Chlamydospore Production, Inoculation Methods and Pathogenicity of Fusarium oxysporum M12-4A, a Biocontrol for Striga hermonthica

medium. In vitro variations in chlamydospore germination were governed by the presence of exogenous carbon, nitrogen, and sorghum root exudates. Ammonium± nitrogen compounds and urea, in combination with glucose had a stronger stimula- tory eVect on chlamydospore germ tube growth than did potassium nitrate. Maximal germ tube elongation occurred when chlamydospores were exposed to urea at a C/N ratio of 10. Some mineral solutions and sorghum root exudates inhibited chlamydospore germ tube elongation; however, arabic gum, a complex polysaccharide, stimulated chlamydospore germ tube elongation and the production of secondary chlamydospores. In Weld trials, chlamydospore powder harvested from small-scale fermenters reduced S. hermonthica emergence by 92%. Complete inhibition of S. hermonthica emergence occurred when the chlamydospore powder was added to the soil at sowing and when sorghum seeds coated with chlamydospores were sown. EVective biological control of S. hermonthica was achieved using a simple fermentation system with sorghum straw as the inoculum growth substrate. For inoculum delivery to the farmers' Welds, sorghum seeds were coated with the inoculum using arabic gum as the adhesive. This simple delivery system permits a uniform inoculation of the Weld as well as the proper positioning of the inoculum in the immediate environment of sorghum roots, where S. hermonthica attaches to its host. To facilitate a broad usage of F. oxysporum M12-4A for the biocontrol of S. hermonthica, we propose an inoculum production strategy based on a cottage industry model that utilizes a liquid fermentation process and inexpensive locally- available substrates including sorghum straw and arabic gum.