Some aspects of virus Y resistance in the potato (Salanum tuberosum)

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Abstract
When the leaves of potato hybrids resistant to virus Y were inoculated, virus development was restricted and within 14 days the virus was inactivated in most instances. There was no evidence to suggest that resistance was due to hypersensitivity. Virus concentration increased gradually in susceptible varieties after inoculation. Four treatments of virus Y inocula were tried; that made with phosphate buffer of pH 7 produced the most lesions on the resistant potato hybrid 11-84. A marked reduction in lesion numbers occurred on 11-84 when sap from virus-free D. stramonium plants or X-infected N. glutinosa plants was added to inoculum of virus Y. Crossbred progenies were developed from two of the resistant hybrids and one of the varieties used to study virus development after inoculation. One progeny contained 68.3 per cent. phenotypes resistant to virus Y and the other had 29.4 per cent. In both progenies there was a strong association between resistance to virus Y and the immune reaction to virus X. The results indicate that immunity and high resistance to virus Y are governed by the nulliplex and simplex conditions of a major gene, while the quadruplex condition controls susceptibility.