Effect of temperature on resistance to Potato virus Y in potato cultivars carrying the resistance gene Ry chc

The effect of cultivation temperatures on the resistance reaction to three Potato virus Y strains ( PVY O , PVY N and PVY NTN ) in potato cultivars carrying Ry chc was examined. When potato plants carrying Ry chc were cultivated at 22 °C, a few small necrotic spots developed on inoculated leaves by 5 days after mechanical inoculation (dpi), and systemic infection of a few symptomless plants was confirmed at 28 dpi by IC ‐ RT ‐ PCR . At 28 °C, distinct necrotic spots developed on inoculated leaves by 5 dpi, and systemic symptoms occasionally appeared at 28 dpi. Thus, high temperature weakens Ry chc ‐conferred resistance. However, the incidence of systemic infection and the titre of virus in resistant cultivars at 28 °C were lower than in a susceptible cultivar. In graft inoculation under high summer temperatures, some plants developed necrosis on the leaves and stem, but PVY was barely detected by RT ‐ PCR in leaves on potato carrying Ry chc . When seedlings from progeny tubers of plants that were inoculated with PVY and grown in a greenhouse at >30 °C in the daytime were examined by ELISA and IC ‐ RT ‐ PCR , PVY was not detected in cultivars carrying Ry chc . These results show that Ry chc confers an extreme resistance to PVY strains occurring in Japan.