Evidence for Heterosis in Italian Ryegrass (Lolium multiflorum Lam.) Based on Inbreeding Depression in F-2 Generation Offspring from Biparental Crosses

Italian ryegrass is one of the most important temperate forage grasses on a global basis Improvement of both dry matter yield and quality of herbage have been major objectives of pastur grass breeding over the last century. F1 and F2 progeny sets derived from controlled pair-crosse between selected Italian ryegrass genotypes have been evaluated for yield and nutritive qualit under field conditions. Linear regression of the performance of F1 families under sward condition on parental genotype means in a spaced plant trial was significant for quality characteristics, but no for herbage yield. This result suggests that phenotypic selection of individual plants from space plant nursery is feasible for improvement of nutritive quality traits, but not for yield. The presenc of significant heterosis within F1 populations was demonstrated by reduced herbage productio in subsequent F2 populations (generated by one cycle of full-sib mating), an up to 22.1% tota herbage yield in fresh weight, and a 30.5% survival rate at the end of the second reproductive cycle Potential optimal crosses for exploiting such heterosis are discussed, based on construction an the inter-mating of complementary parental pools, for the implementation of a novel F1 hybri production strategy.