| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 93 === Hermaphroditic plants are desired for commercial papaya production in most countries. However, the sex type of papaya plant is difficult to be identified during the seedling stage. To obtain the hermaphroditic plants, papayas used to be cultivated by simultaneously planting 2-3 seedlings in a pit. This cultivated method is not efficient and economic. Thus, the development of a rapid technique for sex identification of papaya and the genetic study of sex determination in papaya are very important to papaya industry. DNA-based markers have been recently applied in sex identification of several plants. This study attempted to use the published papaya sex-specific SCAR primers to identify 39 papaya cultivars or lines in Taiwan. The results showed that SCAR W11 and SCAR T12 existed in all hermaphrodite and male plants, but not in the female plants. The DNA fragments corresponding to W11 SCAR of ‘Sunrise’, ‘TSS No.7’, ‘Thailand’, ‘Florida’, NTU005 and NTU007 were cloned and sequenced. Totally 832 nucleotide sequences from the hermaphrodite and male W11 SCAR were determined, and their sequences were similar. The DNA fragments corresponding to T12 SCAR of ‘Sunrise’, ‘TSS No.7’, ‘Florida’, NTU005 were also cloned and sequenced. Totally 838 nucleotide sequences from the hermaphrodite and male T12 SCAR were determined, and their sequences were similar. Based on the different sequences between hermaphrodite and male T12 SCAR, the primer pair T12-165F and T12-834R was designed to amply PCR products only in male plants of ‘Florida’, II-3-4’91 and VII-7-7’91, but not in hermaphrodite and female plants of ‘Sunrise’ and ‘Thailand’. Nonetheless, it needs strict PCR conditons to make the male-specific band appear steadily and needs more other papaya cultivar samples to certify if it was really a male-specific marker in general. SCAR marker is more reliable and reproducible and is a suitable marker for the precise and rapid identification of sex in papaya.
Estimation the genetic relationships among papaya cultigens of Taiwan and other regions and development of a cultivar identification tool based on random amplified polymorphic DNA (RAPD) were established in this study. Twenty-nine selected primers generated a total of 122 reproducible polymorphic amplification fragments among 44 papaya cultigens and other Vasconcellea species of Caricaceae. The average genetic similarity coefficients of 39 papaya cultigens was 0.662 and ranged from 0.322 for a breeding line of NTU selection and ‘Kapoho’ to 0.942 for K1 and K5. The UPGMA and principal component analysis showed a clear distinction into two clusters reflecting the different geographical origins, Taiwan and other regions. The 30 papaya cultigens of Taiwan clustered into two groups that reflected their origins from different breeding or selection programs. A combination of four primers with five markers was found to be optimum for the discrimination of the 11 papaya cultigens of Taiwan. The marker system can discriminate GMO papaya from other papaya sources of Taiwan. This study showed that RAPD could readily dissect genetic differences between the closely related papaya cultivars or lines and provide a simple, quick and economic method to differentiate the difference among papaya population of Taiwan.
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