Genetic variation in the efficiency of nitrogen utilization and photosynthetic activity of flag leaves among the old and modern germplasm of winter wheat.

Genotypic variation in major components of the efficiency of nitrogen utilization and photosynthetic activity of flag leaves among old (released 1881-1963) and modern (released 1969-2003) cultivars of winter wheat was studied in field conditions under varied N fertilization levels (110, 90 and 80 kg N ha-1). Significant genotypic differences were observed for all characters. Their heritabilities ranged from 0.37 to 0.93 and were the lowest for the leaf efficiency of gas exchange, photosynthetic rate, straw N content and the economic index of N utilization efficiency (NUE). Some modern cultivars exhibited an enhanced tolerance to N shortage and several attributes of efficient N utilization (e.g. later senescing and more photosynthetically active flag leaves, increased ability to redistribute N into grains). The genotypes may serve as donors of appropriate characteristics for breeding. The observed cultivar-by-fertilization interactions suggest, however, that evaluations under diverse fertilization regimes may be necessary when searching for improved wheat efficiency and adaptation to less favourable environments.

Genotypic and nutrition-dependent variation in water use efficiency and photosynthetic activity of leaves in winter wheat (Triticum aestivum L.).

Effects of high and reduced NPK nutrition on the genetic variation of components of water use efficiency at the leaf and whole-plant levels were examined in pot-grown old and modern cultivars of winter wheat (Triticum aestivum L.). At the subsequent growth stages, the photosynthetic rate (A), transpiration rate (E), leaf area (LA) and gas exchange efficiency (A/E) were measured on fully developed 4th, 5th, penultimate and flag leaves. At the plant canopy level, the total amount of water transpired was recorded during the whole life cycle to determine the efficiency of water use in the vegetative (WUEveg) and grain (WUEgen) matter formation. Considerable genotypic differences were found for the characters studied. The limited NPK supply caused a decrease in LA, A and A/E, but contributed to an increase in WUEgen. Examined cultivars (C) did not interact with nutrition levels (N) for these characteristics. However, the position of leaves (L) and the C x L and N x L interactions significantly affected the variance in leaf photosynthetic characteristics. A and A/E were negatively correlated with LA, and the flag leaves were photosynthetically less active and less efficient per unit area than the lower leaves. The whole-plant components of WUE were found to be more genetically stable than the photosynthetic leaf characteristics. Some modern cultivars tended to form leaves of higher A and A/E than the older ones, and this corresponds with a more efficient use of water in grain formation (WUEgen) of the former. Stay-green duration of flag leaves and harvest index showed positive correlations with WUEgen. However, no close associations were noticed between WUE components and stress tolerance, and the modern cultivars were usually less tolerant to NPK shortage.