INFLUENCE OF NUTRITION DURING CONIDIATION OF COLLETOTRICHUM-TRUNCATUM ON CONIDIAL GERMINATION AND EFFICACY IN INCITING DISEASE IN SESBANIA-EXALTATA

Conidia of Colletotrichum truncatum (NRRL 13737) were produced in semidefined, liquid media, with total carbon concentrations of 4 g/L and carbon/nitrogen ratios of 80:1, 30:1, and 10:1. Conidia produced in 10:1 medium were longer and thinner than conidia from 30:1 and 80:1 media, and a higher proportion contained two, rather than one, nuclei per conidium. After either 6 or 12 h on cellophane membranes, a greater proportion of conidia produced in the 10:1 medium had germinated compared with conidia from 30:1 and 80:1 media. Germination on attached leaves of Sesbania exaltata was greatest with conidia from 10:1 medium when assayed after either 6 or 24 h. Equality of variance tests implied that the leaf environment had a greater influence on the germination of conidia from 30:1 medium than conidia from 80:1 or 10:1 media. All conidial treatments caused losses in biomass of seedings of S. exaltata. Conidia produced in 10:1 or 30:1 media induced greater reduction in shoot height, and conidia from 10:1 medium induced greater reduction in shoot dry weight than did conidia from 80:1 medium. Further research on increasing the efficacy of mycoherbicide conidia by modifying the phyllosphere environment and the nutritional conditions of the conidiation medium is needed.