Evaluation Of Water Use Efficiency Of Different Young Apple Scion-rootstock Combinations Under Moderate Drought

Water shortage in northwest and semi-arid areas of China is a major factor to limit appleindustry development, and indirectly influence plant responses to nutrients. Improving plantwater use efficiency (WUE) is a critical way to adapt to water deficiency. In our study, fourChinese rootstocks and six cultivars of different scion-rootstock combinations were used toresearch the growth parameters, nutrition contents and WUE, under well-watered andmoderate drought conditions. Moreover, double scion-one rootstock and one scion-tworootstock combinations were used to evaluate water transport and WUE under droughtcondition. This experiment aims at providing some guidance for arid regions orchard to selectappropriate scion combinations and dwarfing rootstock. The main contents are as follows:1. Cultivar ‘Qinguan’(QG) and ‘Pink Lady’(PL) owned the higher long-term water useefficiency (WUEL) under moderate drought condition, while ‘Fuji Nagafu No.2’(FN) hadlower WUELunder drought condition than under well-watered condition, regardless ofrootstocks. Scion genotype plays an important role in relative dry mass gain (RDMG), androotstock genotype determines total water irrigation (TWI). Meanwhile, the scion-rootstockinteraction also significantly affects RDMG and TWI. There is a weak linearity betweenWUELand nutrition contents, hence, the selection of scion-rootstock combination that ownshigher WUEL, nutritional status of plants should also be taken into consideration.2. Two cultivars in one-scion one rootstock combination performed under droughtcondition as follows: PL had higher instantaneous water use efficiency (WUEI) and SPADvalue, but had lower shoot height, dry mass of root, stem and leaf than QG. The QG leafcontents of K and N were higher than PL. P content of QG was similar to PL. All in all, QGperformed better than PL. In double-scion grafting system, double scion Qinguan (D QG) alsoperformed better than double scion Pink Lady (D PL). This study shows that larger canopycan increase plant WUEL; double-scion grafting system can truly expose that different scionsperform on gas exchange, growth parameters, SPAD value, and the nitrogen (N), phosphorus(P), potassium (K) contents as compared to one scion-one rootstock combination.3. The material was three kinds of grafting system, as one scion-two root grafting system as cultivar ‘Gale Gala’(GG) grafted on MP (Malus prunifolia (Willd) Borkh) and T337, GGgrafted on MP, and GG grafted on T337. Under moderate drought condition, the range ofplant height and WUELwere the same as MP>Double-root>T337, after2months treatment.Meanwhile, the trend of photosynthesis parameters (P_N, gs, E) was MP>Double-root>T337,too. The significant effect by the three rootstocks under drought condition was branch root drymass, which GG/T337was obviously lower than GG/MP. In two-root grafting system, branchroot dry mass of T337was slightly lower than MP. In terms of sap flow, daily plant sap flowchanged as MP>Double-root>T337. In addition, there was a small sap flow of double-root innight, which is a way to alleviate drought stress. Under moderate drought, different rootstocksare mainly affected by the rutin and isoquercitin. In a word, double rootstock can improveroot’s development and WUELcompared with one rootstock T337.4. PL applyed alternate deficit irrigation after60days drought treatment (ADI),compared with the drought-stressed plants, those treated via ADI showed better height growth,larger scion diameters, and greater totalleaf area, as well as significantly increased gains indry biomass and rootstock diameters. However, their performance was still much lower thanthose cultivated by continuously well-watered. Sap flow was greater under ADI than underdrought, but less than under control conditions. The average rate of net photosynthesis, totalamount of irrigation water applied, and dry biomass gain had highly and positively linearcorrelations with WUEL. The same was applied to average stomatal conductance and WUEL.By contrast, instantaneous water-use efficiency (WUEI) was very negatively correlated withWUEL. In addition, values for WUELwere much higher from well-watered plantswhencompared with either drought-stressed trees or those treated per ADI. Therefore, the way ofADI following a period of long-term drought can be used to improve growth and WUELbythis cultivar.5. Water transpiration and aquaporin protein expression of four cultivars grafted on MBand MH performed as follow: under moderated drought condition, the gs, E, and total waterirrigation (TWI) of4cultivars grafted on MH higher than those grafted on MB, except forTWI of GG/MH; On the leaf level WUE (P_N/E and P_N/gs), and on the whole plant level WUE(WUEL)4cultivars grafted on MB higher than grafted on MH. Under the drought condtion,the trends of aquaporins of AtPIP1;1, AtPIP2;1, OsTIP1;1, and OsTIP2;1were upward on thelevel of transcriptional. In summary, rootstock controls water transpiration aboveground andleaf WUE, as well as impacts on the whole plant irrigation and WUEL.