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.

Fifteen cultivars of sweet stemmed sorghum were evaluated for green stalk, juice and grain yield in addition to ratooning ability. The characters in the first crop, eleven characters in the ratoon crop and the total yield over two cuts were studied. The cultivar HES 4 showed significant and highest extractable juice yield of 13327 1 per ha from our of 35.5 t/ha of millable greenstalk and 721 kg/ha of jaggery was obtained in addition to 2369 kg/ha of grain yield in the first crop. In ratoon crop. the cultivar SSV 714 showed significant per se performance for green stalk (32.9 t/ha), juice (4338 /ha), jaggery (262 kg/ha) and grain yield (987 kg/ha). Based on the total yield over two cuts, HES 4, SSV 714 and IS 6962 appeared promising in respect of green stalk, juice, jaggery and grain yield and also showed ratooning ability.

Fifteen cultivars of sweet stemmed sorghum were evaluated for green stalk, juice and grain yield in addition to ratooning ability. The characters in the first crop, eleven characters in the ratoon crop and the total yield over two cuts were studied. The cultivar HES 4 showed significant and highest extractable juice yield of 13327 I per ha from our of 35.5 t/ha of millable greenstalk and 721 kg/ha of jaggery was obtained in addition to 2369 kg/ha of grain yield in the first crop. In ratoon crop. the cultivar SSV 714 showed significant per se performance for green stalk (32.9 t/ha), juice (4338 Uha), jaggery (262 kg/ha) and grain yield (987 kg/ha). Based on the total yield over two cuts, HES 4, SSV 714 and IS 6962 appeared promising in respect of green stalk, juice, jaggery and grain yield and also showed ratooning ability.

A total number of 21 sorghum varieties was screened for stress resistance at the vegetative stage of the crop. The grain yield was less affected compared to nonstress. The cultivars viz., SPV 393, KS 7193, KS 6312 and TWC 120 were found to be drought tolerant after evaluating for most of the physiological characters and yield. The intercorrelation of ten characters showed that grain yield showed significantly positive correlation for number of closed stomata both in stress and nonstress condition. Highest non significant correlation was noticed for grain yield and leaf wilting/rolling. DMP/plant and stomata count under stress.

The range of variation for different characters indicated wide differences among the genotypes both in main and ratoon crop. The phenotypic and genotypic co-efficient of variation was high for stem girth, length of fourth internode, total soluble solids and green stalk yield in main crop. High heritability and high genetic advance as per cent of mean for plant height, stem girth, length of fourth internode, green stalk yield, juice yield and jaggery yield both in main and ratoon crop indicated the presence of additive genes for these characters. Non-additive gene action was predominant for number of internodes in both main and ratoon crop. Juice yield showed strong positive correlation with jaggery yield in both main and ratoon crops. The juice yield had high positive direct effect in both main and ratoon crops. Hence, selection for high juice yield might be effective in achieving higher jaggery yield in sweet sorghum.