To obtain sizable improvement of quantitative traits such as grain yield needs to assemble desirable alleles from multiple parents. Population improvement through recurrent selection is a commonly used and well-proven breeding strategy for improving quantitative traits in out-crossing crops. The effectiveness and efficiency of population improvement have also been demonstrated in self-pollinated crops including wheat, oat and barely. We initiated a population improvement project in 2012 for improving grain yield under irrigated condition. Male-sterile lines are being developed by transferring the nuclear gene for male-sterility contained in an IR36 mutant into selected elite lines through backcrossing. Base populations are also being developed by hand-pollination. Rapid generation advance through single seed decent is optimized for quick development of inbred lines from the improved population. Currently, studies are being conducted to (1) develop markers for the male-sterile gene, (2) develop a system for effective progeny-testing, (3) investigate early generation selection using more heritable indirect traits, and (4) how to integrate marker-assisted selection with phenotypic selection.