**3. Biochemical basis of resistance**

The biochemical factors are more important than morphological and physiological factors in conferring resistance. Some biochemical constituents may act as feeding stimuli for insects. Occurrence at lower concentration or total absence of such biochemical leads to non preference, a form of insect resistance [15, 16]. The biochemical constituents like glycoalkaloid (solasodine), phenols, phenolic oxidase enzymes *viz*., polyphenol oxidase and peroxidase are available in plants and these biochemical constituents possess insect resistant properties [17]. It was also recorded that the maximum polyphenol oxidase activity is available in fruit (0.388

in fruit as changes in OD min-1 g-1 of sample). Several workers have reported that the biochemical constituents act as stimulants of resistance mechanism. In brinjal, Praneetha [18] and Prabhu [19] have recorded that the biochemical constituents also contribute to confer resistance to shoot and fruit borer.

Studies on the biochemical basis of resistance to *Leucinodes orbonalis* and their correlation with shoot and fruit borer damage in five selected brinjal genotypes were done during June to December 2005 and it was shown that less susceptible genotypes for both shoot and fruit borer had higher amount of polyphenol oxidase (PPO), phenylalanine ammonium lyase (PAL), lignin and lower reducing sugar. Significant negative correlation was established with per cent infestation of shoot and fruit borer and PPO, PAL and lignin, whereas it was positively correlated with reducing sugar. Negative correlation was observed with the biochemical constituents, PPO, PAL, lignin and reducing sugar but PPO was positively correlated with PAL and lignin content and vice-versa.
