Studies on the disinfection of seed potatoes

Abstract

1. Experiments to compare the effect of drying washed and disinfected seed tubers in ventilated stacks of 10 cwt. boxes with drying in seed chitting trays indicated that, in general, there were no marked differences produced by the two methods with respect to control of storage disease, crop growth and yield. However, there was a tendency for condensation moisture to form on the top boxes of the stacks which was probably associated with a slight increase in soft rot in 1965 and blackleg in 1966-67 and 1967-68. Covering boxes with straw was found to apparently reduce condensation. 2. Commercial washing and disinfection increased the incidence of blackleg in the field despite modifications aimed at reducing damage before disinfection. The washing machine was shown to assist in some way the entry of the blackleg organism into the potato tissues beyond the reach of the disinfectant. Disinfection of unwashed tubers reduced the level of the disease to below that found in untreated tubers. 3. Some evidence was given to account for the generally higher incidence of blackleg in the trials in 1968 than in 1967. Although experiments were planted in different fields in the same area in the two years, it is suggested that the difference in blackleg incidence was the result of the rainfall pattern. 4. Using hot air drying apparatus, it was shown that disinfected and washed and disinfected tubers could be dried satisfactorily with air temperatures up to 212°F when exposed to the hot air stream for up to 3i min. There was no evidence that the hot air affected control of storage diseases, growth of crop, blackleg or yield. 5. Disinfection of unwashed tubers in a prototype disinfection tank for 1/2 - 3/4 min. with an EEMC concentration of 150 ppm showed that storage disease could be reduced and blackleg controlled in the field. However, the presence of soil slightly affected the efficiency of the disinfection process. 6. In the trials over the three years disinfection usually reduced the incidence of skin spot, dry rot and gangrene to a satisfactory level. When this was not the case, delay in applying the treatment of more than three days after lifting was usually the reason. 7. Generally, disinfected tubers gave sprout stimulation, earlier emergence, greater number of stems and tubers than undisinfected tubers. 8. Despite the higher level of blackleg in crops grown from washed and disinfected seed compared with untreated tubers, the yield was not significantly reduced. Unwashed, disinfected tubers produced yields which compared favourably with untreated tubers, showing that plants grown from undisinfected seed were probably more vigorous.