Genetic variation in seed shattering in Italian ryegrass (Lolium multiflorum Lam.) and its feasibility for breeding

Although reducing seed shattering may improve the seed productivity of Italian ryegrass (Lolium multiflorum Lam.), information on genetic variation and improvement in this trait is limited. Therefore, we aimed to identify genetic variation in seed shattering in Italian ryegrass and evaluate its potential for breeding. Seed shattering was assessed by the percentage of shattered seeds, primarily after spike stripping. No significant differences in shattering were observed among five early-maturing varieties, whereas some variation was detected among five medium-maturing varieties, although the differences were not large. Plants within an extremely-early-maturing variety, ‘Minamiaoba’ (n = 36), and a medium-maturing variety, ‘Tachimusha’ (n = 95), exhibited considerable variation in seed shattering, ranging from 10.0% to 85.0% and 0.2% to 92.5%, respectively. The tensile strength of the non-basal florets accounted for the variation observed in ‘Minamiaoba’ genotypes. The correlations between seed shattering and total seed weight per spike (retained and shattered) were weak or non-significant, suggesting that reducing seed shattering could improve seed yield. In progeny derived from pair-crossed half-sibs of the reduced seed-shattering genotype, medium to high correlations (r = 0.46–0.79) for seed shattering were observed among different environmental conditions. Seed shattering in six progeny-parent combinations was also evaluated. The regression coefficients ranged from 0.79 to 0.95 when mean parental values were used as the explanatory variable and progeny values as the response variable, indicating high heritability. The observed wide genetic variation and high heritability suggest that genetic improvements to reduce seed shattering in Italian ryegrass may be relatively easy to achieve.