A comparison of Fusarium avenaceum and Fusarium caeruleum as causes of wastage in stored potato tubers

Abstract

Fusarium avenaceum is reported for the first time as a cause of rotting of potato tubers in Britain. The progress of rotting in tubers infected with F. avenaceum has been compared with dry rot due to F. caeruleum in the laboratory, clamp and potato store. Of the four varieties, Majestic, King Edward, Doon Star and Arran Pilot, tested for susceptibility, King Edward was the most susceptible to F. avenaceum and Doon Star to F. caeruleum.Optimum temperatures for growth on potato‐dextrose agar were 20‐25d̀ C. for F. avenaceum and 20d̀ C. for F. caeruleum; maximum temperatures were > 30 and 30d̀ C. respectively. For infection of wounded potato tubers, cardinal temperatures for F. avenaceum were similar to those on agar, but for F. caeruleum the optimum was 15d̀ C. and the maximum 25d̀ C. The optimum temperature for rotting tended, with both species, to be higher in the more susceptible potato varieties. At low temperatures F. caeruleum caused quicker rotting than did F. avenaceum, even though its rate of growth on agar was scarcely more than half that of the latter.High humidity favoured rotting especially by F. avenaceum; F. caeruleum was more tolerant of relatively low humidity. Both species caused quicker rotting in the clamp than in store, even though there was no appreciable difference in mean temperature between the clamp and the store. This was attributed to the higher atmospheric humidity in the clamp.