Increase in root density induced by coronatine improves maize drought resistance in North China

Drought stress caused by insufficient irrigation or precipitation impairs agricultural production worldwide. In this study, a two-year field experiment was conducted to investigate the effect of coronatine (COR), a functional analog of jasmonic acid (JA), on maize drought resistance. The experiment included two water treatments (rainfed and irrigation), four COR concentrations (mock, 0 μmol L⁻¹; A1, 0.1 μmol L⁻¹; A2, 1 μmol L⁻¹; A3, 10 μmol L⁻¹) and two maize genotypes (Fumin 985 (FM985), a drought-resistant cultivar and Xianyu 335 (XY335), a drought-sensitive cultivar). Spraying 1 μmol L⁻¹ COR at seedling stage increased surface root density and size, including root dry matter by 12.6%, projected root area by 19.0%, average root density by 51.9%, and thus root bleeding sap by 28.2% under drought conditions. COR application also increased leaf area and SPAD values, a result attributed to improvement of the root system and increases in abscisic acid (ABA), JA, and salicylic acid (SA) contents. The improvement of leaves and roots laid the foundation for increasing plant height and dry matter accumulation. COR application reduced anthesis and silking interval, increasing kernel number per ear. COR treatment at 1 μmol L⁻¹ increased the yield of XY335 and FM985 by 7.9% and 11.0%, respectively. Correlation and path analysis showed that grain yields were correlated with root dry weight and projected root area, increasing maize drought resistance mainly via leaf area index and dry matter accumulation. Overall, COR increased maize drought resistance mainly by increasing root dry weight and root area, with 1 μmol L⁻¹ COR as an optimal concentration.