The exogenous GA₃ greatly affected the grain-filling process of semi-dwarf gene Rht4 in bread wheat

Rht4 is characterized as a GA-responsive dwarf gene in bread wheat (Triticum aestivum L.). The responsiveness of Rht4 to exogenous GA₃ was characterized in seedlings, but the effects of exogenous GA₃ on the important morphological and agronomic traits such as plant height, grain-filling rate, and yield components are unclear. In this study, the Rht4 responsiveness of exogenous GA₃ on these traits was evaluated using the homozygous F_4:5 and F_5:6 lines derived from a cross between Jinmai47 and Burt ert937 (Rht4 donor). After exogenous GA₃ application, the plant height of the dwarf lines was, on average, increased by 17.54%, about 7.92% more than that of the tall lines. Compared with the tall lines, application of exogenous GA₃ significantly increased the kernel weight, maximum grain-filling rate (Gmax), average grain-filling rate (Gave) and kernel weight increment achieving Gmax (Wmax) in both superior and inferior grains, while the day on which the maximum grain-filling rate was reached (Tmax) in Rht4 dwarf lines was significantly earlier in the two generations. What is more, the grain number spike^-1 , grain yield plant^-1 , and 1000-kernel weight (TKW) of the dwarf lines notably increased after exogenous GA₃ -treatment, while there was no significant change in the tall lines except for TKW. The quality traits of the dwarf lines with GA₃ -treatment were greatly improved. Taken together, these results suggested that the application of GA₃ could improve the grain-filling process of Rht4 and compensate for some negative influences, which may provide a reference for its application in wheat breeding and promote the characterization of its regulatory mechanisms.