Screening for natural male sterile mutants in alfalfa (Medicago sativa L.) varieties

Although male sterility is important in obtaining heterosis, there is no widespread exploitation of male sterility in alfalfa breeding. Male sterile mutants could provide the basic materials for carrying out seed production in breeding programmes. In order to establish rapid screening methods from which it is feasible to obtain natural male sterile mutants in alfalfa, methods of pollen production and pollen viability were compared by analysing the genetic variance in 19 alfalfa varieties. Both pollen production and pollen viability varied significantly among varieties, and much higher variations existed within varieties than between varieties. It was determined that there was 87.87% variability within varieties for pollen production and 90.85% for pollen viability. No significant difference was observed between different reproductive branches (P=0.589). Screening by individual plant method, there were 58.48% plants with high pollen production, 33.33% with moderate pollen production, 7.36% with trace pollen production, and 0.83% with no pollen production. In total, 6 male sterile mutants were identified from varieties Graze401+z (ms1, M-fon1 and M-fon2), Longzhong (ms2) and Big west (ms3 and ms4), in which four mutants (ms1-ms4) were male sterile but female fertile mutants and two were multi-pistil male sterile mutants (M-fon1 and M-fon2). The mutants ms1-ms4 showed male sterility accompanied with abnormal anther development and pollen grains degeneration. M-fon1 and M-fon2 mutants developed flowers with multi-pistil, as well as no pollen, thereby displaying both male and female sterility.