|MORRISON, JESSE - Mississippi State University|
|BALDWIN, BRIAN - Mississippi State University|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2021
Publication Date: 4/20/2021
Citation: Billman, E.D., Morrison, J.I., Baldwin, B.S. 2021. Breeding heat tolerant orchardgrass germplasm for summer persistence in high temperature stress environments of the southeastern United States. Crop Science. https://doi.org/10.1002/csc2.20492.
Interpretive Summary: Heat and drought stress have been longstanding barriers to incorporating cool-season forage crops into production systems of the southeastern United States. With daily temperatures frequently exceeding 30°Celsius (C), many perennial species often behave as annuals, dying out over summer months due to lack of heat tolerance. Orchardgrass is a cool-season perennial forage that is common in northern livestock and cover crop production systems, displaying greater forage quality than warm-season grasses common in the Southeast. Over three generations (2015-2018) growth chambers were used to control environmental variation, and recurrent phenotypic selection was used to develop a population of orchardgrass germplasm which displays increased germination at very hot temperatures (40°C) and greater ability to persist over hot and dry summer months in the field. Final germination of the germplasm was approximately 82% at 40°C, compared to 38% germination in the unselected, parental population. Stand persistence over summer months increased from approximately 27% to over 56%, with no irrigation or fertilization from May – September. This germplasm can potentially serve as a strong candidate for incorporating vigorous, higher quality perennial forage and cover crops into southeastern production systems.
Technical Abstract: Orchardgrass (Dactylis glomerata L.) could serve as a cool-season perennial in southeastern production systems, but often does not behave as a true perennial under high temperature stress conditions of the region. This work sought to develop heat tolerant orchardgrass germplasm through recurrent phenotypic selection (RPS) that would both reduce secondary seed dormancy caused by high soil temperatures and improve stand persistence and perennation over summer months. Selection was conducted in a growth chamber 40:30°C (12:12 h, light/darkness), with germinated seedlings subjected to an additional 2-3 weeks of 40:30°C conditions. The base germplasm (Cycle 0) and selected individuals (Cycles 1-3) were transplanted into the field, then harvested for seed. Forty-degree germination tests compared mean cumulative germination, velocity of germination within 8 d (VOG8), and realized heritability (h2). Stand persistence was assessed 1 year after transplanting. Results from 2018 tests indicated Cycle 3 seed germination was greater (82%) than all previous cycles of selection and VOG8 was eight times greater than that of Cycle 0. Additive gene action also increased, with final h2 = 0.45, and Cycle 3 stand persistence (56%) was double that of Cycle 0 (27%). These results indicated a significant improvement over the base germplasm for both germination at high temperatures and stand persistence in the field. This could lead to stand survival and greater adoption by southeastern forage producers.