Induction of defence response in peanut elicited by Bacillus sp. CHEP5: A biological strategy for control of smut disease caused by Thecaphora frezzii in the field.

Peanut is susceptible to many diseases; among them, peanut smut disease caused by Thecaphora frezzii is the most damaging, causing yield losses of 30%. Fungicide treatment is not effective to control this disease. In this scenario, biological control would be an alternative to diminish the disease. Systemic resistance induced by a biotic agent is known to be effective against a broad spectrum of pathogens. In this study we evaluated the effect of different inoculation strategies of Bacillus sp. CHEP5, a peanut native strain, on peanut smut incidence and severity in field experiments. Peroxidase activity and accumulation of phenolic compounds were measured as changes associated with induced defensive traits. After three consecutive field trials, we found that Bacillus sp. CHEP5 inoculation protects peanut from T. frezzii because incidence and severity were reduced in two field trials. Furthermore, bacterial inoculation in the furrow followed by foliar application around the date of peg development would be the best strategy to control the disease. In addition, a correlation was found between increase in plant phenolic content and decrease in smut disease parameters. Thereafter, we concluded that Bacillus sp. CHEP5 may reduce smut as a result of plant defence response induction.