Inbreeding and Outbreeding in Short Rotation Ryegrass

Abstract

This report presents the results of some investigations into inbreeding and outbreeding in Short Rotation Ryegrass. Short rotation ryegrass is a hybrid ryegrass which has been developed from a species cross between plants of perennial ryegrass (Lolium perenne) and Italian ryegrass (L. multiflorum), an annual species, Corkill (10). These two species are naturally cross fertilized and are completely interfertile, no barriers to cross fertilization having developed during the course of their evolution. Hybridisation under natural conditions is therefore of common occurrence. The causes of inbreeding depression and related heterosis in naturally cross-fertilized species of plants have been of great interest to plant breeders and geneticists. This interest has been greatly stimulated in recent years by the spectacular results obtained in the practical use of heterosis in the development of "hybrid maize" in America. The relative combining ability of inbred lines is recognised as an important factor in the selection of lines for "hybrid maize" or synthetic varieties in other agronomic plants.