Identification of genetic loci for seed shattering in Italian ryegrass (Lolium multiflorum Lam.)

We have identified a unique genetic locus for seed shattering in Italian ryegrass that has an exceedingly large effect and shows partial dominance for reduced seed shattering. Genetic improvement of seed retention in forage grasses can contribute to improving their commercial seed production. The objective of this study was to identify the genetic loci responsible for seed shattering in Italian ryegrass (Lolium multiflorum Lam.) using F₂ and F₃ progeny from a cross between a reduced shattering genotype and a self-fertile shattering genotype. High negative correlations (- 0.622 in F₂ and - 0.737 in F₃) were found between two methods of measuring shattering: (1) the percentage of seed shattering obtained by manually stripping the spike and (2) the non-basal floret breaking tensile strength (BTS). On the other hand, basal floret BTS showed a non-significant (F₂) or low (- 0.226 in F₃) correlation with the percentage of seed shattering by stripping. We identified a quantitative trait locus (QTL) near the start of linkage group 2, designated as qSH2.1, which was associated with both seed shattering measured by stripping and non-basal floret BTS with exceptionally high LOD values (11.0-34.0); in addition, we detected five minor QTLs. qSH2.1 explained about 2/3 of the total variation in the percentage of seed shattering by stripping at the late dough stage in the F₂ population. The reduced shattering trait was partially dominant, in contrast to the genetic mode in many previous reports on other crops. Candidate orthologs for the previously reported seed shattering genes were not found near the qSH2.1 locus in the ryegrass genome, suggesting that this QTL may be due to a yet-undiscovered gene.