Low Temperature Tolerance At Early Growth Stage Of Maize Hybrids Released In The 1970s-2000s

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 A(3) (GA(3)) 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 GA(3), 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.