Analyses Of The Genetic Diversity Of 167 Wavermelon Germplasm

Watermelon is an important fruit in the world,which is one of the most popular fruits in summer.Because of long-term artificial domestication and hybridization,the genetic background of watermelon breeding materials becomes very narrow.In order to break this bottleneck and use watermelon germplasm resourceseffectively,we should collect and study watermelon germplasm resources continuously and deeply,especially for systematical identification and evaluation of the existing germplasm resources.In this study,167 watermelon germplasm resources were collectedfrom the different regions of the world,using morphological markers and SSR molecular markers,combined with the diversity analysis,clustering analysis and principal coordinate analysis and correlation analysis method,to study their genetic diversity synthetically.Main results are listed as follows:1.29 morphological characters were used to reveal the genetic diversity of 167 watermelon accessions.The Shannon diversity index range was from 0.54 to 2.03 with a mean of 1.50.Mean value of quality charactersand quantitative characters were 1.16,and 1.71,respectively larger than quality traits.The maximumdiversity index was got from seed length(2.03),however the minimum diversity index was surface smoothnessis(0.54).Range of variation coefficient was from 16.43% to 90.73%,and the average coefficient of variation was 34.12%.The largest coefficient of variation was the edge of sugar content(90.73%),while the smallest was width of cotyledon(16.43%).2.All germplasmmaterials are divided into five groups by clustering analysis based on morphological characters.Asian materials were mainly clusted into group?and?.Africa materials were mainly clusted into group?.North America materials were mainly clusted into the group ?.Group ? is a mixed group.Principal coordinates analysis results showed that variance contribution rateof the first three principal coordinatesare 16.24%,10.04% and 8.29%,respectively,which accumulates to 34.57% of the total variance.Allgermplasm materials were divided into four regions,which was basicly consistent with the results of clustering analysis.3.The genotyping of the 167 materials were detected by 22 SSR molecular markers.107 allels were detected,with each primer detecting 2-8 allels per loucs.The average alleles detected for each primer was 4.86.Diversity index range was from 0.54 to 1.61,with a mean of 0.94.Expected heterozygosity(He)range was from 0.27 to 0.77,with a mean of 0.52.Polymorphism information content(PIC)range was from 0.25 to 0.73 with a mean of 0.45.4.The population structure analysis based on the fingerpringting data revealed that the 167 germplasmmaterials were divided into four groups,P1 group containing 13 germplasms(7.78%)and P2 group containing 64 germplasms(38.32%),P3 group containing 73 germplasms(43.71%)and P4 groups containing 17 germplasms(10.18%).The Q values of all germplasm materials were analyzed,and the Q valueof 127(76.05%)germplasm materials were higher than 0.80,while the Q value of the other 40(23.95%)germplasm materials are between 0.49 and 0.80.5.The dendrogram for the 167 watermelon germplasm was analyzed by UPGMA method,which showed that all materials was divided into four groups(????).Among them,material 1 and 55 were divided into group I,and the group?had 148 materials,and the group ? had 17 materials.Principal coordinate analysis showed that all materials can be divided into two large regions,corresponding with clustering 2 broad categories.The materials in first region can be divided into 3 smallerregions,which was consistent with the result of clustering analysis.6.The results oftwo kind markers clustering analysis were detected by mantel test,and correlation coefficient(r)of morphological markers and molecular markers was 0.43,suggesting the consistency of the results of two methods was low.