Monday, November 5, 2007
29-3
Reflectance as a tool to identify genotypic variability for drought tolerance in cowpea.
Shardendu Singh, Mississippi State University, Mississippi State University, Box 9555 Plant & Soil Science Dept, Mississippi State, MS 39762 and K. Raja Reddy, Box 9555, Mississippi State University, Mississippi State University, Department of Plant. & Soil Sciences, Mississippi State, MS 39762.
Screening tools to identify genotypic variability among crops for abiotic stresses such as water deficits will help in breeding programs as well as selecting cultivars for a niche location. The objectives of this study were to evaluate intraspecific response in leaf photosynthesis (Pnet), chlorophyll fluorescence (Flu) and water use efficiency (WUE) of cowpea cultivars for drought tolerance and to investigate relationships between physiological and leaf hyperspectral responses to water stress. An experiment was conducted using fifteen cowpea cultivars seeded in 12-L pots, filled with fine sand, and irrigated with full-strength Hoagland's nutrient solution, three times a day, from emergence to 34 days after sowing. Thereafter, one set of plants continued to receive optimum water and the other set received no water for 20 days. Pnet, Flu and WUE, leaf (LWC) and soil (SWC) water contents were measured at frequent intervals. Cumulative drought response index, CDRI, of each genotype calculated as the sum of four individual stress response indices derived from photosynthesis, fluorescence and two water use efficiency parameters, was used to group genotypes for drought stress tolerance. At the end of the experiment, leaf spectral reflectance of wavelengths of 350 to 2500 nm was measured from control and drought stressed plants. Regression analysis was carried out between spectral features such as thematic mapper bands and indices of water stress and chlorophyll from the literature and CDRI to assess usefulness of reflectance in identifying genotypic tolerance to water deficits among cowpea genotypes. Significant genotypic variability was found among cowpea genotypes for both physiological parameters and reflectance properties under drought stress conditions. Pnet and Flu decreased linearly while WUE increased exponentially with decrease in SWC. In general, the reflectance was greater in stressed plants compared to well-watered plants. The remote sensing reflectance models developed from the multiple linear regression analysis were highly correlated (R2 > 0.81) with CDRI indicating the efficacy of optical techniques in identifying genotypic tolerance for water stress among cowpeas.