Genetic Dissection of an Elite Rice Hybrid Revealed That Heterozygotes Are Not Always Advantageous for Performance

Genetic Dissection of an Elite Rice Hybrid Revealed That Heterozygotes Are Not Always Advantageous for Performance

J. P. Hua^a, Y. Z. Xing^a, C. G. Xu^a, X. L. Sun^a, S. B. Yu^a, and Qifa Zhang^a
^a National Key Laboratory of Crop Genetic Improvement, National Center of Crop Molecular Breeding, Huazhong Agricultural University, Wuhan 430070, China

Corresponding author: Qifa Zhang, Huazhong Agricultural University, Wuhan 430070, China., qifazh{at}public.wh.hb.cn (E-mail)

Communicating editor: A. PATERSON

We introduced an experimental design that produced an "immortalizedF₂" population allowing for complete dissection of genetic componentsunderlying quantitative traits. Data for yield and three componenttraits of the immortalized F₂ were collected from replicatedfield trials over 2 years. Using 231 marker loci, we resolvedthe genetic effects into individual components and assessedrelative performance of all the genotypes at both single- andtwo-locus levels. Single-locus analysis detected 40 QTL forthe four traits. Dominance effects for about one-half of theQTL were negative, resulting in little "net" positive dominanceeffect. Correlation between genotype heterozygosity and traitperformance was low. Large numbers of digenic interactions,including AA, AD, and DD, were detected for all the traits,with AA as the most prevalent interaction. Complementary two-locushomozygotes frequently performed the best among the nine genotypesof many two-locus combinations. While cumulative small advantagesover two-locus combinations may partly explain the genetic basisof heterosis of the hybrid as double heterozygotes frequentlydemonstrated marginal advantages, double heterozygotes werenever the best genotypes in any of the two-locus combinations.It was concluded that heterozygotes were not necessarily advantageousfor trait performance even among genotypes derived from sucha highly heterotic hybrid.

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