Morpho-physiological and biochemical determinants of insect-pest resistance in rice cultivars under South Odisha agro-ecology

A total of ten rice cultivars, namely Swarna (MTU 7029), MTU 1010, Lalat, Gayatri, Khandagiri, MTU 1156 (Satabdi), Kalajeera, Machhakanta, Savitri, and Koraput Local (Red Rice), were evaluated for their morphological, biochemical characters against the key-pests under South Odisha conditions. Morphological variability was pronounced, with plant height ranging from 100 cm (Lalat) to 140 cm (Machhakanta), stem thickness from 5.4 mm (Machhakanta) to 6.8 mm (Gayatri), tiller number from 7.0 (Koraput Local) to 11.0 (Gayatri), panicle length from 20.5 cm (Koraput Local) to 25.0 cm (Gayatri), and grains per panicle from 110 (Kalajeera) to 155 (Gayatri). 1000-grain weight varied from 13.0 g (Kalajeera) to 23.5 g (Gayatri), while maturity duration ranged from 135 days (MTU 1010, Lalat, MTU 1156) to 170 days (Koraput Local). Biochemical analysis revealed chlorophyll contents of 2.05-2.60 mg g^-1 FW, soluble protein 14.2-17.5 mg g^-1 FW, phenolics 1.80-3.50 mg GAE g^-1 FW, and antioxidant activity 36% (Lalat) to 65% (Koraput Local). Proline accumulation was highest in Koraput Local (1.80 μmol g^-1 FW), while total carbohydrates peaked in Koraput Local (125 mg g^-1 FW). Pest incidence showed wide variation: leaf folder infestation ranged from 10.5% (Gayatri) to 17.0% (Koraput Local), yellow stem borer from 12.8 (Gayatri) to 18.5% (Koraput Local), green leaf hopper from 8.9 (Gayatri) to 13.5% (Koraput Local), and Gundhi bug from 6.8 (Gayatri) to 11.0% (Koraput Local). Correlation analysis highlighted strong negative associations of stem thickness (r = -0.95), tiller number (r = -0.94), panicle length (r = -0.93), and grain weight (r = -0.88) with pest infestation, while phenolics (r = +0.82), proline (r = +0.75), and antioxidant activity (r = +0.70) were positively correlated. Landraces such as Kalajeera and Koraput Local expressed higher antioxidant activity, phenolics, and proline but suffered greater pest incidence, whereas improved cultivars like Gayatri and Khandagiri combined superior yield traits (~150 grains/panicle; 22-23 g grain weight) with comparatively lower pest pressure.