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A field experiment was conducted to investigate the effects of paclobutrazol on ear characteristics and grain yield by regulating root growth and root-bleeding sap of maize crop. Seed-soaking at rate of 0 (CK1), 200 (S1), 300 (S2), and 400 (S3) mg L−1, and seed-dressing at rate of 0 (CK2), 1.5 (D1), 2.5 (D2), and 3.5 (D3) g kg−1 were used. Our results showed that paclobutrazol improved the ear characteristics and grain yield, and were consistently higher than control during 2015–2016. The average grain yield of S1, S2 and S3 were 18.9%, 61.3%, and 45.9% higher, while for D1, D2 and D3 were 20.2%, 33.3%, and 45.2%, compared to CK, respectively. Moreover, paclobutrazol-treated maize had improved root-length density (RLD), root-surface area density (RSD) and root-weight density (RWD) at most of the soil profiles (0–70 cm for seed-soaking, 0–60 cm for seed-dressing) and was attributed to enhancing the grain yield. In addition, root-activity, root-bleeding sap, root dry weight, diameter and root/shoot ratio increased by paclobutrazol, with highest values achieved in S2 and D3 treatments, across the whole growth stages in 2015–2016. Our results suggested that paclobutrazol could efficiently be used to enhance root-physiological and morphological characteristics, resulting in higher grain yield.

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Plant hormones play important roles in regulating the occurrence of crop tillers. However, little is known about the relationships and the underlying mechanisms between endogenous hormones and the occurrence of wheat tillers induced by exogenous hormones. In this study, two winter wheat cultivars, Xinong 979 and Xiaoyan 22, were used to investigate the effects of the exogenous application of indole-3-acetic acid (IAA) and zeatin (Z) on the occurrence of wheat tillers and investigate underlying mechanisms regulating the occurrence of tillers. The results showed that the application of IAA inhibited the occurrence of tillers, and external Z application promoted the occurrence rate of tillers under low nitrogen conditions. Further analysis of the results showed that exogenous IAA completely inhibited the growth of tiller buds, while exogenous Z significantly promoted the growth rate of tiller buds in low nitrogen conditions. Endogenous hormones exhibit important functions in regulating the growth of tiller buds, which contents were affected by exogenous hormones. Furthermore, according to the principal component analysis and correlation analysis, the growth of tiller buds was significantly positively correlated with the content of endogenous Z, whereas it was significantly negatively correlated with the ratios of endogenous IAA to endogenous Z (IAA:Z) and endogenous abscisic acid (ABA) to endogenous Z (ABA:Z). Moreover, no significant correlation was observed between the growth of the tiller buds and the endogenous IAA, endogenous gibberellins (GAs), and endogenous ABA content. These results suggested that Z played key roles in regulating the tiller occurrence, and exogenous hormones regulated the growth of wheat tiller buds via affecting the Z contents, thus regulating the occurrence of wheat tiller.

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