SUMMARYRecent trends in climate change resulting in global warming and extreme dry spells during rainy seasons are having a negative impact on grain and fodder production in rain-fed crops in India. Understanding the mechanisms of drought tolerance at various growth stages will help in developing tolerant genotypes. Crosses were made between elite and drought-tolerant sorghums, and F2and F3progenies were evaluated for drought tolerance in multiple locations. Twenty-five F4/F5derivatives along with drought-tolerant check plants (two high-yielding genotypes showing moderate drought tolerance: C43 (male parent of the commercial hybrid CSH 16, tolerant to drought) and CSV 17, (a pure line commercial cultivar released for drought-prone areas) were screened for drought tolerance under a factorial randomized block design with three replications during the rain-free months of April–June in 2007 and 2008 at Tamil Nadu Agricultural University, Kovilpatti, India. In each generation/year, four trials were conducted and water stress at different phases of crop growth,viz. vegetative, flowering and post-flowering (maturity), was imposed by withholding irrigation. Observations were recorded on grain and straw yields, plant height, number of roots, root length, leaf relative water content (LRWC), chlorophyll content and stomatal conductance under all treatments. The traits, grain yield, plant height, average root length and stomatal conductance showed significant mean sums of squares (SSs) for genotype × environment (G × E), suggesting that genotypes had significant differential response to the changing environments. Significant mean SSs due to G × E (linear) were obtained for straw yield, LRWC and chlorophyll content, indicating that the variability is partly genetic and partly influenced by environment. Grain yield was correlated with chlorophyll content (r = 0·43) at the vegetative stage, with number of roots (r = 0·49), LRWC (r = 0·51), chlorophyll content (r = 0·46) and stomatal conductance (r = −0·51) at the pre-flowering stage, and with LRWC (r = 0·50) and stomatal conductance (r = −0·40) at the post-flowering stage, under water stress. Partial least square (PLS) analysis showed that different traits were important for grain yield under water stress at different growth stages. Pyramiding the genes for the traits responsible for high grain yield under stress will help in developing stable genotypes at different stages of plant growth.
Effect of water stress at different growth stages on quantity and quality traits of Virginia (flue-cured) tobacco type
