Early freezes in the spring are becoming increasingly common. To protect farmers from low temperatures (LT), crops need improved LT tolerance. The hypothesis of this paper is that maize (Zea mays L.) hybrids released in the 2000s had higher LT tolerances than those released in the 1970s. In the study, eight popular maize released between 1970 and 2010 were subjected to LT in four different trials. Germination time, growth uniformity, recovery ability from LT stress, and leaf productivity at seedling stage are important indicators in evaluating LT tolerance of maize. Hybrids released in the 1970s had a higher gibberellin A₃ (GA₃) content in seeds, which resulted in faster germination in LT (P = .02). In contrast, plant growth uniformity of the 2000s hybrids were higher than that of the 1970s hybrids in LT (P = .00 at emergence). Upon being returned to warm temperatures, the 2000s hybrids recovered more rapidly than old ones mainly because of the larger root systems, higher GA₃, and indole-3-acetic acid (IAA) content in seedlings. In addition, the 2000s hybrids had a higher chlorophyll content, F_v/F_m, soluble sugar and starch content, and antioxidant enzyme activity in seedlings than old hybrids in LT, which can also contribute to a fast recovery from LT stress. Based on the growth uniformity and recovery ability from LT stress, new hybrids showed a higher LT tolerance than old hybrids during early growth stage. This study showed the genetic tolerance in LT may exist in hybrids that were released 50 yr ago, and that exporting differences between hybrids possible mechanism of temperature tolerance can be identified.

中文翻译：

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1970-2000年代玉米杂交种早期生长阶段的低温耐受性

春季的早期结冰变得越来越普遍。为了保护农民免受低温 (LT) 的影响，作物需要提高 LT 耐受性。本文的假设是2000 年代发布的玉米 ( Zea mays L.) 杂种比 1970 年代发布的玉米具有更高的 LT 耐受性。在这项研究中，1970 年至 2010 年间发布的八种流行玉米在四项不同的试验中进行了 LT。发芽时间、生长均匀度、低温胁迫恢复能力和苗期叶片生产力是评价玉米耐低温性的重要指标。1970 年代发布的杂交种在种子中具有较高的赤霉素 A ₃ (GA ₃ ) 含量，这导致 LT ( P = .02）。相比之下，LT 中 2000 年代杂种的植物生长均匀度高于 1970 年代杂种（出苗时P  = .00）。恢复到温暖的温度后，2000 年代的杂种比旧的杂种恢复得更快，这主要是因为幼苗中的根系更大、GA ₃和吲哚-3-乙酸 (IAA) 含量更高。此外，2000 年代的杂种具有更高的叶绿素含量，F _v / F _m、可溶性糖和淀粉含量以及幼苗的抗氧化酶活性与 LT 中的老杂种相比，这也有助于从 LT 胁迫中快速恢复。基于LT胁迫下的生长均匀性和恢复能力，新杂种在生长早期表现出比老杂种更高的LT耐受性。本研究表明，50年前放出的杂种中可能存在LT的遗传耐受性，并且可以确定杂种之间输出差异的温度耐受性可能机制。