CHARACTERISTICS OF A RESISTANCE-BREAKING ISOLATE OF POTATO VIRUS-Y CAUSING POTATO-TUBER NECROTIC RINGSPOT DISEASE

An Austrian isolate of potato virus Y(NTN), the causal agent of potato tuber necrotic ringspot disease (PTNRD), was serologically compared w ith seven Dutch PVY(N) isolates. Using polyclonal and monoclonal antib odies, it was found indistinguishable from PVY(N). Determination of th e nucleotide sequence of the coat protein cistron and comparison of th e deduced amino acid sequence with coat protein sequences of other pot yviruses revealed a high level of homology with PVY(N) coat protein se quences. This confirmed the close taxonomic relationship of PVY(NTN) w ith the PVY(N) subgroup of potato virus Y. PVY(NTN) is able to overcom e all resistance genes known so far in commercial potato cultivars. Re markably, transgenic PVY-protected tobacco plants are also resistant t o PVY(NTN) infection upon mechanical and aphid-mediated inoculation. T hese experiments indicate that genetically engineered resistance offer s great potential in protection of potato to new aggressive strains of PVY(N).