The Relationship between f Ratio and Seed Yield-Related Traits in Festulolium

Festulolium is the result of hybridization between Lolium and Festuca species. Amphidiploid festulolium produced by crosses between tetraploid Lolium species (L. multiflorum Lam. and L. perenne L.) and Festuca pratensis (F. pratensis Huds.) exhibits genome balance drift, thereby favoring Lolium over numerous generations. In a previous report, we found no decrease in the f ratio (the ratio of total area of Festuca-specific genome regions to the total area of all genome regions) in maternally derived progeny over generations, suggesting that seed yield can cause Lolium-favored genome balance drift. In this study, we investigated seed yield, ripening rate, germination rate, and seed weight in the field for 2 yr in festulolium plants with f ratio over and under 50%. The over 50 f ratio group had significantly lower seed yields, ripening rates, and germination rates than the under 50 f ratio group. Further correlations between seed yield-related traits and f ratio values revealed that germination rate was negatively correlated with f ratio in the over 50 f ratio group. Simulated next-generation f ratios were 2% lower than the actual f ratio values of maternal plants. Our study shows that Lolium-favored genome balance drift can solely be caused by phenotypic differences, regardless of any biases toward Lolium occurring during meiosis.