Diversity and Adaptive Traits of Weedy Rice (Oryza sativa f. spontanea) Biotypes Infesting Rice Fields in Batticaloa District, Sri Lanka

Rice is the most important crop in Sri Lanka, occupying approximately 34% of the total cultivated area. Rice cultivation is constrained by several factors, among which weeds are a major problem, and weedy rice (Oryza sativa f. spontanea) is considered the most troublesome weed due to its close morphological similarity to cultivated rice, making its identification and management difficult. Although weedy rice infestation has been widely reported in Sri Lanka, season-wise characterization of weedy rice during both Maha and Yala seasons has not been previously studied in the Batticaloa District, making this study novel. The objectives of this study were to identify the morphological characters, assess the diversity, and determine the adaptive traits of weedy rice biotypes infesting rice-growing areas of the Batticaloa District during the Maha and Yala seasons. A survey was conducted in rice-growing areas of the Batticaloa District, where eighteen and seven weedy rice-infested locations were selected during the Maha and Yala seasons, respectively. Thirteen morphological traits were recorded to assess the overall variation of weedy rice populations. Data were analyzed using Minitab 17 software, and mean comparisons were performed using Tukey’s test at the 5% significance level. Significant (P < 0.05) morphological variation among locations was observed during both seasons. During the Maha season, significant differences were recorded in number of filled grains per panicle, panicle length, panicle shattering percentage, plant height, and number of tillers, while panicle shattering percentage and plant height showed significant variation among locations during the Yala season. Qualitative traits such as green stem color, red awns, and straw-colored lemma and palea were more prevalent during the Maha season, whereas a higher proportion of red pericarp was observed during the Yala season. Overall, the results demonstrate the existence of considerable morphological variation among weedy rice populations in the Batticaloa District, highlighting the need for location- and season-specific management strategies.