EFFECT OF TETRACHLORONITROBENZENE ON THE SPROUTING AND CROPPING OF POTATO TUBERS

Abstract

Potato tubers dusted with a preparation containing 3% tetrachloronitrobenzene (TCNB) and kept in a nearly closed container in the laboratory showed reduced sprouting. The reduction was greater the lower the temperature and the earlier the application of the dust; it was less marked with tubers lying on a moist substratum. After long exposure, and especially at higher temperatures, sprouts of treated tubers tended to show a ‘witch's‐broom’ appearance. The repressive effect of TCNB on growth rate disappeared as soon as the tubers were brought into ordinary air. To a certain extent the action of TCNB was antagonized by treatment of the tubers with ethylene chlorhydrin. Replicated field experiments over three seasons, with four potato varieties, gave a measure of the check to bulking of the crop which is brought about by winter storage of seed tubers in presence of TCNB. This check was eliminated by airing the tubers before planting, the time necessary for this depending on conditions. An airing period of about 6 weeks, in an unheated greenhouse (apart from sun‐ heat) was found to be sufficient for this purpose. The speed of emergence of the variously treated batches was closely correlated with the yields produced, especially in the earlier liftings. The average number of shoots per plant was significantly increased by the dust treatment and this was reflected in a higher seed/ware ratio in the mature or late‐lifted crop. There was no evidence that the delay in sprouting brought about by TCNB was due to an effect on the respiration rate of the dormant tubers. The concentration of active principle was materially diminished in treated clamps after the period ( c. 5 months) of winter storage. Estimates were also made of the persistence of TCNB on exposed surfaces in still and in moving air.