Potential of Bacillus amyloliquefaciens for Control of Alternaria cosmosa and A. patula of Cosmos sulfurous (Yellow Cosmos) and Tagetes patula (French Marigold)

Alternaria cosmosa and Alternaria patula are seed-borne pathogens of Cosmos sulfurous Cav. (yellow cosmos) and Tagetes patula L. (French marigold), respectively. Bacterial strains were isolated from the two hosts to compare their potential to control the Alternaria species with the control provided by the fungicides, prochloraz and pyrifenox. Eight of 73 strains (11%) from C. sulfurous and four of the 128 (3%) from T. patula were found to be effective antagonists by in vitro screening. The efficacy of these active strains as antagonists of the two seed-borne pathogens was evaluated in laboratory, glasshouse and field experiments. The most effective strains, Cb 6 from C. sulfurous and strain TpE 1 from T. patula, were both identified as Bacillus amyloliquefaciens and were able to reduce disease severity as seed or foliar treatments of their respective host in most experiments