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A major portion of maize is produced under rainfed conditions in the tropics with relatively poor yield because of the unpredictable and irregular distribution of seasonal rainfall, as well as a decline in pre-rainy season rainfall due to climate change, so identification of sustainable production options is utmost needed. Thus, the present studies were conducted in a greenhouse (GH) to ascertain the water stress-tolerant traits of maize and at the field level in the tropical environment of Thailand to see the stimulating possibility of the ascertained traits in a locally popular cultivar using ethephon. Depending on tolerance level, three maize genotypes (Suwan 2301 > Suwan 4452 > S 7328) were tested under different water conditions—well-watered, short-term, and long-term water stress—in the GH. At the field level, the locally popular maize cultivar Suwan 5819 was examined with six ethephon levels (doses in g a.i. ha−1 of ethephon, i.e., T1, 281 at V6 stage; T2, 281 at V6 + 281 at V10 stage; T3, 281 at V10 stage; T4, 562 at V6 stage; T5, 562 at V6 + 562 at V10 stage; T6, 562 at V10 stage) against no ethephon application (T0) under rainfed conditions. Maize suffered from the scarcity of sufficient rainfall during 26–39 days after planting (DAP) and 43–63 DAP in the field. The yield index (YI) was identified from biplot analysis as one of the suitable standards for drought tolerance checks for maize at GH as well as at field level in the tropics. The YI value of observed agro-physio-biochemical traits of maize in GH showed that relative water content (RWC, 1.23), stem base diameter (SBD, 1.21), total soluble sugar (TSS, 1.15), proline (Pr, 1.13), aboveground plant biomass (APB, 1.13), root weight (RW, 1.13), relative growth rate (RGR, 1.15), specific leaf weight (SLW, 1.12), and net assimilation rate (NAR, 1.08) were the most desirable. Efforts were made to stimulate these traits under water stress at the field level. Ethephon application as T1 helped to gain higher kernel yield (KY) (5.26 t ha−1) with the support of higher RWC (90.38%), proline (24.79 µmol g−1 FW), TSS (1629 mg g−1 FW), SBD (24.49 mm), APB (271.34 g plant−1), SLW (51.71 g m−2), RGR (25.26 mg plant−1 day−1), and NAR (0.91 mg cm−2 day−1) compared to others, especially no ethephon application. Furthermore, the attributes SLW, SBD, Pr, heat utilization efficiency (HUE), 100-kernel weight, TSS, electrolyte leakage, and lodging percentage showed a substantial direct effect and significant correlation with KY. Aside from higher KY, ethephon application as T1 tactics resulted in higher values of energy efficiency (1.66), HUE (2.99 kg ha−1 °C days−1), gross margin (682.02 USD ha−1), MBCR (3.32), and C absorption (6.19 t C ha−1), indicating that this practice may be a good option for maize sustainable production under rainfed conditions. [ABSTRACT FROM AUTHOR]