Abstract
Traditional rice genotypes (TRGs) exhibit rich genetic and phenotypic diversity, which confers resilience against various insect pests. The present study explores the resistance traits in TRGs against the devastating foliage feeder, namely, leaffolder (Cnaphalocrocis medinalis Guen.), which spins, folds the leaf and causes significant damage. TRGs are season-specific, photosensitive and locally adapted. In the deltaic zone of Tamil Nadu, a southern state of India, TRGs are cultivated predominantly during two seasons, namely “Kuruvai” (June to August, suited for short-duration genotypes) and Samba (September to January, suited for long-duration genotypes). These seasons are almost analogous to the Kharif and Rabi seasons of North India, respectively. Considering this, a detailed behavioural study was conducted at the Department of Entomology, Annamalai University, Tamil Nadu, India, to observe the process from spinning to complete folding of leaf margins in selected TRGs suited for these two seasons. Observations on time taken for leaf selection, number of binds for making the primary fold, number of head swings from one end to the other end to make a bind, time consumed to construct primary fold, length of primary fold and extension of primary fold after 24 hours revealed that these parameters were significantly influenced by biophysical and biochemical traits of the selected TRGs. Subsequently, correlation analysis showed that C. medinalis larval feeding was positively correlated with the number of binds to form the primary fold, the length of the primary fold, and the number of binds in 24 hours. The time taken to construct the primary fold evinced a significant negative correlation. The resistant genotypes Karunkuruvai and Kothamalli Samba had narrow leaves with dense trichomes. Phenol content exerted a significant negative correlation with spinning. Moisture content showed a significant negative correlation with time taken for primary fold. The present investigation showed that leaf traits of selected TRGs, such as width and length, trichome density, phenol, and moisture content, determine the folding and feeding behaviour of C. medinalis.