Effects Of Magnesium On Yield And Flesh Color Of Citrus

Citrus is the largest fruit in the world,and the pulp is the direct edible part,and the color is an important indicator to judge its appearance quality,which directly stimulates consumers’ purchase desire.Magnesium(Mg)is an essential nutrient element for plants,which not only affects the yield and quality of citrus,but also affects the color of citrus.In this study,two citrus varieties(Satsuma Mandarin and ‘Newhall’ navel orange)were used as experimental materials to carry out field experiments to study the effect of Mg on citrus yield,quality,pulp nutrient content and coloration.Combined with the metabolomic analysis of ‘Newhall’ navel orange pulp.The mechanism of Mg affecting the color of citrus pulp was preliminarily explored.The main findings are as follows:(1)Treatment with different Mg levels could increase the fruit yield of the two citrus varieties to a certain extent,and the treatment with 150g/plant Mg O(T2)was the best and significantly higher than the control.(2)According to the dynamic change analysis of Mg content in the pulp of Citrus at the growth and development stage,Mg application can increase the Mg content in the pulp of Citrus at all growth stages,among which the Mg content in the pulp of Satsuma Mandarin at 150 DAF(at the end of fruit expansion)and 195 DAF(at the stage of fruit quality formation)can be significantly increased;However,the Mg content of ‘Newhall’ navel orange pulp at 195 DAF(fruit quality formation stage)was significantly higher than that of the control by 23.07%.(3)According to the observation and determination of pulp color and color difference indexes in the main development stages of citrus fruits treated with Mg,the appropriate application of Mg can make the pulp color change from orange yellow or yellow to orange red or orange yellow,thus promoting the pulp coloring of the two citrus varieties.The flesh color of Satsuma Mandarin treated with 165 DAF Mg fertilizer was orange,while that of the control treatment was still orange yellow.However,there was no visible difference in flesh color of ‘Newhall’ navel orange during the whole growth and development period.(4)According to the dynamic changes of carotenoid content and the expression of related genes in citrus fruit meat,there are differences in carotenoid metabolism between the two citrus varieties.Mg regulates the down-regulation and up-regulation of upstream genes of carotenoid metabolism in Satsuma Mandarin and ‘Newhall’ navel orange fruit meat,respectively.In 120DAF(middle stage of fruit swelling)～195DAF(stage of fruit quality formation),Mg regulates α-Carotene and β-Carotene Two branches of carotenoids promote the change of flesh color of Satsuma Mandarin,while the regulation of carotenoids in flesh of ‘Newhall’ navel orange is mainly β-Carotene bypass,especially LCYb2 and ZEP gene expression.(5)According to the analysis of metabolite differences in ‘Newhall’ navel orange pulp,a total of 55 differential metabolites were detected in mg treatment,mainly including 49 down regulated metabolites,and only 6 metabolites were significantly up-regulated.KEGG pathway enrichment analysis showed that the differential metabolites were mainly enriched in phenylalanine metabolism,glutathione metabolism,phenylpropane biosynthesis and other metabolic pathways involving chromosomes.