INFLUENCE OF POST HARVEST TEMPERATURE TREATMENTS, STORAGE PERIOD AND HARVEST DATE ON DEVELOPMENT OF SPRAING CAUSED BY TOBACCO RATTLE VIRUS AND POTATO MOP-TOP VIRUS

The frequency of PMTV-spraing and TRV-spraing increased during storage in several cultivars. The only exception was cv. Saturna, where a dec rease was observed in 1992. A spraing inducing treatment of one week a t 18 degrees C followed by one week at 8 degrees C immediately after a n early harvest increased the frequency and provided a rough estimate of the development of spraing in untreated tubers during storage. Unde r most circumstances wound healing at 25 degrees C compared with 15 de grees C resulted in a lower frequency of spraing during the storage pe riod. The date of harvest had an important influence on development of spraing during storage and on the effect of post harvest temperature treatments. Therefore, physiological processes that induce or erase sp raing are strongly related to tuber maturity. The mechanisms controlli ng development of symptoms seemingly are identical for the two spraing inducing vira.