Polygalacturonases are required for rapid colonization and full virulence of Ralstonia solanacearum on tomato plants
Huang. Q Allen. C
Physiological and Molecular Plant Pathology ; 2000 [Vol.57] Pages:77-83
Abstract
Ralstonia solanacearum causes bacterial wilt, a soil-borne vascular disease of many crop plants. Plant cell wall-degrading polygalacturonases (PGs) are significant virulence factors for this pathogen. R. solanacearum mutants lacking PehA (an endo-PG), or PehB (an exo-PG), or both PehA and PehB are all less virulent than the wild-type strain on wounded eggplants. To more closely mimic the natural infection process, unwounded tomato plants were soil-soak inoculated with wild-type and PG mutant strains. All three PG mutants were significantly reduced in virulence on intact tomato plants, despite surviving well in potting mix. Over the course of disease development, populations of PG mutant and wild-type bacteria in plants were significantly different. The PG mutants, especially the two pehA mutants, colonized fewer tomato stems, colonized stems more slowly, and had lower mean bacterial populations in stems than the wild-type strain. These results suggest that PehA and PehB are necessary for rapid host colonization, and that production of these enzymes contributes quantitatively to the ability of R. solanacearum to colonize host vascular tissue and wilt plants. A threshold bacterial population of around 1 × 108 cfu in the centimetre of tomato stem directly above the cotyledons correlated with the appearance of wilt symptoms.
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