Abstract
Rice landraces are lineages developed by farmers through artificial selection during the long-term domestication process. Despite huge potential for crop improvement, they are largely understudied in India. Here, we analyse a suite of phenotypic characters from large numbers of Indian landraces comprised of both aromatic and non-aromatic varieties. Our primary aim was to investigate the major determinants of diversity, the strength of segregation among aromatic and non-aromatic landraces as well as that within aromatic landraces. Using principal component analysis, we found that grain length, width and weight, panicle weight and leaf length have the most substantial contribution. Discriminant analysis can effectively distinguish the majority of aromatic from non-aromatic landraces. More interestingly, within aromatic landraces long-grain traditional Basmati and short-grain non-Basmati aromatics remain morphologically well differentiated. The present research emphasizes the general patterns of phenotypic diversity and finds out the most important characters. It also confirms the existence of very unique short-grain aromatic landraces, perhaps carrying signatures of independent origin of an additional aroma quantitative trait locus in the indica group, unlike introgression of specific alleles of the BADH2 gene from the japonica group as in Basmati. We presume that this parallel origin and evolution of aroma in short-grain indica landraces are linked to the long history of rice domestication that involved inheritance of several traits from Oryza nivara, in addition to O. rufipogon. We conclude with a note that the insights from the phenotypic analysis essentially comprise the first part, which will likely be validated with subsequent molecular analysis.
Highlights
Crop domestication is a complex process mediated by a series of prolific phenotypic changes to modify a wild species so that it is amenable to cultivation, harvest as well as consumption
We evaluate a suite of 29 phenotypic characters from 414 rice landraces to investigate the major determinants of phenotypic diversity
Grain length and DL are highly correlated with component 1 (r2 1⁄4 0.97 for both), Grain width (GW), DW and Seed weight (SW) are correlated with component 2
Summary
Crop domestication is a complex process mediated by a series of prolific phenotypic changes to modify a wild species so that it is amenable to cultivation, harvest as well as consumption. Rice landraces are the groups of lineages that originated and evolved in the field over millennia through selective breeding by generations of farmers, who chose random mutants and gene combinations in domesticated rice, for better yield, grain size and other agronomic or cultural values (Deb 2005). Random mutation as well as frequent hybridization between the landraces and wild relatives over a long time ensured the accumulation of a high phenotypic as well as genetic diversity (Fukuoka et al 2006; Sanni et al 2008). Retention of immense genetic diversity is significant in terms of evolutionary potential to withstand diverse selection regimes, and has important implications in rice breeding to furnish new genes for crop improvement, e.g. abiotic stress tolerance, or pest- or disease-resistance genes (Frankel and Soule 1981). Beginning from the 1960s, a large number of these landraces have been replaced with modern varieties introduced over the past four decades (Heal et al 2004; Deb 2009)
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