RESPONSE OF 4 SORGHUM LINES TO MID-SEASON DROUGHT .1. GROWTH, WATER-USE AND YIELD

Four sorghum (Sorghum bicolor L. Moench) lines were visually selected to represent the most resistant and most susceptible in terms of desiccation tolerance and ability to produce new leaves and grain after release from drought. The lines, representing early-and late-maturing lines in both classes, were grown during the summer and part of the monsoon season at Patancheru, Central India, in a study to investigate the physiological basis of the visual assessments. A control treatment was irrigated throughout, while a stress treatment had water withheld from 20 to 84 days after sowing. During early growth in both irrigation treatments, the resistant lines had slower shoot and root growth rates, slower soil water-extraction rates, but higher root:shoot ratios than the susceptible lines, which may have been responsible for their higher leaf water-potentials in the stress treatment. Dry-matter production per unit of water transpired was also lower in the resistant lines. As drought became more severe, there was greater leaf death in the susceptible lines. In all lines, panicle initiation was delayed by mid-season drought stress, but once it did start, the length of the reproductive period was increased in the resistant lines but decreased in the susceptible. In both treatments, the resistant lines within each maturity group had higher grain-yield than the susceptible lines; in the stress treatment this was largely due to better grain-set and tillering.