EFFECT OF PLANT GENOTYPE, VIRUS ISOLATE AND TEMPERATURE ON THE EXPRESSION OF THE POTATO-TUBER NECROTIC RINGSPOT DISEASE (PTNRD)

The present study shows that a large range of potato cultivars (29/33 tested), widely grown in the world, are susceptible to potato tuber ne crotic ringspot disease caused by potato virus Y. The three factors st udied in this work, which proved to influence the level of tuber necro sis reaction, were, first, the plant genotype, since varietal behaviou r exhibited large differences; second, the virus genotype, since varia tions of virulence occurred between the four isolates tested; and thir d, the environmental conditions, as shown by the different rates of tu ber necrosis obtained under contrasting conditions of temperature as m uch during the growing period as during storage. Three of the cultivar s tested, Spunta, Maris Piper and Thalassa, failed to produce necrotic tubers, although infected with a virulent tuber-necrosing isolate. Th is result, following observations on the inheritance of the tuber necr osis trait, suggests that at least a major dominant gene controls this reaction in non-sensitive cultivars. On the other hand, the extreme r esistance genes (Rv) provide a good resistance to virus infection, thu s, preventing tuber necrosis under held conditions.