dark green, angular leaf sections that were bordered by major leaf veins. Diseased areas were as large as 10 × 3 cm. As the disease developed, affected areas turned tan and papery, and leaf margins sometimes became tattered. The numerous small (6 CFU/ml, and misted onto broccoli (cvs. Patriot and Titleist) and broccoli raab (B. rapa subsp. rapa cv. Spring). Control plants were misted with sterile nutrient broth. After 4 to 5 days in a greenhouse (24 to 26°C), large angular leaf lesions developed on all inoculated broccoli and broccoli raab plants. Strains were reisolated from symptomatic tissue and identified as P. syringae. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. Unlike most P. syringae strains, those isolated from broccoli were sensitive to a bacteriophage recovered from a P. syringae pathovar that infects broccoli raab. These results suggest that the broccoli pathogen may be related to the bacterial blight pathogen of broccoli raab (1). This is the first report of this pathogen causing a disease on commercially grown broccoli. Reference: (1) S. T. Koike et al. Plant Dis. 82:727, 1998.

During the spring and fall of 1999, commercial plantings of the cut flower stock (Matthiola incana) in coastal regions of California developed a severe foliar disease. Abaxial leaf surfaces supported the extensive white fungal growth typical of a downy mildew. Adaxial surfaces of newly infected leaves did not show symptoms, but with time, leaves exhibited extensive, diffuse chlorotic areas and slight twisting. Infected plants were not acceptable for the cut flower market and, therefore, were not harvested. Sporangiophores had main trunks with dichotomous branches ending in slender curved tips that were 2.8 μm long. Sporangia were ovoid, measuring 22 to 25 μm long and 19 to 22 μm wide. The fungus was identified as Peronospora parasitica. Pathogenicity was established by gently pressing diseased leaves onto stock plants (cv. Avalanche), incubating plants in a humidity chamber (20 to 22°C, 100% relative humidity) for 48 h, and keeping plants in a greenhouse. Diffuse chlorotic leaf symptoms developed after 10 days, and the same fungus later developed on abaxial surfaces. Uninoculated plants did not develop downy mildew. Inoculations were conducted a second time, and the results were the same. This is the first documentation of P. parasitica on stock in California.

Chervil (Anthriscus cerefolium) is a culinary herb grown commercially in California. In 1999, chervil plantings in shade houses in coastal California exhibited symptoms of a previously undescribed disease. Tan to gray lesions, surrounded by pinkish tissue, developed on crowns and lower sections of stems. Affected stems wilted, and plants eventually collapsed and rotted. More than 50% of the plants in the early spring planting were diseased. White mycelium and large, irregular, black sclerotia (3 to 6 mm diameter) were observed on infected stems and crowns. Isolations from symptomatic stems, mycelium, and sclerotia produced colonies of Sclerotinia sclerotiorum. Following previously described methods (2), pathogenicity was confirmed by culturing isolates on potato dextrose agar and allowing the fungus to colonize sterilized toothpicks placed on the surface of the agar. The pointed toothpick tips were inserted ≈3 mm deep in stems of potted chervil. Sterile toothpicks were inserted in control chervil plants. All plants were incubated in a mist chamber for 48 h and then kept in a greenhouse. Two other hosts of S. sclerotiorum, cauliflower (Brassica oleracea var. botrytis cv. White Rock) and celery (Apium graveolens cv. Conquistador)were inoculated in the same way. After 7 to 10 days, symptoms and mycelium similar to those originally observed developed on inoculated chervil plants, and S. sclerotiorum was reisolated. Plants left for 14 or more days supported sclerotia. Chervil inoculated with sterile, uncolonized toothpicks did not develop symptoms. Results were similar for cauliflower and celery plants. Pathogenicity tests were repeated, and the results were similar. A separate set of chervil was inoculated by placing sclerotia at the base of plants; these plants also developed disease but at a much lower incidence ( References: (1) M. J. Hims. Plant Pathol. 28:197, 1979. (2) S. T. Koike. Plant Dis. 81:1334, 1997.

Bacterial leaf spot of lettuce (BLS), caused by Xanthomonas campestris pv. vitians, has increased in importance in California over the past 5 years. The pathogen can be seedborne, but it was not recovered from selected commercial lettuce seed lots planted during this time. Survival of X. campestris pv. vitians in association with plant debris was investigated in a 3-year field experiment in Salinas, CA. The initial lettuce spring crop was spray inoculated with X. campestris pv. vitians, which resulted in 100% disease incidence. Spring crops were followed by a 1-month summer fallow period, whereas fall crops were followed by a 5-month winter fallow period. High populations of X. campestris pv. vitians (up to 106CFU/g) were recovered from lettuce plant debris after the 1-month summer fallow and BLS developed on all subsequent fall lettuce crops. During the winter fallow period, X. campestris pv. vitians populations associated with plant debris declined and, by 2 months after harvest, only small populations were detected. Spring crops also developed BLS, but at reduced levels. X. campestris pv. vitians was recovered from leaves of several symptomless weed species collected around commercial infested fields, but not from weeds collected around previously infested fields during fallow periods. During the course of this study, an X. campestris pv. vitians-specific polymerase chain reaction primer pair was developed.

Beginning in 1997, a new disease of spinach was found in the Salinas Valley, Monterey County, CA. Initial symptoms were leaf spots that were 2 to 5 mm in diameter, circular, and gray-green in color. Spots later enlarged, turned tan in color, and became dry and papery in texture, resembling phytotoxicity due to agrichemicals. Although fungal signs were generally absent from the spots, Stemphylium botryosum was consistently isolated and caused identical symptoms when inoculated onto 20 spinach cultivars. Three isolates did not cause disease symptoms when inoculated onto other crop plants representing 16 different genera and a Chenopodium weed species. A fourth isolate showed similar results with the exception of small leaf spots occurring on inoculated fava bean. Isolates produced a Pleospora herbarum teleomorph after 7 months incubation at 5°C. Preliminary experiments with cell-free culture filtrates indicated that phytotoxins apparently were not produced by these isolates. This is the first report of a foliar spinach disease caused by S. botryosum.

In 2000, a foliar disease was observed in commercial field plantings of dill (Anethum graveolens) in coastal California. Initial symptoms consisted of a gray-green discoloration and wilting of the tips of dill leaves. As disease developed, many of the leaves discolored and collapsed, which gave the foliage a blighted appearance and made the leaves unsuitable for harvest. A fungus was consistently isolated from symptomatic leaves. Slow growing colonies were cream-colored, velutinous, and flat with minimal aerial mycelium. Mycelium was hyaline and had clamp connections. Ovoid to subglobose sporogenous cells were abundant and measured 11 to 14 × 12 to 16 μm. Spores were ballistospores that were bilaterally symmetrical, lunate, 16 to 18 × 12 to 13 μm, and germinated with hyphae or secondary ballistospores. The fungus was identified as Itersonilia perplexans Derx (1,2). Pathogenicity was tested by preparing spore suspensions (1 × 104) and spray-inoculating potted dill plants. Plants were placed in a dew chamber for 24 h and then maintained in a greenhouse (23 to 25°C). After 10 days, leaves showed symptoms similar to those observed in the field and the same fungus was reisolated. Control plants sprayed with water did not develop symptoms. Inoculations were repeated and the results were the same. In another experiment, sets of dill plants and flowers of five cultivars of potted florist's chrysanthemum (Dendranthema × grandiflorum [= Chrysanthemum × morifolium]) and one cultivar of Leucanthemum paludosum (= C. paludosum) were spray-inoculated with several dill isolates and incubated as described previously. Dill plants developed symptoms and the fungus was reisolated. However, flowers of the six chrysanthemum cultivars did not develop any petal blight symptoms. Inoculations were repeated and the results were the same. These findings are consistent with previous studies that indicate I. perplexans consists of pathogenic forms that are host-specific to either chrysanthemum and closely related Compositae or to Apiaceae plants such as dill, carrot (Daucus carota subsp. sativus), parsley (Petroselinum crispum), and parsnip (Pastinaca sativa) (1,2,3). To our knowledge, this is the first report of I. perplexans on dill in California, and also appears to be the first record of this disease in North America. References: (1) T. Boekhout. Mycol. Res. 95:135, 1991. (2) T. Boekhout et al. Can. J. Microbiol. 37:188, 1991. (3) A. G. Channon. Ann. Appl. Biol. 51:1, 1963.

In California, Digitalis purpurea (common foxglove) and D. grandiflora (yellow foxglove) are grown as cutflower, potted, and landscape plant commodities. In the spring of 2002, after seasonably wet and cool weather, severe downy mildew was observed on potted common foxglove plants in commercial nurseries in coastal California (Santa Cruz County). Initial symptoms on leaves consisted of light green, rectangular areas that were vein-delimited and measured 2 to 5 × 8 to 12 mm. Such spots later became chlorotic. As disease progressed, chlorotic spots coalesced and turned necrotic. The purple-gray sporulation of the pathogen could be seen primarily on abaxial leaf surfaces. However, in some cases, extensive fungal growth developed on adaxial surfaces of lower leaves. Conidiophores branched dichotomously and measured 278 to 520 μm long from the lower end to the first branches and 11 to 14 μm across at the widest part of the swollen base. Branch ends were slender with curved tips that measured 11 to 22 μm long. Conidia were hyaline, ellipsoid to ovoid, and measured 22 to 31 μm × 17 to 19 μm. Oospores were not observed. The pathogen was identified as Peronospora digitalidis (1,2). Pathogenicity tests were not conducted. However, the consistent association of sporulation with symptoms, the internal hyphal growth giving rise to conidiophores, and the obligate nature of Peronospora pathogens clearly indicated that P. digitalidis was the causal agent of this disease. Field observations indicated that D. purpurea cvs. Alba and Apricot and Foxy hybrids were very susceptible, D. × mertonensis ( = D. grandiflora × D. purpurea) appeared to be moderately susceptible, and D. grandiflora grown in the same area was symptomless. One planting of Foxy hybrid was 100% infected, and the entire lot of several hundred plants was discarded. The disease also was found on Foxy hybrid seedlings grown in propagation greenhouses. To our knowledge, this is the first report of downy mildew caused by P. digitalidis on cultivars of D. purpurea in California and the United States. This disease has been reported previously in Europe, Asia, and New Zealand (1,2). References: (1) G. Hall. Mycopathologia 126:47, 1994. (2) E. H. C. McKenzie and J. M. Dingley. N. Z. J. Bot. 34:263, 1996.

The etiology of three foliar bacterial diseases of crucifers and the relationships between their causal agents were evaluated. Data from LOPAT, carbon utilization tests, and fatty acid analysis indicated that bacterial blights of broccoli and broccoli raab, and leaf spot of broccolini, were caused by strains of Pseudomonas syringae. Data from phage sensitivity, ice nucleation, single carbon source utilization, Polymerase chain reaction using BOXA1R primer (BOX-PCR), and host range analyses were identical for the pathogen causing leaf spot of broccolini and P. syringae pv. maculicola. The broccoli raab and broccoli pathogens infected broccoli raab, all crucifers tested, tomato, and three monocots (California brome, oat, and common timothy). None of the other pathogens tested (P. syringae pv. maculicola, P. syringae pv. tomato, or P. syringae pv. coronafaciens) caused disease on broccoli raab or on both crucifers and monocots. Data from phage sensitivity, ice nucleation, single carbon source utilization, BOX-PCR, and host range analyses were identical for the pathogens from broccoli raab and broccoli, but were different from other pathovars tested, and supported the hypothesis that a new pathovar of P. syringae pv. alisalensis pv. nov. caused a leaf blight on broccoli and broccoli raab.

Phytophthora ramorum S. Werres & A.W.A.M. de Cock was isolated from discolored leaves and cankers on small branches ( References: (1) D. M. Rizzo et al. Plant Dis. 86:205, 2002. (2) S. Werres et al. Mycol. Res. 105:1155, 2001.

Bells-of-Ireland (Moluccella laevis) (Lamiaceae) is an annual plant that is field planted in coastal California (Santa Cruz County) for commercial cutflower production. In 2001, a new leaf spot disease was found in these commercially grown cutflowers. The disease was most serious in the winter-grown crops in 2001 and 2002, with a few plantings having as much as 100% disease incidence. All other plantings that were surveyed during this time had at least 50% disease. Initial symptoms consisted of gray-green leaf spots. Spots were generally oval in shape, often delimited by the major leaf veins, and later turned tan. Lesions were apparent on both adaxial and abaxial sides of the leaves. A cercosporoid fungus having fasciculate conidiophores, which formed primarily on the abaxial leaf surface, was consistently associated with the spots. Based on morphology and its host, this fungus was initially considered to be Cercospora molucellae Bremer & Petr., which was previously reported on leaves of M. laevis in Turkey (1). However, sequence data obtained from the internal transcribed spacer region (ITS1, ITS2) and the 5.8S gene (STE-U 5110, 5111; GenBank Accession Nos. AY156918 and AY156919) indicated there were no base pair differences between the bells-of-Ireland isolates from California, our own reference isolates of C. apii, as well as GenBank sequences deposited as C. apii. Based on these data, the fungus was subsequently identified as C. apii sensu lato. Pathogenicity was confirmed by spraying a conidial suspension (1.0 × 105 conidia/ml) on leaves of potted bells-of-Ireland plants, incubating the plants in a dew chamber for 24 h, and maintaining them in a greenhouse (23 to 25°C). After 2 weeks, all inoculated plants developed leaf spots that were identical to those observed in the field. C. apii was again associated with all leaf spots. Control plants, which were treated with water, did not develop any symptoms. The test was repeated and the results were similar. To our knowledge this is the first report of C. apii as a pathogen of bells-of-Ireland in California. Reference: (1) C. Chupp. A Monograph of the Fungus Genus Cercospora. Cornell University Press, Ithaca, New York, 1954.

Lettuce downy mildew, caused by Bremia lactucae, is the most important foliar disease of lettuce in California. In recent years, there were apparent failures of fungicides containing fosetyl-aluminum (Aliette) to control downy mildew in commercial lettuce fields in California. Consequently, we characterized 134 isolates collected over 2 years from throughout the coastal growing areas of California for insensitivity to the fungicides fosetyl-aluminum and maneb, pathotype, and mating type. Tests using seedlings in controlled growth room conditions demonstrated the widespread occurrence of insensitivity to fosetyl-aluminum in California populations of B. lactucae. Fifty percent of the isolates assayed sporulated profusely in the presence of fosetyl-aluminum applied at rates twice the normal field dosage, and an additional 40% showed moderate sporulation at this rate. Fosetyl-aluminum-insensitive isolates were detected from all regions sampled. Insensitivity was also observed in multiple pathotypes. Insensitivity was not complete, however, because quantitative analysis of the number of lesions on older plants revealed that applications of fosetyl-aluminum could reduce the levels of disease by 50%. Therefore, while fosetyl-aluminum may have utility under low disease pressure in the field, other control measures are required to provide control under conditions favorable to the disease.

A new wilt and root rot disease was observed in 6 and 11 commercial fields of lettuce (Lactuca sativa) in western Arizona during the fall of 2001 and 2002, respectively. Distance between infested sites ranged from approximately 0.5 to 39 km. Five head lettuce cultivars as well as a red leaf lettuce cultivar were affected. Disease symptoms included yellowing and wilting of leaves, as well as stunting and plant death. The cortex of the crown and upper root of infected plants usually was decayed and reddish brown. Disease symptoms first appeared at the time of plant thinning and continued to develop up to plant maturity. Fusarium oxysporum was consistently isolated from symptomatic plant roots. Seeds of cv. Lighthouse were planted in nonsterile vermiculite within 3.0-cm-square × 7.0-cm-deep cells in a transplant tray and thinned to a single plant per cell. When the first true leaves were emerging, 10 individual seedlings were inoculated with a single-spore isolate of F. oxysporum recovered from diseased lettuce root cortex tissue. Inoculum was prepared by growing the fungus on potato dextrose agar in 100-mm-diameter × 15-mm-deep plastic petri dishes at 28°C with a 12-h photoperiod under fluorescent light. Once the fungus completely covered the agar surface, 50 ml of sterile distilled water was added to the dish, and the mycelia and conidia on the surface were scraped off the agar and suspended in the water. This fungal suspension was decanted, and a 2-ml aliquot containing 1.8 × 105 CFU was pipetted into the vermiculite near the stem of each lettuce seedling. Ten plants grown in noninfested vermiculite served as uninoculated controls. After inoculation, plants were maintained in a growth chamber at 28°C with a 12-h photoperiod under fluorescent light for 3 weeks. Symptoms of yellowing, wilt, vascular decay, and often plant death developed during the incubation period on all inoculated plants but not on control plants. Fusarium oxysporum was consistently reisolated from inoculated plants but not from uninoculated plants. The experiment was repeated and yielded the same results. A wilt and root rot disease of lettuce attributed to F. oxysporum f. sp. lactucae was first reported in Japan in 1967 (3) and subsequently in the United States (San Joaquin Valley of California) in 1993 (2), and Italy in 2002 (1). The researchers of the U.S. report did not cite the earlier work from Japan and described the pathogen as F. oxysporum f. sp. lactucum. The Arizona isolate used to demonstrate pathogenicity was of the same vegetative compatibility group as an isolate of the pathogen from lettuce in California reported in 1993. Several companies grow and harvest lettuce in Arizona and California. At the end of production and harvest in the fall, tractors, implements, and harvesting equipment are transported from the San Joaquin Valley in California to western Arizona. The similarity between the isolate of F. oxysporum f. sp. lactucae from western Arizona and the San Joaquin Valley of California suggest a possible introduction of the pathogen into Arizona from California, perhaps on soil adhering to farm equipment. To our knowledge, this is the first report of F. oxysporum f. sp. lactucae infecting lettuce in Arizona. References: (1) A. Garibaldi et al. Plant Dis. 86:1052, 2002. (2) J. C. Hubbard and J. S. Gerik. Plant Dis. 77:750, 1993. (3) T. Matuo and S. Motohashi. Trans. Mycol. Soc. Jpn. 8:13, 1967.

In 1999 and 2000, greenhouse-grown leek (Allium porrum) transplants produced in coastal California (Monterey County) developed a root and basal rot. Affected roots were initially gray and water soaked in appearance and later became pink, soft, and rotted. Basal plates were also affected, becoming water soaked and rotted. Severely affected transplants grew poorly and had chlorotic older leaves; many of these plants collapsed. Disease incidence varied greatly, though some transplant plantings had more than 50% disease. Similar symptoms were found in commercial, field-planted leek crops in the same region. The problem caused significant economic loss to transplant producers because of the loss of plants and the reduction in quality of surviving infected plants. Isolations from transplant and field samples consistently recovered a Fusarium species from both root and basal plate tissues. Single-spore subcultures were grown on carnation leaf agar and incubated under fluorescent light. All isolates produced abundant macroconidia that were stout, thick walled, and had prominent septa. Foot cells were indistinct to slightly notched. Conidiophores were monophialidic. Microconidia were absent and chlamydospores were present. Colonies on potato dextrose agar produced abundant, dense, white, aerial mycelium. The undersurface of these cultures was carmine red. Based on these features, all isolates were identified as Fusarium culmorum. To confirm the identification, a partial sequence (645 bp) of the translation elongation factor (EF-1α) was obtained for one isolate using primers EF-1 and EF-2 (2). The EF-1α sequence from the leek isolate was identical to that of two F. culmorum isolates in Genbank (Accession Nos. AF212462 and AF212463). The next closest match was F. cerealis, which differed from the leek isolate at six nucleotide positions. To test pathogenicity of the leek isolates of F. culmorum, we prepare inocula of four isolates from transplants and three isolates from field plants. A conidial suspension (1 × 105 conidia/ml) of each isolate was applied to the roots of 3-month-old potted leek (cvs. Autumn Giant, Blauwgroene, and Cisco). For the control treatment, leek plants were treated with water. All plants were maintained in a greenhouse at 25°C. After 1 month, inoculated plants showed foliar and root symptoms similar to those observed on the original samples. F. culmorum was reisolated from these symptomatic plants. Control plants did not develop symptoms. Using the same procedures, the seven isolates were inoculated onto other Allium species, but did not cause any symptoms on shallot (A. cepa var. ascalonicum) or eight cultivars of onion (A. cepa). Two of the seven isolates caused slight root symptoms on garlic (A. sativum). All experiments were conducted two times and the results of both tests were similar. To our knowledge, this is the first report of a root and basal rot of leek in California caused by F. culmorum. The occurrence of this disease on transplants grown in a soilless rooting medium and on raised benches in enclosed greenhouses provides circumstantial evidence that the pathogen could possibly be seedborne. This disease was reported recently in Spain (1). References: (1) J. Armengol et al. Plant Dis. 85:679, 2001. (2) K. O'Donnell et al. Proc. Natl. Acad. Sci. 95:2044, 1998.

Epidemics of Verticillium wilt in pepper fields of the central coast of California and isolates of Verticillium dahliae associated with these epidemics were characterized. The mean incidence of wilted plants per field ranged from 6.3 to 97.8% in fields with Anaheim, jalapeno, paprika, or bell peppers. In general, incidence of wilt in jalapeno and bell pepper crops was lower than in crops of other types of pepper. Inoculum density of V. dahliae in the surveyed pepper fields ranged from 2.7 to 66.6 microsclerotia g-1 dry soil, and the correlation between disease incidence and density of microsclerotia was high (r = 0.81, P < 0.01). Distribution of Verticillium wilt was aggregated in a majority of the pepper fields surveyed, but the degree of aggregation varied. Vegetative compatibility group (VCG) characterization of 67 isolates of V. dahliae indicated that 67% belonged to VCG 2, 22% to VCG 4, and 11% to a new group, designated VCG 6. The pathogenicity of isolates of V. dahliae from bell pepper and tomato plants was tested by inoculating 1-month-old bell pepper (cv. Cal Wonder) and tomato (cv. EP 7) seedlings and incubating the inoculated plants in the greenhouse. Seedlings of bell pepper were susceptible only to the isolates of V. dahliae from pepper, whereas seedlings of tomato were susceptible to both pepper and tomato isolates. Pepper isolates belonging to VCG 2, VCG 4, and VCG 6 were highly pathogenic to bell pepper and chili pepper. Temperatures between 15 and 25°C were optimal for mycelial growth of a majority of isolates of V. dahliae. Molecular characterization of pepper isolates of V. dahliae using a polymerase chain reaction (PCR)-based random amplified polymorphic DNA (RAPD) technique revealed minor variation among these isolates, but unique polymorphic banding patterns were observed for isolates belonging to VCG 6. Verticillium wilt of pepper is a major production constraint in the central coast of California. More aggressive isolates of V. dahliae may have been selected in this region as a result of intensive cropping practices.

Jerusalem artichoke or sunchoke (Helianthus tuberosus) is a specialty vegetable that is grown commercially in California. The fleshy tubers are harvested and used as a fresh salad ingredient or cooked vegetable. During 2003, field plantings of Jerusalem artichoke in coastal California (Santa Cruz County) showed symptoms of an unfamiliar disease. Initial symptoms consisted of wilting of new shoots and leaves followed by browning and collapse of all foliage. Crown and lower stem tissues turned tan to brown. In advanced stages of the disease, crown and stem tissues were colonized internally and externally by white, cottony mycelium. Tan, spherical sclerotia that measured approximately 1 mm in diameter formed on the surfaces of the affected crowns and stems. Mycelia and sclerotia also grew on the soil adjacent to infected plants. Isolations from symptomatic crowns, mycelia, and sclerotia produced colonies that were identified as Sclerotium rolfsii. Pathogenicity was tested using two methods that included sclerotial inocula collected from five isolates grown on potato dextrose agar plates. With the first method, sclerotia of each isolate were applied to sets of tubers (10 tubers per isolate) prior to planting tubers into a soilless, peat moss-based medium in pots. With the second method, 3-week-old potted plants were inoculated by placing sclerotia of each isolate adjacent to stem tissue that was 3 cm below the surface of the soilless medium. Noninoculated controls were included for both methods. All plants were incubated in a greenhouse at 21 to 24°C. For the first method, by the third week after planting, 10 to 40% of plants did not emerge because the tubers were rotted and decayed. For the plants that did emerge, wilting of foliage and browning of crown and stem tissue occurred approximately 6 weeks after planting and by 10 weeks, all plants were diseased. S. rolfsii was reisolated from all necrotic tuber, crown, and stem tissues. For the second method, disease symptoms and signs of the pathogen occurred 5 weeks after inoculation and by week 10, 75% of test plants were symptomatic. S. rolfsii was again reisolated from all necrotic tuber, crown, and stem tissues. Symptoms were not observed on any of the noninoculated plants. To my knowledge, this is the first report of southern blight of Jerusalem artichoke in California. This disease has been reported on Jerusalem artichoke in several southern U.S. states (1,2). The two inoculation methods demonstrated that the pathogen could infect propagation organs (tubers) and also emergent stems of this host. References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) S. M. McCarter and S. J. Kays. Plant Dis. 68:299, 1984.

Along California's central coast, delphinium (Delphinium species and cultivars) is grown as a cut flower and potted plant. In the spring of 2003, severe downy mildew was observed on various delphinium crops in Santa Cruz County. The disease was detected on cut flower Delphinium ‘Volkerfrieden’ in a greenhouse and adjacent field production areas. At a different nursery, outdoor, containerized D. grandiflorum ‘Blue Butterfly’ and Delphinium elatum (Pacific Hybrids) were also infected. Initial symptoms on leaves consisted of light green patches. These areas quickly turned dark green to blackish green and often were delimited by the central vein of the leaf. Purple-gray sporulation of the pathogen could be seen primarily on the abaxial leaf surfaces. Symptoms were most severe on older foliage. As disease progressed, the lower leaves withered and dried up, giving the plant a blighted appearance. Disease was most severe on D. grandiflorum ‘Blue Butterfly’, in which the disease affected the entire planting and blighted all foliage with the exception of the youngest leaves on the plant's central leader. For this cultivar, the diseased nursery stock had to be discarded, resulting in significant economic loss. Sporangiophores branched dichotomously, with branches ending in slender, slightly curved tips. Sporangia were slightly purplish, ellipsoid to ovoid, and measured 27 to 36 × 19 to 22 μm. Inside the tissue of older symptomatic leaves, extensive numbers of oogonia and oospores were observed. Oospores were globoid, amber to light brown, verruculose, and measured 25 to 27 μm in diameter. The pathogen was identified as Peronospora ficariae (1). Pathogenicity was demonstrated by spraying sporangial suspensions (1.0 × 104 sporangia per ml) onto the leaves of healthy, potted Delphinium elatum (Pacific Hybrids), incubating the plants in a dew chamber at 18°C for 48 h, and then maintaining them in a greenhouse (22 to 24°C). After 10 to 12 days, inoculated plants developed downy mildew symptoms, and the same pathogen sporulated sparsely on the host. If these plants were again placed in the dew chamber for an additional 24 h, leaf lesions sporulated profusely in the following 48 h. Control plants treated with water did not develop any symptoms or signs of downy mildew. To our knowledge, this is the first report of downy mildew caused by P. ficariae on cultivars of delphinium in California. Reference: (1) G. Hall. Mycopathologia 126:51, 1994.

During February 2004, diseased double impatiens (Impatiens walleriana) plants were received from a commercial grower in southern California. The upper surfaces of symptomatic leaves were pale yellow with no distinct lesions. Diseased leaves later wilted, and severely affected leaves abscised from the stem. At the nursery, only double impatiens plants in the Fiesta series were infected, and some cultivars were more heavily infected than others. Disease incidence in cv. Sparkler Hot pink was nearly 100%. The interior of infected leaves was colonized by coenocytic mycelium. A conspicuous white growth was observed only on the underside of leaves. Sporangiophores were hyaline, thin walled, emergent from stomata, and had slightly swollen bases. Sporangiophore branching was distinctly monopodial. Smaller sporangiophore branches were arranged at right angles to the supporting branches, and tips of branches measured 8 to 14 μm long. Sporangia were ovoid and hyaline with a single pore on the distal ends. Distal ends of sporangia were predominantly flat but occasionally had a slight papilla. Short pedicels were present on the attached ends. Sporangia measured 19.4 to 22.2 (-25.0) μm × 13.9 to 16.7 (-19.4) μm. Oospores were not observed in leaf tissue. On the basis of symptoms and morphology of the organism, the pathogen was identified as Plasmopara obducens J. Schröt. Pathogenicity tests were done on double type cvs. Fiesta, Tioga Red, and Tioga Cherry Red and on single type cvs. Cajun Watermelon and Accent Lilac. Plants were spray inoculated with sporangiospore suspensions (1 × 104 sporangiospores per milliliter), incubated for 24 h in a dew chamber (18 to 20°C), and then maintained in a greenhouse (22 to 24°C). Symptoms and signs of downy mildew developed after 12 days only on inoculated cv. Fiesta plants, and the pathogen morphology matched that of the originally observed pathogen. Nontreated control plants did not develop downy mildew. To our knowledge, this is the first report of downy mildew on impatiens in California. P. obducens is one of two causal agents of downy mildew of impatiens (2,4). The other pathogen, Bremiella sphaerosperma, has dichotomous sporangiophore branching and causes lesions with well-defined margins (2,4). In the United States, the disease has been recorded in the eastern and northeastern states and in Indiana, Minnesota, Mississippi, Montana, and Wisconsin (3). In Canada, the disease has been recorded in Manitoba and Quebec (1). References: (1) I. L. Conners. An Annotated Index of Plant Diseases in Canada and Fungi Recorded on Plants in Alaska, Canada, and Greenland. Research Branch, Canada Department of Agriculture, Publication 1251, 1967. (2) O. Constantinescu. Mycologia 83:473, 1991. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, 1989. (4) G. W. Wilson. Bull. Torrey Bot. Club 34:387, 1907.

From 1999 through 2003, a previously unreported disease was found on commercial Swiss chard (Beta vulgaris subsp. cicla) in the Salinas Valley, (Monterey County) California. Each year the disease occurred sporadically throughout the long growing season from April through September. Initial symptoms were water-soaked leaf spots that measured 2 to 3 mm in diameter. As disease developed, spots became circular to ellipsoid, 3 to 8 mm in diameter, and tan with distinct brown-to-black borders. Spots were visible from the adaxial and abaxial sides. Cream-colored bacterial colonies were consistently isolated from spots. Strains were fluorescent on King's medium B, levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction on tobacco (Nicotiana tabacum cv. Turk). The isolates, therefore, belong in LOPAT group 1 (1). Fatty acid methyl esters (FAME) analysis (MIS-TSBA version 4.10, MIDI Inc., Newark, DE) gave variable results that included Pseudomonas syringae, P. cichorii, and P. viridiflava with similarity indices ranging from 0.91 to 0.95. BOX-polymerase chain reaction (PCR) analysis gave identical banding patterns for the chard isolates and for known P. syringae pv. aptata strains, including the pathotype strain CFBP1617 (2). The bacteria were identified as P. syringae. Pathogenicity of 11 strains was tested by growing inoculum in nutrient broth shake cultures for 48 h, diluting to 10 × 6 CFU/ml, and spraying onto 5-week-old plants of Swiss chard cvs. Red, White, Silverado, and CXS2547. Untreated control plants were sprayed with sterile nutrient broth. After 7 to 10 days in a greenhouse (24 to 26°C), leaf spots similar to those observed in the field developed on all inoculated plants. Strains were reisolated from the spots and identified as P. syringae. Control plants remained symptomless. To investigate the host range of this pathogen, the same procedures were used to inoculate three strains onto other Chenopodiaceae plants: five cultivars of sugar beet (B. vulgaris), and one cultivar each of spinach (Spinacia oleracea) and Swiss chard. In addition, five chard strains and strain CFBP1617 were inoculated onto two cultivars of sunflower (Helianthus annuus), and one cultivar each of cantaloupe (Cucumis melo), sugar beet, spinach, and Swiss chard. All Swiss chard, cantaloupe, sunflower, and sugar beet plants developed leaf spots after 7 days. The pathogen was reisolated from spots and confirmed to be the same bacterium using BOX-PCR analysis. Spinach and untreated controls failed to show symptoms. All inoculation experiments were done at least twice and the results were the same. The phenotypic data, fatty acid and genetic analyses, and pathogenicity tests indicated that these strains are P. syringae pv. aptata. To our knowledge this is the first report of bacterial leaf spot of commercially grown Swiss chard in California caused by P. syringae pv. aptata. The disease was particularly damaging when it developed in Swiss chard fields planted for “baby leaf” fresh market products. Such crops are placed on 2-m wide beds, planted with high seed densities, and are sprinkler irrigated. This disease has been reported from Asia, Australia, Europe, and other U.S. states. References: (1) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470, 1966. (2) J. L. W. Rademaker et al. Mol. Microbiol. Ecol. Man. 3.4.3:1–27, 1998.

Vallad, G. E., Bhat, R. G., Koike, S. T., Ryder, E. J., and Subbarao, K. V. 2005. Weedborne reservoirs and seed transmission of Verticillium dahliae in lettuce. Plant Dis. 89:317-324. The seed transmission of Verticillium dahliae was evaluated in lettuce (Lactuca sativa). Seed collected from lettuce plants infected with V. dahliae were plated with or without surface sterilization on Sorenson’s modified NP10 medium. Of the seed plated with or without surface sterilization, 90 and 66%, respectively, yielded colonies of V. dahliae. The incidence of Verticillium wilt ranged from 55 to 80% among lettuce plants grown from seed harvested from infected plants. All evaluated isolates of V. dahliae were capable of seed transmission in lettuce. A V. tricorpus isolate failed to cause significant disease in lettuce or to become seedborne. Storage of contaminated seed at seven temperatures ranging from –20 to 15°C for up to 72 weeks did not reduce the incidence of V. dahliae in seed, whereas storage at room temperature (23 ± 2°C) for 20 to 52 weeks reduced the incidence of V. dahliae without affecting seed viability. Of the 11 weed species collected from fields with a known history of Verticillium wilt of lettuce, four yielded V. dahliae. Pathogenicity tests demonstrated that isolates of V. dahliae from Sonchus oleraceus, Capsella bursa-pastoris, and Solanum sarrachoides were as virulent as or more virulent than an isolate of V. dahliae from lettuce. These results demonstrate the potential of seedborne and weedborne inoculum to disseminate V. dahliae.

Subbarao, K. V., Kabir, Z., Martin, F. N., and Koike, S. T. 2007. Management of soilborne diseases in strawberry using vegetable rotations. Plant Dis. 91:964-972. The influence of crop rotation on soilborne diseases and yield of strawberry (Fragaria × ananassa) was determined at a site infested with Verticillium dahliae microsclerotia and at another with no known history of V. dahliae infestation during 1997 to 2000. The rotations studied at the V. dahliae-infested site were (i) broccoli-broccoli-strawberry, (ii) Brussels sproutsstrawberry, and (iii) lettuce-lettuce-strawberry; the treatments at the site with no history of V. dahliae were (i) broccoli-broccoli-strawberry, (ii) cauliflower-cauliflower-strawberry, and (iii) lettuce-lettuce-strawberry. The effects of rotation on V. dahliae and Pythium populations, strawberry vigor, Verticillium wilt severity, and strawberry fruit yield were compared with a standard methyl bromide + chloropicrin fumigated control treatment at both sites. Rotations did not alter total population levels of Pythium spp. at either study site. However, V. dahliae microsclerotia were significantly reduced with broccoli and Brussels sprouts rotations compared with lettuce rotations at the V. dahliae-infested site. Reduced propagules led to lower Verticillium wilt severity on strawberry plants in the broccoli and Brussels sprouts rotations than in lettuce-rotated plots. Strawberry vigor and fruit yield were significantly lower in lettuce-rotated plots than in broccoli- and Brussels sprouts-rotated plots. Despite no detectable microsclerotia at the other site, strawberry vigor and fruit yield were greatest in plots rotated with broccoli, intermediate with cauliflower, and lowest with lettuce. None of the rotation treatments were better than the fumigated control for all variables measured. In the absence of fumigation, rotation with broccoli and Brussels sprouts is an effective cultural practice for managing Verticillium wilt in strawberry production; whereas, in fields with no detectable V. dahliae, broccoli is also a feasible rotational crop that enhances strawberry growth and yield. According to a cost-benefit analysis, the broccoli-strawberry rotation system could be an economically viable option provided growers are able to alternate years for strawberry cultivation.

Celery (Apium graveolens) is grown extensively in the coastal counties (Ventura, Santa Barbara, San Luis Obispo, Monterey, and Santa Cruz) of California. In 2004 and 2005, field plantings of celery in Ventura and Monterey counties showed symptoms of a petiole and crown rot. Initial symptoms consisted of a light tan discoloration at the crowns and on outer petioles that were in contact with soil. These discolored areas developed a soft, brown, watery rot. Affected petioles wilted and later collapsed. White mycelium and small (0.5 to 3.0 mm in diameter), irregularly shaped, black sclerotia formed on diseased tissues. Isolations from symptomatic petioles, crowns, mycelium, and sclerotia produced colonies of Sclerotinia minor. Eight-week-old celery transplants (cv. Conquistador) grown in a peat-moss based rooting medium in 10-cm2 pots were used to test pathogenicity. Colonized agar plugs (one plug per plant) from eight celery isolates were inserted into slots made in the potting mix adjacent to the crowns and lower petioles of the transplants. Noncolonized plugs were placed in slots for control celery plants. Twenty plants were used for each isolate and control, and all test plants were incubated in a greenhouse at 21 to 23°C. Disease development was rapid, and after 4 days, inoculated celery plants exhibited brown necrosis at inoculation points. After 9 days, celery crowns were decayed and petioles collapsed. S. minor was reisolated from necrotic crown and petiole tissues. Noninoculated plants were asymptomatic. The experiment was repeated and results were similar. To our knowledge, this is the first report of celery as a host of S. minor in California (2). In the United States, S. minor has been reported on celery in Florida (1). Celery in California is only occasionally infected by S. minor and is more often infected by S. sclerotiorum. Reference: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society. St. Paul, MN, 1989. (2) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997.

Romneya coulteri, known as matilija poppy or coulter's matilija poppy, is a perennial woody shrub (family Papaveraceae) that is native to southern California and northern Mexico. The plant is used in landscape settings and has the largest flowers, measuring up to 16 cm across, of any plant native to California. In August 2006, in Monterey County, CA, landscape plants of R. coulteri were found affected with a powdery mildew disease. Initial symptoms consisted of chlorotic, irregularly shaped, vein-delimited lesions. As disease progressed, grayish white sporulation was visible on lesions on adaxial and abaxial sides of affected leaves. In advanced stages of the disease, lesions expanded up to 2 cm long and the center tissue of the lesions turned necrotic. Symptoms and signs were observed on both mature and younger foliage. The small matilija poppy planting consisted of six or seven plants and all plants were affected by the disease. Epidermal strips from both sides of leaves and leaf cross sections were mounted in drops of lactophenol and aniline blue and examined with a light microscope. These preparations showed that conidiophores developed from endophytic mycelium and emerged through stomates. Conidiophores were sometimes branched and carried one or two conidia. Hyaline, single-celled conidia were dimorphic. Primary (terminal) conidia were lanceolate with distinct apical points and measured 53 to 61 × 17 to 25 μm. Secondary conidia were ellipsoid-cylindric and measured 53 to 67 × 16 to 22 μm. On the basis of these characters, the pathogen was identified as Leveillula taurica (1). Only the anamorph Oidiopsis taurica stage was observed on plants. To prove pathogenicity, diseased leaves were collected from the landscape plantings. One diseased leaf was gently rubbed against one leaf of a potted, healthy matilija poppy. Twelve leaves were inoculated in this way, and plants were kept in a humidity chamber for 48 h and then maintained in a greenhouse (24 to 26°C). After 14 days, chlorotic lesions appeared on inoculated matilija poppy leaves and sporulation of L. taurica was observed several days later. Untreated control plants did not develop powdery mildew. The experiment was repeated and the results were the same. To my knowledge, this is the first report of powdery mildew caused by L. taurica on matilija poppy. There was no indication that the disease affected the growth of the host; however, powdery mildew reduced the quality of the appearance of this ornamental plant. Reference: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980.

Uniform plots of broccoli raab (Brassica rapa subsp. rapa) seedlings were inoculated with a rifampicin-resistant strain of Pseudomonas syringae pv. alisalensis, the causal agent of bacterial blight on crucifers, resulting in 100% disease incidence in mature plants. Diseased plants were incorporated into the soil at maturity and smaller replicated plots were replanted at various times after incorporation. Rifampicin-resistant fluorescent pseudomonads with rep-PCR profiles identical to P. syringae pv. alisalensis were isolated from lesions on plants grown in soil into which the first diseased crop was incorporated. Disease incidence declined in mature plants as the length of time between incorporation of the first planting and seeding of the replanted plots increased. Bacterial population levels in soil decreased over time and bacteria were no longer detectable 3 weeks after incorporation of the diseased crop. In laboratory tests, population levels of P. syringae pv. alisalensis decreased in untreated soil but not in autoclaved soil. Greenhouse studies demonstrated a direct correlation between population levels of P. syringae pv. alisalensis applied to soil and disease incidence in seedlings. However, the decline in bacterial populations in field soils did not wholly account for the decline in disease incidence with subsequent plantings.

Impatiens necrotic spot virus (INSV; family Bunyaviridae, genus Tospovirus) is an important pathogen of ornamental plants in North America and Europe, particularly in the greenhouse industry (2,3). However, INSV is now emerging as a pathogen of vegetable crops. During the 2006 and 2007 growing seasons, lettuce (Lactuca sativa) in Monterey County, CA showed necrotic spotting, leaf chlorosis, and plant stunting typical of symptoms induced by Tomato spotted wilt virus (TSWV). Significant and damaging outbreaks of these disease symptoms were found in numerous romaine, greenleaf, redleaf, butterhead, and iceberg lettuce fields in Monterey and San Benito counties. Samples from symptomatic plants from 21 of 27 fields in Monterey County were negative when tested with TSWV immunostrips (Agdia, Elkhart, IN); however, tests of the TSWV-negative samples with INSV immunostrips were positive. In most fields where INSV was detected, disease development was limited to the edges of fields and disease incidence was 50% and crop loss was experienced. The virus causing the tospovirus symptoms in the TSWV-negative lettuce was sap transmitted to Nicotiana benthamiana and lettuce, where it induced chlorosis and necrosis. Symptoms in N. benthamiana were consistent with INSV infection, and those in lettuce were similar to symptoms observed in the field. Immunostrip tests confirmed that symptomatic N. benthamiana and lettuce plants were infected with INSV. To further confirm the identity of this virus, reverse transcription (RT)-PCR analysis was conducted with an INSV primer pair that directs the amplification of a ~1.3-kb fragment from the small RNA of INSV (4). The 1.3-kb fragment was amplified from RNA from symptomatic lettuce plants that were INSV positive with immunostrips, and not from asymptomatic lettuce. A total of 38 of 54 samples showing tospovirus-like symptoms were confirmed to be infected with INSV by RT-PCR. Sequences of two representative 1.3-kb DNA fragments were 98 to 99% identical with sequences of INSV isolates from Japan, Italy, and The Netherlands (GenBank Accession Nos. AB109100, DQ425096, and X66972). Taken together with the previous identification of the INSV vector, the western flower thrips (Frankliniella occidentalis), in central California lettuce (1), these results confirm that INSV induced tospovirus symptoms in lettuce fields in Monterey County in 2007. To our knowledge, this is the first report of the occurrence of INSV infecting lettuce in California. References: (1) W. E. Chaney. Annu. Rep. California Lettuce Res. Board. 2006. (2) M. Daughtrey et al. Plant Dis. 81:1220, 1997. (3) M. D. Law and J. W. Moyer. J. Gen. Virol. 71:933, 1990. (4) R. A. Naidu et al. Online publication. doi: 10.1094/PHP-2005-0727-01-HN. Plant Health Progress, 2005.

Recently, Apium virus Y (ApVY) was detected in field-grown cilantro (Coriandrum sativum), celery (Apium graveolens), and parsley (Petroselinum crispum) in California. In 2003, cilantro plants growing in three different fields in California (Monterey, San Joaquin, and San Luis Obispo counties) expressed symptoms of mosaic, vein clearing, and stunting. When plant sap was examined by transmission electron microscopy, flexuous, rod-shaped virus particles were observed. Total RNA was extracted from the symptomatic cilantro plants and used as a template in reverse transcription (RT)-PCR using universal potyvirus primers according to Chen et al. (1). The RT-PCR product was cloned into pGEM-T (Promega, Madison, WI) and the insert of 1,713 bp was sequenced (GenBank Accession No. EU515125). Nucleotide sequences from clones derived from three different infected cilantro plants were 89 to 97% identical to ApVY sequences encoding partial sequence of polyprotein in GenBank (Accession Nos. AY049716, EU127499, AF207594, AF203529, and EU255632). In 2007, celery plants showing necrotic line patterns and necrotic lesions on lower leaves and petioles were observed in several fields in two coastal counties in California (Monterey and Santa Clara counties). Flexuous, rod-shaped virus particles were also observed in the sap of those plants. ELISA for Cucumber mosaic virus and RT-PCR for Celery mosaic virus were negative. ApVY specific primers were designed on the basis of a consensus sequence of ApVY identified from cilantro in 2003; reverse primer 5′-GGCTCTTGCTATAGACAAATAGT-3′ and forward primer 5′-GAAGACCAAGCCAATGTGTGTA-3′. The sequence of RT-PCR products (GenBank Accession No. EU515126) amplified from infected celery had 90 to 98% nucleotide identity to ApVY. When the deduced amino acid sequences of NIb and CP regions from both cilantro and celery were used for comparison, they showed 95 to 99% identity with the known ApVY GenBank sequences mentioned above. More than 10 asymptomatic parsley plants growing in fields adjacent to the infected celery were also tested for ApVY and found to be infected. ApVY was previously identified in three Apiaceae weeds in Australia (2) and in celery in New Zealand (3). To our knowledge, this is the first report of ApVY on cilantro, celery, and parsley in California. References: (1) J. Chen et al. Arch. Virol. 146:757, 2001. (2) J. Moran et al. Arch. Virol. 147:1855, 2002. (3) J. Tang et al. Plant Dis. 91:1682, 2007.

From 1998 through 2002, commercial chives (Allium schoenoprasum) in coastal California (Monterey County) were damaged by an undescribed disease. Initial symptoms were chlorosis and tan-colored necrosis at the leaf tips; as the disease progressed, extensive tan-to-light brown discoloration extended down affected leaves, resulting in their death. The damage prevented growers from harvesting affected crops. Stems of the chive plants were unaffected. Diseased plants continued to grow new leaves that subsequently became infected. A fungus was consistently isolated from symptomatic leaves. Isolates grown on potato dextrose agar (PDA) in petri plates incubated at 24°C under fluorescent lights produced extensive mycelial growth without conidia. However, on onion leaf straw agar (2), the isolates produced abundantly sporulating colonies with conidiophores and conidia typical of a Botrytis species. Conidiophores rarely exceeded 1 mm long. Ellipsoidal conidia measured 11 to 17 × 5 to 8 μm. On green bean pod agar (4), the isolates produced a few, black, irregularly shaped sclerotia measuring 1 to 2 mm in diameter. Morphological comparisons were made on PDA between five chive isolates and isolates of the following Botrytis species known to infect Allium species (1): B. aclada BA5, B. allii BA3, B. byssoidea ATCC 60837, B. cinerea from an onion seed crop, B. porri 749, B. squamosa 392, and B. tulipae GC-1. B. elliptica strain MARLI-3 was also compared with the chive isolates. Chive isolates produced floccose, off white-to-light tan mycelium, lacked sporulation (except where mycelium contacted the edge of the plastic petri dish), and did not form sclerotia on PDA, thereby resembling B. byssoidea. Identification of the chive isolates as B. byssoidea was confirmed by ApoI restriction fragment length polymorphism digests of a 423-bp PCR amplicon obtained from each of the five chive isolates and the eight known Botrytis species (1,3). Pathogenicity of the chive isolates of B. byssoidea was confirmed by spraying a conidial suspension (1 × 105 conidia/ml) of each of 12 isolates onto chive (cv. Fine Leaved) and onion (A. cepa cv. Southport White) plants until runoff, incubating the plants in a humidity chamber at 24 to 26°C for 48 h and then maintaining the plants under ambient light in a greenhouse. After 6 to 8 days, inoculated chives and onions developed symptoms similar to those observed in the field and B. byssoidea was reisolated. Noninoculated control chives and onions sprayed with distilled water did not develop symptoms. The experiment was conducted three times and the results were the same. To our knowledge, this is the first report of a leaf blight of chive caused by B. byssoidea in North America. After 2002, the commercial chive plantings were placed on farms further east in Monterey County away from the coast. The disease has not been observed since this move to a drier climate. References: (1) M. I. Chilvers and L. J. du Toit. Online publication. doi:10.1094/PHP-2006-1127-01-DG. Plant Health Progress, 2006. (2) L. A. Ellerbrock and J. W. Lorbeer. Phytopathology 67:219, 1977. (3) K. Nielsen et al. Plant Dis. 86:682, 2002. (4) A. H. C. van Bruggen and P. A. Arneson. Plant Dis. 69:966, 1985.