| Chinese bayberry (Myrica rubra) is native to China and has been cultivated for more than2000years with abundant germplasm resources. Limited molecular markers have been developed and applied to evaluate genetic diversity and management of genetic resources. This thesis presented the development of large set of simple sequence repeat (SSR) markers from a genome survey and preliminary genetic diversity of Chinese bayberry androphytes. It will provide a basis for genetic map construction and breeding in the future, the main results were summarized as followings:1. Development of simple sequence repeat (SSR) markers from a genome survey of Chinese BayberryHere we report, for the first time, a genome survey of whole genome shotgun data of Myrica rubra to develop a large number of simple sequence repeat (SSR) markers to analyse the genetic diversity of the common cultivated Chinese bayberry and the relationship with three other Myrica species. The whole genome shotgun survey of Chinese bayberry produced9.01Gb of sequence data, about26x coverage of the estimated genome size of323Mb. The genome sequences were highly heterozygous, but with little duplication. From the initial assembled scaffold covering255Mb sequence data,28,602SSRs (≥5repeats) were identified. Dinucleotide was the most common repeat motif with a frequency of84.73%, followed by13.78%trinucleotide,1.34%tetranucleotide,0.12%pentanucleotide and0.04%hexanucleotide. From600primer pairs,186polymorphic SSRs were developed. Of these,158were used to screen29Chinese bayberry accessions and three other Myrica species:91.14%,89.87%and46.84%SSRs could be used in Myrica adenophora, Myrica nana and Myrica cerifera, respectively. The UPGMA dendrogram tree showed that cultivated Myrica rubra is closely related to Myrica adenophora and Myrica nana, originating in southwest China, and very distantly related to Myrica cerifera, originating in America. 2. Exploring the genetic diversity of Chinese bayberry androphytes and the potential use in cross breeding programsChinese bayberry is generally dioecious, the female plants have been cultivated for fruit and studied extensively, but male individuals (androphyte) have gained very little attention in the past. Here we described the morphological variation of the male followers in a collection of139androphyte individuals, and compared their genetic diversity with91cultivars using13polymorphic simple sequence repeats (SSR). The staminate inflorescences can be classified in three colors (yellow-green, yellow-red and red) and three shapes (club, cylindrical and long-conical), Yellow-red color and long-conical shape is more frequent. We found that the number of alleles, expected heterozygosity (He), and polymorphism information content (PIC) were slightly lower in the androphyte population than in cultivars, but there was no significant difference (P>0.05). Ten new alleles were found among androphyte individuals that did not exist in any of the cultivars investigated. The accessions of both cultivars and androphytes originating from the same region were generally clustered together. In Bi-qi and Ding-ao cultivars, we found one individual each bearing male inflorescences which are limited to a branch, while in Dong-kui, a large proportion of shoots can bear male flowers due to growing conditions and retarding regulator spray. The pollens can be used for crossing with other cultivars.3. Morphology by Scanning Electron Microscope (SEM) and viability of pollens from different sex individuals of Chinese bayberryScanning electron microscope observation was carried out with the pollens of Chinese bayberry from androphyte (male plant), female individuals with a mutant branch of staminate inflorescence and monoecious plant. The results showed that the size of pollen were in the range of (22.90-23.63)×(20.27-22.10) μm and and three germinal poles were2.90-3.03μm in diameter, respectively. The outside surface of pollen was even granular ornamented. The size of three sources’pollens showed no marked difference. Study on pollen viability through germination and I-KI staining method showed that the germination percentage of pollen was the highest from monoecious plant. The optimal culture medium is composed of5%sucrose,0.01%boric acid and1%agar. |
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