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

Abstract

Forage 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 (VOG 8 ), and realized heritability (h 2 ) 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 VOG 8 was 8 times that of Cycle 0. Total additive gene action was estimated by a calculated realized heritability of h 2 = .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. INTRODUCTIONAbiotic stresses are one of the most prolific problems associated with the widespread cultivation and development of new crops. These refer to any event and/or phenomenon associated with nonliving factors. The major abiotic stress factors most commonly associated with crop damage and loss are drought, flooding, and temperature extremes (Agrios, 2005; Abbreviations: RPS, recurrent phenotypic selection; VOG 8 , velocity of germination within the first 8 days.

Breeding heat tolerant orchardgrass germplasm for summer persistence in high temperature stress environments of the southeastern United States

“…This suggest that we may have reached close to the maximum germination potential under high temperature stress in this germplasm. These findings are consistent with similar work conducted on annual ryegrass germination at high temperatures (Billman et al., 2020). Therefore, further cycles of selection should focus on improving germination velocity.…”

“…To ameliorate this risk, a breeding project was conducted to develop a novel orchardgrass cultivar through recurrent phenotypic selection (RPS) that could tolerate the growing conditions (high temperatures and high relative humidity) in the southeastern United States. Similar work has already been conducted by this team, with success in improving the germination of annual ryegrass at high temperatures and reducing secondary dormancy (i.e., impairment of germination due to adverse environmental conditions; Billman et al., 2020). The breeding objectives were to (a) reduce secondary seed dormancy by selecting seed that germinate at high temperatures, (b) improve heat tolerance of seedlings by screening at high temperatures, (c) increase summer persistence of the species under high temperature stress environments, and (d) determine if other important phenotypic traits were altered during selection for heat tolerance.…”

“…This change in VOG 8 is an artifact of impatience from the those conducting selection. It has been observed in similar work involving selecting seed at germination; inevitably the seed that were selected were the seed that germinated first (Anderson et al., 2009, 2011; Billman et al., 2020; Springer, 2017). The 2018 germination tests indicated an increase in VOG 8 from Cycle 2 to Cycle 3 (3.28x).…”

“…To ameliorate this risk, a breeding project was conducted to develop a novel orchardgrass cultivar through recurrent phenotypic selection (RPS) that could tolerate the growing conditions (high temperatures and high relative humidity) in the southeastern United States. Similar work has already been conducted by this team, with success in improving the germination of annual ryegrass at high temperatures and reducing secondary dormancy (i.e., impairment of germination due to adverse environmental conditions; Billman et al, 2020). The breeding objectives were to (a) reduce secondary seed dor-…”