STEM INFECTION OF COTTON BY XANTHOMONAS MALVACEARUM (E. F. SM.) DOWSON

Abstract

Varying the position of stem inoculation, the concentration of inoculum and the age of plant affected the reaction of cotton, Gossypium sp., to infection with Xanthomonas malvacearum (E. F. Sm.) Dowson.The extent of stem discoloration, internal and external, and the probability of disease ocurring in leaves by bacteria moving within the plant increased (a) the nearer the point of stem inoculation was to the apex, and (b) the higher the concentration of inoculum. The leaf symptoms were not the angular spots typical of primary leaf infection. Instead, bacteria seemed to lodge in, discolour and blacken sections of leaf veins. Then tissue next to the affected veins became water‐soaked and leaf sectors dependent upon these veins died and dried. These symptoms usually developed 14 to 55 days after inoculation in the expanding leaves.The amounts of stem discoloration and the probabilities of leaf symptoms developing were less when hypocotyls of old plants were inoculated than when hypocotyls of young plants were inoculated. The probabilities of leaf symptoms developing were similar, however, when young tissues in young and old plants were inoculated.American cotton, Gossypium hirsutum, was less affected by stem inoculation than Egyptian cotton, G. barbadense. Of the resistance factors against primary leaf infection only B6m gave appreciable stem resistance.