August, 2006

Influence of Temperature, Inoculation Interval, and Dosage on Biofumigation with Muscodor albus to Control Postharvest Gray Mold on Grapes. F. Mlikota Gabler, Institute for Adriatic Crops, Put Duilova 11, 21000 Split, Croatia; R. Fassel, PACE International, LLC, Visalia, CA 93291; J. Mercier, AgraQuest Inc., Davis, CA 95616; and J. L. Smilanick, United States Department of Agriculture–Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648. Plant Dis. DOI: 10.1094/PD-90-1019. Accepted for publication 12 March 2006.

Biofumigation is the use of volatiles produced by microorganisms for the control of other plant pathogens or pests. We found that biofumigation with the fungus Muscodor albus controlled postharvest gray mold of table grapes caused by the fungus Botrytis cinerea. Gray mold is the most common cause of decay of grapes in storage. Postharvest biofumigation of table grapes with M. albus is a flexible approach to manage gray mold because it is compatible with the various phases of the handling process, cold storage, packaging, and shipment of the fruit. M. albus was never in direct contact with grapes during biofumigation. It was effective when 10 or 20 g of M. albus grain formulation per kilogram of grapes was placed inside clamshell containers, as well as within the liner outside the perforated grape cluster bags. It was slightly more effective at ambient room temperature than at 0.5ºC. The treatment can be applied by simply placing active M. albus formulations within packages of grapes. Biofumigation with the natural volatiles from M. albus may be promising to develop into a product for commercial use to prolong the postharvest life of table grapes instead of sulfur dioxide gas-generating pads now used for this purpose.

Virulence and Diversity of Blumeria graminis f. sp. hordei in Israel and in the Czech Republic. Antonín Dreiseitl, Agricultural Research Institute Kroměříž Ltd., Havlíčkova 2787, CZ-76701 Kroměříž, Czech Republic; Amos Dinoor, Department of Plant Pathology and Microbiology, The Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot IL-76100, The Hebrew University of Jerusalem, Israel; and Evsey Kosman, Institute for Cereal Crops Improvement, The George S. Wise Faculty for Life Sciences, Tel Aviv University, Tel Aviv IL-69978, Israel. Plant Dis. DOI: 10.1094/PD-90-1031. Accepted for publication 8 March 2006.

This study revealed large differences between Israeli and Czech populations of the barley powdery mildew pathogen in the frequency of most virulences examined, and particularly virulences for resistance genes originating from Israel. Virulence can be defined as the ability of a pathogen strain to induce disease in a host plant; a gene-for-gene system has been demonstrated for some pathogen–host combinations, including this one, such that each virulence gene developed by the pathogen corresponds to a specific gene for resistance in the host. The pathogen populations in these two countries belong to distinct epidemiological units with little or no movement of the pathogen between them. Because of this isolation, plant breeders should be encouraged to exploit the diversity of host resistance from wild barley in Israel for breeding new cultivars resistant to powdery mildew in Europe and further afield. Some virulences that are abundant in Europe were found to be absent or of low frequency in Israel, suggesting that the corresponding resistance genes in the wild barley in Israel are absent or present in low frequencies. The high frequency of other virulences in the Israeli population suggests that some resistance genes derived from landraces of barley could also be present, along with many others, in the populations of wild barley in Israel. Increasing virulence frequency is associated with rising complexity of the pathogen populations and evolution of so-called super-races. Our results demonstrate that such complex pathotypes are abundant in nature where high host diversity exists.

Identification of Small Grains Genotypes Resistant to Soilborne wheat mosaic virus. L. Cadle-Davidson, Department of Plant Pathology, M. E. Sorrells, Department of Plant Breeding and Genetics, S. M. Gray, United States Department of Agriculture–Agricultural Research Service (USDA-ARS), PPRU, and G. C. Bergstrom, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. DOI: 10.1094/PD-90-1039. Accepted for publication 13 March 2006.

Soilborne wheat mosaic virus (SBWMV) was detected in New York for the first time in 1998, and its range gradually is expanding as infested soil is inadvertently transported to new farm locations. Infected small grain plants show a distinctive foliar mosaic in the spring resulting in significant yield loss. Sowing of resistant small grain cultivars is the most effective method for reducing yield loss due to SBWMV in plants grown in soils infested with the virus. Prior to our study, the reaction of regionally adapted small grain cultivars to SBWMV generally was unknown. Therefore, we evaluated 115 adapted small grain cultivars and breeding lines for their reaction to SBWMV over four growing seasons in a farm field with a history of soilborne wheat mosaic disease. Resistance to SBWMV reduces the percentage of plants that develop viral symptoms. We recorded the percentage of plants of each genotype that showed characteristic symptoms in spring. Overall disease incidence was high in 2 years and low in 2 years of the study. The comparative resistance of particular genotypes with intermediate levels of resistance varied over the years of study, illustrating the need to base cultivar assessments on evaluation in three or more years or distinct field environments. No genotype assessed over multiple years was completely free from infection. However, 41 of the regionally adapted genotypes tested repeatedly expressed strong resistance to SBWMV, providing growers in New York and surrounding states a choice of cultivars resistant to SBWMV. Our results also provide a large number of reference cultivars for those who assess resistance of small grain cultivars in future years or different production areas.

Identification of Small Grains Genotypes Resistant to Wheat spindle streak mosaic virus. L. Cadle-Davidson, Department of Plant Pathology, M. E. Sorrells, Department of Plant Breeding and Genetics, S. M. Gray, United States Department of Agriculture–Agricultural Research Service (USDA-ARS), PPRU, and G. C. Bergstrom, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. DOI: 10.1094/PD-90-1045. Accepted for publication 13 March 2006.

In New York, nearly every field with a history of wheat production is infested with Wheat spindle streak mosaic virus (WSSMV), and planting wheat cultivars resistant to WSSMV is the only practical approach to managing the disease once WSSMV is introduced. Therefore, we evaluated 112 adapted small grain cultivars and breeding lines for their reaction to WSSMV over three growing seasons in a field that had been used continuously for WSSMV evaluation for over 20 years. Resistance to WSSMV reduces the percentage of plants that develop viral symptoms. We recorded the percentage of plants of each genotype that showed characteristic symptoms in spring. The comparative resistance of particular genotypes with intermediate levels of resistance varied over the years of study, illustrating the need to base cultivar assessments on evaluation in three or more years or distinct field environments. No genotype assessed over multiple years was completely free from infection. However, 62 of the regionally adapted genotypes tested repeatedly expressed strong resistance to WSSMV, providing growers in New York and surrounding states a choice of cultivars resistant to WSSMV. Our results also provide a large number of reference cultivars for those who assess resistance of small grain cultivars in future years or different production areas.

Holdover Inoculum of Pseudomonas syringae pv. alisalensis from Broccoli Raab Causes Disease in Subsequent Plantings. N. A. Cintas, USDA, PWA, ARS, 1636 E. Alisal Ave., Salinas, CA 93905; S. T. Koike, University of California Cooperative Extension, Salinas 93901; R. A. Bunch, D’Arrigo Bros. Co., Salinas, CA 93902; and C. T. Bull, USDA, PWA, ARS, 1636 E. Alisal Ave., Salinas, CA 93905. Plant Dis. DOI: 10.1094/PD-90-1077. Accepted for publication 28 March 2006.

The 12 million dollar crucifer industry in Monterey County, CA, provides the United States with the majority of broccoli, cauliflower, and Brussels sprouts, as well as other specialty crucifers such as broccoli raab, consumed annually. Bacterial blight of crucifers is an emerging disease that was first observed in California but has since been reported across the country. Because the pathogen can cause disease on a wide range of plants, it is important to know if susceptible plants are at risk of becoming diseased if they are planted in fields after a diseased crop has been harvested and the residue has been incorporated into the soil. This research demonstrated that the pathogen present in the leaves of a diseased crop caused disease when a second crop is planted after the diseased crop has been tilled into the soil. This is significant for growers because a susceptible crop following a diseased crop is likely to also become diseased. Thus, it is recommended that growers plant something other than crucifers directly after an outbreak of bacterial blight.

Resistance of Strawberry Cultivars to Crown Rot Caused by Colletotrichum gloeosporioides Isolates from Florida Is Nonspecific. S. J. MacKenzie and D. E. Legard, University of Florida, Gulf Coast Research and Education Center, Wimauma 33598; L. W. Timmer, University of Florida, Citrus Research and Education Center, Lake Alfred 33850; and C. K. Chandler and N. A. Peres, University of Florida, Gulf Coast Research and Education Center, Wimauma 33598. Plant Dis. DOI: 10.1094/PD-90-1091. Accepted for publication 25 March 2006.

Colletotrichum crown rot of strawberry is a wilt disease that is most severe in subtropical production regions. In Florida, it is caused mainly by Colletotrichum gloeosporioides, and its occurrence in local summer nurseries is one of the primary reasons why transplants for the winter season are produced in temperate regions. In the current study, resistance to several genetically distinct C. gloeosporioides isolates was determined for strawberry cultivars grown commercially in Florida. The study was conducted to find cultivars with potential for local propagation, to determine which cultivars might be good parents for breeding new resistant cultivars and to determine if resistance to C. gloeosporioides is specific to subsets of isolates or if it is effective against a broad spectrum of isolates. Our results showed that resistance to C. gloeosporioides appears to be effective against all isolates. Although no cultivar was immune to C. gloeosporioides, the cultivar Treasure was substantially more resistant to crown rot than any of the others examined. We also found that resistance to C. gloeosporioides was correlated with resistance to C. fragariae, another pathogen with the ability to cause crown rot.

The Occurrence of PVY(^O), PVY(^N), and PVY(^N:O) Strains of Potato virus Y in Certified Potato Seed Lot Trials in Washington and Oregon. J. M. Crosslin, United States Department of Agriculture, Agricultural Research Service, Prosser, WA 99350; P. B. Hamm, D. C. Hane, and J. Jaeger, Department of Botany and Plant Pathology, Oregon State University, Hermiston Agricultural Research and Extension Center, Hermiston 97838; C. R. Brown, United States Department of Agriculture, Agricultural Research Service, Prosser, WA 99350; P. J. Shiel and P. H. Berger, Center for Plant Health Science and Technology, USDA-APHIS, Raleigh, NC 27606; and R. E. Thornton, Crop and Soils Science Department, Washington State University, Pullman 99164. Plant Dis. DOI: 10.1094/PD-90-1102. Accepted for publication 30 March 2006.

Potato virus Y (PVY) is an economically important pathogen of potatoes wherever the crop is grown. The virus exists as a number of biological types, or strains, that differ in their effects on potatoes and certain other plants, like tobacco. The ordinary strain of the virus, PVY(^O), causes mild symptoms in potato and tobacco. The tobacco necrotic strain, PVY(^N), causes very mild or no symptoms in potato foliage and a systemic necrosis in tobacco. Another strain, PVY(^N:O), also causes systemic necrosis in tobacco and relatively mild symptoms in most varieties of potatoes. In addition to causing reductions in yield, the PVY(^N) and PVY(^N:O) strains are known to cause symptoms in potato tubers, thus reducing the quality of the crop. The primary source of PVY in a commercial field is infection of the seed pieces. For this reason, it is important to determine how widespread the various PVY strains are in commercial seed lots. In this paper, we investigated the occurrence of PVY in hundreds of seed lots from several states and Canadian provinces. Results indicate that PVY is widespread in commercial seed lots. The data also show that the incidence of the PVY(^N:O) strain in particular is increasing in seed lots. This study shows that the current efforts to reduce the incidence of PVY in seed lots are not effective and that additional measures need to be taken to reduce the impact of this important virus to potato production.