Study on Gas Exchange in Different Wheat (Triticum aestivum L.) genotypes under Moisture Stress Conditions

Investigation of stomatal and nonstomatal parameters limiting photosynthesis (p < sub>n) under water stress condition may provide information to understand physiological bases of drought resistance. To investigation of the leaf gas exchange in different advances and old wheat genotypes, a filed experiment was carried out during 2003-04 growing season, at Ghamloo Research Station in Kurdistan province. A split plot designe with two main plots(rainfed and irrigation), and 20 lines and cultivars of rainfed bread wheat (19 advance lines with Sardari as a check) as sub plots with three replications was applied. Using IRGA device and le a f area meter, gas parameters(internal CO2 concentration, stomatal conductance, photosynthesis rate, transpiration, water use effeciency and mesophyl conductance) and leaf surface in both dryland and irrigation plots were measured. According to stress susceptiblity index (SSI), genotypes were divided into three groups of resistant, intermediate and susceptible. Except water use effeciency all parameters were reduced under dryland conditions, but this reduction was less in resistant lines than in susceptible ones. For example Pn reduction in susceptible group was 60% while in resistant group was 11%. Under dryland conditions, reduction in mesophile conductance was higher than stomatal conductance(20% more than stomatal conductance). It was concluded that decrease of P < sub>n under dryland was mainly due to reduced mesophyl conductance (nonstomatal factor)rather than stomatal factors.