Survival of the lettuce anthracnose fungus (Microdochium panattonianum) in Victoria

Soils from anthracnose-infected lettuce fields at Keilor, Werribee South and La Trobe University caused lesions of Microdochium panattonianum to develop when inoculated on to lettuce leaves. Under field conditions conidia lost infectivity within 10 weeks in pasteurized and 6 weeks in non-pasteurized Werribee South soil, 2 weeks in Keilor red and immediately in Keilor black non-pasteurized soils. Soils remained infective for 18 weeks in non-pasteurized and pasteurized Werribee South soils inoculated with conidia and for Hand 16 weeks respectively when the same soils were inoculated with infected leaf discs.
In 1983 and 1984 M. panattonianum survived for 14 and 16 weeks respectively on infected Cos Verdi debris on the soil surface, for 10 and 20 weeks respectively on debris buried at 10 cm depth and for 70 and 58 weeks respectively on debris suspended in the air. The fungus survived for similar periods on infected Winterlake debris on the soil surface and buried at 10 cm depth. In soil the decline of infectivity was primarily influenced by duration of exposure and soil moisture, and in debris by duration of exposure and rainfall that occurred over the 2 weeks preceding each sample. The disease was not transmitted on seed produced on infected plants. Seedlings grown from healthy seed inoculated with conidia did not develop anthracnose after the seed had been stored for 24 days at 5 or 20°C. The significance of these results to the management of lettuce anthracnose in Victoria is discussed.