Physical contact between conidia of Cochliobolus sativus and bacteria in the soil was controlled using pockets consisting of thin (10 μm) filter membranes of different pore sizes. Incorporation of conidia of C. sativus into the soil either held within 10 μm pore size filter membrane pockets or directly was followed by bacterial growth on their surfaces and in soil, respectively. No bacterial growth was observed when conidia were separated from the soil microflora by filter membranes of 0.2μm pore size. Bacterial colonization of conidia did not appear to affect their sensitivity to soil fungistasis. However presence of bacteria on the conidial surfaces was closely associated with rapid reduction in the degree of their nutrient-independence as reflected by inability to germinate in carbon-free media. When conidia were retrieved from the soil after 22 days or fess and placed in nutrient media they germinated readily although they were extensively colonized by bacteria. Bacteria were isolated from surfaces of conidia of C. sativus that had been incubated in soil and retrieved. Washed bacterial cells and cell-free culture filtrates of these isolates inhibited conidial germination to various degrees when tested separately. The inhibitory effect of the isolated colonizers on the conidia was much more pronounced in carbon-free media than in those containing nutrients. Germination of conidia in the presence of bacteria in nutrient media was often associated with repulsion of the bacterial cells from the vicinity of fungal germ tubes. The ability of C. sativus conidia to germinate in the presence of colonizing bacteria is partially related to the sensitivity of the latter to bacteriostatic metabolites secreted by the fungus and seems to be affected by exogenous nutrients.
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Fradkin et al. (1985) studied this question.