Table_1_Genetic dissection of grain traits and their corresponding heterosis in an elite hybrid.xlsx

Rice productivity has considerably improved due to the effective employment of heterosis, but the genetic basis of heterosis for grain shape and weight remains uncertain. For studying the genetic dissection of heterosis for grain shape/weight and their relationship with grain yield in rice, quantitative trait locus (QTL) mapping was performed on 1,061 recombinant inbred lines (RILs), which was developed by crossing xian/indica rice Quan9311B (Q9311B) and Wu-shan-si-miao (WSSM). Whereas, BC1F1 (a backcross F1) was developed by crossing RILs with Quan9311A (Q9311A) combined with phenotyping in Hefei (HF) and Nanning (NN) environments. Overall, 114 (main-effect, mQTL) and 359 (epistatic QTL, eQTL) were identified in all populations (RIL, BC1F1, and mid-parent heterosis, HMPs) for 1000-grain weight (TGW), grain yield per plant (GYP) and grain shape traits including grain length (GL), grain width (GW), and grain length to width ratio (GLWR). Differential QTL detection revealed that all additive loci in RILs population do not show heterotic effects, and few of them affect the performance of BC1F1. However, 25 mQTL not only contributed to BC1F1’s performance but also contributed to heterosis. A total of seven QTL regions was identified, which simultaneously affected multiple grain traits (grain yield, weight, shape) in the same environment, including five regions with opposite directions and two regions with same directions of favorable allele effects, indicating that partial genetic overlaps are existed between different grain traits. This study suggested different approaches for obtaining good grain quality with high yield by pyramiding or introgressing favorable alleles (FA) with the same direction of gene effect at the QTL regions affecting grain shape/weight and grain yield distributing on different chromosomes, or introgressing or pyramiding FA in the parents instead of fixing additive effects in hybrid as well as pyramiding the polymorphic overdominant/dominant loci between the parents and eliminating underdominant loci from the parents. These outcomes offer valuable information and strategy to develop hybrid rice with suitable grain type and weight.

由于杂种优势（heterosis）的有效利用，水稻生产力已得到显著提升，但粒形与粒重相关杂种优势的遗传基础仍不明确。为解析水稻粒形/粒重杂种优势的遗传机制及其与稻谷产量的关联，本研究以籼稻（xian/indica）品种荃9311B（Quan9311B, Q9311B）与武山四苗（Wu-shan-si-miao, WSSM）杂交构建的1061个重组自交系（recombinant inbred lines, RILs）为材料，开展数量性状位点（quantitative trait locus, QTL）定位分析。进一步以RILs为轮回亲本与荃9311A（Quan9311A, Q9311A）杂交构建回交F1群体（BC1F1），并分别在合肥（Hefei, HF）与南宁（Nanning, NN）环境下开展表型鉴定。综合所有群体（RILs、BC1F1及中亲优势（mid-parent heterosis, HMPs）群体）的表型数据，共鉴定到114个主效数量性状位点（main-effect QTL, mQTL）与359个上位性数量性状位点（epistatic QTL, eQTL），涉及千粒重（1000-grain weight, TGW）、单株产量（grain yield per plant, GYP）以及粒长（grain length, GL）、粒宽（grain width, GW）、粒长宽比（grain length to width ratio, GLWR）等粒形性状。差异QTL检测结果显示，RILs群体中的所有加性位点均未表现出杂种优势效应，且仅有极少数位点对BC1F1的表型产生影响。但有25个mQTL既对BC1F1的表型具有贡献，同时也参与调控杂种优势形成。本研究共鉴定到7个QTL区域，可在同一环境下同时调控多种稻谷性状（产量、粒重、粒形），其中5个区域的有利等位基因效应方向相反，2个区域的有利等位基因效应方向相同，表明不同稻谷性状间存在部分遗传重叠。本研究提出了两种培育高产优质杂交稻的策略：一是通过聚合或导入分布于不同染色体、调控粒形/粒重与产量的QTL区域内效应方向一致的有利等位基因（favorable alleles, FA），以实现优质与高产的协同改良；二是在亲本中导入或聚合有利等位基因，而非在杂交种中固定加性效应，同时可聚合亲本间的多态性超显性/显性位点，并剔除亲本中的劣显性（underdominant）位点。本研究结果可为培育粒型与粒重适配的杂交稻品种提供宝贵的参考信息与可行的育种策略。