The saprophytic survival of the fungus Alternaria brassicicola was investigated in leaf debris of broccoli (Brassica oleracea var. italica), at different depths of soil incorporation, periods of the year, and systems of soil management. Infected leaf debris were distributed in field plots, at the soil surface and at depths of 5 and 10cm. Periodically, the debris in the bags were collected and conidia concentrations were quantified for longevity of spore production and extinction rate. Higher spore production longevity was observed on leaf debris in the period with lower temperatures, higher air relative humidity and lower rainfall. The lowest spore production occurred when leaf debris incorporation was made at 10cm depth. In relation to soil management systems, when the inoculum source was deposited at the soil surface no differences in the rate of spore production were observed, but at depths of 5 and 10cm, the rate was significantly higher in the soil under conventional management. The management of Alternaria black spot on broccoli at the area under study can be accomplished by incorporating infected leaf debris in the soil, at least 10cm depth, for no less than a 60-day interval in subsequent brassica plantings.
Brassica oleracea var. italica; Alternaria black spot; inoculum source; sporulation
