Histopathological modifications and biochemical defense responses of muskmelon (Cucumis Melo L.) to root-knot nematode (Meloidogyne incognita)

Root-knot nematodes (Meloidogyne incognita) cause significant damage to muskmelon (Cucumis melo L.), leading to reduced productivity. This study analysed histopathological and biochemical changes in infected plants using Scanning Electron Microscopy (SEM) and biochemical assays. Infected roots showed giant cell formation, vascular disruption, and necrosis, affecting water and nutrient transport. SEM revealed tissue depressions and deformation at nematode feeding sites. Biochemically, infection caused a decline in photosynthetic pigments-chlorophyll a (66.62%), chlorophyll b (71.94%), and total chlorophyll (65.36%). However, defense mechanisms were activated, as shown by elevated total phenol levels (114.5% in leaves, 48.92% in roots) and increased enzymatic activities. Peroxidase rose by 51.47% in leaves and 19.18% in roots, while polyphenol oxidase increased by 25.91% and 36.49%, respectively. Activities of acid phosphatase and phenylalanine ammonia-lyase also rose, indicating activation of the phenylpropanoid pathway. The study highlights M. incognita's dual impact-causing structural damage while triggering plant defense-necessitating integrated pest management strategies.