Using Chlorophyll Fluorescence Technique to Assess Tolerance of Rice (Oryza sativa L.(Genotypes to Air and Water Cold Stresses

The aim of this study was to investigate the effect of cold temperature and cold water stresses on chlorophyll fluorescence parameters in different rice genotypes. Six rice genotypes including Koohsar، Shiroodi and Tarom Hashemi cultivars as well as PSB44، RI96 and IR752 lines were grown under hydroponic conditions. After two weeks، plants were kept as control (28 °C)، cold temperature stress (8 °C) and cold water stress (8 °C) then chlorophyll fluorescence parameters were measured. Cold temperature stress significantly reduced some of the measured parameters including variable fluorescence (Fv)، maximum photochemical quantum yield of photosystem II (Fv/Fm)، effective photochemical quantum yield of photosystem II [Y (II)]، photochemical quenching coefficient (qP) and electron transport rate (ETR); while significantly increased quantum yield of regulated non-photochemical [Y (NPQ)]، quantum yield of non-regulated non-photochemical[Y (NO)]، non-photochemical quenching (NPQ) and Non-photochemical quenching coefficient (qN). Whereas cold water stress had significantly affected minimum fluorescence (Fo)، maximum fluorescence (Fm)، Fv and ETR. Inaddition PB44 line and Tarom Hashemi cultivar in cold temperature stress and RI752 and PB44 lines in cold water stress had the minimum change in fluorescence parameters. cold temperature stress was more effective than cold water stress. In cold temperature stress، PB44 and Tarom Hashemi were most tolareant genotypes while RI96، IR752 and Shiroodi were the most susceptible genotypes. In cold water condition، RI752 and PB44 were the most tolerant genotypes while IR96 and Shiroodi genotypes were the most susceptible genotypes.