Physiological, Biochemical and Morphological Responses of Green Gram to Varying Inoculum Levels of Meloidogyne incognita

The infection with Meloidogyne incognita induced physiological variations, biochemical imbalances, and decline in the nitrogen fixation, leading to severe yield loss in green gram cv. SML-668, that varied with the inoculum levels (100-3000 J₂/kg soil). Increasing inoculum levels caused a progressive rise in the root galling, with maximum disease severity and nematode development. The egg mass production, fecundity (eggs/egg mass), juveniles population (in soil), preadult females, adult females (in side root tissue), reproduction factor, and multiplication factor of M. incognita were recorded highest at 3000 J₂/plant, and the lowest at 100 J₂/plant over the control. A significant decline in the photosynthesis rate (6-32%), and an increase in transpiration rate (8-28%) and stomatal conductance (8-26%) occurred in the plants inoculated with 500-3000 nematode juveniles/plant. The leaf chlorophylls (28-56%), carotenoids (24-52%), and seed protein (24-44%) of the nematode infected plants decreased significantly, with the greatest reductions at 1500-3000 J₂/plant. Phenolic and salicylic acid concentrations increased by 3-30% and 2-18% at 100-1000 J₂/plant, but decreased by 10-28% and 6-15% at 1500-3000 J₂/plant compared to 1000 J₂/plant. The greatest reductions in the plant growth indices (41-74%), yield (32-43%), functional nodules (26%), nodule weight (44%), and leghemoglobin content (32%) occurred at 3000 J₂/plant, whereas the least decline at 100 J₂/plant compared to the control. The non-functional nodules, however, increased with an increase in the inoculum level. The soil population of the juveniles peaked at 3000 J₂/plant.