The effect of epicuticular wax (EW) load on the cuticular transpiration rate (Tc of sorghum [Sorghum bicolor (L.) Moench] leaves was studied. Leaves from bloom, bloomless, and sparse bloom isogenic lines and various bloom‐type hybrids were collected from field plots after anthesis in 1976, 1977, and 1981. Epicuticular wax was extracted with chloroform and quantified using a colorimetric method. The Tc of detached leaves were measured with a humidity sensor in a closed cuvette or calculated from the mass of water lost per unit time under standardized conditions. The Tc increased as EW decreased over the range of 0.1 to 0.03 g m−2 when data from all genotypes were pooled for analysis. However, among the normal (bloom) phenotypes there was no clear association between rates of water loss and EW. These data suggest that EW greater than about 0.067 g m−2 provide an effective barrier to water loss through cuticles of sorghum leaves under most conditions. Although the two methods of measuring Tc produced the same qualitative results, Tc rates calculated from the mass of water transpired under more “realistic” controlled conditions were higher and probably more directly related to rates of water loss under field conditions. Because of its speed and technical simplicity, the water loss method appears superior when large numbers of samples must be evaluated.
In previous research, genetic variation in sorghum(Sorghum bicolor L. Moench) drought avoidance (maintenance of relatively high leaf water potential under conditions of soil moisture stress) was revealed. Practical screening for drought avoidance requires a fast field method. The response of near infrared reflectance from plant leaves to leaf water status stimulated the development of such a method, based on infrared photographic imagery of water‐stressed sorghum breeding nurseries. Aerial infrared photography was performed from several altitudes over water‐stressed and non‐stressed sorghum nurseries at Lubbock, Halfway, and Chillicothe, Texas. Noontime leaf water potentials, as a measure of drought avoidance, were determined in selected strains at each nursery. Total leaf chlorophyll content of the respective strains was determined at Lubbock and Chillicothe. Strain canopy color densities in the resulting infrared color transparencies were analyzed by three methods: l) Scanning densitometry; 2) measurement of integrated light transmittance by manual photometry; 3) visual rating of color density. Over all locations, the best correlations between canopy color density and leaf water potential across strains were obtained with the photometric method. The poorest correlations were obtained with scanning densitometry. For all methods of color density measurement, the correlations with leaf water potential across strains were the best at Halfway. At this location, plant canopies were dense, ground cover was almost complete, and film exposure and development were optimal. Leaf chloroFhyll content in the various strains was not correlated with canopy color density, although one strain presented a consistent exception. The method and some guidelines for its utilization are discussed.
InterDrought-II followed the first InterDrought conference held in Montpellier France in 1995. InterDrought-II was attended by 534 registered participants from 59 countries. A total of 450 posters were presented. Oral presentations were delivered during eight sessions by 28 invited speakers and 44 selected speakers. A total of nine panellists conducted the final discussion of the plenary sessions which led to the conference conclusions and recommendations. These are posted on the conference web site, www.plantstress.com/ID2Despite the importance of drought as a major constraint in food production worldwide, there has, surprisingly, been no other major and dedicated international symposium since the first InterDrought conference in 1995. The objective of the first InterDrought conference was to provide a platform for presenting and debating in a multidisciplinary fashion key issues and strategies relevant for increasing the yield and stability of crops under drought conditions by genetic and crop management approaches. Great advances in understanding the molecular basis of plant response and tolerance to drought stress have been made in recent years. Hundreds of drought-responsive genes have been identified and the function of some has been resolved at the cellular level. However, a huge gap remains between the molecular level science and the interpretation and application of this knowledge at the whole plant level in the field. If we are to advance practical solutions for drought-prone farming, there is increasing demand for cross-talk between the component disciplines which contribute to the understanding and amelioration of plant stress responses. InterDrought-II presented a unique and timely opportunity for this purpose. The main mission of InterDrought-II was to explore the possibilities for the application of novel science and technology to crop improvement and crop management under drought by linking progress made at the molecular level with the physiology and agronomy of plant production under limited water supply in the field. During the conference, effective approaches to achieve better crop productivity under drought conditions as well as the research needed to move forward in this direction were presented and discussed.The Organizing Committee and the International Steering Committee are most grateful to the sponsors who generously supported the implementation of this conference as well as the participation of many young scientists coming from developing countries. We are particularly grateful to the Rockefeller Foundation. The complete list of sponsors is posted on the conference website at www.plantstress.com/ID2. We remain confident that integrated approaches will be instrumental in advancing our understanding of drought tolerance and will allow us to more effectively exploit new knowledge to improve and stabilize crop yields under water-limited conditions. We hope that the legacy of the InterDrought conference series will continue, thus providing inspiration to young scientists willing to pursue th...
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