Morphological and biochemical characterization of resistance mechanisms in eggplant genotypes against Leucinodes orbonalis

This study aimed to investigate the morphological and biochemical traits associated with resistance to the fruit and shoot borer (Leucinodes orbonalis Guenée) in eggplant, with the goal of identifying promising genotypes for breeding programs. Fifty-five eggplant genotypes were evaluated under field conditions in Dhaka, Bangladesh, and assessed for their levels of pest infestation in relation to key physical and chemical plant characteristics. Genotypes bearing green, oblong, or round fruits with high seed counts, spines, and light-colored flowers exhibited lower infestation levels. Among morphological traits, fruit diameter (r = 0.66), pericarp thickness (r = 0.63), and number of primary branches (r = 0.33) were positively correlated with fruit infestation, while stem girth (r = 0.80) showed a significant positive correlation with shoot infestation. Conversely, trichome density (r = −0.76), number of fruits per plant (r = −0.52), fruit yield per plant (r = −0.37), and fruit length (r = −0.27) were negatively associated with infestation. Biochemical analysis revealed negative correlations between fruit infestation and total phenols (r = −0.74) and flavonoids (r = −0.71), while total sugars (r = 0.66), chlorophyll (r = 0.74), moisture content (r = 0.77), and total soluble solids (r = 0.61) were positively correlated. Genotypes G7, G11, G31, and G57 demonstrated strong resistance traits and are recommended as parental lines in resistance breeding. These results emphasize that host plant physical and biochemical defenses reduce herbivore damage by lowering tissue palatability and digestibility, thereby decreasing reliance on chemical pesticides and increasing the sustainability of the defense mechanism of host resistance.