The former two strains were obtained from the culture collection of the Department of Entomology and Plant Pathology, Auburn University, Auburn, AL, USA, while the latter were the commercial PGPR formulations of B. subtilis GB03(Companion®) and B. subtilis FZB24 (FZB24®) purchased from the manufacturers Growth Products Ltd. (New York, USA) and ABiTEPGmbH (Berlin, Germany), respectively.