Root-associated bacteria Bacillus albus and Bacillus proteolyticus promote the growth of peanut seedlings and protect them from the aflatoxigenic Aspergillus flavus CDP2

Abstract

Three isolates of bacteria NNK24, NDP61, and 0405-02, obtained from the surface and the inside of healthy peanut roots, were considered putative epiphytic and endophytic bacteria of peanut plants. 16S rRNA gene sequencing and BLAST search revealed that NNK24, NDP61 belong to Bacillus albus species and 0405-02 belong to Bacillus proteolyticus species. The culture broths of all 3 isolates obtained in the stationary phase showed good antifungal activity, approximately 70%–80% in the in-vitro antagonistic test. Meanwhile, in the in-vivo assay, after 72-hr-incubation of peanut seeds with Aspergillus flavus CDP2 conidia, isolates NNK24 and NDP61 reduced the mold growth from 6.9 log (cfu/g) to 4.5 and 3.9 log (cfu/g), respectively; whereas strain 0405-02 had only a slighter effect on the mold growth. Soaking peanut seeds in bacterial culture broth at 107 cfu/ml for 30 min promoted well seedling growth with the Vigour index (VI) increasing by about 3.6–5.3 times; reduced the Disease severity index (DSI) from 0.59 to 0.18–0.28. At 30 days after planting (DAP) seedlings into the soil, the plant weight and plant length grew approximately by 1.5–1.9 times and 1.4–1.6 times, respectively. Therefore, Bacillus albus NNK24, NDP61 and Bacillus proteolyticus 0405-02 are good candidates for microbial inoculants to promote peanut plant growth and protect them from aflatoxigenic Aspergillus flavus growth in order to develop sustainable agriculture.