How do plants defend themselves against bacterial wilt? Response of resistant and susceptible tomato plants to infection by Ralstonia solanacearum. A. MILLING (1), C. Allen (1)
(1) University of Wisconsin, Department of Plant Pathology, 1630 Linden Dr., Madison, WI 53706
Phytopathology 98:S106

Abstract: Host resistance is the only practical control for bacterial wilt of tomato, caused by diverse strains of Ralstonia solanacearum, but wilt resistance is horizontal, polygenic and its basis is not understood. We used quantitative PCR to measure induction of six defense related genes in resistant or susceptible tomato plants following infection with either a tropical Race 1 strain or a temperate Race 3 strain of R. solanacearum. Tomato plants responded to infection by upregulating marker genes for both the salicylate (SA) and ethylene (ET) signaling pathways, but not the jasmonate (JA) pathway. Both host and pathogen genotype played a critical role in the tomato response to bacterial wilt. The horizontally resistant tomato line H7996 showed a faster and greater induction of the ET and SA signaling pathways than a susceptible cultivar in response to infection by either the tropical or the temperate strain. The susceptible tomato also launched strong defenses following infection by the tropical strain, but the temperate Race 3 strain triggered little defense response in the susceptible host while causing similar symptoms. To explore mechanisms by which the pathogen may evades host recognition and resistance, we also measured defense expression in resistant and susceptible tomato plants infected with R. solanacearum mutants that lack either extracellular polysaccharide production or a functional Type III secretion system.