The Comparative Drought Resistance of Landraces of Sorghum and Millet From Dry and Humid Regions

Abstract

^Department of Field Crops, The Volcani Center, ARO P.O. Box 6, Bet Dagan, Israel and%USDA, ARS, University of Nebraska, Lincoln, NE 68583, USAAccepted: 2 December 1985ABSTRACTIt may be that land-races of sorghum (Sorghum sp.) and millet [Pennisetum americanum (L.) Leeke] whichevolved along geographical gradients of rainfall in Africa and India, differ in their drought resistance. Anyphysiological attributes found to be correlated with low rainfall might be important and effective characteristicsfor crop production in dry regions.Twenty land-races were chosen which evolved along geographical gradients of rainfall, seven millets fromIndia, six sorghums from Mali, and seven sorghums from the Sudan. Races were evaluated for their growthpotential and plant water relations under hydroponics conditions in a growth chamber. A water stress treatmentwas imposed by adding polyethylene glycol-8000 to the nutrient solution, giving a solute water potential of-0-5 MPa, compared with a control solution at 003 MPa.Drought resistance, in terms of relatively less growth inhibition under stress, was higher in races from dryregions than in races from humid regions. Of all the physiological variables measured [carbon exchange rate,(CER), transpiration, transpiration ratio (CER/transpiration), leaf diffusive resistance, leaf water potentialand osmotic adjustment], only osmotic adjustment under stress was generally correlated with average rainfallat each race's origin, indicating greater osmotic adjustment in land-races from drier regions. Races with agreater capacity for osmotic adjustment were characterized by smaller plants with high rates of transpirationand low rates of leaf senescence under stress.The carbon exchange rate per unit leaf area increased as live leaf area decreased under stress due to leafsenescence. Thus, drought resistant races under stress tended to have lower CER per unit live leaf area (butnot per plant) than susceptible races. Transpiration ratios under stress were lower in resistant than in susceptibleraces, mainly because resistant races had higher transpiration.The results for the measured variables showed a general trend for greater drought resistance in sorghumthan in millet, indicating that the commonly observed adapation of the millets to dry environments may bedue to other factors, such as drought escape or heat tolerance.Key words: Sorghum sp. Pennisetum americanum L. (Leeke), water stress, osmotic adjustment, photosynthesis,transpiration, evolution, drought resistance.INTRODUCTION