Changes in Physiological Parameters of Sugar Beet (Beta vulgaris L.) Genotypes in Response to High Temperature under Two Different Climates

Having increased the temperature of different regions, global climate change can affect plants’ growth and development. This study aimed to explore the effects of high temperature on sugar beet (Beta vu-lgaris L.) performance at seedling stage (6–8 leaf stage) in two climatic areas of Iran, Karaj and Moghan, with different relative humidity (RH). Eight sugar beet genotypes, S1-92521, SB26, SHR.02.P4, O.T 607, S1‑92685, S1-92615, SB33-H-1 and 31714, were sown in both sites at two dates, April and July as control and high temperature stress treatments, respectively. Maximal quantum yield of PSII photochemistry in dark (Fv/Fm) decreased by high temperature in both sites, with genotypes S1-92521 and O.T 607 showing the highest value in stress treatment in Karaj. Non-photochemical quenching (NPQ), not affected by high temperature in any sites, was, in general, significantly higher in control treatment than in high temperature in the Moghan, which was attributed to high RH not the high temperature. This decreased net-photosynthetic rate (An), significantly, with genotype SB26 having the highest value in Moghan. Under control, S1-92521 showed the highest NPQ. Genotype SHR.02.P4 had the highest biomass in Karaj and under stress treatment in Moghan. Sugar beet genotypes produced higher biomass in Karaj compared with the Moghan. Finally, it was concluded that the adverse effect on sugar beet in Karaj was due to the high temperature, while in the Moghan, it was because of high RH. The genotypes S1-92521, SHR.02.P4 and SB26 were tolerant to high temperature of which the two latter had better performance under high RH condition.