Temperature-Mediated Changes in Abscisic Acid Levels in Indian Mustard under Early, Timely and Late Sowing Environments in Doon Valley

Temperature variability associated with different sowing environments significantly influences abscisic acid level and productivity in Indian mustard (Brassica juncea L.). The present field study was conducted during the rabi seasons 2023–24 and 2024–25 in the Doon Valley, Uttarakhand, india to evaluate temperature-mediated changes in abscisic acid (ABA) levels under early, timely, and late sowing conditions. Five germplasms (Varuna, Kanti, Maya, Kranti, and Vardan) were assessed at vegetative and flowering stages. ABA was extracted from fresh leaf tissue and quantified using High-Performance Liquid Chromatography (HPLC). Results indicated that timely sowing, associated with comparatively cooler temperature patterns (~13/5°C and ~25/9°C), consistently recorded higher ABA accumulation than early (~26/12°C) and late (~28/13°C) sowing. During 2023–24, timely sowing exhibited an average ABA level of 8.13 µg/g compared to 6.37 µg/g under early sowing. Similarly, in 2024–25, timely sowing recorded 7.62 µg/g, significantly higher than late sowing (5.30 µg/g). ANOVA confirmed a highly significant effect of sowing environment on ABA levels (F = 40.09 and 56.02; p < 0.01). Genotypic variation was evident, with Maya consistently exhibiting the highest ABA accumulation, whereas Kanti and Vardan showed relatively stable abscisic acid regulation under temperature fluctuations. A positive association between ABA concentration and oil yield per plant was observed under timely sowing in both seasons, while oil content (%) showed minimal variation. Reduced ABA levels under early and late sowing corresponded with yield decline, suggesting that ABA-mediated physiological regulation contributes to productivity under favourable thermal conditions. Overall, the study demonstrates that ABA biosynthesis in Indian mustard is highly temperature sensitive, and timely sowing under cooler conditions enhances hormonal accumulation and yield performance. Sowing time thus serves as a critical agronomic factor influencing hormonal dynamics and stress adaptation under field conditions.