Use of Carbon Isotope Discrimination as Tool for Improving Drought Tolerance of Wheat

As in many countries of the region, agriculture in Yemen has been strongly affected by drought conditions, and cereal production is the most concerned. So to this regard, two approaches could be adopted to solve this problem; enhancement of irrigated areas, but negative effects can also be noted as salinity (e.g. Marib, area) and development of foliar diseases. The second approaches is improvement of water use and drought resistance of wheat cultivars: this long-term strategy, which is a part of a general approach giving more attention to the sustainability of farming systems, is at the basis of the present study. Several morphophysiological mechanisms of drought tolerance involved in dehydration tolerance, As for other morphophysiological traits, the possibility of using carbon isotope discrimination (Δ) in breeding for water use efficiency (WUE) in drought prone environments is related to i) the facility of measurement, ii) the existence of variability, iii) high values of heritability, and iv) a good knowledge of eventual associations between Δ and other phenological or morphophysiological traits. The use of stable isotopes has until recently been limited because of the cost of mass spectrometers designed and the requirements for sample preparation. However, the recent linkage of an automatic gas sample preparation apparatus with a dual-inlet mass spectrometer has made the technique more convenient for fast and accurate analysis of stable isotope composition of the most important elements. The present study has been conducted to evaluate the interest of (Δ) in mature kernels as a criterion for the improvement of water use efficiency and yield under drought in tetraploid wheat species. For this purpose, T. durum Om Rabi 5 was crossed by T. polonicum 9 (Tp9) which had been found to be more droughts tolerant and to have a lower □ value of the grain. The F2 population showed a wide segregation for this last trait. Further, divergent selections were made among individual F2 plants, and in F3 progenies for Δ under field conditions. Selected progenies F3 and F4 were evaluated under field conditions for morphological and agronomical traits. Broad sense heritability (h2b), response to selection and realized heritability (h2r) were high. The divergent groups selected for low and high (Δ) exhibited significant differences for days to heading (DH), plant height (PLH), shape of the spike (SSH) and number of spikelets per spike (NSP/S). Correlations were also registered between (Δ) and plant height, harvest index, shape of the spike, spike length, and number of spikes per plant. The potential use of Δ as a criterion for the improvement of water-use efficiency in durum wheat is discussed by taking in account the genetics of this trait (variability, heritability, response to selection) as well as the associations with phenological and morphological traits. Field evaluation of advanced selected lines under Yemeni conditions permitted to select a high numbers of lines adapted to Yemeni rainfed conditions in Sana'a. Thus eighteenth lines were selected; thirteenth were belonging to low (Δ) group (high WUE), and five lines were from high (Δ) (low WUE). These findings clear demonstrated the importance of using Δ as a trait in selection of drought tolerance. (Author)