Analysis of Spore Dispersal Gradients ofBotrytis cinereaand Gray Mold Disease Gradients in Snap Beans

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Abstract
Spore dispersal, spore incidence on blossoms, and pod rot disease gradients from point inoculum sources of B. cinerea were measured over time in 2 snap bean (P. vulgaris) fields. Laboratory-grown inoculum was placed at ground level in a 30 .times. 30-cm square at bloom initiation and removed at full bloom. Dispersal of inoculum, assessed by quantifying the number of viable 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 20-30 times higher than populations at full bloom due to production of secondary inoculum. During the bloom period, incidence of B. cinerea on senescing blossoms averaged 70% at a distance of 0.9 m from the inoculum source, but < 25% at distances greater than 4 m. In one experiment, the incidence of pod rot at harvest averaged 7.2% at 0.9 m from the inoculum source, but only 1.3% at 4.5 m. Spore dispersal gradients (log spore number vs. log distance) showed significant flattening at harvest compared to full bloom, whereas gradients for pod rot incidence at harvest did not flatten compared to incidence of B. cinerea on blossoms at full bloom. Because senescing blossoms are the primary infection court for infection of the pods, the nonsignificant flattening of the pod rod gradient suggests that early arrival of inoculum of B. cinerea on blossoms was important in pod rot development.

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