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

Abstract

The effect on dry rot of the potato of disinfecting seed potatoes with a proprietary organo‐mercury fungicide immediately before they were clamped on lifting, and on their removal from the clamps after 3 or 6 months' storage, has been tested in field trials during two seasons. The incidence of the disease in tubers stored in clamps has also been studied. The tubers used were of the susceptible varieties Ninetyfold and Doon Star, taken from crops grown in contaminated soil. In certain of the tests the natural contamination in the soil adhering to the tubers was reinforced by spraying each tuber with a spore suspension of the dry‐rot fungus.Seed tubers not deliberately bruised on lifting, and whether dipped or not at that time, were practically sound after 3 and 6 months' storage in clamps except in one instance. On removal from the clamps, those not dipped on clamping continued to remain sound when carefully handled and stored for a further period in seed boxes, but they suffered either moderate losses if slightly bruised, or serious losses if severely bruised, at the time they were removed from the clamps. Tubers dipped immediately before being clamped yielded similar results, except that they remained sound when slightly bruised on removal from the clamps.Tubers not dipped, but deliberately bruised either on lifting in July immediately before clamping or on reclamping in October, developed severe dry rot whilst stored in the clamps. The incidence of the disease was not influenced by the location of the tubers within the clamp.In tubers not dipped at lifting and clamping time in July, but lightly bruised and immediately dipped on their removal from the clamps in October, the losses from dry rot were slight. Severe bruising followed immediately by dipping on their removal from the clamp in October, however, resulted in considerable losses.Tubers not dipped at lifting and clamping time in July but, after 3 or 6 months' clamp storage, slightly bruised and immediately dipped, then severely bruised 2 days later, developed appreciable losses; but these losses were far less than in tubers treated similarly except that the dipping was omitted.Tubers dipped on lifting immediately before clamping in July, and slightly bruised and immediately redipped on removal from the clamps in October, remained almost sound; but tubers severely bruised just before the second dipping in October developed a loss of 12%.All the foregoing results were obtained with tubers taken from healthy clamps. Ostensibly healthy tubers taken carefully from clamps containing much dry rot became severely affected with the disease when further stored in seed boxes.