Study On Diversity Of Avocado (Persea Americana Mill) Germplasm Accessions

Avocado(Persea americana Mill)is an evergreen fruit tree belonging to the genus Persea and the family Lauraceae.It is a tropical tree native to Mexico,Central America and South America but it is now grown worldwide.Since avocado is an outcrossing species,great genetic diversity has been generated throughout the evolution process of this crop.This study has aided not only the classification and management of avocado germplasms,but also been useful for innovation and utilization the germplasms from the phenotypic and molecular level.The main results are summarized as followings:(1)On phenotypic analysis,the Euclidean distances based on R-type cluster between 17 phenotypic traits used in the study were far.The range was between 1.13 and 34.87,which indicated that these traits except the overlapping traits that were leaf margin and leaf surface were independent relatively,and could especially indicate that the leaf length was a good morphological index to distinguish the avocado germplasms well in avocado phenotypic analysis.The range of Euclidean distances based on Q-type cluster between 112 avocado accessions used in the study was 0.76-10.82.All the accessions were divided into three main groups in the distance of 9.70.Group 1 included 1 accession(FRT2)that collected in Hainan which had the longest leaf length.Group 2 included 2 accessions that were FET from Guangxi and Y24-15 from Hainan.Group 3 included a total of 109 accessions,which were consist of 10 accessions collected from Yunnan,5 accessions(GY 10,GK3,HS,BK,GK2)collected from Guangxi and 94 accessions collected from Hainan.(2)As the avocado leaves are highly rich in impurities including polysaccharides and polyphenols,the study compared the merits of three kinds of DNA extraction methods.The results showed that the optimum extraction was 2 × CTAB-improved method.Using SSR-PCR optimal reaction system(20?L),which contained about 40ng DNA,1.5mmol/L Mg2+,0.15mmol/L dNTPs,0.5U rTaq polymerase,0.5?mol/L primers,was established by L16(45)orthogonal design.(3)The 23 SSR loci,which were better performance than others,were used to evaluate the genetic diversity of 112 avocado accessions.All the accessions were divided into four main groups in the genetic similarity coefficient of 0.71.Groupl included 1 accession(FET)that collected in Guangxi.Group 2 included 4 accessions(Y1-10,Y3-1,Y6-5,Y10-1)which were from Hainan.Group 3 included 2 accessions(HS,BK)that were collected from Guangxi.Group 4 included the remaining 105 accessions consisted of 10 accessions collected from Yunnan,3 accessions(GY 10,GK2,GK3)collected from Guangxi and 92 accessions collected from Hainan.(4)The 12 ISSR primers with good comprehensive performance were used to evaluate the genetic diversity of 112 avocado accessions.All the accessions were divided into seven main groups in the genetic similarity coefficient of 0.72.Groupl included 1 accession(YN006)that collected in Yunnan.Group 2 included 1 accession(Y26-1)which was from Hainan.Group 3 included 2 accessions(FET,BK)were collected from Guangxi.Group 4 included 1 accession(DL1)that was collected from Hainan.Group 5 included 4 accessions(YN005,YN010,YN016,YN020),which were collected from Yunnan.Group 6 included 18 accessions that collected from Hainan.The remaining 86 accessions consisted of 5 accessions collected from Yunnan,4 accessions collected from Guangxi and 77 accessions collected from Hainan,they all belonging to Group 7.