Genetic composition of yield heterosis in an elite rice hybrid

Abstract

Heterosis refers to the superior performance of hybrids relative to the parents. Utilization of heterosis has contributed tremendously to the increased productivity in many crops for decades. Although there have been a range of studies on various aspects of heterosis, the key to understanding the biological mechanisms of heterotic performance in crop hybrids is the genetic basis, much of which is still uncharacterized. In this study, we dissected the genetic composition of yield and yield component traits using data of replicated field trials of an "immortalized F 2 " population derived from an elite rice hybrid. On the basis of an ultrahigh-density SNP bin map constructed with population sequencing, we calculated single-locus and epistatic genetic effects in the whole genome and identified components pertaining to heterosis of the hybrid. The results showed that the relative contributions of the genetic components varied with traits. Overdominance/pseudo-overdominance is the most important contributor to heterosis of yield, number of grains per panicle, and grain weight. Dominance × dominance interaction is important for heterosis of tillers per plant and grain weight and has roles in yield and grain number. Single-locus dominance has relatively small contributions in all of the traits. The results suggest that cumulative effects of these components may adequately explain the genetic basis of heterosis in the hybrid. epistasis | recombinant inbred intercross H eterosis, or hybrid vigor, refers to the superior performance of the hybrids relative to the parents (1). Utilization of heterosis has tremendously increased productivity of many crops globally. However, the understanding of the underpinning biological mechanism is still fragmentary after a century of debate and quest. Although there have been a range of studies on various aspects of heterosis (2-5), the key to understanding the biological mechanisms of heterotic performance in crop hybrids is the genetic basis (6), much of which is still uncharacterized (7).Three classic genetic hypotheses-dominance (8-11), overdominance (12-15), and epistasis (16, 17)-were proposed as explanations for the genetic basis of heterosis. Although there have been a large number of genetic analyses in plants with results favoring one hypothesis or another (18-31), genetic composition pertaining to heterotic performance of crop hybrids has not been fully characterized in an experimental population. There has been no assessment about the relative contributions of these genetic components to heterosis in a crop hybrid.The following conditions should be met for complete genetic characterization of heterosis relevant to crop production: (i) the genetic materials are based on elite hybrids that have shown timehonored superiority in crop production; (ii) the targets are key traits of agronomic performance; (iii) the experimental population allows identification of all of the genetic components concerned, including dominance (d/a ≤1, where d is the dominant effect and a is the additiv...

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Hybridization in Plants: Old Ideas, New Techniques

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