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CHLOROPHYLL FLUORESCENCE: A POTENTIAL INDICATOR FOR RAPID ASSESSMENT OF WATER STRESS TOLERANCE IN CANOLA (BRASSICA NAPUS L.)

ROUBINA KAUSER¹, HABIB-UR-REHMAN ATHAR², AND MUHAMMAD ASHRAF¹

Abstract: An experiment was conducted to assess the differential morpho-physiological responses to simulated water stress of two canola (Brassica napus L.) cultivars in hydroponic culture. Seeds of two canola cultivars (Cyclone and Dunkeld) were germinated and allowed to grow for three weeks. Three week-old canola plants were grown at 0 MPa (control) or -0.6 MPa (PEG 18.2%) in nutrient solution for further three weeks. Water stress strongly reduced the growth of both canola cultivars. However, cultivar Dunkeld proved to be more drought tolerant as it was higher almost in all growth attributes under water stress conditions, particularly in shoot and root biomass and leaf area. Furthermore, growth of Dunkeld was also higher than that in Cyclone. Leaf chlorophyll ‘a’, carotenoids and quantum yield of PSII was also reduced due to water deficit conditions, but all these were less affected in drought tolerant Dunkeld. Although leaf osmotic potential was lower in water stressed plants of both cultivars, water stress induced reduction in leaf osmotic potential was less in cv. Dunkeld. However, there was no relationship between growth and osmotic adjustment in canola cultivars examined in the present study. Water deficit caused a substantial decrease in photosynthetic rate in both canola cultivars but canola cultivars did not differ significantly in net CO₂ assimilation rate under water stress conditions. Furthermore, parallels between A, and leaf chlorophyll ‘a’ or F_v/F_m of both cultivars can not be drawn under water stress conditions. Thus, the differential drought tolerance in canola cultivars was related to leaf area and root growth. There was no relationship between growth and osmotic adjustment in canola cultivars examined here. Overall, quantum yield of PSII and leaf chlorophyll ‘a’ can be referred as a potential selection criterion for drought tolerance in canola cultivars examined in the present study. 

¹Department of Botany, University of Agriculture, Faisalabad 30840, Pakistan
²Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan-Pakistan
Corresponding Author: Habib-ur-Rehman Athar; habibathar@yahoo.com