Differential response to water deficit stress and shade of two wheat (Triticum durum desf.) cultivars : growth, water relations, osmolyte accumulation and photosynthetic pigments

This study was conducted to investigate the effects of water deficit stress and shading on two wheat cultivars (Triticum durum Desf. cv Om Rabiaa and cv Maali). Comparison was based on growth, leaf water relations, photosynthetic pigments and the accumulation of organic solute. In both cultivars, water stress deficit significantly decreased total dry mass (TDM), leaf area (LA), water potential (Psi w), osmotic potential (Psi pi) and relative water content (RWC). Photosynthetic pigments, i.e. chlorophyll a (Chl a), chlorophyll b (Chl b) and total chlorophyll (Tot Chl), decreased while carotenoids (car) increased. Proline concentration increased significantly in water stressed plants under full light conditions while sugar accumulated more under shade conditions. In addition, shade improved leaf area, leaf water potential, and osmotic potential as well as alleviated the negative drought impact on photosynthesis performance. For the Maali cultivar, the reduction in RWC and its inability to achieve osmotic adjustment (OA) emphasize this cultivar's sensitivity to water deficit stress. For the Om Rabiaa cultivar, the ability to avoid relative tissue dehydration and preserve a higher RWC with a significant increase in OA in shade-treated plants were tolerance mechanisms enabling this cultivar to absorb water effectively and sustain normal growth and productivity under water stress conditions