Diversity and nematocidal activity of culturable bacteria from suppressive soils in Shandong Province, China

Disease-suppressive soil refers to soil in which the incidence or severity of plant diseases is lower than the general environment or the surrounding soil, and this inhibitory effect is attributed to diverse microbes. In this study, bacteria from suppressive soil were cultured, and preliminarily identification was made based on the 16S rRNA gene sequence, and the nematocidal activity was evaluated in both <i>in vitro</i> and greenhouse conditions. A total of 110 isolates were obtained from 13 sampling sites in Shandong Province, China. Using phylogenetic analysis, 110 sequenced isolates were clustered into 16 genera, belonging to 4 phyla, <i>Actinobacteria</i>, <i>Bacteroidetes</i>, <i>Firmicutes</i> and <i>Proteobacteria</i>, indicating that the diversity of cultivable bacteria in suppressive soil is high. Among the genera, <i>Bacillus</i> was dominant; 85 isolates were classified into 30 <i>Bacillus</i> species based on BLAST data. Twenty three of these isolates caused &gt;75% mortality of second-stage juveniles of the root-knot nematode <i>Meloidogyne incognita</i> in <i>in vitro</i> assays. Lastly, pot experiments revealed that the 10 selected strains inhibited the development of <i>M. incognita</i> to different degrees. This is the first investigation of the diversity and nematocidal activity of cultivable bacteria from suppressive soil in Shandong province, China. The results confirmed that suppressive soil is a rich source of bacterial activity against root-knot nematodes.