Breeding a heat‐tolerant annual ryegrass for earlier fall planting in the southeastern United States

Abstract

AbstractForage production in the southeastern United States relies heavily on cool‐season grasses in winter and spring. The most prolific species is annual ryegrass (Lolium multiflorum Lam.), a winter annual. Historically, secondary seed dormancy of ryegrass inhibits germination at soil temperatures in excess of 21°C. Normal planting occurs in early‐mid fall (mid‐October). However, earlier planting (Aug. or Sept.) could expand the grazing period. This work sought use of recurrent phenotypic selection (RPS) to breed an annual ryegrass cultivar that could germinate at high temperatures and survive high temperatures post‐germination. All selections were conducted in a growth chamber at 40:30°C (12:12 h, light/darkness). Germinated seedlings were subjected to 2–3 wk of 40:30°C conditions post‐germination. Selected individuals (Cycle 1) and the base germplasm (Cycle 0) were transplanted to the field in fall 2015, and harvested for seed in spring 2016. Germination tests were conducted to compare mean cumulative germination, velocity of germination within 8 d (VOG8), and realized heritability (h2) at 40:30°C. Selection was repeated twice to reach Cycle 3. Data from the 2018 germination tests indicated that germination of Cycle 3 seed (45.8%) was significantly greater (P < .001) within 14 d than that of all previous cycles. Cycle 3 VOG8 was 8 times that of Cycle 0. Total additive gene action was estimated by a calculated realized heritability of h2 = .41. These data indicate improved germination under high temperatures was achieved in nearly half the population. This will potentially allow for late‐summer planting and greater grazing time.