The effect of post-harvest storage conditions on the development of black dot (Colletotrichum coccodes) on potato in crops grown for different durations

摘要

The effects of post-harvest curing and storage temperature on severity of black dot, caused by Colletotrichum coccodes, were investigated for potato crops grown for different crop durations (days from 50% emergence to harvest) in soils that posed a low, medium and high risk of disease. In field trials over four growing seasons (2005-8), black dot severity at harvest increased with increasing crop duration, within the range 103-146days from 50% emergence to harvest (P<0.05). In field trials over three growing seasons (2006-8), black dot severity on tubers at harvest increased significantly with increasing soil inoculum in each year, within the range 43-4787pg C. coccodes DNA/g soil (P<0.05). Storage trials were conducted to measure the influence of accumulated post-harvest temperature on black dot. In 2005, no difference in black dot severity was observed on tubers stored for 20weeks at 2.5 and 3.5 degrees C. In 2006 (but not 2007), increasing the duration of curing after harvest from 4 to 14days increased black dot severity on tubers from 8.9 to 11.2% (P<0.01) in long duration crops (>131days after 50% emergence) grown under high (>1000pg C. coccodes DNA/g soil) soil inoculum. The number of days of curing did not affect disease severity for shorter duration crops grown at high soil inoculum, or on crops grown at medium or low (100-1000 and <100pg C. coccodes DNA/g soil, respectively) soil inoculum concentrations. Soil inoculum and crop duration together provided a reasonable prediction of black dot severity at harvest and after a 20-week storage period.