| Summary: | 碩士 === 國立屏東科技大學 === 農園生產系 === 92 === One of the promising goals of guava improvement is the breeding of seedless varieties. In order to understand the potential causes of seedlessness and to make use of this knowledge in seedless breeding and cultivation practices, studies have been undertaken to determine ploidy levels, pollen viability, fruit set, and crossability of seedless guava cultivars and lines. Two leaf types, normal and round shapes were identified in seedless guava. Cultivars displaying either leaf type were analyzed by flow cytometry to assess ploidy levels. ‘Normal-leaf’ cultivars were determined to be diploid whereas most ‘Round-leaf’ cultivars were tetraploid with a few being triploid. The pollen shape of diploid cultivars was triangular and that of the tetraploid lines was square with a few pentagonal or round pollen grains also observed. The in vitro pollen germination rate of diploid and polyploid cultivars or lines was tested at the temperatures between 15℃ to 35℃. Germination rate was significantly lower at 15℃; however, there was a tendency for diploid cultivar pollen to have a higher rate of germination than ployploid lines. The rate of germination was also observed over an extended period of incubation for diploid and polyploid lines at 25℃. Germination was nearly completed after 4 hours of incubation in both diploid and polyploid cultivars and lines. Pollen collected from different months of the year also showed a higher germination rate in diploids than in tetraploids. However, pollen germination rate did not differ significantly among months within a year. The pollens from diploid cultivars or lines, both seeded and seedless, grew vigorously after open pollination and selfing. Their pollen tubes can reach to the ovary or ovules 2-3 days after pollination. Pollen tube growth in polyploid cultivars generally did not grow as well as that of diploid cultivars. Only a few pollen tubes can reach the ovary 2-3days after pollination and most of pollen tubes stay in the lower regions of the style. Regarding the effect of pollination on fruit set, all of the treated fruit in ‘Jen Ju Ba’ and ‘Shuei Jing Ba’ dropped off from the plants two weeks after anther emasculation at the bud stage. Treatments of open pollination, selfing, and cross pollination with ‘Shuei Jing Ba’ resulted in 80-90% fruit set in ‘Jen Ju Ba’. However, ‘Shuei Jing Ba’ did not produce any fruit in any of the treatments except in open pollination, which had 20-30% fruit set. Tai Guo Ba seedless varient also had very low fruit set in all pollination treatments. In terms of crossability, seeded diploid guava crossed successfully with both seeded and seedless diploids. In contrast, seedless diploid and polyploid guava achieved only low fruit set in all pollination treatments.
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