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.
