Infection of avocados by the rot fungi Colletotrichum acutatum and Phomopsis sp.

'Hass' avocado fruit were wound-inoculated in the orchard at monthly intervals for 7 months with labelled strains of Colletotrichum acutatum and Phomopsis sp. The strains were single-spore isolates that were selected for their lack of ability to metabolise nitrate (nit strains). Fruit were harvested a month after the last inoculation and placed in the coolstore for 28 days, then placed at 20 degrees C and assessed when ripe. Rot lesions were aseptically removed and placed on potato dextrose agar. Any resultant C. acutatum or Phomopsis sp. colonies were then placed on minimal medium with nitrate. Nit isolates were identified by their lack of ability to grow normally. Only one nit isolate was recovered from 175 fruit wound-inoculated with Phomopsis sp. In contrast, 21 nit isolates were recovered from 175 fruit wound-inoculated with C. acutatum. Examination of the temperature required for spore germination showed that 50% germination occurred in 24 h at 12.6 degrees C for C. acutatum, and at 11.6 degrees C for Phomopsis sp. Both these temperatures were exceeded for four of the 7 months. In three of those four months, more nit isolates of C. acutatum were recovered.