| Citron(Citrus medica L.)is one of the three basic species of citrus.Citron has edible,medicinal,ornamental value and can be used for processing.It is an important material for studying the origin and evolution of citrus,improving and innovating germplasm resources.Southwest China is the origin center of citron.It has abundant and diverse wild citron germplasm resources which have not been fully utilized and there are still great research potential and broad market development prospects in citron.In this study,a systematic evaluation and genetic diversity analysis of fruit sugar-acid and carotenoids in257 citron germplasm accessions were conducted to discover excellent citron germplasm and lay a foundation for the selection and breeding of citrus varieties.The comparison of varieties provided new insights into the origin and evolution of citrus plants.The main results of this study are as follows:1.The sugar and acid content of 119 citron fruit juice sac and 257 citron fruit albedo samples were detected by GC-FID.The results showed that the average content of soluble sugars in citron juice sac was 20.76 mg/g FW,mainly sucrose and fructose,accounting for40.60% and 36.13%,respectively;the average content of total organic acids was 39.05mg/g FW,of which the average content of citric acid was 33.40 mg/g FW,which was the main acid component in citron juice sac;the ratio of total sugar to total acid was between0.06-4.95 and the taste was extremely sour.The citron albedo was significantly different from the juice sac and its soluble sugar content was higher,of which the average content of total sugar was 60.64 mg/g FW,mainly fructose and glucose;the average content of total acid was only 1.38 mg/g FW,mainly malic acid.More than 3/4 of the citron germplasm albedo had a sugar-to-acid ratio above 30.Based on the above,germplasm like MT-41,QZ-1 with suitable sugar-acid ratio and high total sugar content were screened out,which can be used for the breeding of edible citron;QZ-1,MT-71,CH-1,Z-29,Y-49 and other citron germplasms with extreme differences in sugar and acid components can be used for subsequent research and breeding.2.The variation characteristics and genetic diversity of sugar and acid components in citron fruit were analyzed.In general,the total sugar content in juice sac ranged from 3.64-53.67 mg/g FW,with a CV of 56.92%,and the total acid content ranged from 8.20-75.21mg/g FW,with a CV of 52.55%.The variation range of total sugar content in the albedo was 26.36-88.64 mg/g FW,and the CV was only 19.76%,while the variation of acid content was larger,with the range of total acid content is 0.00-6.87 mg/g FW,and the CV was as high as 77.27%,indicating the tissue specificity and germplasm specificity on the accumulation of sugar and acid in the natural population of citron..Hierarchical clustering heat map analysis of sugar and acid content in juice sac and albedo can clearly distinguish Yunnan citron from Tibet citron.The content of sugar and acid in the peel and pulp of citrus fruits such as mandarin,pummelo,orange,kumquat and other citrus fruits was further determined,and principal component analysis and cluster analysis were carried out with the sugar and acid content of the natural population of citron.All resources can be divided into three major groups.Group Ⅰ was mainly Yunnan citron without juice sac;Group Ⅱ was mainly citron with juice sac,including two subgroups: One was part of citrons from Tibet,citron with juice sac from Yunnan and red limonia,the other was some Tibet citrons,aurantium,lemons and rough lemons,etc.;Group Ⅲ was other cultivated citrus varieties.Kumquats were first separated,and then divided into mandarin and pummelo,and sweet oranges were grouped with most of the mandarins.3.Nine carotenoids were detected in 77 citron accessions peel by HPLC,namely violaxanthin,9-cis-violaxanthin,lutein,zeaxanthin,α-cryptoxanthin,β-cryptoxanthin,β-carotene,phytoene and phytofluene.The carotenoid content of various peels varied greatly.The total carotenoid content ranged from 28.32-914.35 μg/g DW,with the average of255.41 μg/g DW,and the CV was as high as 82.98%;the carotenoids components with the highest content were phytoene and phytofluene,the content range was 1.84-627.64 μg/g DW and 0.21-183.18 μg/g DW respectively;the main colored components such as violaxanthin and β-cryptoxanthin were less accumulated in citron peel.The carotenoids in the peel of Yunnan citron were significantly higher than those of Tibet citron,both in total content and in each component.The results of principal component analysis and cluster analysis of 77 resources based on carotenoid content showed that Yunnan citron and Tibet citron were significantly different.They were first divided into different clusters,and then Tibet citron was divided into two clusters.The results were consistent with the clustering on sugar acid. |
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