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Maize yield is limited by water deficit in the arid and semiarid regions of China. Conserving water and enhancing crop water productivity are inevitable requirements for the sustainable development of water efficient agriculture. Plant growth regulators (PGRs) play important roles in maize water stress tolerance. In this study, we investigated the effect of plant growth regulator-brazide, a functional analog of brassinolide (BR), on maize water stress resistance through a two-year (2020–2021) field experiment. The experiment included four water treatments (I100: 4012 m3 ha−1; I80: 3210 m3 ha−1; I60: 2407 m3 ha−1; I40: 1605 m3 ha−1), four PGR concentrations (CK: water; Bra: 0.1 μmol L−1 14-hydroxylated brassinosteroid; B1: 0.1 μmol L−1 brazide; B2: 1 μmol L−1 brazide; B3: 10 μmol L−1 brazide). The results showed that deficit irrigation (I60 and I40) decreased soil water content (SWC), photosynthetic rate (Pn), leaf area index (LAI), aboveground biomass (AB) and yield, but improved crop water productivity (WP c). Under deficit irrigation conditions, 1 μmol L−1 brazide application also increased dry matter accumulation and grain yield, a result attributed to improvement of the photosynthetic rate and increases in the root bleeding saps, water productivity. 1 μmol L−1 Brazide application reduced bare tip length, increasing kernel number per ear, thereby increased the yield of I60 and I40 by 15.1% and 11.4% (p ≤ 0.05; 2020), 16.4% and 20.4% (p ≤ 0.001; 2021), respectively. Path analysis showed brazide improved final yields by increasing thousand grain weight (TGW), photosynthetic rate (Pn) and WP c under deficit irrigation. The increase in TGW with brazide treatment was primarily attributed to the increase of Pn. Overall, Brazide increased maize drought resistance mainly by increasing Pn and WP c , with 1 μmol L−1 brazide as an optimal concentration. • A new plant growth regulator, Brazide, was evaluated in maize. • Brazide increased photosynthetic rate and WUE under deficit irrigation. • Application of brazide improved maize growth and grain yield under deficit irrigation. • 1 μmol L−1 brazide as an optimal concentration for maize in arid region of Northwest China. [ABSTRACT FROM AUTHOR]

Plant growth regulators (PGRs) play crucial roles in maize drought tolerance. However, most of the studies are focused on seedling stage under greenhouse conditions, little is known on the effects of grain yields at later growth stage under field environment. It is hypothesized that exogenous application of PGRs can increase maize drought tolerance at different growth stages under field conditions. Here we used alginate oligosaccharide (AOS) and coronatine (COR) to investigate the effects of these two PGRs on maize drought tolerance in a two-year field experiment. The results showed that both COR and AOS treatments reduced leaf water loss and significantly increased the relative leaf water content by 12.6% and 13.0%, thus significantly decreasing superoxide anion accumulation by 49% and 42% in maize seedlings. There was no big difference between these two treatments in the seedling stage. In the subsequent reproductive growth period, although both COR and AOS treatments significantly increased leaf photosynthesis and above-ground growth, including photosynthetic rate by 41% and 33%, relative chlorophyll content (SPAD value) by 8.0% and 6.5%, leaf area by 22% and 15%, plant height by 8.3% and 5.9%, dry matter accumulation by 23% and 17%, respectively, under drought conditions, the effect of COR was superior to the AOS, as evidenced by membership function values of COR treatment were 0.12 and 0.08 larger than that of AOS treatment in 2020 and 2021, respectively. Ultimately, COR and AOS treatments significantly increased the grain yields by 21.7% and 16.2% in 2020, 22.3% and 15.7% in 2021, respectively, under drought conditions. Path analysis showed both PGRs increased final grain yields by increasing thousand-kernel weight (TKW). While the TKW increase with COR treatment was mainly due to the increase of relative chlorophyll content (SPAD value), AOS treatment mainly increased dry matter accumulation under drought conditions. [Display omitted] • Effects of coronatine (COR) and alginate oligosaccharide (AOS) on drought tolerance examined. • Both COR and AOS treatments improved maize drought tolerance. • Treatment of maize seedling contributed to the whole growth period. • The COR treatment was more pronounced in the reproductive growth period. • The COR treatment was superior to that of the AOS treatment. [ABSTRACT FROM AUTHOR]