Abstract:
Sri Lanka harbors five wild Oryza species: O. nivara, O. rufipogon, O. eichingeri, O.
granulata, and the endemic O. rhizomatis. Accurate taxonomic identification of these
species is essential for biodiversity conservation and rice genetic improvement. However,
it remains challenging due to overlapping morphological characters and habitat-driven
variations. This study develops a dichotomous identification key for Sri Lankan wild Oryza
species based on detailed morphological traits and ecological preferences. Field surveys
were conducted across the dry, intermediate, and wet zones in diverse habitats. Results reveal
clear diagnostic characters distinguishing the five species, supported by significant
segregation in morphological traits. Kruskal-Wallis test was performed to evaluate the
interspecific differences. The embryo: seed length ratio of O. granulata and O. eichingeri
was found to be significantly higher compared to the other species, whereas O. rufipogon
exhibited a significantly lower ratio (H = 13.4, P = 0.009). The seed shape index of O. nivara
and O. rufipogon was significantly higher compared to the other species, while O. rhizomatis
exhibited a significantly lower index (H = 61.44, P = 1.292 × 10⁻¹²). The seed coat ratio
(SCR) of the rice species differed significantly (H = 18.29, P = 0.00109), with O. nivara and
O. rhizomatis exhibiting SCR values greater than 0.5. Morphological traits such as awn,
rhizome, leaf length, panicle structure, stigma colour and presence of pubescence on lemma
or palea shows vast variation among species. Principal component Analysis (PCA) shows
the deviation in the qualitative parameters among the species. Also the wild rice species
shows variation in their micro habitat conditions: O. nivara and O. rhizomatis dominate dry
zones, O. rufipogon prefers intermediate/wet regions, O. eichingeri occurs at forest edges,
and O. granulata thrives in shaded, moist forests. We proposed a dichotomous key
integrating morphological and ecological data, providing a robust framework for species
identification, biodiversity assessments, and conservation planning.
