Selection efficiencies for improving drought/salt tolerances and yield using introgression breeding in rice ( Oryza sativa L.)

The backcross (BC) breeding strategy has been increasingly used for developing high yielding varieties with improved abiotic stress tolerances in rice. In this study, 189 Huang-Hua-Zhan (HHZ) introgression lines (ILs) developed from three different selection schemes were evaluated for yield related traits under drought stress and non-stress conditions in the target and off-season winter nursery environments to assess the selection efficiency of BC breeding for improving different complex traits, and led us to five important results. The first result indicated that the primary target traits should be selected first in the target environments (TEs) in order to achieve the maximum genetic gain. Secondly, BC breeding for drought tolerance (DT) in rice was almost equally effective by strong phenotypic selection in the main target environments and in the winter-season of Hainan. Thirdly, exploiting genetic diversity in the subspecific gene pools is of great importance for future genetic improvement of complex traits in rice. Fourthly, considerable genetic gain can be effectively achieved by selection for secondary target traits among the ILs with the primary traits. Finally, the developed ILs provide useful materials for future genetic/genomic dissection and molecular breeding of complex traits.