ABSTRACT
Summary In order to introduce desirable characteristics from other species, Lolium multiflorum and L. perenne were crossed with Festuca arundinacea and F. pratensis, and three kinds of F1 hybrids were hackcrossed or tricrossed with five species of Lolium and Festuca to the F4 generation. F1 hybrids of L. multiflorum x F. arundinacea were mostly male sterile, with only 0.2 % to 2.5 % stainable pollen and 0.5% to 2.4% viable seeds from backcrosses or tricrosses with five species. F1 hybrids of L. perenne x F. arundinacea and L. perenne x F. pratensis produced extremely sterile pollen with rudimental anthers and 0% to 0.6% viable seeds in backcrosses or tricrosses with four species. Hybrid derivatives with Festuca species as recurrent parents had very low fertility, less than 0.3% fertile pollen and 0% to 1.3% viable seeds, even after the F4 generation. On the contrary, Lolium-like hybrid derivatives produced by pollination with Lolium species increased in pollen and seed fertility as the generation advanced to F4, and enough progeny plants were obtained in the F3 and F4 generations, even with interpollination within hybrid plants. Pollen and seed fertility of the hybrid derivatives varied, depending on the combination of backcross and tricross or on hybrid generation. A correlation coefficient of r = 0.802 between pollen and seed fertility indicates that selection for higher pollen fertility should lead to improvement of seed fertility of hybrids. From these results, I suggest that the breeding technique may be considered effective to improve L. multiflorum and L. perenne if (1) intergeneric hybrids are backcrossed or tricrossed with Lolium species, (2) highly fertile pollen plants are polycrossed within hybrid derivatives, and (3) progeny plants are selected for seed fertility and other desirable characters.
