Leaf infection of cotton by xanthomonas malvacearum (efsm.) dowson

Xanthomonas malvacearum spread more rapidly along vascular tissue than into mesophyll when inoculated to the main veins of susceptible cotton leaves. The extent of spread varied with the concentrations of inocula, tissue age and cotton variety. Increasing concentrations of inocula accelerated the initial spread of disease. Bacteria spread more rapidly in young leaves than in old-increasing age greatly decreased disease in the mesophyll. The initial invasion was quicker in young leaves of young plants than in young leaves of old plants. Three types of behaviour, according to the host's reaction, distinguish Knight's resistance factors : (a) where X. malvacearum spread extensively along veins and into mesophyll of plants containing factors B-3 and B-5; (b) where it was restricted to the point of inoculation in plants containing B-4, B-9 and combinations with B-5m; and (c) where it spread along veins but not appreciably into mesophyll in varieties containing B-2 and B2B3. From this and four other different types of tests, factors B-2 and B-3 seem to increase mesophyll resistance but only B-2 gives appreciable vascular resistance. Further, the vascular bundles in varieties with B-2 seem to be surrounded by an additional 'barrier' which resists X. malvacearum.