Evaluation of chlorophyll index as indicators to screen sorghum genotypes for drought stress tolerance

Sorghum (Sorghum bicolor [L.] Moench) is the fifth most important cereal grown mostly in arid and semi-arid regions. Climate models predict that there is a risk of drought stress in those regions. Quantifying the physiological traits for developing the tolerant lines is efficient but time-consuming process. Therefore, it is necessary to find a rapid tool to identify the drought tolerant germplasm. With this background, the objectives were framed to assess the genetic variability for chlorophyll index and group the diverse set of sorghum genotypes for drought tolerance/susceptibility. Results proved chlorophyll index as an early phenotypic trait to screen the plants for drought tolerance. Drought stress was imposed at booting stage for the period of three weeks in rain out shelter with 29 sorghum genotypes and 4 checks obtained from Indian Institute of Millet Research, Hyderabad, and Agricultural Research Station, Kovilpatti, Tamil Nadu, India. The genotypes such as PEC 17 and PEC 34 were identified as tolerant and EN 55 and EP 87 as susceptible, based on chlorophyll index recorded one week after stress using Z score index. PEC 17 recorded higher chlorophyll index (15.89), photosynthetic rate (37.77 µmol/m²/sec), stomatal conductance (0.43 mol/m²/sec) and grain yield (50.75 g/plant). The percentage increase in epicuticular wax content was higher in PEC 17 (18.5%) contributing to drought tolerance. Thus, the study concluded that crops with higher chlorophyll index under drought can withstand drought at reproductive phenophase and yield better under stress.