Interactions between foliar pathogens and the saprophytic microflora of the wheat (Triticum aestivum L.) phylloplane

Hyphal interference between 10 saprophytic microorganisms isolated from wheat phylloplane against four target pathogens (Septoria tritici, Alternaria triticimaculans, Bipolaris sorokiniana and Drechslera tritici-repentis) were studied microscopically. Antagonism was measured as the ability of the saprophytic microorganisms to induce morphological changes of hyphae and spores of the pathogens and to reduce conidial germination. Typical reactions included formation of chlamydospores, encircled hyphae, plasmolysis, vacuolation and granulation of hyphae. Ungerminated malformed conidia, lysis, and the formation of inflated germ tubes on germinating conidia were also observed. Paecilomyces lilacinus and Bacillus sp. possessed the greatest capacity for interference. Fusarium moniliforme var. anthophilum, Epicoccum nigrum and Chaetomium globosum were next in order of the range and severity of interference. Spore germination of S. tritici was significantly reduced in the presence of P. lilacinus, F. moniliforme var. anthophilum, E. nigrum, Bacillus sp., Cryptococcus sp. and Nigrospora sphaerica, with levels of inhibition of up to 69%. Paecilomyces lilacinus, Cryptococcus sp., F. moniliforme var. anthophilum and N. sphaerica caused a reduction of spore germination of 47-60% with the greatest effect being against B. sorokiniana. Chaetomium globosum, P. lilacinus, Rhodotorula rubra and Bacillus sp. significantly reduced spore germination of A. triticimaculans. E. nigrum, F. moniliforme var anthophilum, Stemphylium sp., P. lilacinus and Bacillus sp. caused the greatest reduction in D. tritici-repentis. Greenhouse experiments on pathogen-antagonist interactions on the wheat phylloplane showed the potential value of some of the antagonists for controlling the pathogens. If parasitism occurs in nature, the native micro-organisms might be useful for biological control by competing with the pathogens and so regulating their colonization of wheat leaves.