Dispersal of Conidia of Botrytis cinerea in Tomato Fields

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Abstract
Conditions influencing dispersal of conidia of B. cinerea were studied in 2 fields of staked tomato [Lycopersicon esculentum] plants near Carpinteria and Chula Vista, California [USA]. Conidia were trapped with a Burkard spore trap (10 l/min) throughout the growing season. In 1 field, trapped conidia averaged < 50 per day when disease incidence was less than 5 decayed fruit/15 plants, but increased 5-fold when disease incidence was 20-30 decayed fruit/15 plants during the last month of the growing season. Circadian periodicity in spore dispersal was observed. Maximum concentrations of spores occurred about midday. This circadian periodicity was positively correlated to changes in temperature and wind velocity and negatively correlated to changes in percent relative humidity and presence of dew. Wind velocities up to 9.6 km/h above the canopy of the tomato field resulted in wind velocities of less than 0.5 km/h at sites of stem cankers located at the bases of the plants. The incidence of disease along a disease gradient from a line source of inoculum showed that the spread of inoculum and subsequent disease incidence was limited to plants within 8 m of the inoculum source. In a wind tunnel, few conidia were dispersed from a 6 cm diameter, sporulating colony grown on potato-dextrose agar that was exposed to wind velocities of about 0.4 km/h. Greater numbers of conidia were released and dispersed from the same colony on agar exposed to higher wind velocities. Spread of conidia of B. cinerea to adjacent plants by air is probably limited by the low wind velocities within the tomato canopy which would affect dispersal of released conidia from sites of sporulation.

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