Novel resistances to four potyviruses in tuber-bearing potato species, and temperature-sensitive expression of hypersensitive resistance to potato virus Y

Novel potyvirus resistance specificities were found in eight tested wild potato species (clones): hypersensitive resistance (HR) to potato Y potyvirus (PVY) strain groups PVY^O in Solanum megistacrolobum and S. polyadenium and PVY^N in S. stoloniferum; HR to potato V potyvirus (PW) in S. maglia, S. polyadenium, S. stoloniferum, S. sparsipilum and S. sucrense, HR to potato A potyvirus (PVA) strain group 1 in S. sucrense, and extreme resistance (ER) to PVA in S. polyadenium. S. commersonii and S. stoloniferum expressed HR to tobacco etch potyvirus (TEV) which has not been reported previously in potato species. The studied clone of S. stoloniferum expressed HR to all potyviruses and potyvirus strains tested. The clone of S. stoloniferum (2n = 48; nuclear DNA content (2C) = 3.6 pg) and S. chacoense (2n = 24; 2C=1.9 pg) were crossed and one hybrid (2n = 36; 2C = 2.9 pg) was obtained. The hybrid expressed HR to all tested potyviruses except PVA, which indicated that HR to PVA was controlled by a gene which is different from the genes (or gene) controlling HR to PVY^O, PVY^N, PVV and TEV in S. stoloniferum. On the other hand, S. chacoense and the hybrid expressed ER to cucumber mosaic cucumovirus (CMV), whereas S. stoloniferum was susceptible to CMV. All tested wild species and the six tested potato cultivars (S. tuberosum subsp. tuberosum) expressed HR to PVV. Expression of HR following infection with PVY^N induced systemic acquired resistance (SAR) in S. chacoense. HR to PVY^N in S. sparsipilum and S. sucrense and to PVY^O in potato cv. Pito was efficiently expressed at lower temperatures (16/18°C) indicated by the development of distinct necrotic lesions and/or vein necrosis in inoculated leaves, whereas the HR was rendered less effective at higher temperatures (19/24°C) which was indicated by the development of systemic infection with leaf-drop and mosaic symptoms.