Enhanced biological control of root-knot nematode, Meloidogyne incognita, by combined inoculation of cotton or soybean seeds with a plant growth-promoting rhizobacterium and pectin-rich orange peel

LC-MS analysis of plant growth-promoting rhizobacterium (PGPR) Bacillus velezensis AP203 supernatants indicated the presence of nematode-inhibiting compounds that increased in abundance when B. velezensis AP203 was grown on orange peel. Meloidogyne incognita J2 were incubated with B. velezensis AP203 spores and orange peel, spores alone, orange peel alone, or with a non-inoculated control, and the combination of B. velezensis AP203 with orange peel resulted in 94% mortality of M. incognita juveniles (p <= 0.05). The J2 mortality rate for B. velezensis alone was 53%, compared to 59% mortality with orange peel, and the non-inoculated control exhibited 7% mortality. When tested on soybeans raised in a greenhouse, it was observed that when grown in the presence of orange peel, B. velezensis AP203 culture broth, cell suspension or supernatant reduced the numbers of M. incognita eggs per g of root at 45 days after planting (DAP) compared to inoculated controls in soybean and cotton (p <= 0.05). Likewise, soybean root length and fresh root weight significantly increased after inoculation with B. velezensis AP203 amended with orange peel. In cotton, shoot and root length significantly increased after inoculation with cell pellets of B. velezensis AP203 amended with orange peel compared to the M. incognita inoculated control. These data indicate that B. velezensis AP203 responds to growth on pectin-rich orange peel by production of biologically active secondary metabolites that can promote plant growth and inhibit root-knot nematode viability.