Root-knot nematodes (RKN) are a soil borne pathogen of plants, feeding on nutrients from the roots. They are a notorious pest of crop species worldwide. RKN infection can result in wilting of the plant, a reduction in plant height and biomass, swollen roots, the formation of roots galls and ultimately crop yield losses. Meloidogyne incognita, an RKN well known for causing damage to a broad range of crop species, has alone been reported to cause 50% of the overall damage to vegetable crops worldwide. Pesticides for RKN control were recently banned due to environmental concerns and RKN-resistant crop varieties are unavailable for most vegetable crops. Plant growth promoting rhizobacteria (PGPR) could however offer a sustainable solution to the RKN problem.
In a new study published in AoBP, Khanna et al. sought to explore eco-friendly methods to control RKN infection using rhizobacterial strains (Pseudomonas aeruginosa and Burkholderia gladioli). These strains were inoculated in RKN infected tomato (Lycopersicon esculentum) plants and the extent of their infection was noted by assessing different plant parameters, such as leaf concentrations of photosynthetic pigments, phenolic compounds, osmoprotectants and organic acids. Transcriptomic analysis was also conducted to evaluate the expression levels of genes associated with phenol and organic acid metabolism. The study revealed that nematode-infected seedlings had reduced levels of plant pigments whilst all other analysed compounds were enhanced in RKN infected plants. Inoculation with PGPR resulted in the activation of defence responses in nematode-infected seedlings by increasing the levels of all analysed compounds. The accumulation of metabolites in plants subjected to nematode infection and inoculated with PGPR shows that this is an effective strategy to overcome nematode stress. The authors conclude that PGPR play a valuable role in stress alleviation for nematode-stressed L. esculentum seedlings and that future work should focus on understanding the mechanisms underlying the nematicidal activities of PGPR.