Eco-physiological analysis on hybrid rice productivity using genome information

水稻（Oryza sativa L.）包括两个亚种，即水稻亚种。粳稻和籼稻。虽然在过去的水稻育种计划中很少使用粳稻与籼稻的亚种间杂交，但水稻育种者已经意识到，粳稻与籼稻的杂交在许多农艺性状如生物量、抗逆性等方面经常表现出显著的杂种优势。本项目旨在阐明这些性状是如何在具有高杂种优势的粳稻杂交分离群体中被遗传控制的。为此，我们利用本实验室培育的Nekken 2（低地粳稻）× Gaya（低地籼稻）重组自交系、Kamenoo（低地粳稻）× Dular（雨养-低地籼稻）重组自交系和IR36（低地籼稻）× Genjah Wangkal（高地粳稻）重组自交系进行了数量性状位点（QTL）分析。我们发现基因间的相互作用（上位性）是许多性状越界分离的主要原因。我们还发现，一些性状(如：分蘖芽休眠和分叶期对它们的产物（如分蘖数）有很大的乘法效应，这表明上位性至少在形态水平上是综合的。

Rice (Oryza sativa L.) includes two subspecies, namely ssp. japonica and ssp.indica. Although japonica-indica intersubspecific cross has been very rarely used in the past rice breeding programs, rice breeders have been aware that hybrid plants between japonica x indica cross frequently exhibit notable heterosis in many agronomic traits such as biomass production, stress tolerances, etc. This project was aimed to clarify how these characters are controlled genetically in segregating populations from japonica x indica crosses that show high heterosis. For this purpose, we carried out quantitative trait locus (QTL) analyses using Nekken 2 (lowland japonica) x Gaya (lowland indica) recombinant inbred lines, Kamenoo (lowland japonica) x Dular (rainfed-lowland indica) recombinant inbred lines, and IR36 (lowland indica) x Genjah Wangkal (upland japonica) recombinant inbred lines which were originally developed in our laboratory. We found that gene to gene interactions (epistasis) are the major cause of transgressive segregation in many traits. We also found that linked small QTLs for some traits (eg. tiller bud dormancy and phyllochron) have a multiplicative large effect on their product (e.g. tiller number), suggesting that epistasis is, at least in part, integrated at morphological level.