Potential of spore-forming bacteria as biocontrol agents of wheat foliar diseases under laboratory and greenhouse conditions

The potential of Bacillus subtilis, Bacillus cereus, Bacillus licheniformis , Bacillus pumilus, Brevibacillus laterosporus and Paenibacillus polymyxa a s bioocontrol agents of Four foliar necrotrophic pathogens of wheat in Arge ntina has been evaluated. The following assays were used: (a) effect of thr bacterial antagonists on fungal growth in the central disk test with paire d cultures, (b) effect of the antagonists on the germination of fungal spor es in the paired suspension assay, and (c) reduction of disease severity in greenhouse experiments. The observed effects were specific for the antagon ist-pathogen combination investigated. In the paired culture rest, most of the bacterial antagonists inhibited the mycelial growth of the four pathoge ns tested at 14 days of the evaluation. B. licheniformis showed the best re sults for controlling Septoria tritici and Drechslera tritici-repentis eas it was the worst against Bipolaris sorokiniana. In the case of Alternaria t riticimaculans, the best were B. laterosporus, P. polymyxa and B. lichenifo rmis. Microscopic examination of excised pieces of the fungal colony perime ters showed clear differences among treatments and controls in hyphal morph ology (plasmolysis and vacuolation of hyphal, irregular texture in the cyto plasm, formation of chlamydospores). In the central disk test, mycelial nec rosis of A. triticimaculans was induced by B. laterosporus, P. polymyxa and B. pumilus. Similar results were obtained with B. sorokiniana in the prese nce of B. licheniformis and B. subtilis and D. tritici-repentis with B. pum ilus. In some combinations, the presence of inhibition haloes or bacterial chemotaxis were observed. In the paired suspension assay, all the bacteria except B. cereus, inhibited the conidial germination of S. tritici. Only P. polymyxa, B. licheniformis and B. laterosporus inhibited the conidial germ ination of A. triticimaculans, B. laterosporus bring the most effective. Al though all the bacteria inhibited the conidial germination of B. sorokinian a, the roost efficient were B. licheniformis, B. cereus and B. laterospors. In greenhouse experiments, P. polymyxa and B. cereus were the most efficie nt to reduce disease severities produced by S. tritici and A. triticimacula ns;on the contrary, these bacteria were not effective against B, sorokinian a and D. tritici-repentis. B. laterosporus BLA 170 showed a good behavior a gainst all the fungal pathogens, particularly for D, tritici-repentis and B . sorokiniana. This is the first report on the efficacy of B. laterosporus against Fungal wheat pathogens.