Genetic diversity analysis in imported wild melon (Cucumis melo L.) germplasm resources based on morphological characters

Abstract: 【Objective】Melon (Cucumis melo L.) is one of the most important crops with a high variabilityin fruit traits among different gemplasm, ranging from non-sweet fruits that are inedible or harvested be⁃fore maturity and consumed as vegetables, to sweet fruits with high sugar concentrations that are eaten insalads or as dessert, melon could be divided in two group based on ovary pubescence or edible value withmelon group and wild melon group, wild melon genotypes possess slender vines, monoecious flowers andsmall, inedible fruits, mainly distributed in Asia, Africa, and Oceania etc. India is rich in wild melon andsemi-wild melon germplasm resource, and was considered as origin center of melon according to the recent research results, studying on wild melon originated form India is help for exploring melon originatingand spreading, the aims of this study were to provide the scientific basis for the evaluation, classification,and effective utilization of the imported wild melon germplasm which mainly oriented from India.【Methods】100 accessions wild melon germplasm introduced form the North Central Regional PI Station (the U.S.A.), which originated form India (92 accessions ), Costa Rica (1 accession), Maldives (2 accessions), Amer⁃ica (1 accession) and China (1 accession), all germplasm planted at Zhongmou County, Zhengzhou, HenanProvince, China, fruit characters data were collected during planting period, including 7 quality charac⁃ters with fruit shape, ground color of fruit skin, vein color of fruit skin, vein shape of fruit skin, flesh color,flesh texture, flesh taste, and 9 quantitative characters with fruit length, fruit width, index fruit shape,weight of single fruit, flesh thickness, total soluble solid content, 1 000-seed weight, seed length, seedwidth to analyze the genetic diversity. To carry out germplasm clustering and genetic relationship analysis,thin skin melon‘Guang xi li gua’, thick skin melon‘Kalakekouqi’‘Sairekekouqi’, wild melon‘Mapao’‘Wild melon’, dudaim melon‘Kangua’which originated from China were also used as stan⁃dard germplasm in this study.【Results】The diversity index (Shannon’s index, H’) range of quality charac⁃ters for the imported melon germplasm was 0.17-1.88 with the average of 0.98, ground color of fruit skin,vein color of fruit skin, vein shape of fruit skin had greater diversity index with excess of 1.0, ground colorof fruit skin the manly showed light yellow (42% of total germplasm) and yellow (29% of total germplasm),vein color of fruit skin were mainly deep green (19% of total germplasm), red brown (17% of total germ⁃plasm), vein shape of fruit skin were mainly dot (18.0% of total germplasm), speckle (22.0% of total germ⁃plasm), streak (23.0% of total germplasm), and 30% of total germplasm had no vein shape of fruit skin.Flesh texture and flesh color were mainly crisp and white with 91.0% and 80.0% of total germplasm re⁃spectively, most germplasm flesh taste were sour (96.0% of total germplasm) and a few germplasm fleshtaste were bitter (4.0% of total germplasm). Quantitative characters for the imported melon germplasmwere 0.98 and 1.79, respectively, which showed quantitative characters had more rich genetic diversity,the variation coefficient of 5 fruit quantitative characters were more than 30%, the maximum variation coefficient was that of fresh fruit weight with 100%, and flesh thickness followed it with 63.27%, fruit diameter, fruit shape index, seed width had smaller variation coefficient with 4.22% , 18.01% , 16.92 and15.15%, respectively. Germplasm cluster analysis showed that all melon germplasm could be divided intotwo groups at Euclidean distance 3.0 based on UPGMA method with GroupⅠand GroupⅡ, GroupⅠincluded standard germplasm of cultivated melon‘Guangxi Ligua’‘Kalakekouqi’‘Sairekekouqi’and dudaim melon‘Kangua’, were total 92 accessions germplasm with complex fruits traits, could be consideredas semi-wild germplasm group, GroupⅡ included standard germplasm of wild melon and were total 14 ac⁃cessions germplasm with light fruits (most fruits were less 0.1 kg) and acid or bitter of flesh taste, could beconsidered as wild germplasm group, furthermore, GroupⅠcould be divided into Subgroupⅰthat included standard germplasm of thin skin melon and Subgroup ⅱ that included standard germplasm of thickskin melon, which mean thin skin melon and thick melon maybe evoluted from wild germplasm indepen⁃dently.【Conclusion】Fresh fruit quantitative characters of the imported melon germplasm had more rich ge⁃netic diversity than quality character, and fresh fruit weight had the maximum variation, was consistentwith the results of previous studies on cultivated melon and wild melon. The results of germplasm clusteranalysis showed that wild melon germplasm mainly oriented from India were closely correlated to Chinacultivated melon and wild melon germplasm, e.g. most imported wild melon germplasm could be clusteredone group with thick skin melon‘Kalakekouqi’‘Sairekekouqi’from China, showed that thick skin mel⁃on had more closed relationship with wild melon germplasm, inferred the imported wild melon germplasmmay play important role for the origin and evolution of China cultivated melon, and India may be a origincenter of cultivated melon.