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 ( $h_{Realized}^2$). 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 $h_{Realized}^2$ = .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.

中文翻译：

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在美国东南部高温胁迫环境下育种耐热果园草种质以实现夏季持久性

果园 ( Dactylis glomerata)L.) 可以作为东南部生产系统中的冷季多年生植物，但在该地区的高温胁迫条件下通常不会作为真正的多年生植物。这项工作旨在通过循环表型选择 (RPS) 开发耐热果园种质，这将减少由高土壤温度引起的次生种子休眠并提高夏季几个月的林分持久性。选择是在 40/30 °C（12/12 小时，光照/黑暗）的生长室中进行的，发芽的幼苗在 40/30 °C 的条件下再经受 2-3 周。将基础种质（周期 0）和选定的个体（周期 1-3）移植到田间，然后收获种子。40 度发芽试验比较了平均累积发芽率、8 d 内发芽速度 (VOG ₈)，并实现了遗传性 ( $H_{\mathrm{电阻}\mathrm{电子}\mathrm{一种}升\mathrm{一世}z\mathrm{电子}d}^2$）。移植后 1 年评估站立持久性。2018 年的测试结果表明，第 3 周期种子发芽率（82%）高于之前所有的选择周期，VOG ₈是第 0 周期的 8 倍。附加基因作用也增加，最终$H_{\mathrm{电阻}\mathrm{电子}\mathrm{一种}升\mathrm{一世}z\mathrm{电子}d}^2$ = .45，周期 3 10 个月持久性的初步数据 (56%) 是周期 0 (27%) 的两倍。这些结果表明，在高温发芽和田间林分持久性方面，基础种质都有显着改善。这可能会提高林分生存率，并被东南部的牧草生产者更多地采用。