UTILIZATION OF INDUCTION AND QUENCHING KINETICS OF CHLOROPHYLL-A FLUORESCENCE FOR INVIVO SALINITY SCREENING STUDIES IN WHEAT (TRITICUM-AESTIVUM VARS KHARCHIA-65 AND FIELDER)

The potential of utilizing induction and quenching kinetics of chlorophyll a fluorescence as consistent and reliable markers for in vivo salt (sodium sulphate) tolerance screening studies was investigated by comparing two wheat (Triticum aestivum L.) varieties with varying responses to salinity, viz. Kharchia-65 (salt-tolerant) and Fielder (salt-susceptible). Three-week-old seedlings were treated with a range of salt concentrations (0 to 2 %) over a 1- to 2-week period. Both the maximum rates of fluorescence induction and quenching measured from leaf sections decreased significantly in Fielder compared with Kharchia-65 as the salt concentration increased. Alterations in other fluorescence parameters, such as the maximum yield of fluorescence signal in the absence and presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea by the variety Fielder indicated a minimal reduction in the size of the primary electron acceptor pool associated with photosystem II following salt stress. In contrast, these parameters were altered to a lesser extent by salt treatments in Kharchia-65. The effect of salinity stress on leaf morphology of both varieties indicated no major anatomical alterations apart from a negligible increase in leaf thickness. Total chlorophyll content of Kharchia-65 increased significantly as a result of salt stress, owing to an increase in both chlorophyll a and chlorophyll b, whereas Fielder showed no significant variations. The results indicate that total fluorescence quenching and maximum rates of both induction and quenching appear to be reliable indicators for in vivo screening of salt-tolerant wheat genotypes.