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Potato mop-top virus (PMTV) causes mop top disease in potato. This disease can result in a decline in tuber quality causing economic losses to growers due to the production of necrotic lesions and discolored tissue in infected tubers. Due to the soilborne nature of PMTV, identifying and developing host resistance against the virus is considered the best disease management option. Very little is known about the sensitivity of U.S. potato cultivars to PMTV-induced tuber necrosis. The current study is aimed at investigating the sensitivity of a large number of potato cultivars to PMTV-induced tuber necrosis. Sixty-three cultivars representing all market-types were evaluated in North Dakota over a 2-year period for virus-induced tuber necrosis incidence and severity. PMTV-induced tuber necrosis (P < 0.0001) and severity (P < 0.0001) were significantly different among cultivars. Cultivars were categorized into sensitive, insensitive, and moderately sensitive/insensitive groups based on the virus-tuber induced necrosis data from both years. Based on data from ND trials, six cultivars (Red Endeavor, Viking, Dakota Jewel, Dark Red Norland, Nicolet, and Modoc) were rated as sensitive and 43 were rated as insensitive to PMTV-induced tuber necrosis. Four cultivars, including Bannock Russet, Gemstar Russet, Lelah, and Waneta showed zero PMTV incidence over 2 years. These results will help growers in making individual or coordinated decisions for the management of PMTV-induced tuber necrosis under field and storage conditions. [ABSTRACT FROM AUTHOR]

The article offers information on ribotyes of polymyxa graminis in wheat samples infected with soilborne wheat viruses in China. Topics discussed include genus Polymyxa, DNA extraction of wheat roots and polymerase chain reaction, and Sequencing and phylogenetic analysis. Also being discussed is wheat sample collection.

Field trials were conducted from 2010 to 2013 at four locations in Illinois to evaluate the impact of cover crops (cereal rye [Secale cereal], brown mustard [Brassica juncea], winter canola [B. napus], and winter rapeseed [B. napus]) on soybean [Glycine max] stands and yield, diseases, pathogen populations, and soil microbial communities. Cover crops were established in the fall each year and terminated the following spring either by using an herbicide (no-till farms), by incorporation (organic farm), or by an herbicide followed by incorporation (research farm). Although shifts in soilborne pathogen populations and microbial community structure were not detected, cover crops were found to induce general soil suppressiveness in some circumstances. Cereal rye and rapeseed improved soybean stands in plots inoculated with Rhizoctonia solani and decreased levels of soybean cyst nematode in the soil. Cereal rye increased soil suppressiveness to R. solani and Fusarium virguliforme, as measured in greenhouse bioassays. Cereal rye significantly improved yield when Rhizoctonia root rot was a problem. [ABSTRACT FROM AUTHOR]

Dry bean (Phaseolus vulgaris L.) is a globally important leguminous food crop. Yields can be reduced by high incidence of soilborne oomycetes that cause seedling disease. Breeders have attempted to develop Pythium root rot-resistant bean varieties; however, relationships between dry bean and most soilborne oomycete species remain uncharacterized. Oomycete species (n = 28), including Pythium spp. and Phytopythium spp.. were tested in a growth chamber seedling assay at 20°C and an in vitro seed assay at 20°C and 26°C to evaluate their pathogenicity and virulence on 'Red Hawk' dark red kidney bean and 'Zorro' black bean. Root size or disease severity was significantly impacted by 14 oomycete species, though results varied by bean variety, temperature, and assay. Of these 14 pathogenic oomycete species, 11 species exhibited significant differences in DS1 due to temperature on at least one bean variety. Pythium aphanidermatum, P. myriotylum, P. ultimum. P. ultimum var. sporangiiferium, and P. ultimum var. ultimum were the most virulent species in both assays, causing seed rot and pre-emergence damping-off of dry bean. Oomycete species were clustered into three groups based on symptom development: seed rot pathogens, root rot pathogens, or nonpathogens. Intraspecific variability in virulence was observed for eight of the 14 pathogenic oomycete species. Improved understanding of Pythium and Phytopythium interactions with dry bean may enable breeders and pathologists to more effectively evaluate strategies for oomycete seedling disease management. [ABSTRACT FROM AUTHOR]

Eight fungal isolates (ELRF I to 8) were recovered from necrotic roots of Easter lilies, Lilium longiflorum cv. Nellie White, grown in a field in the U.S. Pacific Northwest. The eight fungal isolates were identified by sequencing and molecular phylogenetic analyses based on their ITS i DNA region. Five isolates were identified as Fusarium oxysporum, two as F. tricinctum, and one as Rhizoctonia sp. AG-I. This constitutes the first report of Rhizoctonia sp. AG-I infecting lilies worldwide and the first report of F. tricinctum infecting lilies in the United States. To study and validate their pathogenicity, pure cultures of each isolate were used to infect the roots of Easter lily plants growing in vitro. In addition, Easter lily plants growing in vitro were infected either with or without Pratylenchus penetrans, the root lesion nematode, prior to placing a culture plug of fungus 1 cm from a lily root. Pratylenchus penetrans is a nematode species commonly found in the sampled fields. The presence of both nematode and Rhizoctonia sp. AG-1 isolate ELRF 3 in infected lilies was evaluated by molecular analyses, confirming the infection of roots 3 days after inoculation, prior to development of disease symptoms. Necrosis and root rot developed more rapidly with all eight fungal isolates when there had been prior infection with P. penetrans, the major nematode parasitizing Easter lily roots in the field in Oregon. [ABSTRACT FROM AUTHOR]

The decline and death of strawberry plants in Spanish fruit production fields have mainly been attributed to the soilborne pathogens Macrophomina phaseolina, Phytophthora cactorum, and Fusarium spp. Inoculum sources of M. phaseolina and P. cactorum, and the incidence all three genera, were investigated in nurseries and fruit production fields over three consecutive seasons. M. phaseolina inoculum sources consisted of fumigated preplant fruit production soils (50%) and fumigated nursery soils (47%), although the pathogen could not be detected in nursery mother and runner plants. P. cactorum inoculum sources included nursery (20%) and preplant fruit production (17%) fumigated soils, and nursery runner plants (up to 15%). In fruit production plants, the average incidence of M. phaseolina and P. cactorum were 4.2 and 3.7%, respectively. Fusarium spp. inoculum sources could not be accessed extensively due to the lack of effective quantitative real-time PCR assays. Limited testing of nursery plants showed that Fusarium oxysporum f. sp. fragariae (Fof) was absent. In field production plants and soil, F. solani was the main pathogenic Fusarium spp., with Fof only identified once in a fruit production plant. Ineffectively fumigated soils in nurseries and production fields, along with infected runner plants, can be inoculum sources of soilborne strawberry pathogens in Spain. [ABSTRACT FROM AUTHOR]

The article presents the study that investigates the threat posed by peanut smut to the peanut production in Argentina. The topics discussed include the origin of peanuts in South America, oil and butter as the primary focus and manufactured products in Argentina, and the use of fungicides in the management of different soilborne diseases in peanuts.

Various physical and chemical factors in soil can inhibit the detection and quantification of soilborne plant pathogens using quantitative polymerase chain reaction (qPCR) assays. A multiplexed TaqMan qPCR assay, including a competitive internal positive control (CIPC), was developed to identify and (where necessary) compensate for inhibition in the quantification of resting spores of Plasmodiophora brassicae from soil. The CIPC amplicon was developed by modifying a sequence coding for green fluorescent protein so that it could be amplified with P. brassicaespecific primers. Addition of CIPC at 5 fg/p.1 to the singleplex qPCR assay designed to quantify P. brassicae genomic DNA did not reduce the sensitivity, specificity, or reproducibility of the assay. Each of the soil samples, either artificially inoculated or naturally infested with P. brassicae, exhibited no amplification of the CIPC. When the samples were diluted and reassessed, the quantification cycle of the CIPC relative to the control (water only) was delayed in each sample. The magnitude of the delay was used to adjust the estimate of resting spore concentration. The corrected concentration estimates were significantly higher than the unadjusted estimate, which indicated the presence of DNA inhibitors in samples even after dilution. The only exception was a mineral soil sample inoculated with a low concentration (103 spores/g) of resting spores. The assay was optimized for use on a range of soil types. A sample of 0.25 g for mineral soil and 0.10 g for high-organic-matter soil was optimum for recovery of DNA of P. brassicae. The assay represents an improvement over exisdng assays for estimating resting spore concentration in infested fields. [ABSTRACT FROM AUTHOR]

Onion stunting caused by Rhizoctonia spp. is an important soilborne disease on very sandy soils in the Columbia Basin of Oregon and Washington. From 2010 to 2013, 251 isolates of Rhizoctonia or Rhizoctonia-like spp. were obtained from soil and onion plant samples collected from inside and outside patches of stunted plants in 29 onion fields in the Columbia Basin. Sequence analysis of the internal transcribed spacer (ITS) region was used to identify the isolates, with 13 anastomosis groups (AGs) or subspecies detected. The most frequent was Waitea circinata var. circinata (25%), followed by Rhizoctonia solani AG 3 (17%), R. solani AG 4 (14%), Ceratobasidium sp. AG A (10%), R. solani AG 8 (7%), Ceratobasidium sp. AG K (6%), R. solani AG 2-1 (6%), W. circinata var. zeae (6%), R. solani AG 5 (4%), Ceratobasidium sp. AG G (2%), R. solani AG 11 (2%), and R. solani AG 1-1B and AG 10 (each <1%). However, the distribution of AGs and subspecies varied depending on whether soil or onion plants samples were collected within or adjacent to patches of stunted onion plants. In an attempt to predict the risk of onion stunting for a field prior to planting, DNA concentrations of AG 2-1, AG 3, AG 4, and AG 8 were quantified from bulk soil samples collected from each of nine growers' fields approximately 1 month before onion sowing in 2012. The preplant DNA concentrations did not show a significant association with the amount of stunting observed in the fields during the growing season. In contrast, the frequency of isolation and DNA concentration of R. solani AG 8 detected in soil samples collected during the growing season were greater from inside patches of stunted onion plants than from adjacent healthy areas of an onion crop sampled in 2012, but not for soil samples collected similarly from an onion crop in 2013. AG 2-1, AG 3, and AG 4 DNA concentrations did not differ significantly in soil sampled inside versus outside stunted patches in the fields sampled in 2012 and 2013. Relationships between the number of bulbs harvested or bulb weight versus severity of stunting were defined using correlation and regression analyses for six onion cultivars grown in seven fields surveyed in 2012 and 2013. Onion stunting reduced the average marketable bulb yield by 25 to 60% within stunted patches of the six cultivars. Stunting did not reduce onion plant stand but consistently reduced the size of bulbs, and yield reduction increased with increasing disease severity. [ABSTRACT FROM AUTHOR]

Verticillium dahliae is a ubiquitous soilborne fungus and the causal agent of smoke tree vascular wilt, which presents a major threat to the famous "red-leaf' scenery of the Fragrant Hills Park in Beijing, China. In this study, we detected the presence of the fungus based on the amount of fungal DNA in planta and in the soil by using quantitative nested real-time polymerase chain reaction (QNRT-PCR). The QNRT-PCR assay results were highly specific for V. dahliae and could detect disease wilt dynamics over time in different plant tissues. Tests with QNRT-PCR in infested soils showed the detection of soil inoculum densities as low as 1 microsclerotium/g of soil. The QNRT-PCR data showed strong correlation between the quantity of pathogen DNA and the Verticillium wilt disease severity rating, suggesting that quantification of V. dahliae soil inoculum could be conducted to assess Verticillium wilt risk before planting. These data indicate that QNRT-PCR is a sensitive and reliable method to monitor the soilborne pathogen V. dahliae in planta and in soil. The results of this study can be useful in the devel-opment of new disease control measures for Verticillium wilt and assess-ment of the risk of V. dahliae infection of smoke tree before planting. [ABSTRACT FROM AUTHOR]

Fungicides not reaching target organisms result in decreased disease control. In the southeastern United States, foliar-applied fungicides are routinely used to manage peanut (Arachis hypogaea) diseases. Irriga-tion is often applied to wash fungicides from treated foliage to obtain maximum control of diseases caused by soilborne pathogens. Adminis-tering irrigation before fungicide residues have dried may adversely impact foliar disease control. A microplot study was conducted in 2003, 2004, and 2005 to evaluate the redistribution of azoxystrobin, tebuconazole and flutolanil plus chlorothalonil following different irrigation timings. Standard fungicide regimes were subjected to 1.3-cm of irrigation 0, 6, 12, 24,48, or 96 h after application, and a nonirri-gated control was included. Microplots not receiving irrigation were covered while irrigation treatments were administered. Irrigation tim-ing was significant for the number of early leaf spot (Cercospora arachidicola) lesions per leaf. Leaf spot was more severe when irrigation was administered immediately following fungicide applications, and was significantly reduced with a 6- and 12-h delay prior to an irri-gation event, whereas maximum control was obtained when irrigation was delayed for 24 h or later. To further quantify fungicide residue distribution, Sclerotium rolfsii was used to bioassay foliage and pods. Lesion development on leaflets, which was greater for earlier irrigation timings, did not differ for the 12-h and later timings and was generally similar to the nonirrigated controls. Pod colonization for all fungicides increased according to a quadratic function of irrigation timing, with the least colonization occurring at the 0-h timing. Colonization of pods treated with azoxystrobin was similar for all irrigation timings; whereas, suppression was greatest for tebuconazole at earlier irrigation timings. This study demonstrates that irrigation can be used to redistribute fungi-cides applied to peanut foliage to improve control of soilborne pathogens but administering irrigation within 24 h may decrease leaf spot control. [ABSTRACT FROM AUTHOR]

The article focuses on the status and management of verticillium wilt, considered to be a major threat to olive production. It says that verticillium wilt is olive is caused by Verticillium dahliae Kleb, a soilborne fungus, in which it states that the said fungus is the most soilborne disease the affect worldwide olive production. It discusses the syndromes and symptoms of the said olive plant disease, adding that the disease has two syndromes such as defoliating (D) and non- defoliating (ND).

Groundnut (Arachis hypogaea) is an economically important legume crop in Vietnam and many other countries worldwide. Stem and pod rot, caused by the soilborne fungus Scierotium rolfsii, is a major yield-limiting factor in groundnut cultivation. To develop sustainable measures to control this disease, fundamental knowledge of the epidemiology and diversity of S. rolfsii populations is essential. In this study, disease incidence was monitored in eight groundnut areas in central Vietnam with a total of 240 observational field plots. The results showed that 5 to 25% of the field-grown groundnut plants were infected by S. rolfsii. Based on internal transcribed spacer (ITS) ribosomal DNA sequence analyses, three distinct groups were identified among a total of 103 randomly selected S. rolfsii field isolates, with the majority of the isolates (n = 90) in one ITS group. S. rolfsii isolates originating from groundnut, tomato, and taro were all pathogenic on groundnut and relatively sensitive to the fungicide tebuconazole but displayed substantial diversity of various genetic and phenotypic traits, including mycelial compatibility, growth rate, and sclerotial characteristics. [ABSTRACT FROM AUTHOR]

Verticillium dahliae, causal agent of Verticillium wilt of potato, persists in soil as microsclerotia and can be found in infected tubers used for seed. The effects of naturally infected tubers and soilborne inoculum on Verticillium wilt symptoms were compared in the greenhouse. Infected and noninfected tubers were grown in infested and noninfested potting soil. Chlorosis and necrosis were measured and converted to area under senescence progress curves (AUSPC). Aboveground stems and progeny tubers were assayed for V. dahliae. Plants from infested soils exhibited significantly greater AUSPC than plants from noninfested soil. Plants grown from infected and noninfected tubers had similar AUSPC and interactions between infected tubers and infested soil were not observed. The pathogen was isolated from the vascular system of 94% of plants grown in infested soils and 8% of plants grown from infected tubers in noninfested soil. Plants grown in infested soil contained microsclerotia on 46% of stems while plants grown from infected tubers in noninfested soils exhibited microscierotia on <1% of stems. Infected progeny tubers were only recovered from plants grown in infested soil. Seed tuber infection did not contribute to premature senescence or potential inoculum production, indicating that management efforts should focus on reducing soilborne inoculum. [ABSTRACT FROM AUTHOR]

Chemical control of soilborne peanut (Arachis hypogaea) diseases requires deposition of fungicide on plant tissues near the soil. Four applications of a protectant fungicide, chiorothalonil (1.26 kg al/ha), or a systemic, azoxystrobin (0.21 kg a.i./ha), pyraclostrobin (0.21 kg a.i.Iha), or prothioconazole (0.08 kg a.i./ha) plus tebuconazole (0.15 kg al/ha), were sprayed either (i) early in the morning (3:00 to 5:00 AM., with folded and wet leaves), (ii) during daylight (10:00 A.M. to 12:00 P.M., with unfolded and dry leaves), or (iii) in the evening (9:00 to 10:00 P.M., with folded and dry leaves). All timings of systemic fungicides provided similar control of foliar diseases. Early-morning applications of pyraclostrobin and prothioconazole plus tebuconazole decreased stem rot (caused by Scierotium rolfsii) at digging compared with day and evening applications. All systemic fungicides increased yield when applied at early-morning compared with day applications. Spray coverage, density, and droplet size were higher with night than day applications, and differences were more evident in the lower canopy layers. These results suggest that applications made early in the morning to folded, wet leaves can improve spray penetration of peanut canopies, thus improving stem rot control and increasing yield. [ABSTRACT FROM AUTHOR]

Earthworm densities have been regarded as reliable indicators of soil health, but their role in suppression of plant disease has not received much attention. Several greenhouse studies were done to determine if soils infested with soilborne pathogens and augmented with earthworms (Lumbricus terrestris) could reduce disease of susceptible cultivars of asparagus (Asparagus officinalis), eggplant (Solanum melongena), and tomato (Solanum lycopersicum). Soils planted with asparagus were infested with Fusarium oxysporum f. sp. asparagi and F. proliferatum, eggplant with Verticillium dahliae, and tomato with F. oxysporum f. sp. lycopersici Race 1. In each host-disease system, earthworm activity was associated with an increase in plant growth and a decrease in disease. In general, plant weights were increased 60 to 80% and estimates of disease (area under the disease progress curve, percent vascular discoloration, and percent root lesions) were reduced 50 to 70% when soils were augmented with earthworms. Soil dilutions on selective media revealed that densities of fluorescent pseudomonads and filamentous actinomycetes were consistently higher for rhizosphere soils augmented with earthworms. In the studies with Verticillium wilt of eggplant, compared to the controls, the densities of total bacteria and Mn-transforming microbes were reduced in the presence of earthworms while population densities of bacilli and Trichoderma spp. were not affected. Disease suppression may have been mediated through microbiological activity. These studies suggest that strategies to increase earthworm densities in soil should suppress soilborne diseases. [ABSTRACT FROM AUTHOR]

Stem rot of peanut, caused by the soilborne fungus Sclerotiunz rolfsii, is greatly influenced by environmental conditions. Disease management programs rely heavily on fungicides, which are applied on a calendar-based program. To determine whether improved control of stem rot could result from weather-based spray advisories, models were constructed using what is currently known about the biology of S. rolfsii and etiology of stem rot epidemics in peanut. Spray advisories based on soil temperature, precipitation, and host parameters were tested, along with advisories focusing on soil temperature and precipitation or precipitation alone. The advisories were evaluated and compared with the currently used calendar-based program over four locations annually for 3 years. Fungicide application timing had a significant effect on both stem rot control and resulting pod yields. In general, stem rot control following the advisories considering soil temperature, precipitation, and canopy growth was similar or better than that offered by the calendar-based program, but yields generally were comparable. The AU-Pnut advisory for foliar diseases also was effective for scheduling azoxystrobin applications for stem rot. [ABSTRACT FROM AUTHOR]

Incorporating Brassica spp. residue to reduce populations of soilborne fungi and manage damping-off and Fusarium wilt of watermelon (Citrullus lanatus var. lanatus) was studied in two field experiments. Treatments included incorporating flowering Brassica napus cv. Dwarf Essex canola or B. juncea cv. Cutlass mustard and laying black polyethylene mulch at incorporation or 1 month after incorporation, methyl bromide, and a nontreated control. In both years, glucosinolates were identified and quantified in the shoots and roots of the flowering plants. In both years, the total concentration of glucosinotates incorporated per square meter was significantly higher for B. juncea than for B. napus. Isothiocyanates were inconsistently detected in the amended soils and none were detected more than 12 days postincorporation. After incorporation in 2004 and 2005, amended plots had higher populations of Fusarium oxysporuin and Pythium spp. than the methyl bromide treatment, and in some treatments, populations were higher than in the control. Fluorescent Pseudomonas spp. were not suppressed in amended soils, and their populations were significantly higher in some amended treatments than those in methyl bromide-treated soils or nontreated control soils. Incidence of damping-off and severity of Fusarium wilt on seedless watermelon cv. Tri-X 313, which is susceptible to Fusarium wilt, were not consistently lower in brassica-amended soils or methyl bromide-treated plots than in nontreated control plots. Therefore, under spring conditions and methods used in this study, neither biofumigation nor methyl bromide fumigation in coastal South Carolina was an effective disease management tool for two soilborne pathogens of watermelon. [ABSTRACT FROM AUTHOR]

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 an- other 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 sprouts-strawberry, 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, straw- berry 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. [ABSTRACT FROM AUTHOR]

The article focuses on the growing popularity of grafted vegetables in Israel and suggests that the use of grafted vegetables will likely become more common as a replacement for soil fumigation as a means for managing soilborne diseases. The technology's integration with other environment-friendly technologies could ease the transition into the post-methyl bromide era. Rootstock-scion compatibility as a major obstacle to increased usage of the grafting technology is cited.

Increasing restriction of agrochemicals is motivating development of ecology-based cropping systems, including green manures, to manage soilborne diseases. Green manures have shown promise in suppressing Verticillium dahliae, but information about effect of different green manures and optimal application rates remains limited. Therefore, we conducted two single-year field experiments comparing effects of Austrian winter pea (Pisum sativum ‘Melrose’), broccoli (Brassica oleracea var. botrytis ‘Excelsior’), and Sudan grass (Sorghum vulgare var. sudanense ‘Monarch’), amended at 6, 12, or 24 Mg ha-1, on soil populations and root infection by V. dahliae, wilt severity, and yield of Russet Burbank potato. Inoculum density was reduced relative to the nonamended, infested control by all broccoli treatments, Austrian winter pea applied at 12 and 24 Mg ha-1, and Sudan grass applied at 12 Mg ha-1. Root infection was not reduced by any green manure treatment. Median wilt severity was reduced approximately 70% by all green manures applied at 24 Mg ha-1 and 74% by Austrian winter pea applied at 12 Mg ha-1. Tuber yield was reduced approximately 20% in nonamended, V. dahliae-infested controls relative to the noninfested controls. No green manure treatment improved yield relative to the nonamended, infested control. [ABSTRACT FROM AUTHOR]

Soybean severe stunt (SSS), caused by the Soybean severe stunt virus (SSSV), is a soilborne virus disease affecting soybean (Glycine max) first described in Delaware in 1988. Lack of breeding programs directed at incorporating resistance to SSSV in new cultivar releases necessitated alternative methods of SSS control. The effect of crops in 2-year rotations on the dagger nematode (Xiphinema americanum), the putative nematode vector of SSSV, and SSS severity were examined. Two years of continuous corn or grain sorghum, wheat followed by ‘HT-5203’ soybean, or 2-year fallow, reduced both dagger nematode density in the soil and SSS severity. Crop rotation to the SSSV-tolerant HT-5203 soybean as a single crop for 2 years increased dagger nematode populations and SSS severity. Greenhouse studies indicated that corn, wheat, marigold, castor, and fallow treatments reduced dagger nematodes the most after 14 weeks compared with ‘Essex’ and HT 5203 soybean. [ABSTRACT FROM AUTHOR]

Combinations of soil fumigation with a mixture of 1,3-dichloropropene (1,3-D) plus chloropicrin (Pic) and soil solarization for 7 days were evaluated under different plastic films and sequences of application for their effects on soilborne pests and marketable yield of fresh market tomato (Lycopersicon esculentum) and pepper (Capsicum annuum). Shank injection of fumigants under a virtually impermeable film (VIF) using a novel application apparatus dramatically improved their retention in the soil. Survival of Fusarium oxysporum f. sp. lycopersici in soil declined significantly when fumigation or solarization was combined with VIF compared with either soil disinfestation treatment applied under low-density polyethylene. When compared with an untreated control, significant reductions in yellow nutsedge (Cyperus esculentus), purple nutsedge (C. rotundus), and root-knot nematodes (Meloidogyne spp.) were achieved with a reduced dosage of fumigant when applications were made 7 days after planting beds were covered with VIF. A 7-day delay in fumigant application in beds covered by low-density polyethylene significantly increased marketable yield of pepper when compared with an untreated control. The results demonstrate that chemical and nonchemical soil disinfestation methods can be combined with novel application technology and procedures to improve their spectrum of pest control and reduce fumigant application rates. [ABSTRACT FROM AUTHOR]

Soils naturally infested with cultures of aviruliferous Polymyxa betae and viruliferous P betae carrying two sugar beet benyviruses, Beet necrotic yellow vein virus (BNYVV) and Beet soilborne mosaic virus (BSBMV), alone and in combination, were compared with noninfested soil for their effects on seedling emergence, plant fresh weight, and virus content as measured by enzyme-linked immunosorbent assay (ELISA). Studies examined sugar beet with and without resistance to the disease rhizomania, caused by BNYVV. The Rz gene, conferring resistance to BNYVV, did not confer resistance to BSBMV. BSBMV ELISA values were significantly higher in single infections than in mixed infections with BNYVV, in both the rhizomania-resistant and -susceptible cultivars. In contrast, ELISA values of BNYVV were high (8 to 14 times the healthy mean) in single and mixed infections in the rhizomania-susceptible cultivar, but were low (approximately three times the healthy mean) in the rhizomania-resistant cultivar. Results indicate BNYVV may suppress BSBMV in mixed infections, even in rhizomania-resistant cultivars in which ELISA values for BNYVV are extremely low. Soils infested with P betae, and with one or both viruses, showed significantly reduced fresh weight of seedlings, and aviruliferous P betae significantly decreased sugar beet growth in assays. [ABSTRACT FROM AUTHOR]