EFFECTS OF HUMIDITY, LEAF WETNESS, TEMPERATURE AND LIGHT ON CONIDIAL PRODUCTION BY PHAEOISARIOPSIS-PERSONATA ON GROUNDNUT

Controlled-environment studies of conidial production by Phaeoisariops is personata on groundnut are described. With constant relative humidi ty (RH), conidia were only produced above a threshold (94 . 5% RH) and there was a linear increase between 94 . 5% RH and 100% RH. Conidial production was less with continuous leaf wetness (resembling heavy dew ) than with continuous 98-99% RH, but it was similar with intermittent leaf wetness and intermittent 98-99% RH (8 h at 70% RH each day). Wit h alternate high (greater than or equal to 97% RH) and low humidity, d aily conidial production depended both on the duration of high RH and on the low RH value. With 99% RH at night (12 h), night-time conidial production decreased with the previous daytime RH. After conidial prod uction had started, small numbers of conidia were produced even when t he RH was well below the threshold (94 . 5%). Conidia were produced in continuous light when the photon flux density was 2 mu mol/m(2)/s., b ut production was completely inhibited with 60 mu mol/m(2)/s. With con stant RH, more conidia were produced with a 12 h photoperiod than in c ontinuous darkness. However, more than 75% of the conidia were produce d in the dark. With continuous darkness, more conidia were produced du ring the night (18.00-06.00 h) than during the day, but this biologica l rhythm was overcome with a (light-night)/(dark-day) regime. With con stant 98-99% RH there was a linear increase in conidial production wit h temperature between 10 and 28 degrees C, and virtually no conidia we re produced at 33 degrees C. The daily production of conidia increased with time for 2 to 6 days, depending on the treatment.