Developing Green Super Rice by Exploiting the Hidden Genetic Diversity of the Primary Gene Pool of Rice

As the most important grain crop in China, rice production has more than doubled since 1960s, resulting primarily from the Green Revolution (GR) - the rapid adoption of semi-dwarf rice cultivars (SRCs) and hybrid rice. The spreading of SRCs in China has been accompanied by steadily increased inputs such as chemical fertilizers and pesticides and by increased yield losses from major biotic/abiotic stresses. To achieve sustainable yield increases in rice needed by China population increase in next 1-2 decades, there has been a call for a secondary GR in rice that better balances ecological stewardship conservation and productivity by developing “Green Super Rice (GSR) cultivars that can produce high and stable yield under less inputs.

To achieve this goal, China established its National Rice Molecular Breeding Network (CNRMBN) consisting of major rice research/breeding institutions across China in 1998. CNRMBN has four major objectives: (1) Fully exploit the maximum genetic diversity in the primary gene pool of rice by massive introgression of “green” traits from a mini-core collection of the rice world rice germplasm into elite Chinese genetic backgrounds (GBs); (2) Develop large numbers of trait-sepcific introgression line sets (ILs) in elite Chinese rice GBs; (3) Efficiently discover genes/alleles and genetic networks responsible for important green traits of rice; (3) Establish the material, information, and technological platforms for the national rice molecular breeding programs; (4) Adopt molecular breeding strategies for highly efficient development of GSR hybrid and inbred rice cultivars that produce high and stable yields with less inputs for major target environments in China. After 13 years of efforts, significant progress has been made, including thousands of ILs in 46 elite Chinese rice GBs which have one or more target traits introgressed from 400+ donors representing a mini-core collection of the world rice germplasm. DNA markers were then used to characterize the donor segments in these ILs associated with the introgressed traits. These IL sets and their associated genetic information have provided the material and information platform for large scale molecular breeding. Our results indicated that there is rich source of hidden genetic diversity for most complex traits in the primary gene pool of rice. We further developed a molecular breeding strategy to exploit this hidden diversity for improving multiple traits by BC breeding, marker-based gene-flow tracking, allelic mining and characterization of QTLs/QTL networks for target traits, and directed trait improvement by designed QTL pyramiding. Examples in each step of the molecular breeding strategy will be presented.