Isolation and characterization of cassava root endophytic bacteria with the ability to promote plant growth and control the in vitro and in vivo growth of Phytopythium sp.

Abstract

Among the biotic factors affecting the production of cassava (Manihot esculenta Crantz), root rot is one of the most severe diseases worldwide. In Brazil, one of the principal limitations for cassava production, mainly in the Amazon region, is soft root rot disease, which may be caused by Phytopythium sp. On the other hand, microorganisms beneficial to plants, such as plant growth-promoting bacterial endophytes, have been progressively used to replace chemical pesticides and industrial fertilizers, which can drastically contaminate the environment. Thus, our main aim here was to isolate and characterize endophytic bacteria associated with roots of cassava, regarding their ability to control the growth of Phytopythium sp. and promote plant growth. A total of 21 endophytic bacteria that showed distinct abilities to solubilize calcium phosphate, synthesize indol acetic acid and siderophores, were isolated. Among them, 6 isolates belonging to the genus Bacillus (B. aryabhattai, B. velezensis and B. cereus) and 1 other isolate, Klebsiella pneumonia, were identified based on their 16S rRNA gene sequences. B. velezensis isolate 21Y and B. aryabhattai isolates 4W and 23Y were able to inhibit the in vitro and in vivo growth of Phytopythium sp. Cassava plants inoculated with B. cereus isolate 15Y and B. aryabhattai isolates 4W, 16Y and 23Y by irrigation of substrate and foliar spray showed increased biomass. In addition, increased biomass was observed in cowpea plants generated from seeds microbiolized with B. aryabhattai isolates 23Y and 4W. Thus, our findings may contribute to sustainable agriculture, since they revealed cassava endophytic bacteria able to promote plant growth, as well as inhibiting growth of the pathogen that causes soft root rot of cassava in the Amazon region.