Effects of temperature and relative humidity on conidial germination and viability, colonization and sporulation of Monilinia fructigena

Experiments were conducted to investigate the effects of temperature and re lative humidity (RH) on the in vitro germination and viability of conidia o f the apple brown rot fungus (Monilinia fructigena), and on colonization an d sporulation on detached fruits by M. fructigena. Conidia only germinated under near-saturation humidity (greater than or equal to 97% RH) and the ra te of germination initially increased with temperature to a maximum at appr oximate to 23-25 degreesC and then decreased. Conidia germinated rapidly - more than 70% of viable conidia had germinated within 2 h at 20 and 25 degr eesC. The rate of colonization on detached fruits increased log-linearly wi th increasing temperature. Sporulation on detached fruits was not observed at 5 or 25 degreesC; sporulation appeared to be unaffected by either temper ature (10-20 degreesC) or RH (45-98%) once infection was established. Detac hed conidia remained viable for a long period of time, up to 20 days, the l ongest assessment time in this study, depending on storage temperature (10 or 20 degreesC) and RH (45 or 85%). Temperature appeared to be more importa nt than RH in affecting conidial viability. Low temperature and high RH res ulted in reduced loss of conidial viability Storage at 10 degreesC and 85% RH for up to 20 days appeared not to affect conidial viability. These resul ts indicate that environmental conditions during the main UK growing season s are unlikely to be limiting factors for the development of brown rot on a pple.