Competitive saprophytic colonization of pigeon-pea substrate by Fusarium udum in relation to environmental factors,chemical treatments and microbial antagonism

The competitive saprophytic colonization (CSC) of pigeon-pea substrates by Fusarium udum was studied in relation to environmental factors, chemical treatments and microbial antagonism. CSC was best at 22°C, good at 30°C, but at 40°C the substrate was vigorously colonized by Coprinus lagopus and Aspergillus nidulans which suppressed colonization by F. udum. High competitive saprophytic ability of F. udum was noted at pH 7 and 9 at soil moisture contents between 5 and 30%. At pH 4 and 5 F. udum was replaced by A. flavus and A. nidulans. The CSC of F. udum decreased in the soil-sand inoculum mixture amended with the fungicides bavistin, dithane Z-78 and difolatan. The herbicides 2,4-D and machete also reduced CSC by F. udum whereas urea promoted it. Colonization of pigeon-pea substrate by F. udum was highly suppressed by antagonism from Pénicillium citrinum, A. niger, Micromonospora gtobosa, A.flavus, A. terreus and Trichoderma viride when these were used in inoculum mixtures with F. udum or when substrates had already been colonized by them. Otherwise F. udum was shown to have a high competitive saprophytic ability.