Response of four sorghum lines to mid-season drought. I. Growth, water use and yield

Abstract

In arcas of thc \cnl~-arid tropics ~h t l r c sorghum 1 5 gro\$n. d l o~~g h l at some \trtge of crop g r o~t h 1s cjl'ten the main f'actol-ciius~ng low y 1eld5. I o address t h~s pruhlcm. the International Crops Kcscarcli In5t1tutc l i~r the Scnii-.Arid Troptcs (1C'RIS.AT) has Initiated a rewarch prograrnnie to s t~i d y the broadcr

Response of three sorghum (Sorghum bicolor L. Moench) varieties to soil moisture stress at different developmental stages

“…The general increase in RlS for all sorghum varieties under water stress, especially at the vegetative stage (42%) observed in this experiment, confirms other reports (Mathews et al, 1990;AI-Karaki et al, 1995). Preferential allocation of carbon to developing deep roots, or in the case of the present pot experiment, more below-ground biomass at the expense of shoot growth, especially in early exposure to stress, is a classic drought avoidance mechanism.…”

“…[t reflects high water absorption capacity, which would enhance survival during subsequent drought exposures (Tschaplinski et al, 1998). Increases in RIS in response to early water stress were reported to be proportional to drought tolerance of sorghum genotypes (Mathews et al, 1990) but in our study genotypic differences were not sign ificant. The decrease in RIS at flowering for Segaolane and Mahube, suggests that these varieties, once committed to seed production, continue to invest more in stem (panicle) weight rather than root biomass in times of water stress.…”

“…Donatelli et al (1992) reported that physiological development may be hastened or delayed depending on the stage of the crop cycle and the magnitude of the water deficiency. Mathews et al (1990) found that drought experienced after panicle initiation delayed flowering but physiological maturity was advanced. The rationale is that the plants are committed to seed production and, in order to produce some grain, maturity is hastened by stress.…”

“…(Donatelli, Ham~er & Vanderlip, i 992) and the I extent to which grain yield is affected (Fussell, Bidinger & Bieler, 1991;Badly et al,11993;. For example, panicle initiation and flowering are delayed by water stress experienced ~ither very early or very late in the growing season and the largest reductions in yield occur from stress imposed during bo~ting and flowering stages (Garrity, Sullivan & Watts, 1984;Mathews et al, 1990;Craufurd, Flower & Peacock, 1993;.…”

“…High root/shoot ratios (RlS), together with deep roots, are important mechanisms for surviving drought in many species (Gardner, Pearce & Mitchell, 1985) and there are reports of genotypic variations in RlS in sorghum (Mathews et al, 1990;AI-Karaki, Clark & Sullivan, 1995). Reduction in leaf area in response to water stress can occur either through hastened leaf senescence or a decline in leaf expansion, and the extent of the reduction ap'pears to be dependent on relative tolerance of sorghum varieties (Krieg, 1994;Stout et al, 1980, Ashraf & Ahmad, 1998.…”