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Genetics

Several Genes in Lycopersicon esculentum Control Hypersensitivity to Xanthomonas campestris pv. vesicatoria. J.- F. Wang, Department of Plant Pathology, University of Florida, Gainesville, Present address: The Asian Vegetable Research and Development Center, Shanhua, Tainan, Taiwan; J. B. Jones(2), J. W. Scott(3), and R. E. Stall(4). (2)(3)Gulf Coast Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Bradenton; (4)Department of Plant Pathology, University of Florida, Gainesville. Phytopathology 84:702-706. Accepted for publication 5 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-702.

Resistance in tomato (Lycopersicon esculentum) accession Hawaii 7998 (H7998) to bacterial spot caused by Xanthomonas campestris pv. vesicatoria is associated with a hypersensitive reaction. In F₁ plants from a cross of H7998 with the susceptible tomato genotype Florida 7060, the time between infiltration of leaves with a high-inoculum concentration (5 × 10⁸ cfu/ml) and the appearance of necrosis and bacterial growth after infiltration of leaves with a low-inoculum concentration (5 × 10⁵ cfu/ml) were intermediate to the two parents. The times for confluent necrosis among plants in the F₂ population injected with a race 1 strain or with a race 2 strain converted to avirulence with the avrRxv gene ranged from those of the susceptible parents to those of resistant parents but included intermediate times and clearly showed continuous distribution. We hypothesize that hypersensitivity like that of H7998 is controlled by three recessive genetic loci. Seven genotypes from a segregating backcross population that had different times to confluent necrosis after inoculation were asexually propagated and inoculated. Electrolyte leakage and bacterial growth in leaf tissue of the genotypes were correlated with ratings for necrosis, and different groups of plants could be distinguished. The hypersensitive reaction in H7998 is controlled by more than one gene and does not appear to fit the gene-for-gene hypothesis.