Background: The root-knot nematode Meloidogyne graminicola has become a serious threat to rice production as a result of the cultivation changes from transplanting to direct seeding. The nematicidal activity of Aspergillus welwitschiae have been investigated in vitro, and the disease control efficacy of the active compound has been evaluated under greenhouse and field conditions. Results: The active compound αβ-dehydrocurvularin (αβ-DC), isolated by nematicidal assay-directed fractionation, showed significant nematicidal activity against M. graminicola, with a median lethal concentration (LC₅₀) value of 122.2 μg mL^− 1. αβ-DC effectively decreased the attraction of rice roots to nematodes and the infection of nematodes and also suppressed the development of nematodes under greenhouse conditions. Moreover, αβ-DC efficiently reduced the root gall index under field conditions. Conclusions: To our knowledge, this is the first report to describe the nematicidal activity of αβ-DC against M. graminicola. The results obtained under greenhouse and field conditions provide a basis for developing commercial formulations from αβ-DC to control M. graminicola in the future.

The root-knot nematode Meloidogyne graminicola is an important pathogen in rice, causing huge yield losses annually worldwide. Details of the interaction between rice and M. graminicola and the resistance genes in rice still remain unclear. In this study, proteome-wide analyses of the compatible interaction of the japonica rice cultivar “Nipponbare” (NPB) with M. graminicola were performed. In total, 6072 proteins were identified in NPB roots with and without infection of M. graminicola by label-free quantitative mass spectrometry. Of these, 513 specifically or significantly differentially expressed proteins were identified to be uniquely caused by nematode infection. Among these unique proteins, 99 proteins were enriched on seven Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. By comparison of protein expression and gene transcription, LOC_Os01g06600 (ACX, a glutaryl-CoA dehydrogenase), LOC_Os09g23560 (CAD, a cinnamyl-alcohol dehydrogenase), LOC_Os03g39850 (GST, a glutathione S-transferase) and LOC_Os11g11960 (RPM1, a disease resistance protein) on the alpha-linolenic acid metabolism, phenylpropanoid biosynthesis, glutathione metabolism and plant–pathogen interaction pathways, respectively, were all associated with disease defense and identified to be significantly down-regulated in the compatible interaction of NPB with nematodes, while the corresponding genes were remarkably up-regulated in the roots of a resistant rice accession “Khao Pahk Maw” with infection of nematodes. These four genes likely played important roles in the compatible interaction of rice with M. graminicola. Conversely, these disease defense-related genes were hypothesized to be likely involved in the resistance of resistant rice lines to this nematode. The proteome-wide analyses provided many new insights into the interaction of rice with M. graminicola.

Background Potassium (K), an important nutrient element, can improve the stress resistance/tolerance of crops. The application of K in resisting plant parasitic nematodes shows that the K treatment can effectively reduce the occurrence of nematode diseases and increase crop yield. However, data on K₂SO₄ induced rice resistance to Meloidogyne graminicola are still lacking. To evaluate rice resistance against M. graminicola induced by K2SO4 and to further clarify its mechanism is essential for the rational use of K fertilizer to ensure the safety of rice production.Results In this work, K₂SO₄ treatment effectively reduced the numbers of both galls and nematodes in rice roots, and delayed the development of nematodes to the adult stage. Rather than by affecting the attractiveness of roots to nematodes and the morphological phenotype of giant cells at feeding sites, such effect was achieved by rapidly stimulating hydrogen peroxide (H₂O₂) accumulation, increasing callose deposition. Meanwhile, such induced resistance required the active participation of the potassium channel OsAKT1 and the potassium transporter OsHAK5. The numbers of both galls and nematodes were higher in both gene deficient plants than that in the wild-type plants, and the K₂SO₄-induced resistance showed weaker in the defective plants than in the wild-type plants.Conclusions K₂SO₄ treatment effectively induces rice resistance to root-knot nematode M. graminicola. The mechanism of inducing resistance is to prime the basic defense of rice, up-regulating the expression of resistance-related genes and with the involvement of K⁺ channel and transporter. These laid a foundation for further study on the mechanism of rice to defense against root-knot nematodes and the effective use of potassium fertilizer to improve rice resistance against nematodes in the field.