Tolerance of isolates of Colletotrichum coffeanum to prochloraz-Mn in Kenya

Abstract

Coffee berry disease, caused by Colletotrichum coffeanum is a serious disease of Coffea arabica in Kenya. Control of this disease is achieved mainly through the use of fungicides which currently include chlorothalonil and prochloraz-Mn (Octave). Fungicide resistance in C. coffeanum to benzimidazoles has been well documented. Isolates of C. coffeanum highly sensitive to prochloraz-Mn have been shown to acquire tolerance to high levels of prochloraz-Mn in culture. These isolates were able to grow and sporulate in malt extract agar (MEA) amended with 250 mig ml-1 prochloraz-Mn. The prochloraz-Mn tolerant isolates of C. coffeanum showed low level of tolerance to benomyl. The benomyl tolerant isolates of C. coffeanum equally showed low level of tolerance to prochloraz-Mn. The prochloraz-Mn and benomyl tolerant and sensitive isolates were found to be highly pathogenic and induced sporulating lesions on seedlings and berries of coffee cv. SL 28 which is very susceptible to C. coffeanum. Mixed inoculation tests using prochloraz-Mn and benomyl tolerant isolates and prochloraz-Mn tolerant and sensitive isolates of C. coffeanum showed that the prochloraz-Mn tolerant isolate was competitive