Hypovirulent isolates of Colletotrichum gloeosporioides induce resistance to anthracnose in detached mango fruits and seedlings

Abstract

Colletotrichum gloeosporioides [(Penz.) Penz. & Sacc] causes anthracnose in various tropical crops, including mango (Mangifera indica L.). In Puerto Rico, estimated losses ¡n mango fruits are as high as 75%. Intensive chemical applications used to control this disease have resulted in fungicide resistance and potential environmental pollution. An alternative control could be inducing resistance in mango with hypovirulent isolates of C. gloeosporioides. Hypovirulent (HV) mutants were obtained by conidial mutagenesis using ultraviolet light. Mycelial plugs (4 mm) of HV mutants were used to inoculate the surface of detached mango fruits, either 24 or 120 h previous to the virulent isolate inoculation. Fruits were kept in humid chambers (i.e., 100% RH). Lesion size was measured eight and 14 days after inoculation with the virulent isolate. Mango seedlings were inoculated with the HV mutants, as described above, 120 h prior to the virulent isolate inoculation and kept under shade-house conditions. Lesion size was measured four and 10 days after inoculation with the virulent isolate. Fourteen days after inoculation, three HV mutants reduced lesion size in detached fruits by 50%. Locally induced resistance (in situ) was observed in middle leaves of mango seedlings. All three HV mutants tested reduced lesion development in middle leaves of mango seedlings 10 days after inoculation. Hypovirulent isolates HV-49 and HV-165 induced systemic resistance to the upper leaves of the plant. The HV mutants appeared to inhibit pathogen development by activating defense mechanisms in mango fruits and seedlings.