RHIZOSPHERE STUDIES IN RELATION TO VARIETAL RESISTANCE OR SUSCEPTIBILITY OF TOMATO TO VERTICILLIUM WILT

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Abstract
The density of fungi in the rhizosphere and the nature of fungi on the rhizoplane of five varieties of tomato, some susceptible and some resistant to infection by Verticillium, were determined. The numbers of fungi were higher in the rhizospheres of the susceptible varieties, Bonny Best and John Baer, than in the resistant ones, Loran Blood and Moscow. However, in the rhizosphere of the resistant variety Geneva 11, the numbers of fungi did not differ appreciably from those for the susceptible varieties. Among the fungi isolated from the rhizoplane, a species of Fusarium was dominant on the varieties Bonny Best, John Baer, and Geneva 11 and Trichoderma viride Pers. was dominant on the varieties Loran Blood and Moscow. In vitro, the rhizoplane fungi did not show antagonism, either against Verticillium or amongst themselves. Nevertheless, disease intensity was reduced in vivo when roots of susceptible varieties were inoculated with Verticillium in association with Trichoderma. Verticillium grew equally well in root exudates of all the varieties. Similarly, Fusarium and Trichoderma grew well in the exudate of the susceptible Bonny Best and the resistant Geneva 11. Chromatographic analyses of root exudates of the different varieties, collected aseptically, revealed the presence or absence of several amino acids, glucose, and fructose.