Functional trait diversity of wild rice species in Sri Lanka: implications for field identification and application

Abstract

The study assessed the variations in morphologically, physiologically and anatomically distinct traits of wild rice species in Sri Lanka; O. nivara, O. rufipogon, O. eichingeri, O. rhizomatis and O. granulata, which could be useful in rice breeding. The wild rice species were grown in a common garden, and the morphological traits were measured soon after heading. The results showed qualitative parameters such as the panicle type, awning, stigma colour, lemma and palea pubescence, seed coat colour, blade pubescence and ligule shape, are distinctive among the five species and are promising characters in their field identification. ANOVA revealed that the quantitative traits, such as flag leaf length, flag leaf width, culm length, culm diameter, panicle length, 100 grain weight and plant height are useful for further confirmation of species. The highest net photosynthetic rate (5.86 µmol m -2 s -1 ), high cluster width of the base (61.4 µm), and trichome density (184.33 per 25 mm 2 area) were observed in O. rufipogon compared to the rest, and such desirable traits are effective in rice breeding. Moreover, transpiration rates, stomatal conductance and substomatal CO 2 concentration are ideal physiological traits to be considered in super rice breeding. Significant correlations were observed between transpiration and photosynthesis processes. Thus, our study provides a clear picture on habitat preferences, life cycle, distinctive morphologies and diverse functional traits to be effectively used in field identification and future utilisation of wild relatives of rice in the plant breeding programmes.

Phenological and morphological variations of Oryza rufipogon and O. nivara in Sri Lanka and their evolutionary implications

“…Phenotypic divergence is the first step towards local adaptation and speciation and has thus been extensively explored across plant species (Mazer et al 2022;Mitchell-Olds et al 2007;Richardson et al 2014;Rieseberg et al 2002;Wadgymar et al 2022). In the present study, based on both in situ observation and common garden experiment, we demonstrated two distinct morphological groups, corresponding to O. rufipogon and O. nivara, and substantial phenotypic variation within species in many traits, consistent with previous studies (Banaticla-Hilario et al 2013a;Cai et al 2019;Eizenga et al 2022;Guo et al 2016;Oka 1988;Sandamal et al 2021). Specifically, O. nivara has a shorter culm, early flowering, shorter and less exserted panicles with more compactness and has more spikelets per panicle with shorter anthers.…”

“…First, we found significant difference between species in flowering phenology, as revealed by either in situ observation or common garden experiment. For in situ observation, O. rufipogon exhibited a prolonged life cycle with two flowering peaks while O. nivara displayed a notably shorter life cycle with a single flowering peak, as reported in Sandamal et al (2021). This reflects the differences in typical environments/habitats where O. rufipogon (in wet zone) and O. nivara (in dry zone) grow.…”

“…Consequently, flowering phenology has been considered to be a magic trait that facilitates genetic differentiation and triggers the divergence of multiple traits in response to the environments (Lowry et al 2008;Servedio et al 2011;Sugai et al 2023). Although substantial investigations of flowering time have been conducted on rice cultivars (Oka 1988;Vicentini et al 2023), flowering phenology and its variation within and between wild rice species remain largely elusive despite some efforts (Morishima et al 1961;Morishima et al 1984;Oka 1988;Xu et al 2020;Sandamal et al 2021). In the present study, we found varying degrees of phenological variation between species, between populations within species, and between in situ observation and common garden experiment, which may be caused by both genetic elements and environmental variables such as water availability and temperature (Cai et al 2019;Kuroda et al 2005;Morishima et al 1984;Sang and Ge, 2007;Vaughan et al 2008).…”

“…However, common garden experiment showed a different pattern of flowering phenology, particularly for O. nivara that flowers continuously for almost an entire year. This suggests that the flowering phenology or life cycle of O. nivara is highly flexible depending on environmental conditions, with water availability being a primary determinant (Huang et al 2013;Liu et al 2015;Sandamal et al 2021;Sang and Ge 2007;Vaughan et al 2008). It also implicates that O. nivara, at least for the Sri Lankan populations, might not be an annual plant in the strict sense because it can consistently survive and succeed when ample water is available.…”

Phenotypic Characterization of Oryza nivara (Sharma et Shastry) Collected from Different Ecological Niches of Sri Lanka

“…In particular, the wild species closely related to cultivated rice have a valuable gene pool and play a pivotal role in rice breeding programs by contributing genes resistant to biotic stresses and tolerance to abiotic stresses [2,5,11]. The species of the genus Oryza are widely diverse morphologically [12][13][14][15][16] and are genetically represented by distinct genome types, which provide a valuable opportunity to investigate variations of rice breeding programs [13,17]. Due to their high genetic compatibility with cultivated rice, species possessing the AA-genome are the most accessible genetic resources among the wild relatives [18].…”