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Extreme Resistance to Tomato Yellow Top Virus and Potato Leaf Roll Virus in Lycopersicon peruvianum and Some of its Tomato Hybrids. Sher Hassan, Graduate student, Department of Plant Pathology, Washington State University; P. E. Thomas, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. Phytopathology 78:1164-1167. Accepted for publication 4 April 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-1164.

Plants in populations of Lycopersicon peruvianum, U.S. Department of Agriculture Plant Introduction (P. I.) 128655, and two, selected F5 hybrid progenies of P. I. 128655 L. esculentum were graft inoculated with specific isolates of tomato yellow top virus and potato leaf roll virus. Both viruses could be recovered from some, but not all, of the plants of both the parent and the hybrid populations 9 wk later by graft or aphid transmission. Virus isolates that could not be recovered from a plant would not pass through stem sections of the same plant that were grafted between infected stocks and healthy, susceptible scions in 16 wk, but limited movement into one stem section was detected at 16 wk. Plants that were not invaded by one virus isolate often were invaded by other isolates of the same virus when challenged by graft inoculation. Invasion required extremely long periods of union between test plants and infected graft scions. Virus isolates that could not be recovered from plants 8 wk after graft inoculation often were recovered from the same plants after 24 wk. Virus isolates recovered from plants after graft inoculation frequently were not retained in new growth on cuttings of the same plants after severance from the scion source of virus. The longer the time required for virus to invade a test plant, the less likely it was that the virus would be retained after separation from the scion. Virus concentration in plants that retained virus was below that detectable by enzyme-linked immunosorbent assay. All 16 P. I. 128655 plants tested against 10 virus isolates contained at least one isolate 24 wk after graft inoculation, but five of the plants would not retain any of the isolates independently of the infected scion.