High-Throughput Sequencing Reveals the Effect of the South Root-Knot Nematode on Cucumber Rhizosphere Soil Microbial Community

Due to long-term cultivation in greenhouses, cucumbers are susceptible to root-knot nematode (RKN), resulting in reduced yield and quality. The objective of this study was to investigate the effect of RKN on the rhizosphere microbial community of cucumber. Understanding the composition of rhizosphere bacterial and fungal communities and the possible interaction between microorganisms and RKN is expected to provide a reference for the eco-friendly control of M. incognita in the future. Three different groups were selected for sampling based on the RKN incidence and root galling scale (NHR, 0%, no root galling; NR, 5–15%, root galling scale 1–2; NS, 60–75%, root galling scale 4–5). Soil properties were determined to evaluate the effect of M. incognita on rhizosphere soil. High-throughput sequencing was used to examine the bacterial and fungal communities in rhizosphere soil. The results showed that the contents of soil nutrients and enzyme activities were significantly lower in the NS than in the NHR. The alpha diversity showed that M. incognita had a greater effect on rhizosphere soil bacteria than on fungi. In beta diversity, there were significant differences among the three groups by PCoA (p = 0.001). Furthermore, bacteria and fungi with significant differences in relative abundance were screened at the genus level for a correlation analysis with soil factors, and a correlation analysis between the bacteria and fungi was performed to study their relationships. A redundancy analysis (RDA) of rhizosphere microorganisms and soil properties showed a negative correlation between nematode contamination levels and soil nutrient content. Finally, we predicted the interaction among RKN, soil factors, and the rhizosphere microbial community, which provided evidence for the prevention of RKN via microecological regulation in the future.