| Apple(Malus × domestica Borkh)is one of the most important economic tree crops in China,and its area and output rank first in the world.China is one of the origin and evolution centers of apple genus in the world,and it has abundant germplasm resources.In the past 50 years,China has selected and breeded a large number of apple varieties with various characteristics by various breeding methods such as hybridization,bud selection,seed selection,and mutagenesis,and some apple varieties have also been introduced from abroad.However,we lack clear understanding of the source,genetic variation and genetic relationship of some apple varieties.In this study,the important economic traits of 300 apple cultivars were statistically analyzed to understand the genetic variation of fruit traits in apple germplasm resources in China.And draw the pedigree of the main varieties of the three families.At the same time,85 SSR markers were used to analyze the genetic relationship of 159 apple germplasm resources collected,in order to provide a theoretical basis for the evaluation and mining of apple germplasm resources and apple breeding parents.The main results are as follows:(1)Among the 300 cultivated apple varieties,152 were selected from abroad,accounting for 50.67%;148 were selected in China,accounting for 49.33%.According to the classification of variety sources,the most varieties were obtained by cross(149,49.67%),followed by bud varieties(90,30.00%),breeding varieties(32,10.67%)and mutagen varieties(1,0.33%),of which 28 are unknown sources,accounting for 21%.According to the classification of fruit peel,the red apple varieties were the most(262,87.33%),followed by the yellow-skin apple varieties(21,7.00%)green-skin apple varieties(17,5.67%).The fruit ripening period of 300 apple varieties is mainly concentrated in August,September and October.Among them,mature varieties in September accounted for the most,accounting for 34%;mature varieties in October and August accounted for 29.33%and 20.33%respectively;mature varieties accounted for 11.33%in July;very early(June)and very late(In November),the proportion of varieties was the smallest,accounting for 2.67%and 2.33%respectively.According to the pedigree analysis based on 300 apple varieties,the hybrid progeny selected from the parental combinations with different geographical origins or botanical traits had strong heterosis.(2)85 pairs of primers were screened for 8 apple varieties,and 15 pairs of primers with high polymorphism,clear band type and high resolution were selected to analyze genetic diversity and genetic relationship of 159 apple germplasm resources.56.47%of the primers could successfully amplify a specific SSR marker band;38.82%of the primers were polymorphic.A total of 98 alleles were amplified from 15 pairs of SSR primers in 159 apple materials,and each pair of primers amplified 6.53 alleles on average.The polymorphism information content(PIC)of the primers was 0.56-0.72 with an average of 0.64.The Shannon's Information Index(I)for each point varies from 0.92-1.66 with an average of 1.37.Different data indicate that 15 pairs of SSR primers can effectively reveal the genetic diversity of 159 provenances in apples.(3)159 apple materials were clustered by MEGA6.0 software,and cluster analysis was carried out according to rootstock,variety and all varieties.Cluster analysis of 43 Apple Rootstocks showed that apple rootstocks could be divided into six groups.Most of them are consistent with the traditional classification,but there are also different phenomena,which are supposed to be related to the spread and integration of wild resources.In this study,'Bianyehaitang' was classified into one class with Nic29,M9-T337 and PAJAM2.Cluster analysis of 116 cultivated apple varieties showed that the cultivars could be divided into five groups.Most of the cultivars with the same or similar pedigrees were clustered together,and the individual cultivars were distributed in other groups.'Hongrouguo' and 'Shouhong' were separately classified into one group.A cluster analysis of 159 apple germplasm resources showed that germplasm resources were divided into six categories.'Shouhong' in group I were clustered with the other three unrelated cultivars,suggesting that there might be more complex genetic diversity among the distant cultivars. |
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