Integrating agro-physiological traits and yield performance in soybean ( <i>Glycine max</i> L.) resistance to fall armyworm ( <i>Spodoptera frugiperda</i> ) through genotype analysis

Fall armyworm (<i>Spodoptera frugiperda</i>) is a major invasive pest threatening soybean production, and identifying resistant genotypes is essential for sustainable crop protection. This study evaluated 36 soybean genotypes for their resistance to <i>S. frugiperda</i> based on leaf damage intensity and frequency, resistance classification, morphophysiological traits, and yield components. The research was conducted under field conditions using a randomized complete block design (RCBD) with three replications. Armyworm damage was assessed at 36 and 41 days after planting (DAP), and all quantitative data were analyzed using ANOVA followed by the Scott-Knott test at a 5% significance level. Data were presented as mean ± standard deviation (SD). Significant variation was evident among genotypes, with attack intensity at 41 DAP ranging from 18.31 ± 10.64% to 61.20 ± 11.39%, and attack frequency from 33.38 ± 16.92% to 95.49 ± 5.35%. Based on mean intensity values, one genotype was categorized as strongly resistant (SR) (UB 2), four as resistant (R) (UBASK24, UBASK35, GBG, TGM), and a broader set as moderately resistant (MR), while highly susceptible (HS) genotypes included UBASK15, UBASK62, UBASK64, UBASK32, UBASK36, and UBASK14. Morphophysiological traits exhibited wide variation, including leaf trichome density (13.56-42.11 trichomes 0.25 cm^-2), plant height (38.42-78.67 cm), and flowering time (31-47 DAP), while yield traits identified TGM, UBASK35, UBASK24, and GBG as the highest-performing genotypes. Overall, UB 2, UBASK24, UBASK35, GBG, and TGM are promising parental candidates for breeding soybean resistance against <i>S. frugiperda</i>, integrating strong resistance expression with favorable agronomic performance.