Pak. J. Bot., 38(5): 1739-1743, 2006. CHLOROPHYLL FLUORESCENCE IN DIFFERENT WHEAT GENOTYPES GROWN UNDER SALT STRESS MUHAMMAD AKRAM * , SHAFQAT FAROOQ, MUHAMMAD AFZAAL, FARAH NAZ, AND RUBINA ARSHAD Nuclear Institute for Agriculture and Biology (NIAB), P.O. Box 128, Jhang Road, Faisalabad, Pakistan Abstract To assess the genotypic variation for efficiency of photo-system-II (Fv/Fm) in wheat genotypes containing introgression from chromosomes 1D, 3D and 5D of Aegilops tauschii and whether it could be used as a selection criteria for salt tolerance, 32 wheat genotypes were grown under field conditions and subjected to varying levels of salinity stress (10, 15 and 20 dS m -1 ). For most of the wheat genotypes, we observed Fv/Fm value greater than 0.8 at higher salinity levels compared to that of control. The minimum value of 0.8 for the efficiency of PSII (Fv/Fm) shows the health and vigor of the plant. A lower value indicates that a proportion of PSII reaction centers are damaged, a phenomenon called photo-inhibition, often observed in plants growing under stress conditions. Although salt stress reduced grain yield in all wheat genotypes, it is not positively associated with F v /F m . In conclusion, F v /F m can not be referred as a selection criterion for salt tolerance in wheat genotypes examined in the present study. Keywords: Chlorophyll fluorescence, Fv/Fm, Photosynthesis, salinity Introduction Photosynthesis often reduces in plants growing under abiotic stresses such as salinity (Ashraf, 2004), water deficit (Athar & Ashraf, 2005). Photosynthesis is particularly reduced when plants are grown under saline conditions, which leads to reduced growth and productivity, e.g., in wheat (Raza et al., 2006), Ammi majus L (Ashraf et al., 2004). Since photosynthesis occupies the central position in providing link between the internal metabolism of plant and the external environment, therefore, any change in external environment will affect photosynthetic ability of a plant in both negative and positive ways. Chlorophyll fluorescence has proved particularly useful in salinity-tolerance screening programs (Jimenez et al., 1997) because the effects of salt damage can be detected prior to visible signs of deterioration (West, 1986). Analysis of fluorescence characteristics such as the nature and intensity of the emission bands, quantum yield, and induction kinetics, reflects the properties of the chlorophyll molecules and their interaction with the external environment and also with associated physiological processes (Hall & Rao, 1999). It has been used since long by crop physiologists to evaluate response of various crop species to determine the influences of abiotic stresses at various stages of plant growth to have a quantitative assessment to be used in ranking plant species for their tolerance and/or sensitivity towards environmental stresses (Maxwell & Johnson, 2000). While working with canola (Brassica napus L.) cultivars, Kauser et al. (2006) suggested that F v /F m can be used as an efficient selection criterion to discriminate canola cultivars for water stress tolerance. In the present study, 32 wheat genotypes containing introgression from chromosomes 1D, 3D, and 5D were tested using chlorophyll fluorescence. The objectives * Corresponding Author: Muhammad Akram; Email: zombi-786@hotmail.com