Effect Of Rootstock On Photosynthetic Characteristics And Fruit Quality Of Citrus Cv. ’Huangguogan’

This study investigated the variation patterns in the leaf net photosynthetic rate (Pn), transpiration rate(Tr), intercellular CO2 concentration (Ci) and stomatal conductance (Gs) by using LI-6400 portable photosynthesis system in Citrus cv.’Huangguogan’ trees(CK) grafted using Poncirus trifoliate(HG/PT), Citrus reticulata(HG/CR), and Citrus junos(HG/CJ) rootstocks. Meanwhile,this paper made analysis on leaf concentrations of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) Rubisco activase (RCA) and the expression level of rbcL,rbcS and rca, Moreover, we analyses and compares the quality dynamics of fruits.The results showed that:1 The effect of rootstocks on the photosynthetic characteristics of Citrus cv. ’Huangguogan’ Pn of grafting trees and CK increases with the increase of PAR, upward trend in basically the same, the general result is HG/CJ>HG/CR>HG/PT>CK; Gs increase before decrease with the increase of PAR,and the maximum value of three grafting trees and CK shows that HG/CR>HG/PT>HG/CJ>CK;Ci decreases with the increase of PAR and basically the same, the minimum value of three grafting trees and CK shows that CK<HG/CJ<HG/PT<HG/CR; The value of Tr is HG/CR>HG/PT>HG/CJ>CK;The light response curves of WUE is similar to the light response curves of Pn, the general result is HG/CR>HG/CJ>CK>HG/PT.2 The effect of rootstocks on the diurnal change of photosynthetic of Citrus cv. ’Huangguogan’ Diurnal variations of leaf Pn in ’Huangguogan’ exhibited bimodal curves. Trees grafted on Citrus junos and Poncirus trifoliate rootstocks showed higher leaf Pn values. The rootstocks had little effect on the Ci and the result is CK>HG/CR>HG/CJ>HG/PT; the diurnal changes of Gs show roughly unimodal type curves,the value of Gs in grafting trees were higher than in CK, The average of the Gs is HG/CJ>HG/PT>HG/CR>CK; The diurnal variation curve of Tr showed the single apex types, the value of CK was lower significantly than grafted trees. The average of the Tr is HG/CJ>HG/CR>HG/PT>CK; Numerical value of WUE varies with HG/CJ is minimum,while HG/PT is maxmum.3 The effect of rootstocks on the photosynthesis key enzyme of Citrus cv. ’Huangguogan’ The diurnal variation of Rubisco was consistent to that of net photosynthesis rate, the general result is HG/CJ>HG/PT>HG/CR>CK. The diurnal variation of RCA was consistent to that of Rubisco, The value of RCA is HG/CJ>HG/PT>HG/CR>CK. Leaf concentrations of the two photosynthetic enzymes in grafted trees were significantly higher than those in CK at different points in time, The value of RCA is HG/CJ>HG/CR>HG/PT>CK and the value of Rubico is also HG/CJ>HG/CR>HG/PT>CK.4 The effect of rootstocks on the expression of photosynthesis key enzyme gene of Citrus cv.’Huangguogan’ This suggests that appearance of peak value of key enzymes gene expression was showed in different time between grafted trees and CK. And the value is HG/CJ>HG/CR>HG/PT>CK. The appearance of maximum expression of rbcS is earlier than that of rbcL, the maxmum value of three grafting trees and CK shows that HG/CR>HG/CJ>HG/PT>CK, the peak value of rca gene expression shows that HG/CJ>HG/PT>HG/CR>CK.Gene expression of the two photosynthetic enzymes in grafted trees were significantly higher than those in CK at different points in time. HG/PT,HG/CJ, and CK reached their maximum values on March 15, while HG/CR on March 5. The transcriptional level of rca was increasing with fruit ripening, and the levels of rca were higher in all grafting combinations compared to CK. Particularly, HG/CJ had the highest level of rca genes, The level of rca mRNA increased rapidly during fruit ripening and reached the maximum value on March 5 in HG/CJ and on March 15 in HG/PT, HG/CR, and CK.5 The effect of rootstocks on the fruit quality of Citrus cv.’Huangguogan’ Compared with CK, the peak values of total soluble solids (TSS) were postponed to different degrees in grafted trees, CK produced fruits with the highest vitamin C content compared to CK, VC of HG/PT and HG/CR was lower by 20.25% and 20.35%, respectively, VC of HG/CJ was higher by 3.5%; Compared to CK, TA of HG/PT, HG/CR and HG/CJ was lower by 0.4%,2.0% and 3.9%, respectively. The total sugar content of HG/PT, HG/CR, and HG/CJ was higher by 6.77%,18.26%, and 10.19%, respectively. There was no significant difference with skin color between the grafted trees and CK. Fruit across diameter and fruit vertical diameter with grafted trees were significantly higher than that in CK, Among them, the volume of HG/CJ is the largest. In addition, grafting maked the single fruit weigh to improve greatly, had low effect fruit shape index.