Author
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Sinclair, Thomas |
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Submitted to: Soybean Research World Conference Proceedings
Publication Type: Proceedings Publication Acceptance Date: 1/5/2004 Publication Date: 2/1/2004 Citation: Sinclair, T.R. 2004. Physiological traits for ameliorating drought stress. Proceedings of the VII World Soybean Research Conference, Empbrapa, Londrina, PR, Brazil. 245-252. Interpretive Summary: Soil water deficits seem to be a cause of yield losses in virtually every year for all non-irrigated soybean. Approaches to ameliorate these losses by genetically modifying the physiological behavior of soybean plants are discussed in this paper written by a USDA,ARS, scientist located at the Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL. Three traits are considered in detail. One involves deeper rooting so that plants can access any water that might be stored at depth in the soil. The experimental difficulties in investigating deeper rooting have meant that this trait is still virtually unexplored. A second trait is one of water conservation. In this approach, plants would grow more slowly but water would be conserved in the soil for use in dry periods. There are some indications that for certain environments this could be a quite useful trait. The third trait, which makes soybean so vulnerable to water deficits, is ameliorating the sensitivity of nitrogen fixation to soil drying. Nitrogen fixation is extremely sensitive to water deficits, but now cultivars have been identified that confer tolerance. Continued attention on these three traits is likely to result in substantial progress in ameliorating the negative impacts of water deficits on soybean yields. Technical Abstract: The pattern of physiological responses to drying soil appears to be closely linked to decreases in soil hydraulic conductivity as the soil dries. Hence, physiological amelioration of stress needs to focus on possibilities for either accessing more soil water or slowing the rate of soil water extraction. Deeper rooting appears to be a critical approach to increasing the amount of water available to plants, although the difficulty of documenting differences in rooting depth among genotypes has resulted in little progress in this approach. Water conservation can be achieved by slightly decreasing plant gas exchange, which results in a decreased growth rate, but depending on the environment, can result in long-term increases in mean crop yield. It is speculated that slow-wilting genotypes of soybean that appears to have drought tolerance may result from one of these two traits. Finally, symbiotic nitrogen fixation rates decrease with soil drying well in advance of plant gas exchange. Genotypes have been identified that exhibit substantial nitrogen fixation tolerance to drought stress and this trait in improved genetic backgrounds results in yield increase. On-going research has provided exciting possibilities for ameliorating drought stress in soybean, and the future may be even more promising as these traits are combined in superior cultivars. |
