Comprehensive evaluation of fruit sugar and acid quality of mango germplasm based on principal component and cluster analysis

Abstract:【Objective】Mango is an important tropical fruit and known as the‘king of tropical fruits’. Mango germplasm resources are very rich in China. The composition and content of fruit sugar and acid directly affect the quality and commercial value of fruit. Therefore, it is necessary to study the composition and content of sugar and acid and their genetic diversity of mango germplasm.【Methods】In current study, 148 mango germplasm resources were used as experimental materials and high performance liquid chromatography (HPLC) was used to detect the composition and content of sugar and acid in mango fruits. Individual sugars content: 1.0 g of the pulp was weighed, and, 5 mL of 80% ethanol solution was added, then it was centrifuged with 10 000 r·min^-1 at 4 ℃ for 10 min, and the supernatant was transfered to a 15 mL centrifuge tube, the residue was extracted twice with 2 mL of 80% ethanol solution, the supernatants were transferred again to the centrifuge tube, then the tube was put in a water bath at 90 ℃ to evaporate to dryness, and it was diluted to 10 mL with ultrapure water. A 1 mL over 0.45 μm filter membrane was taken for HPLC analysis. Difference detector in HPLC is RI-1530: flow rate is 1.0 mL·min^-1, column temperature is 27 ℃, sample intake amount is 10 μL, and the determination time is 15 min; organic acids content: 0.5 g of pulp sample was weighed, then it was ground with 5 mL of 0.2% metaphosphoric acid in ice bath, and was centrifuged with 10 000 r·min^-1 for 10 min, take the supernatant; the residue was fully washed with 4 mL of 0.2% metaphosphoric acid and then was centrifuged, ake the supernatant; combine the supernatant, It was diluted to 10 mL with 0.2% metaphosphoric acid and mixed. A 1 ml sample was taken and filtered by a 0.45 μm filter membrane to be tested and then detected by HPLC using a C18 column (250.0 mm × 4.6 mm × 5.0 μm) with a loading volume of 10 μL for 30 minutes.【Results】Mango fruit pulp mainly contained three kinds of individual sugars namely fructose, glucose and sucrose, and six kinds of organic acids, namely oxalic acid, tartaric acid, malic acid, ascorbic acid, citric acid and maleic acid; the content of citric acid and ascorbic acid were significantly and positively correlated with the total acid content, while the sucrose content was significantly and positively correlated with the total sugar content in 148 mango germplasm resources. It was found that the tartaric acid, total acid, sugar-acid ratio, fructose, glucose and sucrose content were the main reason of genetic diversity of fruit quality in mango germplasm resources by principal component analysis. According to the composition and contents of fruit sugars, the 148 mango germplasm resources could be divided into four categories at the genetic distance of 2.5 by the cluster analysis. The first category contained 111 accessions of germplasms and the second category had 34 accessions of germplasms, the third category had 2 accessions of germplasms and the fourth category had only 1 accessions of germplasm. According to the composition and contents of fruit acids, the 148 germplasm resources could be divided into four categories at the genetic distance of 5.0, The first category contained 113 accessions of germplasm resources, including 82 accessions of ascorbic acid-accumulating germplasms such as Cuba Sankre, Guifei 1 and Xiaojimang; and 28 accessions of malic acid- accumulating germplasms such as Jinlong, African Elephant and Liuzhou Luzon and Xiaoqingpi, Carrie, and Sandersha Sdg, the second category contained 27 accessions of mango germplasm resources, most of them were citric acid accumulation type, such as Ganhong, Hongmang No.6 and Guangxi No.4, the third category included Bao Zai’ an, Zineya No.1, Guangxi No.4, Yuanjiang Ivory, and Dasanian, they did not contain malic acid or had extremely high content of malic acid, the fourth category contained only Amygdalus mango 1030 and Guangxi No.8, they were all ascorbic acid accumulation type.【Conclusion】The 148 mango germplasm resources could be divided into sucrose-accumulating type fruits and fructose-accumulating type fruits by the cluster analysis according to the content of sugar components; meanwhile, they could be divided into ascorbic acid-accumulating type fruits, malic acid-accumulating and citric acid type fruits according to the content of acid components. The components and contents of sugars and acids varied greatly with different mango germplasm resources, and the diversity index of each sugar and acid was over 5. The variation ranges of acid components in the fruits of different mango germplasm resources were much larger than those of the sugar components, peculiarly, the variation range of the citric acid was the largest. The content distribution of sugars followed the normal distribution, the acid components followed the normal distribution only in ascorbic acid. The correlation coefficient between the content of citric acid and the content of total acid was the largest; meanwhile, the correlation coefficient between the content of sucrose and the content of total sugar was the largest. The sucrose and citric acid contributed the most to the diversity of the 148 mango germplasms in the present experiment. These results would provide important information for the conservation of mango germplasm resources and the breeding of new mango varieties.