INTRODUCTION: Tiller height higher than main stem is one of the important factors affecting the uniformity and mechanized production of sorghum. Sorghum with tiller height equal to that of the main stem can be densely planted and harvested mechanically. Endogenous hormones play an important regulatory role in the process of plant height development. Understanding the impact of endogenous hormones on the height difference between main stem and tiller in sorghum is of great significance for the improvement of sorghum varieties with tiller higher than the main stem.
RATIONALE: To further explore the effects of endogenous hormones on height difference between main stem and tiller of sorghum, Sorghum K35-Y5 with the similar height of main stem and tiller and 1383 with higher tiller than main stem were used to measure the plant height and endogenous hormone contents in main stem booting stage, tiller booting stage, main stem flowering stage and tiller flowering stage, and analyze the dynamic change and correlation, laying a foundation for studying the regulatory mechanisms of main stem and tiller height in sorghum and for improving plant architecture.
RESULTS: The height difference of main stem and tiller in different stages showed that the main stem of K35-Y5 was higher than that of tiller in the first three periods, and the height of main stem and tiller was basically the same at tiller flowering stage. The main stem height of 1383 was higher than that of tiller in main stem booting stage, the height of main stem and tiller was basically the same in tiller booting stage, and the height of tiller was higher than that of main stem in the latter two stages. Analysis of dynamic changes of endogenous hormone in different stages showed that GA₃ content in main stem and tiller was basically consistent with the change of plant height. The dynamic change of ABA in K35-Y5 main stem and tiller is basically the same, which was significantly higher than main stem of 1383 tiller in main stem flowering stage. The contents of IAA, ICA, tZR, IPA, Dx and JA showed a decreasing trend. ACC, SA, JA and H₂JA had no obvious characteristics. The correlation analysis showed that the difference of tiller and main stem was positively correlated with the relative content of GA₃ at tiller booting stage, main stem flowering stage and tiller flowering stage, and positively correlated with the relative ratio of GA₃/ABA at main stem flowering stage and tiller flowering stage.
CONCLUSION: The height difference of main stem and tiller was closely related to the relative content of GA₃ at tiller booting stage, main stem flowering stage and tiller flowering stage. Through the treatment of GA₃ and subsequent paraffin section analysis, we found that spraying GA₃ affects cell elongation to achieve the improvement of plant height uniformity. This will be of great significance for the breeding of sorghum varieties suitable for mechanized production.

Differences in growth, height (A), and the GA₃ contents (B) of main stem and tiller of K35-Y5 and 1383 at different stages. * and ** indicate significant differences at the 0.05 and 0.01 levels, respectively.