A Genetic Analysis of the Association Between Resistance toMeloidogyne incognitaand a Necrotic Response to Infection by a Strain of Potato Virus Y in Tobacco

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Abstract
The genetic basis for the association between resistance to the root-knot nematode M. incognita, and a severe vascular necrosis in response to infection by the MSNR strain of potato virus Y (PVY-MSNR) in tobacco (N. tabacum L.) was investigated. More than 15,000 F2 plants derived from root-knot resistant .times. root-knot susceptible crosses were inoculated with both pathogens. All plants that did not develop necrosis in response to the virus were root-knot susceptible; i.e., recombination between root-knot resistance and the necrotic response to the virus was not detected. Each trait is controlled by a single, dominant gene located on chromosome G of tobacco by monosomic and nullisomic analysis. The virus-induced necrosis may be a pleiotropic response of the gene controlling root-knot resistance. Plants possessing both root-knot and PVY resistance developed little or no necrosis. PVY resistance is conditioned by a recessive gene that apparently is epistatic to the gene conditioning root-knot resistance. A search was made among Nicotiana spp. for a new source of root-knot resistance not associated with the necrotic reaction to PVY-MSNR. N. tomentosa, accession 58, was highly resistant to the nematode and appeared immune to the virus.