Phenotypic variation in Oryza rufipogon highlights differential adaptation to dry and intermediate climatic zones of Sri Lanka

Abstract

Oryza rufipogon, a wild rice species with the AA genome, is closely related to Asian cultivated rice and exhibits high genetic compatibility with it. It is a perennial, primarily cross-pollinated species with photoperiod sensitivity, typically found in persistently wet habitats. Phenotypic plasticity in O. rufipogon enables the species to adapt to diverse and changing environmental conditions, such as variations in water availability, temperature, and soil type. This flexibility supports its survival across a wide geographic range and makes it a valuable genetic resource for improving stress tolerance, yield stability, and climate resilience in cultivated rice (Oryza sativa). Although O. rufipogon has predominantly been reported in wet and intermediate zones of Sri Lanka, this study confirms its presence in the dry zone, particularly in the Trincomalee district. This study aims to evaluate the morphological diversity of two O. rufipogon populations collected from Matara (Intermediate Zone) and Trincomalee (Dry Zone) districts in Sri Lanka, to identify specific traits contributing to phenotypic plasticity, potential speciation by distance and ecological adaptation. Each population was randomly sampled with 20 individuals, ensuring a minimum spacing of 5 meters between individuals to maintain the genotypic diversity. A pot experiment (42cm x 42cm x 42cm) was conducted under common garden conditions in a completely randomized design over 6 months at the Faculty of Agriculture, University of Ruhuna (Latitude 06.060337°N and Longitude 80.5681455°E) for phenotypic evaluation. The Trincomalee populations was labeled R5, and the Thihagoda population as R4. Twelve key quantitative traits and eight qualitative traits were measured. The Trincomalee population (R5) exhibited significantly greater plant height by 23.72% (217.47 ± 5.08a cm), leaf length by 41.65% (43.2289 ± 1.0813a cm), seeds per panicle by 20.29% (60.2222 ± 2.3647a), panicle length by 27.59% (30.9600 ± 0.4713a), culm length by 35.78% (169.0911 ± 4.4966a), panicle excretion by 85.25% (32.1961 ± 0.7038a) and seed length by 9.60% (0.80 ± 0.006a cm) compared to the Matara population (R4 ), indicating enhanced growth potential in R5 (P < 0.05). In contrast, no significant differences were observed in qualitative traits, suggesting a conserved morphological pattern in these descriptors. This study demonstrates significant morphological divergence in quantitative traits of the dry zone (Trincomalee) population, particularly in plant height, panicle length and seed yield, reflecting adaptive plasticity to arid environments. These findings suggest the potential utility of dry zone O. rufipogon germplasm in breeding climate-resilient cultivated rice. Breeding programs aimed at developing climate-resilient cultivated rice varieties can benefit from these insights.