A novel plant growth regulator ameliorates chilling tolerance for spring maize in Northeast China

Chilling has become a major meteorological disaster affecting the spring maize (Zea mays L.) production region in Northeast China. Our objective was to assess the effect of a novel plant growth regulator on relieving chilling stress among early- and late-maturing maize cultivars in three different regions in Northeast China. Field experiments were conducted in Haerbin country, Suihua country, and Yi-an county in 2011 and 2012. Two widely planted maize cultivars (early maturing—‘Fengdan 3’ and late maturing—‘Zhengdan 958’) in Northeast China were planted. A PKN (a combination of synthetic plant growth regulator, its principal components were polyaspartic acid, kinetin and α-naphthalene acetic acid) solution was applied to the maize surfaces at the six-expanded-leaf stage. The results demonstrated that spring maize yield was significantly influenced by region, cultivar and PKN; spring maize planted in the low-latitude region (Haerbin) had a higher yield than that in the high-latitude region (Suihua and Yi-an countries); the late-maturing cultivar had a higher yield than the early-maturing cultivar. In comparison to the control treatment, the PKN treatment increased the spring maize yield significantly. The variation in the grain yield across regions, cultivars and PKN treatments was mainly due to variation in the kernel weight. Compared to the control, the PKN treatment significantly increased kernel weight. Moreover, the PKN treatment increased the leaf area index, net assimilation rate, ear-leaf sucrose content, and sucrose synthase and sucrose phosphate synthase activities. In addition, the abovementioned indicators increased more for late-maturing cultivars than for early-maturing cultivars in the high-latitude region. In conclusion, PKN can be used to partly relieve chilling stress for spring maize, especially for late-maturing cultivars in high-latitude regions.