A Study On Molecular Identification And Genetic Evaluation Of Olive Cultivars In China

Olive(Olea europaea subsp.europaea var.europaea L.)is an evergreen tree species of the genus Olea in Oleaceae.It is a world-famous oil species,mainly cultivated in the Mediterranean region.According to statistics,there were as many as 1,250 records of olive cultivar names,which were scattered in 54 countries and regions.The problem of homonym and synonym was very serious.Since the 1950 s,more than 150 olive cultivars have been introduced to China from abroad and widely planted in Gansu,Sichuan,Yunnan and other provinces.The current cultivated area has reached about 110,000 hectares,which has produced important economic,ecological and social benefits.However,due to the long age of introduction,the poor management of cultivar records and other reasons,the nomenclature confusion of the olive cultivars,such as the homonym,the synonym,and the wrong name,was more serious,causing many inconveniences for the production and scientific research of olive in China.Based on the above problems,this study focused on the 113 accessions from Wudu olive orchard which was rich in germplasm resources.Olive cultivar identification,genetic evaluation and parental analysis of main cultivated cultivars were carried out using the SSR markers and the development of single-copy nuclear gene markers.The purpose was to provide a basis for further promoting the breeding and high-yield cultivation of olive cultivars in China.The main findings obtained are as follows:(1)Data integration was carried out on the two important olive cultivars SSR marker databases WOGBC(World Olive Germplasm Bank of Cordoba)and OD(Olea databases)in the world.The data difference between the same loci of the same cultivar was corrected.It was found that the allelic values of the same cultivar between the two database cultivars were not completely consistent,indicating that the phenomenon of homonym and synonym in olive cultivars was very common.Eight pairs of SSR primers shared among them were selected to identify the 113 olive cultivars from Longnan,Gansu province.A total of 26 olive cultivars were identified,with a success rate of only 23.0%.It can be seen that the SSR marker had obvious deficiencies in the olive cultivars identification.(2)Based on the olive genome,eight single-copy nuclear gene markers were successfully developed.The evaluation of genetic parameters of 20 olive cultivars showed that most of the eight single-copy nuclear gene markers were highly polymorphic loci.The NJ(neighbor-joining method)tree constructed based on the SNP variation can separate all the olive cultivars tested.Thus the accurate identification of the olive cultivars was achieved.(3)The NJ tree of 113 accessions was constructed based on the eight single-copy nuclear gene markers with O.europaea subsp.cuspidata as the out-group.According to the positional relationship on the branches of phylogenetic tree,nine unnamed olive cultivars were identified by reference literature analysis.Two synonyms and five homonyms were identified.13 wrong names were cancelled,and six cultivars were suspected.Finally,combined with the original record information,87 accessions and 61 cultivars were successfully identified.And it was concluded that the accessions numbered 98 was O.europaea subsp.cuspidata var.chrysophylla Lam.,introduced from abroad.(4)The genetic diversity and genetic structure of the 50 identified cultivars from 5 countries were analyzed using 14 SSR markers and 8 single-copy nuclear loci.It was found that there was a certain genetic differentiation between olive cultivars in different countries,but a larger gene flow effect(Nm>1)restricted this differentiation.Phylogenetic and Structure analysis showed that the genetic relationship between the selected olive cultivars in China and these from Italy was relatively close.According to the research conclusions and literature,he female parents of the five selected cultivars in China were all introduced from Italy.In fact,most of the orchards that were selected for new cultivar breeding were mixed with the cultivars from Italy.This should be the main reason for the close genetic relationship between the cultivars selected in China and those introduced from Italy.(5)Paternal analysis of the four main cultivars,‘Chenggu 32',‘Arbequina',‘Hojiblanca' and ‘Picual' in Wudu olive orchard was performed using 14 fluorescent-labeled SSR makers.A total of 114 germplasm resources including O.europaea subsp.cuspidata were used as candidate fathers.The results showed that the main true father of ‘Chenggu32' and ‘Picual' progenies was both ‘Arbequina',and ‘Manzanilla' was the main true father of ‘Arbequina' and ‘Hojiblanca' progenies together.This provided a basis for olive cultivars configuration and new germplasm creation.