Inoculum concentration, leaf age, wetness duration, and temperature in relation to infection of strawberry leaves by Diplocarpon earlianum
1994
Zheng, J. (Agriculture Canada, Harrow, Ontario.) | Sutton, J.C.
Inoculum concentration, leaf age, leaf wetness duration, and temperature markedly, and often interactively, affected numbers of lesions produced by Diplocarpon earlianum on strawberry leaves. Incidence of lesions at sites on leaves inoculated with 10-microliter droplets of inoculum increased linearly with concentration of the inoculum (0 to 1 X 10(4) conidia/mL). Density of lesions on leaves sprayed with spore suspensions containing 0 to 8 X 10(4) conidia/mL increased in a pattern resembling a saturation curve. Number of lesions increased quadratically and diameter of lesions increased linearly with leaf age. Density of lesions increased quadratically with wetness duration at 10-30 degrees C. In some conditions of persistent wetness (greater than or equal to 24 h) at 20-30 degrees C, lesion density peaked then markedly declined. Minimum wetness duration for infection ranged from 5 to 15 h, depending on leaf age and temperature. Density of lesions at 20 degrees C was near optimum after 21 h wetness in leaves 9-10, 15-17, and 22-24-days-old, and after 34 h in leaves 2-3 days old. Density of lesions in leaves 15-16 days old was high after 18 h wetness at 15-30 degrees C and after 24 h wetness at 10 degrees C. Observations of infection under various wetness and temperature conditions in the field generally agreed with those under controlled conditions. A polynomial model was developed that predicted lesion density effectively under controlled conditions and was moderately effective in the field
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