DISPERSAL OF PASSALORA-PERSONATA CONIDIA FROM GROUNDNUT BY WIND AND RAIN

In experiments where groundnut plants with sporulating late leaf spot lesions were exposed to increasing 'gusty' and 'steady' wind speeds, c onidia were more effectively removed by gusty winds than by steady win ds of the same mean wind speed. Rain drops dislodged conidia more effi ciently than wind, with large drops dispersing conidia more effectivel y than small ones. No conidia were caught in still air. After most of the conidia had been removed by exposure to high wind speeds, rain was found to remove additional conidia. When plants were exposed to conti nuous wind or rain, most of the conidia were dispersed during the firs t few minutes, and the concentration of conidia then declined exponent ially with time. From field observations on rain-free days, airborne c oncentrations of conidia tended to increase as the wind speed increase d during the day and with a further increase in wind speed, concentrat ions decreased. On rainy days, the onset of the first shower coincided with a phenomenal increase in the airborne concentrations of conidia.