Chlorophyll fluorescence as a possible tool for salt-stress tolerance screening in the sunflower

The effect of salt stress of known intensity and duration on chlorophyll fluorescence in sunflower plants was studied aiming to identify salt-tolerant and salt-sensitive genotypes. The experimental design was a completely randomized in a factorial arrangement among 10 genotypes and two salt levels, with four replications. Seeds were sown in sand, and after germination were transplanted to plastic pots with nutrient solution or nutrient solution containing 100 mM of NaCl and placed in a greenhouse. After 27 days, ground fluorescence (F(0)), maximum quantum yield of PS2 F root F(m), the F root F(0) ratio and effective quantum yield of photosystem 2 - PS2 (Y) were evaluated. The photochemical (qP) and non-photochemical (q(N), q(CN) e NPQ) coefficients were also calculated. Salt stress increased F0 and reduced F root F(m), F root F(0), and Y, suggesting salt-induced structural damage in the thylakoid membranes. These effects were more pronounced in genotype AG-960 and lowest in AG-975. The highest increases in qN, qCN and NPQ were also found in genotype AG-960 in contrast with that observed in AG-975. Thus the AG-975 and AG-960 genotypes were characterized as the most salt-tolerant and salt-sensitive, respectively. The other genotypes showed intermediate tolerance to salt stress. Our results suggest that chlorophyll fluorescence could be used as a tool for the screening of sunflower genotypes for salinity tolerance.