Exogenously Used 24-Epibrassinolide Promotes Drought Tolerance in Maize Hybrids by Improving Plant and Water Productivity in an Arid Environment

Abstract

The influence of 24-epibrassinolide (EBR₂₄), applied to leaves at a concentration of 5 μM, on plant physio-biochemistry and its reflection on crop water productivity (CWP) and other agronomic traits of six maize hybrids was field-evaluated under semi-arid conditions. Two levels of irrigation water deficiency (IWD) (moderate and severe droughts; 6000 and 3000 m³ water ha^-1, respectively) were applied versus a control (well-watering; 9000 m³ water ha^-1). IWD reduced the relative water content, membrane stability index, photosynthetic efficiency, stomatal conductance, and rates of transpiration and net photosynthesis. Conversely, antioxidant enzyme activities and osmolyte contents were significantly increased as a result of the increased malondialdehyde content and electrolyte leakage compared to the control. These negative influences of IWD led to a reduction in CWP and grain yield-related traits. However, EBR₂₄ detoxified the IWD stress effects and enhanced all the above-mentioned parameters. The evaluated hybrids varied in drought tolerance; Giza-168 was the best under moderate drought, while Fine-276 was the best under severe drought. Under IWD, certain physiological traits exhibited a highly positive association with yield and yield-contributing traits or CWP. Thus, exogenously using EBR₂₄ for these hybrids could be an effective approach to improve plant and water productivity under reduced available water in semi-arid environments.

Keywords: brassinosteroids; irrigation water deficit; physiological parameters; water output of yields; yield-contributing traits.

Figure 1

Influence of 24-epibrassinolide application on plant height (A), number of rows/ear (B), number of grains/row (C), 1000-grain weight (D), grain yield (E) and biological yield (F) of six maize hybrids grown under three irrigation regimes over the two growing seasons of 2018 and 2019. The bars on the top of the columns represent the LSD (p ≤ 0.05).

Figure 2

Biplot of the principal components analysis representing the relationship among the evaluated physiological and agronomic traits of six maize hybrids grown under three irrigation regimes over two growing seasons. Chl is total chlorophyll content, Car is the carotenoids content, Phot is the photochemical activity, Fv/Fm is the photosynthetic efficiency, Net is the net photosynthetic rate, Tran is the transpiration rate, Stom is the stomatal conductance, MDA is malondialdehyde, RWC is the relative water content, MSI is the membrane stability index, EL is the electrolyte leakage, S.Sug is soluble sugar, Pro is the proline content, POD is peroxidase, CAT is the catalase activity, SOD is the superoxide dismutase activity, PH is the plant height, NRE is the number of rows per ear, NGR is the number of grains per row, TGW is the 1000-grain weight, GY is the grain yield (kg ha⁻¹), BY is the biological yield (kg ha⁻¹), CWPg is the crop water productivity of the grain yield (kg m⁻³), and CWPb is the crop water productivity of the biological yield (kg m⁻³).