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The unculturable bacterium 'Candidatus Liberibacter soianacearum' (CLso) is responsible for a growing number of emerging crop diseases. However, we know little about the diversity and ecology of CLso and its psyllid vectors outside of agricultural systems, which limits our ability to manage crop disease and understand the impacts this pathogen may have on wild plants in natural ecosystems. In North America, CLso is transmitted to crops by the native potato psyllid (Bactericera cockerelli). However, the geographic and host plant range of the potato psyllid and CLso beyond the borders of agriculture are not well understood. A recent study of historic herbarium specimens revealed that a unique haplotype of CLso was present infecting populations of the native perennial Solanum umbelliferum in California decades before CLso was first detected in crops. We hypothesized that this haplotype and other potentially novel CLso variants arc still present in S. umbelliferum populations. To test this, we surveyed populations of S'. umbelliferum in Southern California for CLso and potato psyllid vectors. We found multiple haplotypes of CLso and the potato psyllid associated with these populations, with none of these genetic variants having been previously reported in California crops. These results suggest that CLso and its psyllid vectors are much more widespread and diverse in North American natural plant communities than suggested by data collected solely from crops and weeds in agricultural fields. Further characterization of these apparently asymptomatic haplotypes will facilitate comparison with disease-causing variants and provide insights into the continued emergence and spread of CLso. [ABSTRACT FROM AUTHOR]

Along with bacteria, fungi can represent a significant component of animal- and plant-associated microbial communities. However, we have only begun to describe these fungi, much less examine their effects on most animals and plants. Bacteria associated with the honey bee, Apis mellifera, have been well characterized across different regions of the gut. The mid- and hindgut of foraging bees house a deterministic set of core species that affect host health, whereas the crop, or the honey stomach, harbors a more diverse set of bacteria that is highly variable in composition among individual bees. Whether this contrast between the two regions of the gut also applies to fungi remains unclear despite their potential influence on host health. In honey bees caught foraging at four sites across the San Francisco Peninsula of California, we found that fungi were less distinct in species composition between the crop and the mid- and hindgut than bacteria. Unlike bacteria, fungi varied substantially in species composition throughout the honey bee gut, and much of this variation could be predicted by the location where we collected the bees. These observations suggest that fungi may be transient passengers and unimportant as gut symbionts. However, our findings also indicate that honey bees could be vectors of infectious plant diseases as many of the fungi we found in the honey bee gut are recognized as plant pathogens. [ABSTRACT FROM AUTHOR]

Almond band canker and prune Cytospora canker have become more severe in the last decade, especially in young orchards, in California. To test our hypothesis that young trees from nurseries could carry the canker-causing pathogens at latency phase to new orchards through transplanting, a multiyear survey on latent infection of canker-causing pathogens of budwood and young trees of almond and prune nurseries in California was conducted. A total of more than 1,730 samples including shoots of rootstocks and scions and grafting union cuttings were collected from 11 nurseries. A real-time quantitative PCR assay was applied to quantify the latent infection levels by six canker-causing pathogen taxa: Botryosphaeria dothidea and species of Cytospora , Diplodia , Lasiodiplodia , Neofusicoccum , and Phomopsis. For almond, the average incidences of latent infection caused by Lasiodiplodia spp. (43.6%) and Neofusicoccum spp. (24.2%) were significantly greater than those by the other four pathogen taxa. The molecular severity (MS) of latent infection caused by Neofusicoccum spp. (3.6) was significantly greater than those caused by other pathogen taxa, except for Lasiodiplodia spp. (2.6). For prune, the average incidence of latent infection caused by Cytospora spp. (13.5%) was significantly higher than those caused by B. dothidea (1.5%) and Diplodia spp. (1.3%) but not significantly higher than those caused by Lasiodiplodia spp. (6.9%), Neofusicoccum spp. (6.3%), and Phomopsis spp. (7.7%), respectively. Moreover, the average MS values caused by Cytospora spp. (3.8) and Neofusicoccum spp. (3.2) were the highest followed by those caused by B. dothidea (1.4), Lasiodiplodia spp. (2.2), and Phomopsis spp. (2.3). Different almond varieties showed various levels of susceptibilities to different canker-causing pathogens. This study concluded that Lasiodiplodia and Neofusicoccum are the predominant pathogen species in almond, and Cytospora is the most important canker-causing pathogen species in prune in nurseries. These findings confirmed the observations of predominancy of canker-causing pathogens in almond and prune orchards in California., Competing Interests: The author(s) declare no conflict of interest.

Aims: A real-time quantitative PCR (qPCR) assay was established to quantify the inoculum densities in the air and rainwater for six canker-causing pathogen groups in prune and walnut orchards in California. Methods and Results: The previously published DNA primers to target six pathogen groups including Botryosphaeria dothidea, Cytospora spp., Diplodia spp., Lasiodiplodia spp., Neofusicoccum spp. and Phomopsis spp. were used in a qPCR assay. Air samples from Burkard spore traps and rain samples from special rain collector devices were collected periodically from various prune and walnut orchards. Using the qPCR approach, we were able to quantify the concentrations of these pathogen groups in rainwater and air samples and study the dynamics of pathogen inoculum in orchards showing severe canker potential. Phomopsis spp. and Diplodia spp. were not found in all rain samples in prune orchards, although they were detected in the 2016 in the walnut orchard. The other four pathogen groups were quantified at varying concentrations in the prune and walnut orchards. Cytospora spp. in some cases showed higher concentrations in the rainwater in prune orchards. Conclusions: The rainy season during winter and early spring is a highly risky period of time for infection by the pathogens when the inoculum of these pathogens can easily spread by air and rain water, thus serving as an important inoculum source for disease initiation. The different studied pathogen groups showed different concentrations during the growing season, indicating the complexity of the components of canker-causing species in various tree crops. Significance and Impact of the Study: This study showed the applicability of the qPCR assay in the quantification of inoculum in tree orchards to help reveal the mechanisms of canker disease epidemics and to help design disease management strategies. [ABSTRACT FROM AUTHOR]

The Citrus yellow vein clearing virus (CYVCV) causes a viral disease that has been reported in some citrus-growing regions in countries in Eurasia including Pakistan, India, Türkiye, Iran, China, and South Korea. Recently, CYVCV was detected in a localized urban area in a town in the middle of California's citrus-growing region and marks the first occurrence of the virus in North America. CYVCV has been reported to be spread by aphid and whitefly vectors and is graft and mechanically transmitted. Hence, it is an invasive pathogen that presents a significant threat to the California citrus industry, especially lemons, which are highly symptomatic to CYVCV. To elucidate the origin of the CYVCV California strain, we used long-read sequencing technology and obtained the complete genomes of three California CYVCV isolates, CA1, CA2, and CA3. The sequences of these isolates exhibited intergenomic similarities ranging from 95.4% to 97.4% to 54 publicly available CYVCV genome sequences, which indicated a relatively low level of heterogeneity. However, CYVCV CA isolates formed a distinct clade from the other isolates when aligned against other CYVCV genomes and coat protein gene sequences as shown by the neighbor network analysis. Based on the rooted Maximum Likelihood phylogenetic trees, CYVCV CA isolates shared the most recent common ancestor with isolates from India/South Asia. Bayesian evolutionary inferences resulted in a spatiotemporal reconstruction, suggesting that the CYVCV CA lineage diverged from the Indian lineage possibly around 1995. This analysis placed the origin of all CYVCV to around 1990, with South Asia and/or Middle East as the most plausible geographic source, which matches to the first discovery of CYVCV in Pakistan in 1988. Moreover, the spatiotemporal phylogenetic analysis indicated an additional virus diffusion pathway: one from South Asia to China and South Korea. Collectively, our phylogenetic inferences offer insights into the probable dynamics of global CYVCV dissemination, emphasizing the need for citrus industries and regulatory agencies to closely monitor citrus commodities crossing state and international borders.

Predicting where crop pests and diseases can occur, both now and in the future under different climate change scenarios, is a major challenge for crop management. One solution is to estimate the fundamental thermal niche of the pest/disease to indicate where establishment is possible. Here, we develop methods for estimating and displaying the fundamental thermal niche of pests and pathogens and apply these methods to Huanglongbing (HLB), a vector‐borne disease that is currently threatening the citrus industry worldwide.We derive a suitability metric based on a mathematical model of HLB transmission between tree hosts and its vector Diaphorina citri, and incorporate the effect of temperature on vector traits using data from laboratory experiments performed at different temperatures. We validate the model using data on the historical range of HLB.Our model predicts that transmission of HLB is possible between 16 and 33°C with peak transmission at ~25°C. The greatest uncertainty in our suitability metric is associated with the mortality of the vectors at peak transmission, and fecundity at the edges of the thermal range, indicating that these parameters need further experimental work.We produce global thermal niche maps by plotting how many months each location is suitable for establishment of the pest/disease. This analysis reveals that the highest suitability for HLB occurs near the equator in large citrus‐producing regions, such as Brazil and South‐East Asia. Within the Northern Hemisphere, the Iberian peninsula and California are HLB suitable for up to 7 months of the year and are free of HLB currently.Policy implications. We create a thermal niche map which indicates the places at greatest risk of establishment should a crop disease or pest enter these regions. This indicates where surveillance should be focused to prevent establishment. Our mechanistic method can be used to predict new areas for Huanglongbing transmission under different climate change scenarios and is easily adapted to other vector‐borne diseases and crop pests. [ABSTRACT FROM AUTHOR]

Olive knot, caused by Pseudomonas savastanoi pv. savastanoi, is a limiting disease in the production of table and oil olives in California. The genetic variability among 152 strains from major production areas of California was determined using BOX, ERIC, and REP primers in repetitive element sequence-based polymerase chain reaction. Overall genetic variability was low, and strains shared at least 82% similarity. Phenetic analyses identified several genotypes but most strains belonged to one of two major groups. Three copper-resistant strains had two fingerprints that were distinct from any of the sensitive strains, indicating that they may have been introduced (torn other production areas or hosts. In inoculations, two copper-resistant strains were mostly equally as virulent as two copper-sensitive strains. Inoculum was exuded at high levels (>108 CFU/g of knot tissue) within 10 min from hydrated olive knots, and concentrations were 2- to 3-log higher than the minimum needed to induce knot formation. Arbequina olive was significantly more susceptible to infection and developed a higher incidence of knots on leaf scar and lateral wounds (59.7 to 80.6% incidence) than Manzanillo (47.4 to 68.2% incidence). In wound-healing studies, both types of wounds were less susceptible to infection ≥10 days after injury, indicating a critical period for infection and application of bactericides during favorable environments. [ABSTRACT FROM AUTHOR]

The Orthotospovirus impatiens necrotic spot virus (INSV) is a thrips-transmitted pathogen of lettuce that has rapidly emerged as a serious threat to production in the Salinas Valley of Monterey County, California. As a first step toward understanding the severity of the virus, we utilized Spatial Analysis by Distance IndicEs (SADIE) to characterize the distribution and progression of INSV outbreaks and thrips infestations in two commercial lettuce fields. In both fields, INSV incidence rapidly increased from 15.86% ± 1.77 to 80.24% ± 2.60 over the course of 7 weeks and aggregated at specific edges in both fields as early as 3 weeks after planting (I a = 1.63, P a = 0.0100, and I a = 1.53, P a = 0.0300). In one of the fields, thrips populations aggregated in areas that also experienced the most INSV (I a = 1.2435, P a = 0.0400, week 3; I a = 1.4815, P a < 0.0001, week 6; I a = 1.5608, P a < 0.0001, week 9), while in the second field, thrips were distributed randomly despite the aggregated effects that were observed for INSV incidence. Economic analysis estimated that the virus accounted for over $475,000 in losses for the two fields, while stakeholder surveys documented over 750 fields that experienced INSV infection during the 2021 season in Monterey County alone. These studies enhance our knowledge on the epidemiology of thrips and INSV under current lettuce production practices in the Salinas Valley, while elucidating the economic consequences and broader challenges that are associated with managing thrips-transmitted viruses.

In recent years, an emerging, undescribed postharvest disease was observed on mandarin fruit after extended storage in California. We collected decayed mandarin fruit from three citrus packinghouses in the Central Valley of California in 2015 and identified this disease as Mucor rot caused by Mucor spp. Mucor rot occurred in 11 of the 15 grower lots sampled, and the percentage of Mucor rot in the total decayed fruit varied among affected grower lots, ranging from 3.3 to 93.1% with an average of 49.2%. In total, 197 isolates of Mucor spp. were obtained from decayed mandarin fruit and identified based on internal transcribed spacer sequence and morphological characteristics. Of the 197 isolates, 182 (92.4%) were identified as Mucor piriformis, 7 (3.6%) were M. circinelloides (6 M. circinelloides f. lusitanicus and 1 M. circinelloides f. circinelloides), 4 (2%) were M. racemosus f. racemosus, 3 (1.5%) were M. hiemalis, and 1 (0.5%) was M. mucedo. All species grew at 0 and 5°C, except M. circinelloides, which did not grow at 0°C. Mycelial growth was arrested at 27°C for M. piriformis; 35°C for M. racemosus f. racemosus, M. circinelloides f. lusitanicus, M. hiemalis and M. mucedo; and 37°C for M. circinelloides f. circinelloides. Optimal mycelial growth occurred at 20°C for M. piriformis and M. mucedo, 25°C for M. racemosus f. racemosus and M. hiemalis, 27°C for M. circinelloides f. lusitanicus, and 30°C for M. circinelloides f. circinelloides. M. piriformis grew significantly faster than the other four species at 5 and 20°C, and M. mucedo was the slowest in growth among the five species. Sporangiospores of M. piriformis, M. racemosus f. racemosus, and M. hiemalis germinated at both 5 and 20°C. M. circinelloides germinated at 20°C but did not germinate at 5°C after incubation for 48 h. All five Mucor spp. caused decay on mandarin fruit inoculated with the fungi, and the lesion size caused by M. piriformis was significantly larger than that caused by other species at both 5 and 20°C. Our results indicated that Mucor rot in mandarin fruit in California is caused by Mucor spp. consisting of M. piriformis, M. circinelloides, M. racemosus f. racemosus, M. hiemalis, and M. mucedo, with M. piriformis being the dominant and most virulent species. Previously, M. racemosus was reported on citrus. This is the first report of Mucor rot in citrus caused by M. piriformis, M. circinelloides, M. hiemalis, and M. mucedo. [ABSTRACT FROM AUTHOR]

Botrytis is an important genus of plant pathogens causing pre- and postharvest disease on diverse crops worldwide. This study evaluated Botrytis isolates collected from strawberry, blueberry, and table grape berries in California. Isolates were evaluated for resistance to eight different fungicides, and 60 amplicon markers were sequenced (neutral, species identification, and fungicide resistance associated) distributed across 15 of the 18 B . cinerea chromosomes. Fungicide resistance was common among the populations, with resistance to pyraclostrobin and boscalid being most frequent. Isolates from blueberry had resistance to the least number of fungicides, whereas isolates from strawberry had resistance to the highest number. Host and fungicide resistance-specific population structure explained 12 and 7 to 26%, respectively, of the population variability observed. Fungicide resistance was the major driver for population structure, with select fungicides explaining up to 26% and multiple fungicide resistance explaining 17% of the variability observed. Shared and unique significant single-nucleotide polymorphisms (SNPs) associated with host and fungicide (fluopyram, thiabendazole, pyraclostrobin, and fenhexamid) resistance-associated population structures were identified. Although overlap between host and fungicide resistance SNPs were detected, unique SNPs suggest that both host and fungicide resistance play an important role in Botrytis population structure.

Pierce's disease of grapevines, caused by a strain of the bacteria Xylella fastidiosa, threatens an industry with a farm value of production exceeding $3 billion per year. The grape industry incurs substantial costs from losses of vines to the disease and efforts to mitigate damage. Additional costs are borne by the public in providing programs that aim to contain the disease and develop longer-term solutions, and by the citrus, nursery and grape industries in complying with those programs. Aggregating the costs of vine losses, industry assessments, compliance costs, and expenditures by government entities, we estimate the cost of Pierce's disease in California is approximately $104.4 million per year. Of that, $48.3 million funds Pierce's disease activities undertaken by various government agencies, the nursery and citrus industries and the UC system, and $56.1 million is the cost of lost production and vine replacement borne by grape growers. [ABSTRACT FROM AUTHOR]

Stem-end rot of harvested avocado fruit commonly occurs wherever the crop is cultivated. Multiple fungal species have been described as causal agents. To determine the causal pathogens of stem-end rot in California, fungal isolations were conducted from symptomatic fruit, and fungi were identified by morphological and molecular techniques. In 2010 and 2011, a total of 177 isolates were recovered from 290 avocado fruit collected from seven orchards in one of the major avocado growing areas in Southern California. The majority of isolates was identified as Neofusicoccum luteum (65%), with the remainder either as Colletotrichum gloeosporioides (33%) or Phomopsis sp. (2%). In a pathogenicity test, N. luteum caused significantly (P < 0.05) more severe stem-end rot than either C. gloeosporioides or Phomopsis sp. No significant (P > 0.05) differences in stem-end rot severity were observed between inoculations with N. luteum isolated from fruit stem-end rot and N. luteum or N. parvum isolated from branch cankers. This confirms that stem-end rot of avocado can be initiated by fungi causing branch cankers. Although low humidity and rainfall during much of the growing and harvest seasons in California are considered unfavorable conditions for the development of avocado stem-end rot, the identification of the causal pathogens is of value when decays have to be managed during outbreaks, and it stresses the importance of managing branch cankers. [ABSTRACT FROM AUTHOR]

Phytophthora root rot (PRR) of avocado (Persea americana), caused by Phytophthora cinnamomi, is the most serious disease of avocado worldwide. Previous studies have determined that this pathogen exhibits a primarily clonal reproductive mode but no population level studies have been conducted in the avocado-growing regions of California. Therefore, we used amplified fragment length polymorphism based on 22 polymorphic loci and mating type to investigate pathogen diversity from 138 isolates collected in 2009 to 2010 from 15 groves from the Northern and Southern avocado-growing regions. Additional isolates collected from avocado from 1966 to 2007 as well as isolates from other countries and hosts were also used for comparative purposes. Two distinct clades of A2 mating-type isolates from avocado were found based on neighbor joining analysis; one clade contained both newer and older collections from Northern and Southern California, whereas the other clade only contained isolates collected in 2009 and 2010 from Southern California. A third clade was also found that only contained Al isolates from various hosts. Within the California population, a total of 16 genotypes were found with only one to four genotypes identified from any one location. The results indicate significant population structure in the California avocado P. cinnamomi population, low genotypic diversity consistent with asexual reproduction, potential evidence for the movement of clonal genotypes between the two growing regions, and a potential introduction of a new clonal lineage into Southern California. [ABSTRACT FROM AUTHOR]

In an attempt to improve semiochemical-based treatments for protecting forest stands from bark beetle attack, we compared push-pull versus push-only tactics for protecting lodgepole pine (Pinus contorta Douglas ex Loudon) and whitebark pine (Pinus albicaulis Engelm. ) stands from attack by mountain pine beetle (Dendroctonus ponderosae Hopkins) in two studies. The first was conducted on replicated 4.04-ha plots in lodgepole pine stands (California, 2008) and the second on 0.81-ha plots in whitebark pine stands (Washington, 2010). In both studies, D. ponderosae population levels were moderate to severe. The treatments were 1) push-only (D. ponderosae antiaggregant semiochemicals alone); 2) push-pull (D. ponderosae antiaggregants plus perimeter traps placed at regular intervals, baited with four-component D. ponderosae aggregation pheromone); and 3) untreated controls. We installed monitoring traps baited with two-component D. ponderosae lures inside each plot to assess effect of treatments on beetle flight. In California, fewer beetles were collected in push-pull treated plots than in control plots, but push-only did not have a significant effect on trap catch. Both treatments significantly reduced the rate of mass and strip attacks by D. ponderosae, but the difference in attack rates between push-pull and push-only was not significant. In Washington, both push-pull and push-only treatments significantly reduced numbers of beetles caught in traps. Differences between attack rates in treated and control plots in Washington were not significant, but the push-only treatment reduced attack rates by 30% compared with both the control and push-pull treatment. We conclude that, at these spatial scales and beetle densities, push-only may be preferable for mitigating D. ponderosae attack because it is much less expensive, simpler, and adding trap-out does not appear to improve efficacy. [ABSTRACT FROM AUTHOR]

Since 1995, lettuce in coastal California, where more than half of the crop in North America is grown, has consistently suffered from severe outbreaks of Verticillium wilt. The disease is confined to this region, although the pathogen (Verticillium dahliae) and the host are present in other crop production regions in California. Migration of the pathogen with infested spinach seed was previously documented, but the geographic sources of the pathogen, as well as the impact of lettuce seed sparsely infested with V. dahliae produced outside coastal California on the pathogen population in coastal California remain unclear. Population analyses of V. dahliae were completed using 16 microsatellite markers on isolates from lettuce plants in coastal California, infested lettuce seed produced in the neighboring Santa Clara Valley of California, and spinach seed produced in four major spinach seed production regions: Chile, Denmark, the Netherlands, and the United States (Washington State). California produces 80% of spinach in the United States and all seed planted with the majority infested by V. dahliae comes from the above four sources. Three globally distributed genetic populations were identified, indicating sustained migration among these distinct geographic regions with multiple spinach crops produced each year and repeated every year in coastal California. The population structure of V. dahliae from coastal California lettuce plants was heavily influenced by migration from spinach seed imported from Denmark and Washington. Conversely, the sparsely infested lettuce seed had limited or no contribution to the Verticillium wilt epidemic in coastal California. The global trade in plant and seed material is likely contributing to sustained shifts in the population structure of V. dahliae, affecting the equilibrium of native populations, and likely affecting disease epidemiology. [ABSTRACT FROM AUTHOR]

Armillaria altimontana, previously considered North American biological species (NABS) X, is described as new. To date, it appears that A. altimontana prefers higher-elevation, mesic sites within the dry, conifer forest zone of western interior North America. This species has been found on hardwoods and conifers and is associated most commonly with Abies-dominated forest types in southern British Columbia, Washington, Oregon, Idaho and northern California. Partial elongation factor 1-alpha (tef1) sequences were generated from six isolates of A. altimontana originating from three locations in northern Idaho. Phylogenetic analyses of all 10 North American Armillaria species were carried out with maximum parsimony and maximum likelihood. Results indicate that isolates of A. altimontana formed a monophyletic group and clustered with A. calvescens, A. cepistipes, A. gallica and A. nabsnona, which is in agreement with recent phylogenetic studies of Armillaria. [ABSTRACT FROM AUTHOR]

McKay, A. H., Förster, H., and Adaskaveg, J. E. 2012. Distinguishing Galactomyces citri-aurantii from G. geotrichum and characterizing population structure of the two postharvest sour rot pathogens of fruit crops in California. Phytopathology 102:528-538. A growth assay in lemon juice and polymerase chain reaction amplifications using newly designed species-specific primers from endopolygalacturonase and β-tubulin genes rapidly differentiated isolates of the morphologically similar fruit sour rot pathogens Galactomyces citriaurantii and G. geotrichum. Isolates of both species were collected from agricultural soils and decaying fruit at locations within and outside California, including worldwide locations, and were used in population genetic studies based on amplified fragment length polymorphic (AFLP) DNA markers. For all four geographically defined subpopulations (three counties of California and locations outside California) among 97 isolates of G. citri-aurantii and for the two subpopulations (origin within or outside California) among 35 isolates of G. geotrichum, the proportion of polymorphic loci and haplotypic diversity was high. In total, 82 unique haplotypes were identified for G. citri-aurantii for the four subpopulations and, of these, 80 haplotypes were unique among subpopulations. For G. geotrichum, 25 unique haplotypes were identified among the two subpopulations and no haplotype was shared. Indices of genetic differences (FST) between subpopulations within each species were all low (e.g., 0.038 for G. geotrichum and 0.085 to 0.226 for G. citriaurantii), indicating a low level of genetic differentiation. Following clone correction, mating type segregation ratios for G. citri-aurantii did not significantly (P > 0.1) deviate from a I:l ratio for all four subpopulations or the entire population. Tests of the index of association (IA) and parsimony tree-length permutation tests (PTLPT) supported a random mating structure for clone-corrected data for the Kern, Tulare, and Ventura County subpopulations and the null hypothesis of random mating could not be rejected. Additionally, PTLPT also supported random mating for the "outside of California" population. For G. geotrichum, random mating was only tested using IA and PTLPT and the null hypothesis of random mating was not rejected (P > 0.05) using clone-corrected data. Further evidence that sexual recombination likely occurs in both species of Galactomyces was the lack of grouping consistency in the unweighted pair-group method with arithmetic mean clustering of AFLP data. A high confidence based on bootstrap values was obtained for only a few of the nodes in each of the two trees. A mixed reproduction system with an out-crossing sexual mating system and a prolific asexual phase is proposed for both species. [ABSTRACT FROM AUTHOR]

The sour rot pathogen of peach (Primus persica var. persica) and nectarine (P. persica var. nectarina) fruit, Geotrichum candidum, can cause significant postharvest losses in California fruit production. Harvested peach and nectarine fruit, treated with fungicide at the packinghouse hut culled after inspection because of disease and defects, were collected for further assessment and pathogen isolation. The incidence of fruit with sour rot was 3.4 ± 1.0 to 26.1 ± 2.3%. Culled fruit that had been treated with postharvest fungicides from five different orchards had a significantly higher incidence of sour rot when compared with nontreated fruit. Since August 2006, propiconazole has been used as a postharvest treatment to protect peach and nectarine fruit against sour rot. The mean effective concentration that inhibits 50% of mycelial growth (EC50) value of 57 isolates of G. candidum to propiconazole collected before and during 2006 was 0.072 μg/ml. However, 61 isolates from propiconazole-treated, diseased fruit collected from 2007 to 2009 had a mean EC50 value for mycelial growth of 0.378 μg/ml, a fivefold shift in mean sensitivity. Propiconazole applied as either a protective or curative treatment significantly reduced disease severity and decay development in fruit inoculated with a propiconazole-sensitive isolate. The fungicide was significantly less effective when applied as a preventive or a curative application to fruit that were inoculated with a less-sensitive isolate of G. candidum. Under laboratory conditions, isolates of the pathogen less sensitive to propiconazole were stable over multiple transfers on fungicide-free medium. The potential for the development of G. candidum populations with reduced sensitivity to propiconazole and the increased risk of crop loss due to the practice of returning culled fruit to production orchards are discussed. [ABSTRACT FROM AUTHOR]

Members nf the family Bou-yosphaeriaceae cause branch cankers and dieback no California avocado trees. Morn intensive pruning, a practice associated with high-density planting that is becoming more cornuson in the California avocado industry, may increase the occorrence of branch canker. This study was undertaken to identify and chueacterize the Botryosphaeriaccae spp. involved in the branch canker disease complex in order to develop future management strategies. From 2008 to 2009, branch cankers were sampled frons four or five trees from each of eight avocado groves in five California counties. Six Botryosphaeriaceae spp. were identified based on morphology as well as phylogenetic analysis of the internal transcribed spacer region (ITS I 5.8S-ITS2) and a partial seqnence of the α-tubnlin gene. These six species included Neofusicocum australe, N. luteum, N. parvuin, an unknown Neofusicoccum up., Fusiroccusn aesculi, and Dothiore Ito iberica. Members of She Botryosphaeriaceae were isolated front all avocado-growing regions sampled in California; however, incidence and distribution of species varied. This report is she first description of the isolation of D. ibericu irons avocado branch cankcrs in California. [ABSTRACT FROM AUTHOR]

The article presents the biology of the Canadian weed Onopordum acanthium L. It is described as a biennials whose seedlings consist of a relatively large, fleshy and sparsely branched which is surmounted by a pair of 1.25-2 cm long, glabrous entire cotyledons that are pale green with whitish venation. It refers to Onopordum acanthium as a strongly competitive species that infests small grain fields in Nevada and northeastern California. It indicates its response to herbivory such as mammals and birds, disease and higher plant parasites.

The article presents abstracts on plant diseases which include a new Rhizoctonia-like fungus causing basal leaf blight of kikuyugrass in southern California, Fusarium solani causing fusarium crown and root rot in Tarragon being grown in California and foliar, stem and fruit lesions observed on watermelon and pumpkin in Tanzania.

Diatrypaceous fungi have been isolated from cankered wood of grapevines (Vitis vinifera) in California. However, the pathogenicity of these fungi and their potential to cause diseases in grapevine was unknown. A series of pathogenicity tests were conducted to determine if these fungi were grapevine pathogens. In all experiments, species of the family Diatrypaceae were re-isolated from the margins of developing lesions, although frequency of re-isolation and average length of vascular discolorations varied among isolates. Cryptovalsa ampelina, Diatrype stigma, and Eutypa leptoplaca were capable of colonizing dormant canes and causing vascular necrosis. Cryptosphaeria pullmanensis, C. ampelina, D. stigma, Diatrype whitmanensis, and E. leptoplaca infected and caused lesions in green shoots of the new vegetative growth. Diatrype oregonensis and Diatrypella verrucaeformis isolates did not produce lesions that were significantly different from those produced in the control shoots and canes. This suggests that D. oregonensis and D. verrucaeformis fungi may be saprophytic rather than pathogenic to grapevine. [ABSTRACT FROM AUTHOR]

Pierce's disease and almond leaf scorch disease have been chronic problems for California grape and almond growers, respectively. Both diseases are caused by the xylem-limited, bacterial pathogen Xylella fastidiosa, which is transmitted by xylem-feeding insects. We evaluated the potential for alfalfa to serve as a source of vectors and inocula in California. Analysis of Geographic Information Systems maps on the distribution and abundance of grape, almond, and alfalfa plantings determined that 94,521 ha of almond and grape were planted within 1.6 km of an alfalfa field. Seasonal trends of X. fastidiosa detection were monitored outdoors and in the greenhouse in five needle-inoculated alfalfa cultivars (CUF101, Moapa69, WL342, WL530HQ, and WL625HQ) over 2 years. Results suggest that cool winter temperatures reduced X. fastidiosa populations to undetectable levels but did not eliminate infections. Sampling of alfalfa fields to assess incidence of X. fastidiosa corroborated this result, with positive samples detected in summer only. Incidence of X. fastidiosa in alfalfa during summer was low, with only 6 positive samples out of 1,156 samples collected over 3 years. Insect trapping in alfalfa fields over 3 years found that the green sharpshooter (Draeculacephala minerva) was the most abundant vector. Within alfalfa fields, green sharpshooter abundance was highest in weedy areas, suggesting a preference for weeds over alfalfa. These results confirm that weedy alfalfa fields can serve as an important source of vectors. Incidence of X. fastidiosa in alfalfa was low, possibly due to preference of vectors for weeds over alfalfa. [ABSTRACT FROM AUTHOR]

Almond leaf scorch disease (ALSD) caused by Xylella fastidiosa is potentially a serious threat to the almond industry in San Joaquin Valley of California. Knowledge of X. fastidiosa behaviour in the plant host under field conditions is important for disease control and this issue is being addressed in this project. Occurrence of ALSD is strongly influenced by environmental factors. In 2006, the earliest leaf scorching symptoms were observed in June, whereas in 2007, the earliest occurrence of leaf scorching symptoms was in July, a delay of 1 month. In both years, PCR detected X. fastidiosa 1 month before of symptom expression. PCR was slightly more sensitive than cultivation method for early bacterial detection. However, uneven bacterial distribution and random sampling errors may have contributed to the differences among the assays. Correlation between cultivation and PCR detection was greater than 90%. During the processing of a large number of samples, we noticed occasional failures in PCR amplifications of some samples, interfering result interpretation. We developed an array-PCR protocol using primers from seven housekeeping genes to correct the deficiency. [ABSTRACT FROM AUTHOR]

Sweetgum dieback and leaf scorch of purple-leafed plum are two new diseases of southern California landscape ornamentals. Samplings were conducted in 2003 and 2004 and 28 of 105 sweetgum (Liquidambar slyrac(flua) and 38 of 62 purple-leafed plum (Prunus cerasifera) plants tested positive for Xylella fastidiosa by enzyme linked immunosorbent assay. In all, 3 strains of X. fastidiosa were isolated from sweetgum and 13 from purple-leafed plum. All sweetgum strains and some purple-leafed plum strains grew on PW but not PD3 media. Strain PC045 from purple-leafed plum and strain LS022 from sweetgum were inoculated into their original hosts in addition to almond, oleander, and grapevine plants. Sweetgum plants also were inoculated with strains causing Pierce's disease, almond leaf scorch, and oleander leaf scorch. Strain PC045 caused symptoms in purple-leafed plum and almond plants within 6 months, and the pathogen was recovered from 93 and 100% of inoculated plants, respectively. Inoculation of grapevine and oleander plants with PC045 did not result in disease or recovery of the pathogen. In all, 5 of 25 sweetgum plants inoculated with LS022 showed symptoms after 9 months, and the pathogen was recovered from 3 of these plants. Inoculation of grapevine, oleander, and almond with LS022 resulted in no disease or recovery of the pathogen from the plants. A strain of Pierce's disease, a strain of oleander leaf scorch, and two strains from almond did not cause disease in sweetgum. These results confirm the role of X. fastidiosa strains as pathogens of purple-leafed plum and sweetgum, and that strains from sweetgum are unique in their host range. [ABSTRACT FROM AUTHOR]

Numerous ornamental nurseries in 32 California counties were surveyed for leaf spots as part of the California Department of Food and Agriculture mandated surveys targeting Phytophthora ramorum. Tissue collected during the 2005 and 2006 surveys was initially screened by a Phytophthora-speciflc enzyme-linked immunosorbent assay. All positives samples were further tested using polymerase chain reaction to determine if P rarnoru,n was present. P rarnoruni was detected in 1% of the total number of samples taken during the surveys. A total of 377 isolates were identified as species of Phytophthora other than P ramorum, and their identity was determined by internal transcriber spacer (ITS) sequences. Subsets of the putative ITS-species were further verified using accepted morphological characters. Thirteen species of Phytophthora were found: P. cactoru,n, P. cainbivora, P. citri cola, P citrophthora, P cryptogea, P foliorunz, P. gonapodyides, P hibernalis, P nemorosa, P. `Pgchlamydo', P pseudosyringae, P syringae, and P tropicalis. P syringae and P citricola made up 55% of the total number of isolates. Species thought to be strictly forest pathogens, P nernorosa and P pseudosyringae, each made up less than 4% of the isolates. To test pathogenicity of acquired isolates, subsets of different species of Phytophthora were inoculated onto leaves of selected host plant genera. Of the 66 pathogenhost genera combinations tested, 44 resulted in lesion formation. Disease symptoms appeared as dark, water-soaked lesions with irregular margins and were similar among Phytophthora species. [ABSTRACT FROM AUTHOR]

Fungal species in the family Botryosphaeriaceae have been recently recognized as the most common fungi isolated from grapevine (Vitis vinifera) cankers in California. However, the role of these fungi in causing grapevine dieback as well as their status as canker-causing agents was unknown. Therefore, pathogenicity studies were conducted to determine their importance as grapevine pathogens in California. A total of 72 isolates representing all nine Botryosphaeriaceae species isolated from grapevine cankers from California were used in five different pathogenicity studies. Overall, experiments showed all nine Botryosphaeriaceae species able to infect both young and mature tissues as well as green shoots of the new vegetative growth causing cankers, vascular discoloration, and/or otherwise dark streaking of the wood. However, virulence varied among species. Lasiodiplodia theobromae was the most virulent species followed by Neofusicoccum luteum, N. parvum, and N. australe, all categorized as highly virulent. Botryosphaeria dothidea was considered intermediately virulent and Diplodia inutila, D. seriata, Dothiorella iberica, and D. viticola were shown to be weakly virulent. This study shows species of Botryosphaeriaceae to be much more important pathogens on grapevines than originally thought, and some of them, in view of their virulence, should be considered high risk for causing severe and rapid canker and dieback diseases in the grapevine industry in California. [ABSTRACT FROM AUTHOR]

Because the role of soil inoculum of Phytophthora ramorum in the sudden oak death disease cycle is not well understood, this work addresses survival, chlamydospore production, pathogen suppression, and splash dispersal of the pathogen in infested forest soils. Colonized rhododendron and bay laurel leaf disks were placed in mesh sachets before transfer to the field in January 2005 and 2006. Sachets were placed under tanoak, bay laurel, and redwood at three vertical locations: leaf litter surface, litter—soil interface, and below the soil surface. Sachets were retrieved after 4, 8, 20, and 49 weeks. Pathogen survival was higher in rhododendron leaf tissue than in bay tissue, with >80% survival observed in rhododendron tissue after 49 weeks in the field. Chlamydospore production was determined by clearing infected tissue in KOH. Moist redwood-associated soils suppressed chlamydospore production. Rain events splashed inoculum as high as 30 cm from the soil surface, inciting aerial infection of bay laurel and tanoak. Leaf litter may provide an incomplete barrier to splash dispersal. This 2-year study illustrates annual P. ramorum survival in soil and the suppressive nature of redwood-associated soils to chlamydospore production. Infested soil may serve as primary inoculum for foliar infections by splash dispersal during rain events. [ABSTRACT FROM AUTHOR]

A pear bait monitoring system was used to detect and quantify Phytophihora ramorum propagules in streams that flow through woodland areas with sudden oak death in Santa Cruz County, CA from 2001 to 2007. Stream propagules were detected most frequently or occurred in highest concentrations in winter and spring. The stream propagule concentration was characterized with statistical models using temperature and rainfall variables from 2004 to 2007. The highest concentrations of propagules occurred when stream sampling was preceded by about 2 months with low maximum daily temperatures and by 4 days with high rainfall. The occurrence of propagules in streams in the summer was mostly associated with infected leaves from the native host Umbellaria californica that prematurely abscised and fell into the water. When the stream water was used for irrigating rhododendron nursery stock from 2004 to 2007, disease occurred only three times in the two wettest springs (2005 and 2006) on plants sprinkler irrigated with stream water with relatively high concentrations of propagules. Disease incidence was described with a statistical model using the concentration of infective propagules as measured by pear baiting and consecutive hours of leaf wetness measured by electronic sensors at rhododendron height. The concentration of infective propagules was significantly reduced after water was pumped from the stream and applied through sprinklers. [ABSTRACT FROM AUTHOR]

Spiroplasina citri, a phloem-limited pathogen, causes citrus stubborn disease (CSD). Losses due to CSD in California orchards have grown over the past decade. To investigate the possibility of introduction or emergence of a new strain, a study of genetic diversity among S. citri strains from various locations was conducted using random amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR) of 35 strains cultured from 1980 to 1993, and of 35 strains cultured from 2005 to 2006. Analysis using 20 primer pairs revealed considerable diversity among strains. However, no unique genetic signatures were associated with recently collected strains compared with those collected 15 to 28 years ago, and no geographically associated pattern was distinguishable. S. citri strains from carrot arid daikon radish contain some unique DNA fragments, suggesting some host plant influence. Multiple strains from single trees also showed genetic diversity. Sequencing of five RAPD bands that differed among strains showed that diversity-related gene sequences include virus fragments, and fragments potentially encoding a membrane lipoprotein, a DNA modification enzyme, and a mobilization element. No differences in colony morphology were observed among the strains. The lack of correlation between PCR patterns and isolation date or collection site is inconsistent with the hypothesis that recent infections are due to the introduction or emergence of novel pathogen strains. [ABSTRACT FROM AUTHOR]

Understanding the historical framework in which species interactions have diversified across landscapes may help to partition the effects of vicariance and geographically variable selection in shaping the geographical mosaic of coevolving species. We used phylogeographical analyses of the pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae) to define the historical processes that may have structured interactions of this species with its host plants across major biogeographical breaks in western North America. Using 648 bp of cytochrome oxidase I and amplified fragment length polymorphisims, we identified deep genetic breaks among some populations consistent with some definitions of cryptic species. A combination of phylogenetic and population genetic approaches indicates that different historical processes may have structured G. politella genetic diversity in four regions: northern Pacific Northwest, southern Oregon, southern Sierra Nevada, and the remainder of California. The northern Pacific Northwest had high genetic diversity likely due to glacial refugia and subsequent spatial expansion, concordant with some other taxa. Populations in southern Oregon possessed unique, closely related haplotypes with restricted gene flow, possibly indicating a long-standing set of populations in this endemic-rich region. Analyses of California populations showed evidence of restricted gene flow and spatial expansion with many closely related haplotypes that occupy a broad geographical range. Southern Sierra Nevada populations were genetically distinct and highly diverse, possibly due to a localized glacial refugium. Together, these results suggest that vicariance and population expansion, possibly in combination with geographically variable selection, have shaped the diversification of G. politella and its interactions with its host plants. [ABSTRACT FROM AUTHOR]

Late blight (LB) is one of the most aggressive tomato diseases in California. Accurately detecting the disease will increase the efficiency of properly controlling the disease infestations to ensure the crop production. In this study, we developed a method to spectrally predict late blight infections on tomatoes based on artificial neural network (ANN). The ANN was designed as a back-propagation (BP) neural network that used gradient-descent learning algorithm. Through comparing different network structures, we selected a 3-25-9-1 network structure. Two experimental samples, from field experiments and remotely sensed image data sets, were used to train the ANN to predict healthy and diseased tomato canopies with various infection stages for any given spectral wavelength (µm) intervals. Results of discrete data indicated different levels of disease infestations. The correlation coefficients of prediction values and observed data were 0.99 and 0.82 for field data and remote sensing image data, respectively. In addition, we predicted the field data based on the remote sensing image data and predicted the remote sensing image data with field data using the same network structure, and the results showed that the coefficient of determination was 0.62 and 0.66, respectively. Our study suggested an ANN with back-propagation training could be used in spectral prediction in the study. [ABSTRACT FROM AUTHOR]

Almond leaf scorch (ALS) disease has been present in California's almond-growing regions for over 60 years. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem-feeding sharpshooters and spittlebugs. Currently, there are no effective management techniques that prevent trees from becoming infected. Within affected orchards throughout California's Central Valley, disease incidence and the risk of tree-to-tree spread appears to be low. Consequently, the decision to remove or keep infected trees depends on lost productivity. We compared yield and vitality between infected and uninfected almond for cvs. Sonora and Nonpareil. Sonora was examined at three sites over 3 years and Nonpareil was examined at one site over 2 years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than those of Nonpareil. Yields of infected trees did not decline incrementally over years; rather, they fluctuated similarly to those of uninfected trees. In addition, no infected trees died during the course of the study. These results are in direct contrast to previous anecdotal reports which suggest that yields of infected trees incrementally decline and infected trees eventually die. A simple economic model was developed to determine conditions under which rouging infected trees would increase returns. Based on the model, orchard age, yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to remove ALS-affected trees. [ABSTRACT FROM AUTHOR]

Polymerase chain reaction (PCR)-based detection of citrus stubborn disease was improved using primers based on sequences of the P89 putative adhesin gene and the P58 putative adhesin multigene of Spiroplasma citri. Real-time PCR also was developed with detection limits estimated to be between 10-4 and 10-4 ng by serial dilution of a recombinant S. citri plasmid into DNA extracts from healthy Madam Vinous sweet orange. PCR for the detection of S. citri by these new primers was validated by comparing culturing of the pathogen, the traditional method of diagnosis, with PCR assays from samples taken from two citrus plots in Kern County, CA. Fruit columella was collected from 384 and 377 individual trees in each of two fields, respectively; one portion was used for culturing and the other for DNA extraction and PCR. PCR results matched those of culturing 85 to 100% of the time depending on the primers used. More importantly, PCR detected S. citri from culture-negative trees in 5 to 15% of the cases, suggesting that PCR performed as well or better than culturing for detection of S. citri in field samples. Real-time PCR proved to be the best method for detection. Differential reaction of the samples to the P58 primer pairs suggested that two populations of S. citri occur in historical and present-day field isolates. Citrus stubborn disease incidence was estimated to be 58.3 and 3.7% in the two orchards. The results presented here support the use of PCR for reliable detection of S. citri in field trees. [ABSTRACT FROM AUTHOR]

Turfgrass anthracnose, caused by Colletotrichum cereale (ex. Colletotrichum graminicola), is an important disease of turf used on golf course putting greens. Recent management of the disease has become increasingly difficult, partly due to the possible development of practical resistance to the Qol fungicides. In all, 558 single-conidia isolates of C. cereale were collected from 10 California golf courses, 8 of which had been exposed to Qol fungicides and 2 where no fungicides had been used. Isolates were tested using a mycelial expansion assay on azoxystrobin- amended media. For the two nonexposed populations, in vitro 50% effective dose (ED50) values ranged from 0.0060 to 0.089 pg/mI. All isolates from the exposed populations could not be fully inhibited by doses of azoxystrobin as high as 8.0 pg/mI. A subset of these isolates were tested in vitro with the Qol fungicides pyraclostrobin and trifloxystrobin and found to be similar in re- sponse, indicating that these isolates were fully cross-resistant to all three fungicides. In green- house pot experiments, three isolates nonresponsive to Qol fungicides in vitro were not con- trolled by label rates of the fungicides. Spore germination assays also were examined; for 10 isolates identified as sensitive by mycelial expansion assays, ED50 values for axoystrobin ranged from 0.0040 to 0.0047 pg/mI; for 25 isolates identified as Qol-resistant, 93 to 100% of the co- nidia germinated at azoxystrobin concentrations as high as 8.0 pg/mI relative to the nonamended check treatments. Mitochondrial cytochrome b genes from a subset of IS isolates (12 resistant and 3 sensitive) were partially cloned and sequenced; all resistant isolates had an alanine substitution that corresponded to position 143 of the gene product. These results indicate that Qol resistance is present in California populations of C. cereale and is contributing to the difficulty in controlling this disease. [ABSTRACT FROM AUTHOR]

Longevity of conidia of Penicillium digitatum (cause of citrus green mold) and arthroconidia of Geotrichum citri-aurantii (cause of sour rot of citrus) was determined under controlled temperature and relative humidity (RH) or ambient summer conditions in central California. Longevity at low RH was longer than at high RH. Hours to kill 99% of the conidia (LT99) of nine P. digitatum isolates were determined at 50°C and 75 or 95% RH. At 75 and 95% RH, the LT99 was 24.9 and 4.9 h, respectively. The LT99 was 30 and 42 days, respectively, for conidia of P. digitatum under ambient conditions at two outdoor locations. The LT99 of arthroconidia of G. citri-aurantii from colonies cultured on potato dextrose agar was briefer than that of conidia of P digitatum. At 45°C and 75 or 95% RH, the LT99 was about 4 and 2 h, respectively, whereas at 50°C, none was viable after 1 h at either humidity. Sanitation is an important practice for managing these diseases. Since there was little or no survival of either fungus after 1 day at 50°C and 75% RH or higher, we conclude that commercial sanitation could employ a similar regime. [ABSTRACT FROM AUTHOR]

The article presents abstracts of research about professionalism/service/outreach in the field of phytopathology presented at the 2007 American Phytopathological Society meeting held in San Diego, California. They include "Sequence and recombination analysis of potato virus Y," "Blueprint for learning: Constructing courses" and "Sustainable approaches to the management of plant-parasitic nematodes and disease complexes."

The article presents abstracts of research about plant disease management presented at the 2007 American Phytopathological Society meeting held in San Diego, California. They include "Model validation: What comes under the umbrella of validation concepts for pathogen/disease detection and forecasting models," "National effort to validate risk assessment models for Fusarium head blight (FHB) of wheat" and "The multiple challenges of mycotoxin detection and quantification in silages."

The article presents abstracts of research about plant epidemiology, ecology and environmental biology presented at the 2007 American Phytopathological Society meeting held in San Diego, California. They include "Assessing the severity of phoma stem canker in canola," "Pathogen threat assessment is predictive plant pathology" and "Principles of invasion biology: A foundation to predict pathogen invasiveness."

The article presents abstracts of research about plant diseases presented at the 2007 American Phytopathological Society meeting held in San Diego, California. They include "An overview of Sclerotiniaceae," "Biology of Sclerotinia homeocarpa and epidemiology of dollar spot" and "The global threat posed by Ug99."

The article presents abstracts of medical research presented at the 2007 American Phytopathological Society meeting held in San Diego, California. They include "The occurrence of mycotoxins in corn (maize) plant debris," "Simultaneous macroarray detection of eleven potato viruses and Potato spindle tuber viroid" and "Molecular diversity of grapevine Rupestris stem pitting-associated virus in Washington State vineyards."

In laboratory studies and experimental packingline trials that closely simulated fungicide treatments under commercial conditions, the ‘reduced-risk’ fungicides fenhexamid and fludioxonil were highly effective in managing postharvest brown rot and gray mold decays of peach, nectarine, and plum caused by Monilinia fructicola and Botrytis cinerea, respectively. Tebuconazole was more effective against brown rot than against gray mold. Additionally, fludioxonil and tebuconazole significantly reduced the incidence of Rhizopus rot caused by Rhizopus stolonifer. In laboratory studies, the QoI fungicide azoxystrobin was not consistent in its decay control activity. The high efficacy of fenhexamid and fludioxonil against brown rot and gray mold was substantiated by low effective concentrations necessary (≤0.063 mg/liter)for 50% inhibition of mycelial growth in vitro. In general, fungicides applied 14 to 16 h after wound inoculation were significantly more effective than those applied before inoculation. These results indicate that the fungicides act mainly as protectants that do not penetrate deeply enough into the fruit to prevent decay from wounds that extend below the fruit epidermis. Laboratory treatments of plum fruit generally were less effective than those of peach or nectarine fruit. Comparative studies using either low-volume spray or high-volume, in-line drench applications over a roller bed demonstrated that drench applications were significantly more effective in reducing postharvest decays of inoculated plum fruit. Decay incidence using fenhexamid or fludioxonil was <1.1%, whereas incidence after the spray applications was between 25.2 and 40.4% for brown rot, between 12.0 and 24.3% for gray mold, or 62.6% for Rhizopus rot (fludioxonil only). This research identified effective replacements for iprodione, a fungicide voluntarily canceled by the manufacturer in 1996. [ABSTRACT FROM AUTHOR]

Botryosphaeria spp. recently have been identified as important grapevine pathogens worldwide. To date, Botryosphaeria rhodina has been the only species associated with cankers on Vitis vinifera in California. A field survey of 166 vineyards in 21 counties was conducted in order to determine the occurrence of other Botryosphaeria spp. in California. In all, 1,735 samples of cankered trunks, cordons, and spurs were collected. Botryosphaeria spp. were the most common fungi isolated from grapevine cankers in California. Morphological identification along with phylogenetic analysis of the internal transcribed spacer region (ITS 1-5.8S-ITS2) of the nuclear ribosomal DNA (rDNA) and a partial sequence of the β-tubulin gene showed that at least seven Botryosphaeria spp. occur on grapevines in California: B. australis, B. dothidea, B. lutea, B. obtusa, B. parva, B. rhodina, and B. stevensii. Botryosphaeria spp. were found in grapevine cankers in all grape-growing regions surveyed in California, whereas incidence and distribution varied with location. Grapevine cankers in California have been associated mainly with Eutypa dieback. However, the frequent recovery of Botryosphaeria spp. from cankers in this study indicates that the role of these fungi in grapevine health needs to be more carefully considered. [ABSTRACT FROM AUTHOR]

Beginning in 2000 and continuing into 2004, a previously undescribed disease caused significant damage to romaine lettuce (Lactuca saliva) in the coastal Salinas Valley of California. Symptoms were brownish black, sunken cavities on the crown and upper taproot. Cavities were firm, lacked signs of fungal growth, and resulted in cracking and weakening of the crown. Affected plants were stunted, uneven in growth, and unmarketable. Crisphead lettuce also developed these symptoms, although disease incidence was always lower than that for romaine. A fungus was consistently isolated from cavities. Using morphological features and molecular methods, the fungus was identified as Phoma exigua. Pathogenicity of isolates from romaine and crisphead lettuce was demonstrated on both of these lettuce types. Replicated field studies showed that azoxystrobin, boscalid, and cyprodinil + fludioxonil fungicides effectively controlled the disease. This is the first report of a crown disease caused by P exigua in the United States. A similar disease, Phoma basal rot on greenhouse grown lettuce in the United Kingdom, had been previously observed, but no report has been published. [ABSTRACT FROM AUTHOR]

The sequence of the genome of a Rupestris stem pitting-associated virus (RSPaV) isolated from a declining Syrah grapevine in California, designated the Syrah strain (RSPaV-SY) was determined. The genome of this strain had an overall nucleotide identity of 77% in comparison with RSPaV sequences in GenBank; the coat protein was the most conserved gene among RSPaV sequences and the replicase was the least conserved gene. Phylogenetic analysis of partial coat protein and replicase gene sequences showed RSPaV-SY clustered independently from the majority of RSPaV isolates. [ABSTRACT FROM AUTHOR]

The article discusses the diagnostic protocol for the plant pest Phytophthora ramorum. This organism is a relatively described species of Phytophthora causing high mortality of oak trees in California. It has symptoms which can be diverse. These include three distinct syndromes including sudden oak death, ramorum shoot dieback, and ramorum leaf blight.

For better characterization of the risk of pitch canker (caused by Gibberella circinata, anamorph =  Fusarium circinatum) to Douglas fir ( Pseudotsuga menziesii), Californian isolates, selected exotic isolates, and ascospore progeny of a cross between wild-type Californian isolates were tested for aggressiveness to this host species. In addition, seedlings from representative provenances of P. menziesii in California were tested for susceptibility to pitch canker. The results revealed only minor differences between isolates, but differences in susceptibility between trees were often significant. The majority of the tested trees were relatively resistant as indicated by the development of only very short lesions, but some were clearly susceptible. [ABSTRACT FROM AUTHOR]

The population structure of Botrytis cinerea was investigated by using transposable elements, DNA fingerprinting generated by microsatellite primed-polymerase chain reaction (MP-PCR), and sensitivity to the hydroxyanilide fungicide, fenhexamid, for 234 isolates collected from fig, grape, kiwifruit, pea, and squash in California. Among 234 isolates tested, 195 had two transposable elements, Bozy and Flipper (transposa type), 38 had only the Boty element (Boty type), and one had neither of these elements (vacuma type). Four of these 234 isolates, which belonged to hie Bosy type, were resistant to fenhexamid. A phenogram generated based on MP-PCR mark- ers showed that the isolates were not clustered based on their source hosts or the presence of transposable elements. Analysis of molecular variance (AMOVA) showed that there were no significant genetic differentiations among isolates collected from grape, kiwifruit, pea, and squash at the Kearney Agricultural Center. A more detailed analysis based on AMOVA partition of the total genetic variance indicated that 96% of the variation occurred within populations. The parsimony tree length permutation (PTLPT) and index of association (IA) analyses of MP-PCR data set were consistent with absence of sexual recombination in sampled populations of this pathogen. [ABSTRACT FROM AUTHOR]

This study investigated phylogenetic divergence, morphological difference, and pathogenic variation among Cytindrocarpon species isolates associated with black foot disease of grapevine (Vitis sp.) in California. To assess phylogenetic divergence, we sequenced the internal transcribed spacer (ITS) of the nuclear ribosomal DNA (rDNA), partial beta-tubulin (BT) gene introns and exons, and the small subunit mitochondrial rDNA. Isolates associated with black foot disease belonged to two paraphyletic species, Cylindrocarpon destructans and C. macrodidymum. The morphology of these isolates was in agreement with published descriptions of both species. We found that C macrodidymum isolates were reliably distinguishable from C destructans isolates in culture by a unique orange-dark brown colony color on 2% malt extract agar and genetically by a species-specific 52-bp DNA insertion in the BT region. Selected isolates of each species inoculated onto grapevine rootstock 5C caused typical black foot disease symptoms. This is the first report of C. macrodidymum in California. [ABSTRACT FROM AUTHOR]