Breeding Annual Ryegrass (Lolium multiflorum) for Improved Heat Stress Tolerance.

Annual ryegrass (Lolium multiflorum) is a cool-season forage grass that is used for beef operations throughout much of the southeastern United States. The species is high in forage nutritive value and grows rapidly in cool conditions during fall and winter. Early fall or late summer planting of annual ryegrass is highly desirable, as it increases available forage earlier in the season. However, temperatures during late summer and early fall in states that rely on annual ryegrass for forage (such as Mississippi, Alabama, Georgia, and Texas) often exceed 32°C. These temperatures are highly detrimental to annual ryegrass production, thus creating the need for a heat-tolerant annual ryegrass cultivar that can germinate and survive heat stresses as a seedling. The objective of this research was to develop a heat tolerant annual ryegrass cultivar that will germinate earlier in the growing season through recurrent phenotypic selection. Seed of the cultivar Marshall and subsequent cycles of selection were subjected to high temperature germination stress in germination chambers at 40°C in 2015, 2016, and 2017. Seedlings that successfully germinated and survived in the 40°C conditions for two weeks were selected for advancement. In 2016, seed from cycle 1 were compared to the original population of Marshall using a two week germination test to determine if improvements to heat tolerance had been made, with identical tests comparing cycle 2 to Marshall occurring in 2017. No differences were observed in 2016, but differences were observed in 2017 cumulative germination between cycle 2 and Marshall. These data indicate that recurrent phenotypic selection for quantitative traits is viable in annual ryegrass.