Evaluation Of Alkaline Resistantce And Environmental Adaptability On Citrus Rootstocks

Citrus is a kind of fruit that grows well under slightly acid conditions.Soil in groves with high pH will have poisonous effect on citrus growth and uptake and transportation of nutrients.Rootstocks provide the underground part of plants,and their adaptation to the soil can affect the yield,fruit quality and economic return directly.Therefore,selection of the rootstocks tolerant to high pH condition is the most fundamental avenue to solve the problems of citrus production in the alkaline soil.It is of great importance for citrus production and rootstock breeding on the evaluation of alkaline resistane and mechanism research.In this study,six different citrus rootstocks including Donghu No.1(Poncirus.trifoliata),Shiikuwasha(C.Depressa Hayata),Huangyanzhi(P.trifoliata),Wangcangdayezhi(P.trifoliata),Ziyang Xiangcheng(C.junos Tanaka)and US-812(C.reticulate×P.trifoliata)were used as materials.They grew in NFT(Nutrient Film Technique)hydroponic system under pH 9.0 using pH 6.0 as control.The symptoms of leaves under alkaline stress were observed.The growth status on plant height,stem diameter,fresh weight and parameters on photosynthesis was measured and compared.The nutrients of leaves and roots of the rootstocks were determined after long-term treatment,and the transcriptomic expression of Shiikuwasha under alkaline conditions was analyzed.The main results were as follows:1.The time that symptoms occurred and the damage degree of the leaves varied among the different rootstocks under alkaline treatments(pH9.0).The clustering results based on the rate and indexes of alkaline damage 40 days after treatment indicated that Shiikuwasha and US-812 possess good tolerance to alkaline stress,followed by Ziyang Xiangcheng and Wangcangdayezhi,while Donghu No.1 and Huangyanzhi were susceptible.2.The growth of the rootstocks was significantly suppressed 350 days after treatment at pH 9.0 compared to the control,and the suppression varied based on their tolerence to the stress.The plant height,stem diameter and fresh weight of Shiikuwasha were mostly suppressed,followed by Ziyang Xiangcheng.Plant height of Huangyanzhi,stem diameter of US-812 and fresh weight of Donghu No.1 were influenced least by the stress.3.Alkaline stress affect the uptake and transportation of the the nutrients in rootstocks.The content of manganese(Mn)deceased significantly,while potassium(P)and copper(Cu)accumulated significantly in leaves of the rootstocks 350 days after treatment.Potassium(K),iron(Fe)and zinc(Zn)in Shiikuwasha and US-812 accmulated the most,and magnesium(Mg)in Shiikuwasha were higher than that in other rootstocks.However,nutrients in roots were significantly different between alkaline stress and the control,and nitrogen(N),sulfur(S)and manganese(Mn)decreased significantly under the stress.The content of magnesium(Mg)and zinc(Zn)in US-812 were higher than those in other rootstocks and the control.The content of iron(Fe)and zinc(Zn)in Ziyang Xiangcheng were the highest.4.They photosynthesis was affected under the stress.Photosynthetic rate of the six rootstocks decreased,while other indexes such as stomatal conductance,intercellular CO2 concentration and transpiration rate fluctuated among different rootstocks.The photosynthetic rate of Huangyanzhi and Wangcangdayezhi decreased due to the decease of CO2 which was limited by stomata,while that of other rootstocks reduced due to the non-stomatal factors.5.The results of RNA-seq analysis on Shiikuwasha 10 days after treatment indicated that 663 genes expressed differentially at log2 | FC | ≥3,which were involved in many physiological activities such as transcriptional regulation,signal transduction,active oxygen removal,osmotic regulation,photosynthesis,physiological metabolism et al.GO analysis showed that 76 DEGs distributed in 11 GO enrich pathways.Eight important genes associated to alkaline resistance of citrus rootstock were screened by qRT-PCR.Conclusion: Tolerance to alkaline stress varied based on their genotypes,Shiikuwasha and US-812 possessed good tolerance to high pH condition at early stage.Growth of the rootstocks was greatly suppressed by the stress,and photosynthesis was also affected.That the uptake and transportation of nutrients were influenced among the different rootstocks showed thatdifferent rootstocks probably havedifferent preference to the nutrients.Eight genes closely related to alkaline tolerance were screened based on the RNA-seq analysis.This research has layed the foundation for further elucidation on the mechanism research on alkaline resistance of citrus rootstocks.