Study On Salt Tolerance And Techniques For Increasing Yields Of Several Sugar Beet Cultivars

The effect of NaCl on seedling emergence and plant growth for three sugar beet cultivars,and the cultivation techniques for increasing yields and sugar content in beetroots of sugar beetin controlled conditions or in field were investigated in this paper. Therefore, the aim of thepresent study was to understand how to increase yields and sugar content in beetroots of sugarbeet when planted these cultivars in saline soils of Yellow River Delta.1. The effect of NaCl on seedling emergence and plant growth for three sugar beet cultivars:High salinity markedly decreased final seedling emergence in three cultivars KWS3418,Tianyan309and SD06, especially in SD06, while salinity had no adverse effect on total seedlingemergence after the recovery experiment, this trait may protect young seedlings of these cultivarsfrom being damaged by high salinity during early seedling establishment stage. Low salinity(0.5%NaCl) had no significant effect on shoot and root dry weights, while1.0%and1.5%NaClinhibited shoot and root dry weights of these cultivars. Salinity had no significant effect on themaximal efficiency of PSII photochemistry (Fv/Fm), while it decreased the actual PSIIefficiency (ΦPSII) in all cultivars. Concentrations of Na+and Cl-in leaves and roots wereincreased with increasing NaCl in all cultivars. There was no significant difference among thecultivars in concentrations of Na+and Cl-in leaves and roots in different concentrations of NaCl,except that Cl-concentration in leaves of Tianyan309was lower than that in KWS3418whenplants were treated with1.5%NaCl. Salinity decreased the contents of chlorophyll a, b andchlorophyll a+b in leaves of these sugar beet cultivars. High salinity markedly decreased netphotosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2concentration (Ci) andtranspiration rate (Tr) in all cultivars. The decrease of photosynthesis may be partly due to theincrease of stomatal limitation factor (Ls). In conclusion, Tianyan309and KWS3418presentedhigher ability in adaptation to salinity compared to SD06during seedling emergence stage.Tianyan309may employ superior mechanisms at regulating the uptake and/or transport of Cl-compared to KWS3418, and this trait may relate to their different responses of photosynthetic ability of two cultivars to salinity.2. Increasing NO3-supply improved shoot and root dry weights, increased NO3-concentration,but decreased Cl-concentration in leaves and roots of KWS3418, regardless of NaClconcentration. Higher NO3--N supply also increased leaf nitrate reductase activity, concentrationof chlorophyll, net photosynthetic rate (Pn) and actual PSII efficiency (ΦPSII) in leaves, but hadno significant effect on leaf Fv/Fm. Higher NO3--N supply increased soluble sugar concentrationin roots, but had no positive effect on leaf sugar concentration. The results indicate thatincreasing NO3-supply can help sugar beet to mediate ion homeostasis, to increase the ability ofphotosynthesis, and subsequently to increase the growth under high salinity. The interactiveeffects of salinity and nitrate availability can significantly increase soluble sugar in roots of sugarbeet.3. Shoot and root dry weights increased with0.5mmol/L P（KH2PO4）supply, while1mmol/LKH2PO4had no significant effect on the biomass of KWS3418when seedlings were culturedwithout NaCl. High salinity markedly inhibited the growth, but supplying KH2PO4could notincrease the growth of plants under high salinity. Higher P supply increased the K+concentrationin leaves and roots, which may help plants to maintain ion homeostasis. The interactive effects ofsalinity and phosphorus nutrition can significantly increase soluble sugar in roots of sugar beet.4. In field condition, plastic mulching together with ridging cultivation significantly increasedthe yields and sugar content in beetroots of KWS3418, Tianyan309and SD06. Plastic mulchingcultivation could decrease salt content in saline soils where these sugar beet cultivars wereplanted.