The effect of low temperatures on Colletotrichum acutatum and Colletotrichum gloeosporioides causing body rots of avocados in New Zealand

Abstract

The effect of extended periods at low temperatures on spore germination, survival and appressorial formation in Colletotrichum acutatum and C. gloeosporioides, and on pre-formed appressoria of C. gloeosporioides, was studied on water agar on glass slides on a temperature gradient plate. C. acutatum was more tolerant of low temperatures than was C. gloeosporioides. The addition of peptone to simulate endogenous nutrients on the avocado fruit surface affected spore germination and survival only slightly, and the effect was not statistically significant. These trends in vitro were also apparent in isolations from fruit rots. Infections by C. acutatum were not reduced by storage at 5.5°C before ripening. Incidence of infections caused by C. gloeosporioides was significantly fewer in fruit coolstored at 5.5°C for 30 days prior to ripening at 20°C than in fruit stored at 20°C. In the two lines of fruit studied, coolstorage reduced body rots in one line but not the other. The rots on the line of fruit not affected by coolstorage were mainly caused by C. acutatum. These results suggest that in coolstored fruit, the reduction in incidence of rots caused by C. gloeosporioides, but not of rots caused by the closely related fungus C. acutatum, was due to the greater sensitivity of spores of C. gloeosporioides to cold temperatures. Survival of pre-formed appressoria of C. gloeosporioides was not affected by temperatures used for coolstorage of avocados.