Harnessing the hidden genetic diversity for improving multiple abiotic stress tolerance in rice (Oryza sativa L.)

To develop superior rice varieties with improved yield in most rainfed areas of Asia/Africa, we started an introgression-breeding program for simultaneously improving yield and tolerances of multiple abiotic stresses. Using eight BC1 populations derived from a widely adaptable recipient and eight donors plus three rounds of phenotypic selection, we developed 496 introgression lines (ILs) with significantly higher yield under drought, salt and/or non-stress conditions in 5 years. Six new varieties were released in the Philippines and Pakistan and many more are being evaluated in multi-location yield trials for releasing in several countries. Marker-facilitated genetic characterization revealed three interesting aspects of the breeding procedure: (1) the donor introgression pattern in specific BC populations was characteristic; (2) introgression frequency in different genomic regions varied considerably, resulting primarily from strong selection for the target traits; and (3) significantly lower heterozygosity was observed in BC progenies selected for drought and salinity tolerance. Applying strong phenotypic selection under abiotic stresses in early segregating generations has major advantages for not only improving multiple abiotic stress tolerance but also achieving quicker homozygosity in early generations. This breeding procedure can be easily adopted by small breeding programs in developing countries to develop high-yielding varieties tolerant of abiotic stresses. The large set of trait-specific ILs can be used for genetic mapping of genes/QTL that affect target and non-target traits and for efficient varietal development by designed QTL pyramiding and genomics-based recurrent selection in our Green Super Rice breeding technology.为培育适配亚洲、非洲多数雨养地区的高产优良水稻品种，我们启动了一项可同时提升产量与多重非生物胁迫耐受性的回交育种计划。我们采用8个由广泛适配的受体亲本与8个供体亲本构建的回交一代（BC1）群体，历经三轮表型选择，于5年内培育出496个在干旱、盐胁迫及/或非胁迫条件下产量显著提升的导入系（introgression lines, ILs）。其中6个新品种已在菲律宾、巴基斯坦正式登记推广，另有数十个品种正在多国开展多点产量鉴定试验，筹备后续推广工作。借助标记辅助遗传解析，我们揭示了该育种流程的三项关键特征：（1）特定BC1群体的供体基因组导入模式具有特异性；（2）不同基因组区域的导入频率差异显著，这主要源于对目标性状的高强度选择；（3）针对干旱与盐胁迫耐受性筛选的BC1后代群体，其杂合度显著降低。在早期分离世代开展非生物胁迫下的高强度表型选择，不仅可有效提升多重非生物胁迫耐受性，还能加速早期世代的群体纯合进程，具备多重核心优势。该育种流程可被发展中国家的中小型育种项目轻松采用，用于培育兼具高产与非生物胁迫耐受性的优良水稻品种。这套大规模的性状特异性导入系群体，可用于目标性状与非目标性状相关基因/数量性状位点（quantitative trait locus, QTL）的遗传定位，同时也可借助我们的绿色超级稻（Green Super Rice）育种技术体系，通过定向QTL聚合与基因组学辅助轮回选择，高效开展新品种培育工作。