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

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 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 wk 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 (hRealized2). Stand persistence was assessed 1 yr 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 hRealized2 = .45, and preliminary data from Cycle 3 10‐mo‐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 improved stand survival and greater adoption by southeastern forage producers.