Effectiveness of population improvement through recurrent selection for scab resistance in wheat using dominant male-sterile gene ms2

An original base population with wide genetic variability was developed by multiple-parent cross-ing,intermating and recrossing using the dominant male-sterile gene ms2（Tal）.Then the phenotypic recurrentselection was conducted for the male-sterile plants in order to improve the population and develop a gene poolwith increased resistance to scab in wheat.Generations RC-RCand RC-RCfrom the resistance resource poolwere evaluated for the resistance and the effect of population improvement was analyzed in Nanjing undersoil-surface inoculation with F.graminearum-diseased seeds in 1988/1989 and single-floret inoculation withascospore suspension of G.zeae in 1991/1992,respectively.The experimental results of the soil-surfaceinoculation indicated that the numbers or percentages of diseased spikelets and seeds per spike of themale-fertile plants were decreased significantly and the comprehensive resistance of the population to scab wasobviously increased.The percentages of uninfected seeds per spike in generations RC,RCand RCwere49.2%,65.5% and 70.7%,respectively.The frequencies of plants with lower than 30% of diseased spikeletand seed percentages in the population were increased by 40% and 36%,respectively,through 2 cycles of se-lection.Under the condition of the single-floret inoculation,the results further demonstrated that the resistanceto the fungal spread could be improved significantly through the phenotypic recurrent selection.Theopportunity of obtaining superior resistant plants from the population would be enhanced gradually with thedevelopment of the gene pool.On average,from RCto RC,the population mean of diseased spikelets ofinoculated spikes was reduced by 8.6% and the frequency of resistant plants with fewer than 4 diseasedspikelets per inoculated spike was increased by 4.2%,respectively,per cycle.The frequency of susceptibleplants with more than 10 diseased spikelets in inoculated spikes was decreased by 9.2% after 4 cycles of se-lection.The genetic variance for resistance reduced remarkably but no significant decrease in the geneticcoefficient of variation was found during the first 4 cycles of selection.