Herbaspirillum seropedicae promotes maize growth but fails to control the maize leaf anthracnose.

Herbaspirillum seropedicae is an endophytic diazotrophic bacterium and a plant growth promoting bacteria. Colletotrichum graminicola causes the anthracnose, one of the most destructive maize diseases worldwide. The main objective of this work was to evaluate the effects of H. seropedicae SmR1 strain on the plant growth and leaf anthracnose of maize plants grown in substrate amended or not amended with humic substances. In the first assay, plants were pre-treated with H. seropedicae and inoculated with C. graminicola at 7, 14 and 21 days after treatment (DAT). In the second assay, plants were treated with H. seropedicae, grown in substrate amended with humic substances and inoculated at 3 and 7 DAT. The anthracnose severity was assessed by measurement of necrotic and chlorotic leaf area, and bacteria were quantified in leaves by quantitative PCR. H. seropedicae did not affect the disease severity in maize leaves, although it efficiently colonized the leaf tissues and it promoted maize leaf growth. Humic substances improved H. seropedicae colonization in maize.