Role of inoculum sources of Botrytis cinerea in the epidemiology of gray mold of snap beans Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m613n205m

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  • Spore dispersal gradients and pod disease gradients from point inoculum sources of Botrytis cinerea were measured over time in two snap bean field experiments. Laboratory grown inoculum was placed at ground level in a 30 x 30 cm square at bloom initiation and removed at full bloom. Dispersal of inoculum, assessed by quantifying spores washed from bean foliage, was limited to within 3 m from the inoculum source during bloom. At harvest, the spore populations on plants were 20 to 30 times higher than populations at full bloom due to secondary production of inoculum. At two sampling times during bloom, incidence of B. cinerea on senescing blossoms averaged 70 percent at a distance of 0.9 m from the inoculum source but less than 25 percent at distances greater than 4 m. In one experiment, the incidence of pod rot at harvest averaged 7.2 percent at 0.9 m from the inoculum source but only 1.3 percent at a distance of 4.5 m. Spore dispersal gradients analyzed by regression of the form log Y = a + b log X showed significant flattening at harvest compared to full bloom, whereas gradients for pod rot incidence at harvest did not flatten when compared to incidence of B. cinerea on blossoms at full bloom. Blossom infections early in the bloom period from point inoculum sources were important in pod rot development. To determine if within-field inoculum sources are important in pod rot development in commercial snap bean production, an observational study was conducted in five bean fields in Oregon's Willamette Valley. Senescing cotyledons were the initial plant tissue colonized by Botrytis cinerea. Young stem tissues and leaf tissues also became diseased and served as within-field inoculum sources. The number of these inoculum sources before bloom varied between fields and ranged from 14.8 to 0.2 per 5 m row. The number of spores per plant at bloom initiation and the incidence of B. cinerea on blossoms at full bloom was positively correlated with the number of prebloom inoculum sources within a field. Using the number of inoculum sources prior to bloom as a predictive variable, 50 percent of the variation in the incidence of pod rot among fields could be explained. A multiple regression model, which included the number of inoculum sources before bloom, frequency of irrigation, duration of leaf wetness due to irrigation and rain, and canopy size explained 82 percent of the variation in percent pod rot among fields.
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