CHEN Yan-hui ,GAO Hui-fang ,WANG Sa ,LIU Xian-yan,HU Qing-xia ,JIAN Zai-hai ,WAN Ran ,SONG Jin-hui ,SHI Jiang-li

1 College of Horticulture,Henan Agricultural University,Zhengzhou 450002,P.R.China

2 Henan Key Laboratory of Fruit and Cucurbit Biology,Zhengzhou 450002,P.R.China

3 Xianyang Academy of Agricultural Sciences,Xianyang 712034,P.R.China

Abstract Recent investigations on pomegranate products have significantly increased and successfully drawn consumers’ attention to nutritional and medicinal values,promoting the pomegranate industry’s development worldwide. However,little information on pomegranates grown in China is available. Morphological and chemical characterizations of fruits and arils from 20 pomegranate cultivars in six regions of China were investigated. Combined with overall scores by principal component analysis,‘Yushiliu No.1’,‘Taishanhong No.2’,‘Tunisia’ and ‘Mollar’ were promising cultivars,and Chinese researchers bred the first two. It was surprising that ‘Mollar’ had bigger fruit size and more aril moisture grown in China than in Spain.Cultivars with higher anthocyanin content in arils were ‘Turkey’,‘Moyu’ and ‘Red Angel’,which might be used as the source of natural red food colourants. While red husk ‘Hongruyi’ and ‘Hongshuangxi’ with higher vitamin C,aril moisture and lower titratable acid in arils,might also be promising cultivars for further various utilization. Furthermore,the comparison of ‘Tunisia’fruits from four regions revealed that cultivation locations had more influence on fruit traits than genotypes. Maturity index classification was established for Chinese pomegranate cultivars. Therefore,the results would provide a valuable guide for agricultural cultivation,industrial utilization,and breeding.

Keywords:Punica granatum L.,fruit morphological characteristics,aril assessment,husk colour,vitamin C,anthocyanin content

1.Introduction

Pomegranate (Punica granatumL.) native to Persia,is one of the critical and oldest horticulture crops. It was introduced into China with a long history,and cultivated widely in many regions. China with diverse climatic conditions is one of the world’s biggest pomegranate producers,and the major pomegranate orchards are in Henan,Shandong,Shaanxi,Sichuan provinces and Chongqing City (Sarig and Galili 2012;Karimiet al.2017). Recently,the market is growing with good prospects,and frequent consumption of fruits has promoted the rapid development of the pomegranate industry. Thousands of hectares of pomegranate fields have become a pillar of the local and new agriculture industry development in China.

Pomegranate is one of the most important commercial fruit crops in fresh consumption and industrial food processing. Additionally,extracts from pomegranate peels,seeds,and leaves are used for medicinal purposes,such as reducing mammary tumorigenesis,atherogenic modifications,heart disease,and cancer chemoprevention and chemotherapy (Maliket al.2005;Bishayeeet al.2016;Karimiet al.2017;Khwairakpamet al.2018;Chaveset al.2020;Guerrero-Solanoet al.2020). All these are attributed to various bioactive components and beneficial nutrients in pomegranate fruit. Furthermore,pomegranate wastes were also used as a sustainable source for nutraceuticals and other applications (Spilmontet al.2015;Talekaret al.2018;Verottaet al.2018). In recent years,a large number of studies have shown significant differences in fruit characteristics such as quality,antioxidant activity,polyphenol,anthocyanin,organic acid,and sugar contents among cultivars or clones (Melgarejoet al.2000;Tzulkeret al.2007;Hasnaouiet al.2011;Zaouayet al.2012;Melgarejo-Sánchezet al.2015;Alcaraz-Mármolet al.2017).Suggesting aptitudes for fresh consumption and processed products depended on the respective fruit characteristics.

Generally,fruit quality and consumption customs depended on a series of appearance and inner quality changes in fruit during fruit ripening or postprocessing(Bouzayenet al.2010),which included modifications in fruit colour,taste (sugar and organic acids contents),aroma (production of volatile compounds),and texture (fruit softening). For pomegranates,cultivars have been classified into three groups (sweet,sour-sweet,and sour) based on organoleptic characteristics and chemical compositions(Melgarejoet al.2000). In addition,pomegranates cultivars have been classified into two groups,soft-seed and hardseed according to the seed firmness,which is also an important economic trait. In 1986,a soft-seed pomegranate cultivar ‘Tunisia’ was introduced in China. It has acquired full acceptance due to its consumption and beneficial health properties. Up to now,‘Tunisia’ has been widely grown in Henan,Yunnan and Anhui provinces of China. Considering the difference in growing regions,environmental conditions,the fruit characteristics were not the same.

With market demand and frequent cultural communication,it has been more critical to evaluate fruit characteristics and potential utilization with high economic interests,among different cultivars and different regions (Tehranifaret al.2010). Therefore,many comparative studies on various nutritional ingredients and antioxidant activity in pomegranate fruit (including peels,arils,seeds,even waste),were extensively investigated by many countries,including Spain (Melgarejoet al.2000;Calín-Sánchezet al.2011;Melgarejo-Sánchezet al.2015),Iran (Tehranifaret al.2010;Akhavanet al.2015),Turkey (?aliskan and Bayazit 2012),USA (Gilet al.2000),Israel (Dafny-Yalinet al.2010),Italy (Ferraraet al.2011,2014),Tunisia (Elfallehet al.2011;Zaouayet al.2012) and so on. However,those of pomegranate fruits grown in China were not available,though,China had abundant germplasm resources and various environmental conditions. For that reason,this study aims to evaluate fruit characteristics from 20 pomegranate cultivars grown in China. Combined with PCA and genetic divergence analysis,this would provide a useful reference for commercial utilization and breeding new germplasms.

2.Materials and methods

2.1.Plant materials and region information

The fruits from 20 pomegranate cultivars were cultivated in commercial orchards in six different regions of China,which belonged to warm temperate continental climate with four clearly defined seasons. Of them,‘Tunisia’ fruits were from four regions,Xingyang (XY),Luoyang (LY) and Nanyang(NY) of Henan Province and Fuyang (FY) of Anhui Province,respectively (Table 1). The fruit samples were harvested at the commercial mature stage from September till November in 2019. Immediately,the fruit were transported to the laboratory at Henan Agricultural University,Zhengzhou,China. Fruits with defects (sunburn,cracks,bruises,and cuts in the husk) were discarded and only healthy fruits with uniform in size and appearance were tested. Fifteen fruitsper cultivar (5 fruits from each biological duplication) were investigated. Husks were carefully cut at the calyx zone and 5–6 times longitudinally on the fruit with sharp knives,and arils were manually separated and mixed,as well as removing inner white parts of the fruit for aril juices.

Table 1 Geographical location and environmental information of six pomegranate-producing regions in China

2.2.Assessment of fruit morphological characteristics

The full fruit weight and hundred-aril weight were calculated with electronic balances (JY-502,Shanghai,China),with an accuracy of ±0.01 g. Seed firmness was determined in each fruit using a GWJ-II Texture Analyzer (Zhejiang Top Instrument Co.,Ltd.,Zhejiang,China). The means of 10 seeds from each fruit were calculated by a constant speed to measure pressure of the probe on the seed,and the data were expressed in Newtons (N). Fruit shape index of each fruit were expressed as the ratio of fruit length to diameter.Fruit length (without calyx) and diameter (the maximum width in the middle of fruit) were measured using digital calipers with 0.01 mm accuracy,respectively.

Colour measurement was made in fruit husk on four opposite faces at the equatorial zone,using the highprecision colorimeter (HP-C210,Shanghai,China) to determine the chromaticity values L＊ (lightness),a＊ (green to red),and b＊ (blue to yellow). The mean values for L＊,a＊and b＊ parameters were calculated for each fruit.

2.3.Assessment of tastes and nutritional values in pomegranate arils

The aril moisture percentage was determined after being dried in a hot air oven at 115°C until reaching a constant weight (about 6 h). The formula is:Aril moisture percentage(%)=(FW–DW)/FW×100 (FW means fresh weight and DW means dry weight).

The soluble solids content (SSC) of pomegranate aril was analyzed by a WY060T handhold refractometer (Chengdu Qingyang Huarui Optical Instrument Factory,Sichuan,China),with values being presented as Brix degree. The titratable acid (TA) in pomegranate arils was measured using acid-base neutralization titration method by titrating 5 mL of juice to reach the endpoint of pH 8.2 with 0.1 mol L–1NaOH and recording the titration volume. The results were expressed as citric acid percentage. Maturity index(MI) was calculated by the ratio of soluble solids content to titratable acidity.

The vitamin C content in arils was acquired by a 2,6-dichlorophenol indophenol (DCIP) titration method(Deutsch 1973). About 0.5 g of fresh arils,ground with liquid nitrogen,was mixed with 50 mL of 2% (m/v) oxalicacid solution. Then,10 mL of the solution was transferred to a triangular flask (50 mL),and the DCIP solution that had been calibrated was immediately performed for sample solution titration. The terminal point was recorded with a reddish appearance at 15 s fadeless. Vitamin C content was determined by the consumed volume of the DCIP solution.

Total anthocyanin content was determined according to the pH differential method as described by Lakoet al.(2007). Absorbance was measured in a UV-visible spectrophotometer (L9,Shanghai) at 510 and 700 nm in buffers at pH 1.0 and 4.5 using:A=[(A510?A700) pH 1.0?(A510?A700) pH 4.5] with molar extinction coefficients of cyanidin-3-glucoside for pomegranate fruit juice. Results were expressed as mg of cyanidin-3-glucoside per L of pomegranate juice.

2.4.Statistical analysis

All measurements were performed in technical triplicate.This research was conducted using a factorial design with different cultivars and fruit quality. Principal component analysis (PCA),Pearson correlation analysis and one-way ANOVA were performed with SPSS Statistics v.20 (IBM,Chicago,IL,USA). Significant differences (＊,P＜0.05)between mean values were evaluated by one-way ANOVA and Duncan’s multiple range test. The dendrogram of hierarchical cluster analysis was conducted using Ward linkage and squared Euclidean distance.

3.Results and discussion

3.1.Diversity of fruit morphological characteristics

Fruit size is a varietal characteristic that may fluctuate depending on climatic and agricultural conditions except for genotypes,and also partly affects the market price (Ferraraet al.2011). In Table 2,the mean fruit weight was 444.26 g among 20 cultivars,ranging from 289.25 g (‘Dongyan’)to 1 072.35 g (‘Yushiliu No.1’),generally higher than the previous reports from other countries,from 196 to 674 g of 30 pomegranate accessions (363 g of mean value) in Tunisia(Hasnaouiet al.2011),186–551 g of 29 ones in Israel (Dafny-Yalinet al.2010),196.89–315.28 g of 20 ones (Tehranifaret al.2010) and 106.60–496.91 g of 100 ones in Iran (Khadiviet al.2018),168.9–574.9 g of 8 ones in Italy (Ferraraet al.2011),and similar to 300.10–854.63 g from six clones grown in Spain (Melgarejo-Sánchezet al.2015). ‘Mollar’is cultivated widely in Spain. From Table 2,compared with previous reports on ‘Mollar’ fruit weight in Spain,449.96 g obtained in our study was about 100 g higher than 333.50 g(ME14) and 350.04 g (ME16) (Hernándezet al.2014),and much higher than 256 g (Martínezet al.2006). Two sour‘Yushiliu’ cultivars that were bred by China showed the highest value,which was in step with the result that fruit weight was significantly positively correlated with TA (Table 3). Among‘Tunisia’ from four regions,the order was FY (548.03 g)＞NY(448.94 g)＞XY (373.25 g)＞LY(320.20 g),and the average value was 422.61 g. Notably,the order of rainfall distribution from high to low among the four regions was in line with that of fruit size,suggesting that annual average rainfall might be an important factor of fruit size.The latter two ‘Tunisia’ fruits,were not far apart (140 km) and had more similar climatic conditions,which might lead to little difference.Taken together,it was concluded that the variation of fruit weight was mainly influenced by cultivation location rather than pomegranate genotypes. It was interesting to highlight that fruit size was generally bigger grown in China than in other countries,and over 444.26 g of the mean fruit weight was from 10 tested cultivars (including six cultivars original from China).

Fruit diameter was between 8.03 cm (‘Dongyan’) and 13.80 cm(‘Yushiliu No.1’),and fruit length varied from 7.22 cm (‘Red angel’) to 11.00 cm (‘Yushiliu No.1’) (Table 2).It was found that fruit shape index ranged little between 0.80 and 0.97,closing to roundness,but had a significant difference. Among‘Tunisia’ fruits,the value was 0.91 or so except FY. Tehranifaret al.(2010) reported that the ratio was between 0.88–1.61,suggesting slenderer shape of the fruit in Iran,compared with our selected pomegranate cultivars.

Hundred-aril weight is the key trait for evaluating edible portion.From Table 2,it ranged between 24.26 g (‘Mudan’) to 68.40 g(‘Yudazi’),and the highest was 10 g higher than the second ‘Dongyan’,nearly three times higher than the lowest. Similar to our present finding,the range was reported indifferent cultivars by Ferraraet al.(2014) and Khadiviet al.(2018),respectively. Hasnaouiet al.(2011) reported the range of 34.8–70.3 g,suggesting higher hundred-aril weight.Additionally,‘Tunisia’ fruits ranked the upper-middle except NY,the highest for FY (56.59 g). The average hundred-aril weight of 47.3 g in our present study was little lower than 49.8 g from 30 Tunisia accessions (Hasnaouiet al.2011),but much higher than 35.35 g from 100 Iranian genotypes(Khadiviet al.2018).

Table 3 Correlation analysis of 15 fruit and aril characteristics among different pomegranate cultivars1)

Pomegranate seed firmness affects sensory and edibility. Generally,people prefer soft-seed pomegranate fruit. The cultivars with the lowest firmness were ‘Red Angel’＜‘Turkey’＜‘Mollar’,while the ones with the hardest were ‘Yudazi’＞‘Yushiliu No.1’＞‘Jinhong’. Therefore,for fresh consumption of ‘Yushiliu No.1’,the advantages were the biggest size and higher aril yield,but the disadvantage was a harder seed. FY among four ‘Tunisia’ fruits and‘Taishanhong No.2’ both exhibited bigger fruit size and higher hundred-aril weight,but in view of seed firmness,soft-seed ‘Tunisia’ (FY) might be more suitable for fresh than hard-seed ‘Taishanhong No.2’.

The colour of fruit husk has always been an important appearance quality attribute,which influences consumer behavior (McGuire 1992),especially,the intensive red colour. Husk colour varied largely among 20 cultivars in this study (Table 2). The L＊ value is a measure of the colour in the light-dark axis;the higher,the lighter,nearly white. L＊value ranged from 21.93 to 72.80 with significant difference,which accorded with 20.60–68.9 reported by Dafny-Yalinet al.(2010). The first three were ‘Mollar’,‘Yudazi’ and‘Daqingpitian’. Among four ‘Tunisia’ fruits husks appeared similar but with a significant difference,the highest 64.71 for NY,whereas the lowest 59.77 for LY. ‘Turkey’ and ‘Red Angel’ fruits had red coloration with the highest 67.88 and 67.18 of a＊ value,respectively,while ‘Daqingpitian’ exhibited a green yellowish color with the lowest 10.86,followed by ‘Mollar’. For four ‘Tunisia’ fruits,the a＊ value order was LY＞NY＞FY＞XY. The change of a＊ value among 20 tested cultivars was further supported by the photos taken naturally in the laboratory (Fig.1). Dafny-Yalinet al.(2010)reported the range from–2.00 to 48.5 for a＊ value (29 Israeli genotypes),and above 48.5 of a＊ value was seven cultivars in the present study. In addition,a＊ value of husk had significantly positive correlation with anthocyanin content in arils (＊,P＜0.05) (Table 3),which might be a good indication that red color husk could respond to consume tendency for nutritional value,such as higher anthocyanin content. The b＊ value presents from grey to yellow. ‘Daqingpitian’ showed yellow for 35.10 of the b＊ value,followed by XY and FY. In summary,‘Turkey’ and ‘Hongruyi’ could attract consumers for their bright and red coloration,while green yellowish‘Daqingpitian’ stood out among pomegranates whose husks were generally red,because of its higher L＊ and b＊ value.

Fig.1 Husk colour of 20 cultivars grown in China. The pictures were taken using the same camera and under the same light conditions,which can naturally exhibit the husk colour.

3.2.Assessment of tastes and nutritional value in pomegranate arils

The arils are the edible part of pomegranate fruit,also,are used for fresh juice,canned beverages,beverages,jellies or jams. The moisture percentage,SSC,TA in arils and the ratio of SSC/TA determine the sensory attributes of pomegranate juice (Aarabiet al.2008). The aril moisture ranged from 75.09% (‘Turkey’) to 83.00% (XY) (Table 4),close to 76.3–81.6% in Spain and 77.0–82.2% in Moroccoreported by Alcaraz-Mármolet al.(2017) and Martínezet al.(2012),respectively. Noticeably,only one (‘Turkey’) among 20 cultivars tested was below 76.3%. Moreover,that of‘Tunisia’ from four regions ranked 1st,3rd,4th and 6th,respectively (Table 4). Regarding to ‘Mollar’,82.24% in the present study was superior to both 81.98 and 79.28% grown in Spain (Martínezet al.2006;Alcaraz-Mármolet al.2017).

The SSC is an important organ oleptic quality of the juice. Of the 20 cultivars studied,the SSC varied from 13.27 (‘Mudan’) to 16.53 °Brix (‘Turkey’),15.30 °Brix for the mean,the sweetest ones (over 16 °Brix),e.g.,‘Turkey’,‘Moyu’,‘Dazitian’,‘Red angel’,and ‘Yudazi’ (Table 4). The range of present SSC value was very close to the reported 12.36–16.32 °Brix by Martínezet al.(2006),higher than 11.37–15.07 °Brix in Iranian genotypes (Tehranifaret al.2010),but lower than 13.7–19.1 °Brix in other reports(Dafny-Yalinet al.2010;Ferraraet al.2011,2014;Martínezet al.2012;Alcaraz-Mármolet al.2017;Khadiviet al.2018).Regarding to ‘Mollar’,14.87 °Brix in the present study was lower than the previous result (15.4–17.6 °Brix) by Alcaraz-Mármolet al.(2017). These differences in SSC,along with four ‘Tunisia’ fruits may be ascribed to climatic conditions and likely the temperature influencing sugar accumulation.

While TA value exhibited much difference,from 0.23 to 1.56%,which was lightly lower than 0.37–4.6% of northern regions (e.g.,Turkey,Russia,Georgia and Macedonia),and very similar to 0.25–1.1% reported by Dafny-Yalinet al.(2010),but lightly higher than the result reported by Martínezet al.(2006). The cultivars with the highest TA value were ‘Yushiliu No.2’,‘Yushiliu No.1’and ‘Turkey’. In fact,consumer appreciation is related more to SSC/TA than to SSC or TA. The finding that SSC/TA had a significant negative correlation with TA was from Table 3,suggesting that TA had a much greater effect on SSC/TA taste. The higher SSC/TA was‘Hongshuangxi’,‘Hongruyi’,‘Tunisia’(NY),‘Taishanhong No.1’ and ‘Milu’(Table 4),proving their better taste.

MI value,is one of the most reliable indicators of pomegranate fruit maturity,depending on the cultivar and climatic conditions(Shwartzet al.2009;Fawole and Opara 2013). Based on previous studies on MI (Martínezet al.2006;Alcaraz-Mármolet al.2017) and sensory evaluation,MI classification criteria for Chinese pomegranate cultivars was established,the sweet cultivars for 31–66,soursweet cultivars for 16–28 and sour cultivars for 8–13. Therefore,sweet cultivars included ‘Tunisia’ from four regions,‘Hongruyi’,‘Milu’,‘Taishanhong No.1’,‘Mollar’,‘Hongshuangxi’ and‘Yanzhihong’,sour-sweet cultivars for ‘Red Angle’,‘Yunongzaoyan’,‘Yudazi’,‘Dongyan’,‘Taishanhong No.2’,‘Dazitian’,‘Jinhong’ and‘Daqingpitian’,sour cultivars for‘Turkey’,‘Moyu’,‘Mudan’,‘Yushiliu No.1’ and ‘Yushiliu No.2’.

As the most important antioxidant,vitamin C content is gen erally regarded as a nutritional parameter to evaluate the fruit quality. Vitamin C contents in ‘Yunongzaoyan’(10.10 mg 100 g–1),‘Tunisia’(FY) (10.00 mg 100 g–1) and‘Hongshuangxi’ (9.20 mg 100 g–1)were obviously higher than the others,followed by those that showed no significant difference,e.g.,‘Tunisia’ (XY),‘Tunisia’(NY),‘Red Angel’,‘Jinhong’,‘Daqingpitian’ and ‘Yanzhihong’,about 7.00–7.60 mg 100 g–1(Table 4). Vitamin C contents in the present study ranged 4.60–10.10 mg 100 g–1(Table 4),while 0.0–12.0 mg 100 g–1in 25 Iranian pomegranate genotypes (Aarabiet al.2008),and 9.91–20.92 mg 100 g–1of 20 Iranian pomegranate genotypes (Tehranifaret al.2010).

Anthocyanins both provided antioxidant capacity and reflected colour parameters. A total of 20 cultivars chosen for this study differed significantly in anthocyanin contents(Table 4). ‘Moyu’ with 255.80 mg L–1was 52 folds higher than‘Yudazi’ with 4.90 mg L–1,and higher the previous reports 1.8–175.4 mg L–1in Tunisia and Iranian pomegranate cultivars,respectively (Hasnaouiet al.2011;Akhavanet al.2015). Specifically,three cultivars (‘Moyu’,‘Red Angel’ and ‘Turkey’) with over 175 mg L–1possessed remarkable higher anthocyanin content,indicating that they could be used as a source of natural red food colourants. In addition,there was no significant difference (＊,P＜0.05) among ‘Tunisia’ arils from four regions. Therefore,the differences of light,temperature,altitude and agronomic factors in cultivation locations had a lower influence on the anthocyanin content,than genetic make-up. Accordingly,Hasnaouiet al.(2011)thought that the composition (including anthocyanin)of the pomegranate fruits determined by cultivar rather than cultivation location. Furthermore,as Table 3 shown,anthocyanin content had a strongly significant positive correlation with SSC and TA (＊＊,P＜0.01),unlike the previous report that anthocyanin content had significant positive correlation with SSC but negative with TA (Dafny-Yalinet al.2010).

3.3.PCA analysis

To achieve a better understanding of the trends and relationships among the studied 20 cultivars,five PCs represented 85.81% of the total variation (Table 5) and provided a good summary of data. Meanwhile,the analysis of two-dimension scatter plots displayed fruit quality distribution according to the five principal components(Fig.2). From Table 5,PC1 representing 32.36% of total variance was highly positively contributed by aril moisture percentage,L＊ value and hundred-aril weight while negatively by anthocyanin content and a＊ value. PC2 accounted for 25.33% of the total variation. It correlated positively with fruit weight and TA,and negatively with the ratio of SSC to TA,fruit shape index and a＊ value. PC3 contribution rate was 12.29%,positively linked to vitamin C content,and negatively linked to fruit shape index. PC4 with contribution rate 8.12% and PC5 accounted for 7.71%.Taken together with Fig.2,such information indicated that fruit morphological characteristics including fruit weight,b＊ value,a＊ value and fruit shape index,and anthocyanin content and SSC/TA in arils were more contributed to evaluate fruit quality.

Fig.2 Scatter plots of principal component analysis of 15 fruit and aril quality parameters of pomegranates. FW,fruit weight;FD,fruit diameter;FL,fruit length;FSI,fruit shape index;HAW,hundred-aril weight;AMP,aril moisture percentage;SF,seed firmness;AC,anthocyanin content;VC,vitamin C content;SSC,soluble solids content;TA,titratable acid.

The synthetical score was the accumulated sum of the factors’ score of each sample and the weight value of each principle component (Nieet al.2019). The 20 cultivars were ranked according to the comprehensive scores. The higher the score,the better the comprehensive characteristics of fruit quality. The results showed ‘Yushiliu No.1’,‘Tunisia’FY,‘Taishanhong No.2’,‘Mollar’ and ‘Tunisia’ XY gainedhigher scores,and two ‘Tunisia’ fruits ranked the top five(Table 6),suggesting ‘Tunisia’ adapted to different climatic conditions in China,while ‘Yushiliu No.1’ and ‘Taishanhong No.2’ were prominent in fruit size. Moreover,the similar conclusion that ‘Tunisia’ was appropriate for popularization,also referred by Xueet al.(2017). Soft-seed cultivar ‘Mollar’had high comprehensive scores,and was a good option for fresh consumption,as it was observed in ‘Mollar’ from Spain(Alcaraz-Mármolet al.2017).

Table 5 Eigenvalues and proportion of variation associated with each principal component in pomegranate cultivars

Table 6 Final marks from the rotated component matrix of the principle component analysis

3.4.Cluster analysis

The dendrogram of hierarchical cluster analysis was conducted using Ward linkage and squared Euclidean distance. The 20 cultivars were divided into six main groups in the cluster analysis at a squared Euclidean distance of 9 (Fig.3). The first group consisted of ‘Tunisia’ from four regions,‘Mollar’,‘Yanzhihong’ and ‘Daqingpitian’,and they were sweet soft-seed cultivars introduced from abroad,except the sour-sweet cultivar ‘Daqingpitian’ original from China. While bigger fruit size of ‘Taishanhong No.2’,‘Jinhong’,‘Dazitian’,‘Yushiliu No.1’ and ‘Yushiliu No.2’belonged to the second group,and they were sour-sweet cultivars except two ‘Yushiliu’ cultivars (sour). The third group was formed by soft-seed cultivars ‘Yunongzaoyan’,‘Hongshuangxi’ and ‘Hongruyi’ that they possessed red coloration of the husk and higher aril moisture. Hardseed cultivars ‘Taishanhong No.1’,‘Milu’,‘Dongyan’ and‘Yudazi’ were from the fourth group. The fifth group had only sour cultivar ‘Mudan’ with smaller fruit size. ‘Turkey’,‘Moyu’ and ‘Red Angel’ were clustered into the last group,and they ranked in the first three of anthocyanin content.In conclusion,the dendrogram of hierarchical CA could present a relationship among different cultivars due to similar characteristics clustered.

Fig.3 The dendrogram of 20 pomegranate cultivars based on 15 fruit and aril quality parameters by hierarchical cluster analysis.

4.Conclusion

Nowadays,fruit morphological traits and nutritional values in aril are studied widely,but little information is available in Chinese pomegranate cultivars. For this reason,20 cultivars grown in China were investigated. In view that fruitscharacteristics are influenced by agricultural conditions and climatic factors,we collected fruits from several commercial orchards and satisfied water and fertilizers requirements.The results revealed that significant differences were found in the fruit morphological characteristics,tastes and nutritional values among cultivars. ‘Yushiliu No.1’,‘Taishanhong No.2’,‘Mollar’ and two ‘Tunisia’ (FY and XY) proved to be excellent cultivars due to their comprehensive scores,of which,bigger

size of ‘Taishanhong No.2’ and ‘Yushiliu No.1’ were bred by Chinese scientists. ‘Moyu’,‘Red Angel’ and ‘Turkey’,with outstanding higher anthocyanin content could be used as the source of natural red food colourants,while ‘Hongruyi’and ‘Hongshuangxi’ original from China,possessed higher vitamin C,aril moisture and lower TA in aril,as well as red husk,and might be also promising cultivars for further various utilization. Furthermore,maturity index classification was established for Chinese pomegranate cultivars.According to the hierarchical cluster analysis,the cultivars with similar traits were classified into six groups,helpful for exploring the potential genetic relationship of 20 cultivars.In conclusion,the obtained results can be beneficial to establish core germplasm and explore potential commercial values.

Acknowledgements

This research was funded by the Key R&D and Promotion Projects of Henan Province,China (192102110152).

Declaration of competing interest

The authors declare that they have no conflict of interest.