Pollen Germination and Interspecific Hybridization of Torenia
Date Issued
2016
Date
2016
Author(s)
Lin, Ting-Ann
Abstract
Wishbone flower (Torenia fournieri Linden) is an important summer bedding worldwide. Taiwan-native and trailing Torenia benthamiana Hance could be used for breeding. Commercial T. fournieri cultivars, T. benthamiana, yellow wishbone flower (T. baillonii Godefr.), and tetraploid torenia hybrid (T. fournieri × T. benthamiana) Cb5-M612.were included in this study. The objectives were to 1) observe floral organ arrangements in relation to pollen transmission and pollination, 2) measure in vitro pollen germination, 3) observe pollen tube, capsule, ovule, embryo, and endosperm after self- and cross-pollination, 4) document progeny phenotypes from crossing various T. fournieri cultivars with T. benthamiana. In Cb5-M612 and T. baillonii, the base of longer-paired stamen had appendages, and the pollen sacs are fused. The filament extension, caused pollen sacs outward, resulting in lever action by insect forage to transmit pollen. Longer-paired stamen of Cb5-M612 positioned to lever action at 1 and 2 days after anthesis, whereas T. baillonii positioned from anthesis to 2 days after anthesis, and subsequently lost lever action due to the separation pollen sacs. Stigma of both species was bilabiate when longer-paired stamen reached the lever action position. Cb5-M612 and T. benthamiana had higher pollen germination percentage at anthesis, and decreased thereafter, while T. baillonii had lower pollen germination at 1 day before anthesis, and increased afterwords. Pollen from longer- and shorter-paired stamen in Cb5-M612 had higher germination percentage at anthesis. In T. baillonii, pollen from longer-paired stamen had the lowest germination percentage at 1 day before anthesis. The germination of pollen from shorter-paired stamen did not differ 1 day before or after anthesis. Pollen germination on stigma and pollen tube growth to the end of style was observed at 8 hours after pollinating Cb5-M612 with T. fournieri ‘Kauai Rose’, but no sign of pollen germination or pollen tube growth was seen in the reciprocal cross. Pollen germination and pollen tube growth could be observed at eight hours after pollinating T. baillonii with T. benthamiana, but no seed was obtained subsequently. Anatomical observation revealed that embryo and endosperm developed well after self-pollinating T. baillonii without emasculation. Contrastly, after emasculation, those self-pollinated at two days before anthesis resulted in retarded embryo, and degenerating endosperm at 16 days after pollination, when embryo only reached globular stage. For T. benthamiana × T. baillonii with, capsule enlarged only slightly at 4 days after pollination, embryo reached globular stage and endosperm continued to develop at 8-12 days after pollination, and ovule was shriveled and both embryo and endosperm were degenerating at 16 days after pollination. Torenia fournieri ‘Kauai’ series, ‘Duchess Rose’, and ‘Panda Rose’ were pollinated with T. benthamiana. Their hybrid ovules were then cultured on medium containing 3 g·L-1 sucrose, 7 g·L-1 agar, and 8 g·L-1 Hyponex No.1 at 18 days after pollination. Germination of the hybrid ovules ranged from 70% to 90%. The F1 hybrid progenies between T. fournieri and T. benthamiana were all trailing, and the flower color ranged lavender to violet, with yellow spot near throat on labiate corolla lobe. Internode and inflorescence lengths of the progenies were shorter when ‘Kauai Rose’ was used as female parent, as compared to ‘Clown Rose’ and ‘Duchess Rose’.
Subjects
Torenia
Pollen Germination
Interspecific Hybridization
Type
thesis
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