Study On The Optimum Leaf-Fruit Ratio Of 5-Year-Old Camellia Oleifera ’Huaxin’

Camellia oleifera Abel.is an evergreen shrub or small tree belonging to the genus Camellia(Camellia L.)in the family Theaceae,and is one of the four major woody edible oil species in the world.In recent years,the planting area of C.oleifera in China has been increasing year by year.However,there is no scientific and reasonable proportion to carry out flower thinning,fruit thinning,flower preservation,fruit preservation and other nurturing measures,resulting in C.oleifera in the production of the phenomenon of alternate bearing cycle,which in turn seriously affects the yield and quality of C.oleifera.In this experiment,from the pre-bred 5-year-old C.oleifera ’Huaxin’ potted seedlings,well-grown and uniformly growing C.oleifera seedlings were selected for the study and treated with different leaf-fruit ratios by manual pruning,controlled pollination and fruit thinning.This treatment was control(CK,no fruit),high leaf-fruit ratio(HR,leaf-fruit ratio of 36:1),medium leaf-fruit ratio(MR,leaf-fruit ratio of 18:1)and low leaf-fruit ratio(LR,leaf-fruit ratio of 9:1),respectively.In this experiment,we conducted phenotypic determination,anatomical observation,photosynthetic physiological characteristics and transcriptomics(late October)of C.oleifera ’Huaxin’ to investigate the mechanisms related to the optimal leaf-fruit ratio and leaf color change suitable for the growth of C.oleifera ’Huaxin’.The main results are as follows:1.Study of different leaf-fruit ratios on C.oleifera growth and fruit quality.According to the observation in late June,except for LR treatment,the overall color of the trees was green,and the trees grew fast and new growth was obvious when the fruit load was low.With the extension of treatment time and the decrease of leaf-fruit ratio,the yellowing phenomenon of leaves gradually deepened,while the number of flower bud differentiation also decreased with the decrease of leaf-fruit ratio,and when the leaf-fruit ratio was 9:1(low leaf-fruit ratio),the number of flower bud differentiation was 0.In late October,the study on mature C.oleifera fruits found that the fruits under HR treatment were the largest,the skin was red,the fresh seeds were large and full,and the oil bodies in the seed kernel expanded to the inner cell.However,the fruit size under LR treatment was small,the peel was red or green,and the cell volume and oil body volume were smaller than those under HR and MR treatments.In addition,leaf-fruit ratio also had a significant effect on fruit fatty acid content,which was reduced by 8.65%and 11.74%under the MR and LR treatments,respectively,compared with the HR treatment(P<0.05).Therefore,when the leaf-fruit ratio of C.oleifera ’Huaxin’ is 36:1,it can meet the nutrients required for tree growth and bud differentiation,and also improve the fruit quality of C.oleifera.2.Study on photosynthetic physiological characteristics of C.oleifera with different leaf-fruit ratios.It was found that the net photosynthetic rate(Pn)of new leaves(leaves growing spring in 2021)was always higher than that of old leaves(leaves growing before 2021)from June onwards in seedlings,regardless of sunny or cloudy days,and all old leaves showed a decreasing trend of Pn as the treatment time was extended.In sunny new leaves,Pn was basically higher in the HR treatment than in all other treatments except September.As observed by dissection and chloroplast fluorescence,the lower the leaf-fruit ratio,the smaller the leaves,and the deeper the yellowing of the leaves in October,as well as the lower chloroplast content,chlorophyll content,and nitrogen content,the lower the Pn.In addition,the starch content,soluble sugar content,abscisic acid content and malondialdehyde content were higher in HR and LR treatments than in CK treatment,with significant differences(P<0.05).Overall,when the leaf-fruit ratio of C.oleifera ’Huaxin’ was 36:1,Pn was higher in the HR treatment than in the other treatments and the leaf color was green.3.Transcriptomic analysis of C.oleifera under different leaf-fruit ratios.In the previous study,it was found that leaf color differed significantly under different leaf-fruit ratios.In order to explore the principle,leaves with different leaf-fruit ratios in late October(the most significant difference)were collected for the study.Using Illuminna RNA-Seq technology,4,2290 unigenes were successfully identified.Among them,122,120 and 1064 differentially expressed genes were up-regulated in CK_vs_HR,CK_vs_MR and CK_vs_LR,respectively,and 13,36 and 351 differentially expressed genes were down-regulated,respectively.The pathways involved in leaf color changes,such as flavonoid biosynthesis and carotenoid biosynthesis,were screened by KEGG enrichment analysis,and key genes such as PAL,COM1,OMT1,GSVIVT-1,CAD1,CYP98A2 and At4g20840,and transcription factors such as MYB and bHLH were selected.