| Summary: | 碩士 === 國立屏東科技大學 === 農園生產系所 === 104 === Guava (Psidium guajava L.) is an important economic fruit crop, belonging to Myrtaceae family. Through cultivar introduction and selection, bud sport and hybridization over years, many cultivars have developed in Taiwan. Due to the similarity in their appearance, different cultivars cannot be easily distinguished from each other. Therefor to establish a rapid and effective method for cultivars identification will help to select parents and to improve breeding efficiency. In this study, simple sequence repeat (SSR) markers in guava have been developed based on ‘Pearl’ draft genome sequence database using next generation sequencing to establish molecular fingerprinting of 32 guava cultivars and breeding lines in Taiwan. In total 30.4 Mb (6.72% of the assembled genome) of repetitive elements (excluding low-complexity sequences) was identified in guava genome. Among them, 5.39 Mb (1.19% of the assembled genome) was identified as SSRs with di-, tri-, tetra-, penta- and hexa-nucleotide motifs. There were 59,883 SSR loci in the assembled genome. The most abundant type of repeat motif was dinucleotide (68.9%), followed by trinucleotide (22.7%). The most dominant repeat motif in dinucleotide motifs of SSRs were (AG)n (13.2% of the total assembled genome), followed by (CT)n (12.9%). In total 262 SSR primer pairs were designed and screened based on their amplification quality (based upon production of polymorphic bands without stutter bands and repeatability). Forty-one SSR primer pairs met the quality standand (28%), and were further used for 32 guava genotype analysis. Total of 168 alleles were detected, from these 41 primer pairs ranging from two to seven with an average of 4.1 alleles per locus. Three to twelve band configurations were produced by each primer pair with an average of 7. Mean values of gene diversity index of each primer pair was 0.62, while that observed heterozygosity was 0.17. The average polymorphism information content and probability of identity of all loci were 0.58 and 0.097, respectively. Cluster analyses based on NJ (Neighbor-Joining), UPGMA (Unweighted Pair-Group Method with Arithmetic mean) and PCoA (Principal Coordinate Analysis) methods using different coefficients showed that the genotypes analyzed in general can be divided into four basic clusters. On the other hand, six selected SSR primer pairs were employed to analyze genetic diversity of ‘Emperor’ and its parents and another 12 guava cultivars in Taiwan. In total 25 polymorphic bands and 31 band configurations were amplified from these primer pairs. Except ‘Seedless Shui-Mi’ and ‘Crystal’, the rest of genotypes were able to distinguished from each other using these six SSR primer pairs. In addition, five out of these six primer pairs produced both parents-specific alleles in ‘Emperor’. This will help to identify cultivar ‘Emperor’ and maintain the rights of nursery suppliers who owns ‘Emperor’ cultivar patent.
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