Interactions between Meloidogyne incognita and endophytic bacteria in cotton and cucumber

Abstract

Greenhouse studies with cotton and cucumber were made to determine the effects of inoculation of the parasitic nematode Meloidogyne incognita on population dynamics of indigenous bacterial endophytes and introduced endophytic bacterial strains JM22 ( Enterobacter asburiae) and 89B-61 ( Pseudomonas fluorescens) applied as seed treatments. Internal communities of endophytic bacteria in roots were generally largest in the presence of M. incognita. Recovery of JM22 from cucumber roots was positively, but not significantly, associated with soilborne nematode inoculum size, except at 2 weeks after inoculation. The internal populations of 89B-61 applied to seed also increased with nematode applications. The diversity of indigenous bacterial endophytes changed within 7 d after M. incognita inoculation. Species richness and diversity of endophytic bacteria were slightly, but not significantly, greater for nematode-infested plants than for non-infested plants. Alcaligenes piechaudii and Burkholderia pickettii occurred only in nematode-infested plants, whereas Brevundimonas vesicularis was mainly isolated from nematode-free plants. Agrobacterium radiobacter and Pseudomonas spp. were the most common taxa found in both treatments, accounting for a total of 41% and 37% of the community for non-inoculated and inoculated plants, respectively. JM22 colonized cotton roots internally and was also found in high numbers on the root surface around nematode penetration sites and on root galls where the root tissue had been disruptured due to gall enlargement. Single cells of JM22 were attached to the cuticle of M. incognita juveniles. Endophytic bacteria and M. incognita form complex associations, and an understanding of these associations will aid efforts to develop and manage microbial communities of endophytic bacteria for practical use as biocontrol agents against plant-parasitic nematodes and soil-borne pests and pathogens.