LEAF GAS-EXCHANGE AND RELATED LEAF TRAITS AMONG 15 WINTER-WHEAT GENOTYPES

Many investigations have been conducted during the past few decades to understand the nature of photosynthetic differences among Triticum spp. and related species, yet only limited information on photosynthetic and water use efficiency differences is available among wheat (Triticum aestivum L.) genotypes. The purpose of this preliminary study was to examine leaf-gas exchange and related leaf traits among winter wheat genotypes in the field to characterize genotypic-related variation in photosynthesis and water-use efficiency. Fifteen winter wheat genotypes, 13 developed in the central and southern Great Plains of the USA and 2 from the USSR, were planted into a Nunn clay loam (fine, montmorillonitic, mesic Aridic Arguistoll) near Fort Follins, CO, in September 1987. Leaf-gas exchange measurements were performed approximately weekly on flag leaves of all genotypes from 27 May (early heading stage) through 20 June 1988. Significant genotypic effects were found for photosynthetic rate per leaf area (CER), leaf conductance (g(s)) leaf water-use efficiency (WUE(g) = CER/g(s)), the ratio of intercellular [CO2]/ambient [CO2], specific leaf weight, and chlorophyll concentration. Among the genotypes with the lowest water use efficiencies were the two old, large-leaved Soviet genotypes and the two oldest Great Plains genotypes surveyed, 'Vona' and 'Sturdy'. Negative associations of leaf size with CER and WUE(g) were mostly due to differences in leaf size and CER between the relatively small-leaved Great Plains genotypes and the large-leaved Soviet genotypes. Significant variation for WUE(g) among the winter wheat genotypes was due to genotypic-related differences in both photosynthetic capacity and g(s).