Assessment of enzyme activity in root-knot nematode resistant and susceptible solanaceous plants

The present investigation was carried out to determine the changes in enzyme activities in roots and leaves of three distinct sources of nematode resistance viz., Solanum torvum (IC618029), chilli (EC402105) and tomato (Hissar Lalit - resistant and MHTO-101- moderately resistant) due to infection with root-knot nematode, Meloidogyne incognita. The plants displayed a resistance response by limiting nematode reproduction, producing significantly fewer galls and egg masses per root system. Higher activities of peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase were observed in the resistant plants compared to the susceptible plants; the activity was higher in the roots than in the leaves. Peroxidase activity in the roots increased by 236 per cent in S. torvum and 139 per cent in chilli, compared to less than 70 per cent increase in the respective susceptible plants. Polyphenol oxidase activity increased by 71, 93, and 96 per cent in resistant tomato, S. torvum, and chilli, respectively, compared to 60, 73, and 89 per cent in their susceptible plants. Similarly, phenylalanine ammonia-lyase activity increased by 6 to 25 per cent in the resistant plants, while it ranged from 29 to 74 per cent in the susceptible plants. These findings suggest that enzyme activity levels varied among the three resistant sources, indicating that a combination of these enzymes and other defense compounds may contribute to nematode resistance. Resistant tomato genotypes exhibited a reduced catalase activity, with an increase of only 11.7 to 20.7 per cent following nematode infection, whereas susceptible plants showed a much higher increase (112 to 135 per cent). This indicates that catalase inhibition could serve as a biochemical marker for identifying resistance source in tomato.