The effect of disinfecting and bruising seed potatoes on the incidence of dry rot (Fusarium caeruleum (Lib.) Sacc.)

Abstract

The effect of bruising and of disinfecting (‘dipping’) seed potatoes with a proprietary organo‐mercury preparation on the incidence of dry rot in them was tested in field trials during three seasons. The tubers used were of the susceptible variety Ninetyfold, taken from crops grown in contaminated soil, harvested immature in July to early August each year under farm conditions, and stored in boxes.Seed tubers not deliberately bruised, whether dipped or not at lifting time, remained practically sound until planting time in the fallowing season, if left undisturbed in their boxes.Tubers deliberately bruised, either at digging time or 1‐2 weeks later, but not dipped, developed severe dry rot with few exceptions. The disease had run its course by mid‐October. When undipped, sound tubers were bruised in October, they contracted severe dry rot, but dipping such tubers immediately before bruising reduced the loss satisfactorily in five out of six trials.Tubers bruised at digging time and immediately dipped suffered little from dry rot in almost all cases. Delayed dipping of bruised tubers checked the disease in some trials but not in others. Seed tubers severely bruised 1‐2 weeks after being dipped remained practically sound except in one instance, whereas tubers severely bruised approximately 3 months after being dipped, subsequently developed severe dry rot in four out of six tests, unless they had been redipped immediately before they were bruised.Inoculation of healthy tubers with soil samples showed that the fungus is widely distributed in potato fields in Cheshire. Dipping killed all, or almost all, of the fungus in the soil adhering to the seed tubers.The results are discussed and suggestions are made for further investigations and for practical control measures.