Regulation of spraying 14-hydroxylated brassinosteroid on spike and fertile floret development and carbon and nitrogen metabolism of winter wheat under drought stress

Objectives Clarifying the regulation effect of spraying 14-hydroxylated brassinosteroid (14-HBR) on the development of spike and fertile floret in winter wheat under drought stress.

Methods A field experiment was conducted with large-spike (Zhoumai16, ZM 16) and multi-spike (Yumai49-198, YM 49-198) wheat cultivars. The three treatments in the study were foliar spraying of 0.05 µmol/L of 14-HBR (DBR) or clear water (DCK) under moderate drought stress (i.e., the relative water content of 0–40 cm soil layer was 47.38%–61.91%.), and spraying of clear water under normal irrigation condition (WCK; the amount of irrigation was 750 m³/hm² during jointing stage). Development of young panicle, dry matter accumulation dynamics, yield and yield components were measured.

Results Efficient water supply reduced the number of fertile florets and the floret fruit number. The number of florets per panicle of the two cultivars were in the order: WCK > DBR > DCK. Compared to DCK, spraying 14-HBR could not offset the water stress completely, but effectively reduce floret degeneration and abortion, increase the number of fertile florets of the two wheat cultivars. Compared with DCK, DBR increased the dry matter and N accumulation of spike and non-spike organs, soluble sugar content in spike organs, soluble sugar ratio of spike/leaf, N accumulation ratio of spike/non-spike organ, and C/N ratio of spike organs of the two cultivars after 6 days of spraying 14-HBR, but decreased the dry matter ratio of spike/non-spike organ, soluble sugar content of leaf and C/N of leaf. DBR significantly improved grain number per spike (ZM16 16.04% and YM49-198 15.07%) and yield (ZM16 28.93% and YM49-198 26.86%). The spike number and 1000-grain weight of DBR and DCK treatments were not significantly different.

Conclusions Spraying 14-HBR increased yield mainly by improving the grain number per spike, and the effect was better in large-spike cultivar (ZM16) than that in multi-spike cultivar (YM 49-198). Under moderate drought stress, spraying 14-HBR before wheat florets degradation could promote the material production of source organs, regulate the distribution of spike and leaf soluble sugar, spike and non-spike organs dry matter and nitrogen, decrease the leaf C/N value, increase the spike C/N value, and enhance the transport capacity of sugar and nitrogen from source organs to spike sink organs. Thus, spraying of 14-HBR optimized the development of spike and floret and improved drought tolerance.