Effect of sowing dates on the phenology, grain yield and stress tolerance indices of barley (Hordeum vulgare L.) genotypes under subtropical conditions of Punjab

In order to assess the effect of terminal heat stress  on the in vitro screened heat tolerant (n=9) and susceptible (n=3) genotypes of barley, a field trial was conducted during rabi 2019-20 and 2020-21 at Punjab Agricultural University, Ludhiana, Punjab, India. Barley genotypes were sown under timely (November 26) and late sown (December 26) conditions so that late sown crop encounters heat stress during its reproductive stages of growth. The results showed that timely sown crop took significantly higher number of days to attain physiological maturity as compared to late sown crop. For anthesis and physiological maturity, timely sown crop accumulated higher growing degree days (GDD) in comparison to late sown crop. Tolerant genotypes (viz., BL 1515, BL 1729, BL 1780, BL 1784, BL 1786, BL 1792, BL 1794, BL 1797 and IBYT-E24) recorded higher number of GDD for attaining physiological maturity in comparison to susceptible genotypes (viz., BL 1723, IBON 23 and IBYT-E15) under late sown conditions. Likewise, heat use efficiency (HUE) was also lower in susceptible genotypes as compared to tolerant genotypes particularly under late sown conditions. Results also indicated that under timely sown conditions, grain yield of tolerant genotypes was statistically at par to susceptible genotypes; but under late sown conditions, tolerant genotypes out yielded susceptible genotypes. Among the tolerant genotypes, BL1786 had the highest grain yield under late sown conditions and it was statistically similar to three other tolerant genotypes namely BL1780, BL1784 and BL1792. Tolerant genotypes recorded lower tolerance index (TOL) and stress susceptibility index (SSI) values in comparison to susceptible genotypes; however, exhibited higher values of yield stability index (YSI). Correlation studies indicated that number of days taken to physiological maturity is the most crucial phenological stage determining seed yield of barley under late sown conditions.