Evaluation of semi-hybrid perennial ryegrass populations

Abstract

The yield potential of modern forage cultivars is a limit to production from pasture- based agriculture, and may influence profitability. Hybrid vigour has increased yield in a range of plant species, but is only partially captured in conventional forage breeding systems. The objective of this research was to assess the potential for harnessing hybrid vigour in a semi-hybrid breeding system for perennial ryegrass (Lolium perenne). Paired crosses among eight parental sources, including four cultivars and four ecotypes, were used to create 28 semi-hybrid populations. Parents, semi-hybrids and check cultivars were trialled in pure grass plots under rotational grazing for 2 years in the Manawatu. Dry matter yield data were used to estimate cumulative and seasonal patterns of hybrid vigour expression for cultivar x cultivar semi-hybrid combinations. The mean level of high parent heterosis was less than 2%. However, one combination exhibited significant (p<0.05) high parent heterosis of 7% for cumulative yield. Seasonal levels of heterosis expression ranged up to 11% in winter and 19% in spring, with lower expression in the summer and autumn. These data suggest hybrid vigour may be expressed in some combinations among current populations, and that further experiments to identify superior combinations are warranted. Adoption of a semi-hybrid breeding system for variety development would have implications for population improvement, seed production and certification, and plant variety rights. Keywords: Lolium, heterosis, hybrid, yield