Lignification and defence gene expression mediated resistance in indigenous rice variety Mappilai Samba to root-knot nematode Meloidogyne graminicola

Abstract

Rice (Oryza sativa) is a vital staple crop that nourishes billions globally. However, its ability to sustain food security is jeopardized by pests and diseases, particularly the rice root-knot nematode (RKN), Meloidogyne graminicola, which threatens productivity. This study explores the defense responses of the traditional rice cultivar Mappillai Samba against this nematode. Using molecular, biochemical, histological, metabolomic profiling, gene expression and molecular docking approaches, we have unraveled the defense mechanisms employed by Mappillai Samba to fend off M. graminicola. The indigenous variety Mappillai Samba exhibited resistance, evident through a low Gall Index (2), fewer adult females (6.6), egg masses per gram of root (3.6) and eggs per egg mass (13.4), with a Multiplication Factor (MF) of 1.02. In contrast, CBMAS 14065 was highly susceptible, displaying 52.8 adult females and a Gall Index of 3. Our findings highlight the activation of specific defense-related genes (OsPAL1, OsPAD4, OsCAD6, OsWRKY13 and OsNPR1) and the accumulation of secondary metabolites such as phenolics, alkaloids and terpenoids, which are crucial for the plant's resistance. Microscopic analysis revealed changes in root morphology and Mappillai samba showed reduced giant cell formation despite nematode penetration into the root system. This comprehensive analysis highlights lignification and defense gene activation as core resistance strategies in Mappillai Samba. These insights into rice-nematode interactions emphasize the potential of Mappillai Samba as a valuable genetic resource for breeding nematode-resistant rice varieties, thereby contributing to sustainable rice production and food security.