Abstract

Seeds of four lettuce (Lactuca sativa L.) genotypes viz., Great Lakes (GL), Paris Island cos, Kagraner Sommer (KS) and Isadora were assessed for their response to salt at the germination and seedling stages. The germination rate of the four varieties was comparatively studied under 0, 50, 100, 150 and 200 mM sodium chloride (NaCl) treatments. Differential response of genotypes to salt concentration was observed. Final germination percentage (FG%) decreased with increasing salinity in GL, Paris Island cos and Isadora varieties, and was annulated at the highest salt concentration in GL, the most sensitive variety. However, in the less sensitive, KS, FG% was decreased by 60% compared to the control at 200 mM. KS and GL varieties were selected as stress-tolerant and stress-sensitive varieties, respectively, and were used for further characterization. Dry weights (DWs) of radicles and hypocotyls were reduced by NaCl 100 and 150 mM in GL and only at 150 mM NaCl in KS. The activities of several antioxidant enzymes during germination were determined. Both varieties had the same malondialdehyde (MDA) content under 100 and 150 mM NaCl. The highest gaiacol peroxidise (GPX) activity was detected in GL seedlings at NaCl 50, 100 and 150 mM, respectively. Catalase (CAT) decreased at 50 and 100 mM NaCl, respecively. Total ascorbate (AsA + DHA) decreased in GL and increased significantly in KS. Our results suggest that tolerance of KS to salt may be due to a better protection mechanism against salinity induced oxidative damage relative to GL variety.

Key words: Germination, lettuce, NaCl, growth, antioxidant activities, ascorbate.