The Seedling Performance And Mechanism Of Rootstock-scion Interaction Of 'Yujincheng' Orange On Three Rootstocks

As we all know, the rootstock-scion interactions of citrus affect the economic benefits of citrus orchards by impact on plant horticultural traits, physiological activity and resistance. The previous studies of rootstock-scion interactions focused on plant joeing and dwarfing, rootstock-scion physiological metabolism, stress resistance and affinity of rootstock-scion combination, and so on. Whilst, the abnormal leaf chlorosis of Yujincheng orange on Carrizo rootstock becoming more and more serious in Sichuan and Chongqing areas in the past few years. However, the mechanism of abnormal leaf chlorosis is still unclear. In this study, Yujincheng orange seedlings on three rootstocks were used to study the influence of rootstock-scion interactions on biochemical metabolism in the progress of callus formation, mineral nutrition metabolism, photosynthesis metabolism, sugar nutrition metabolism, resistance to reactive oxygen species (ROS). In all, we aimed to explore the cause and physiological mechanism of abnormal leaf yellowing of Yujincheng orange systematically, and the above results can provide a theoretical basis of controlling abnormal leaf yellowing of Yujincheng orange.The results were presented as following:1. The influence of Yujincheng orange (Citrus sinensis Osbeck var Yujincheng orange) seedlings grafted on three rootstocks Trifoliate (Poncirus trifoliate L. Raf.), Citrus junos(C. junos Sieb. ex Tanaka) and Carrizo (P. trifoliate x C. sinensis Osbeck var Carrizo citrage) on callus formation and development of rootstock-scion grafted interface were investigated. The results showed that the changes of protein contents in callus of three rootstock-scion combinations present double-apex curves. And higher protein accumulation of early stage and polyphenol content of later stage in callus of Yujincheng orange on Citrus junos, which may be more conducive to wound healing at early stage and conducting tissue morphogenesis of the grafting interface at later stage. However, the grafting interfaces of Yujincheng orange on Trifoliate and Carrizo rootstocks accumulated protein later and phenolic compounds contents lower than grafted on Citrus junos, which may not be contribute to callus formation in early and conducting tissue morphogenesis after metaphase to block up conducting tissue.2. The influence of Yujincheng orange (C. sinensis Osbeck var Yujincheng orange) seedlings grafted on three rootstocks Trifoliate (P. trifoliate L. Raf.), Citrus junos(Citrus junos Sieb. ex Tanaka) and Carrizo (P. trifoliate x C. sinensis Osbeck var Carrizo citrage) on carbohydrate synthesis, water metabolism and growth were also investigated. The results showed that there were significant differences in carbohydrates accumulation among Yujincheng orange on different rootstocks. and the starch content in leaves and shoot of grafted seedlings on Trifoliate and Carrizo were higher than on Citrus junos. And the carbohydrate content in taproot and fibrous roots of Yujincheng orange on Citrus junos were higher than on Trifoliate. Whilst, the abnormal yellowing Yujincheng orange on Carrizo rootstock had higher starch content in leaves and lower starch content in roots than the health plant. The above results indicated that sieve tubes of Yujincheng orange on Carrizo may exist some obstacles leading to carbohydrates excessive accumulation in upper side of graft site.3. The influence of Yujincheng orange (C. sinensis Osbeck var Yujincheng orange) seedlings grafted on three rootstocks Trifoliate (P. trifoliate L. Raf.), Citrus junos(C. junos Sieb. ex Tanaka) and Carrizo (P. trifoliate x C. sinensis Osbeck var Carrizo citrage) on mineral metabolism were measured. The results found that the mineral nutrients of Yujincheng orange plant on three rootstocks primarily accumulated in the leaves, branches and fibrous roots. And N, P, K, Ca concentrated in the leaves and branches. However. Fe, Mn, Cu and Zn accumulated in fibrous roots. And the rootstock had a significant influence on mineral elements uptake and transportation. Yujincheng seedlings on Carrizo can absorb nitrogen and transport phosphorus from root to aerial parts most efficiently, but had the lowest content of Mg and Ca. Although Yujincheng seedlings on Citrus junos can absorb P, K, Cu, Zn and Mn in root most efficiently, leaves had lower content. And Ca and Mg content in underground and aboveground tissue of Yujincheng seedlings on Citrus junos were higher than on the other two rootstocks, which indicated that Citrus junos rootstock had higher absorption of Ca and Mg and transportation ability to aerial parts. However, whether its transportation of P, K, Cu. Zn and Mn from root to tissue of aerial parts existing handicaps need to study further.4. The influence of Yujincheng orange (C. sinensis Osbeck var Yujincheng orange) seedlings grafted on three rootstocks Trifoliate (P.trifoliate L. Raf.). Citrus junos(C. junos Sieb. ex Tanaka) and Carrizo (P. trifoliate x C. sinensis Osbeck var Carrizo citrage) on ROS metabolism were determined. The results showed that three rootstock of Yujincheng orange had a significant impacts on leaves protein components, free amino acids and nitrogen. Whist, the resistance to cold of Yujincheng seedlings on Carrizo are weaker than on the other two rootstocks by comparing with MDA contents and SOD. CAT activity in different grafted seedlings, and the resistance to cold of Yujincheng seedlings on Trifoliate are strongest.