Embryo rescue and polyploidization of interspecific crosses between Torenia fournieri and T. benthamiana
Date Issued
2012
Date
2012
Author(s)
Guo, Meng-Hua
Abstract
Wishbone flower (Torenia fournieri Linden) is one of the important summer bedding plants in Taiwan. There are Taiwan-native Torenia species, which could be used for breeding to develop domestic cultivars. However, post-fertilization barriers were known to exist when interspecific crossing. The objectives of the study were to 1) develop suitable conditions of ovule culture for producing progenies from crossing T. fournieri ‘Clown Rose’ and T. benthamiana, 2)investigate the floral traits of the progenies, 3) to observe endosperm and embryo development of selfed and crossed progenies, 4) determine the cold tolerance in progenies from crossing T. fournieri and T. benthamiana, and 5) induce polyploidization of the hybrid progenies with colchicines treatments to improve ornamental characteristics.
The ovules were taken 12, 14, 16, and 18 days after pollination (DAP) from crossing T. fournieri ‘Clown Rose’ with T. benthamiana and were cultured on Hyponex medium. Germination percentage was higher (12%-31%) when ovules were taken at DAP 16 and 18, as compared with 0.4% at 12 and 14 DAP. Time after pollination is vital for the success of ovule culture of the crossed progenies.
The ovules were taken 8, 12, and 16 DAP from crossing T. fournieri ‘Clown Rose’ with T. benthamiana and were higher cultured on 1/2MS medium with 0%, 3%, 6% or 12% sucrose. Germination percentage was higher when ovules were taken at 16 DAP than there at 8 or 12 DAP. Culture medium with 0%, 3%, or 6% sucrose increased germination percentage, while 12% sucrose significantly reduced germination. Capsules of self-pollinated T. fournieri ‘Clown Rose’, and those cross-pollinated with T. benthamiana were collected and sectioned at 8, 12, and 16 DAP. More embryo and endosperm development were observed in self-pollination than cross-pollination. At 8 DAP, embryo sac was fully occupied by endosperm in self-pollinated T. fournieri ‘Clown Rose’, whereas cross-pollinated ones had fewer embryo and endosperm cells. At 12 DAP, endosperm cells were enriched, and the embryo was at torpedo stage in self-pollinated T. fournieri ‘Clown Rose’. The cross-pollinated embryo remained at globular stage at 12 DAP. At 16 DAP, mature-seedlike embryo sac with thick-walled endosperm and enlarged endothelial cells were observed in selfed ‘Clown Rose’, whereas the development of cross-pollinated endosperm was significantly slower, without complete endothelial cells.
The hybrid progenies from crossing T. fournieri ‘Clown Rose’ with T. benthamiana were semi-prostrate. Corolla color ranged between violet and purple-violet. All flowers had papillae petals with yellow dot and corolla tube with strip pattern.
Torenia fournieri ‘Clown Rose’, T. benthamiana, and their hybrids were placed in natural light rooms with day/night temperature 30/25 oC and 15/13 oC for two months. T. fournieri ‘Clown Rose’ plants died when grown of 15/13 oC for two months, while the hybrid progenies flowered although grew slowly.
To induce polyploidization of progenies from crossing T. fournieri ‘Clown Rose’ with T. benthamiana, the stem section of the hybrids were treated in vitro with 1.25, 2.5, or 5 mM colchicine for 24, 48, 72, or 96 hours. A low concentration (1.25 mM) of colchicine concentration increase survival rate and plant height of the explants. The colchicine-induced polyploidy progenies had bigger pollens and flowers, longer guard cells, and fewer stomata density than the diploid ones. A fertile polyploid hybrid was obtained, as the progeny produced seeds that could germination. The ploidy level of the colchicine-treated individuals were analysed by flow cytometry. These techniques confirmed that, of the 14 putative polyploids, only code no.234 was tetraploid, and thirteen were mixoploid.
Subjects
torenia, interspecific hybridization
embryogenesis
embryo rescue
polyploidization
Type
thesis
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