Zulkarnain, Zulkarnain (2003) BREEDING STRATEGIES IN STURT’S DESERT PEA, Swainsona formosa (G.Don) J.Thompson, USING IN VITRO AND IN VIVO TECHNIQUES. S3 thesis, University of New England, Australia.

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One of the impediments to the commercialisation of Sturt’s desert pea (Swainsona formosa) as a cut flower is the release of large amounts of pollen grains during anther dehiscence. These pollen grains may stain the petals and, so reduce the quality of the flowers. In addition, self-pollination can occur during transportation causing flowers to degenerate quickly. This project was undertaken with the objective to investigate strategies to overcome such problems through plant a breeding approach. Two strategies were employed, the induction of haploid plant production via anther culture and the induction of tetraploid plants using colchicine and oryzalin. Crossing diploid with tetraploid plants leads to the production of triploid plants. Either haploids or triploids are sterile and produce no pollen grains. The results of these two strategies are presented in this thesis. The determination of chromosome number is a prerequisite step for both strategies. This study showed that by using root tip and anther squashes, the number of chromosomes in S. formosa was 2n = 2x = 16. This finding confirmed the base chromosome number of x = 8 in the tribe Galegeae. Understanding plant embryology is not only crucial for taxonomic purposes but also for breeding programmes. Therefore, the embryological development and sexual reproduction of S. formosa was also investigated. The anthers of S. formosa were found to be tetrasporangiate, with a 3-layered wall below the epidermis. The wall was comprised of a layer of endothecium, middle layer and secretory tapetum. Pollen grains were triporate and shed at a 2-cell stage. The ovules were campylotropous with a zigzag micropyle. Multiple embryo sacs were occasionally found but only one mature embryo was formed in the seed. The seed coat was composed of a single layer of thick-walled palisade cells on the outside followed by a single layer hypodermal sclereids on the inside. Seed germination was epigeal. In order to support the breeding programme of S. formosa, methods of pollen preservation were also developed. It was found that pollen grains could be stored at 4oC for up to 28 days without significantly losing their viability. Pollen longevity could be extended beyond 2 months when stored at -10oC and under dry conditions. These findings provided a simple and economically sound method for storage of S. formosa pollen. Although pollination was often prevented by the presence of stigmatic cuticle, the stigma was found to be receptive from one day before anther dehiscence. The receptivity reached its peak within 4 days after anther dehiscence. These results provide a valuable background to the conventional breeding of this species to create hybrids through cross-pollination. The size of floral buds has been effectively used as a morphological predictor to determine the stage of microspore development within anthers in S. formosa. Therefore, anther preparation during subsequent experiments relied on this indicator. Of the variables tested, auxin and cytokinin were found to play a key role in anther development following culture initiation. Callus proliferation was enhanced by pre-treating the anthers with mannitol starvation at 4oC followed by introduction to a double-phase medium supplemented with Ficoll-400. Embryogenic callus was produced and embryogenesis was detected but these embryos did not originate from microspores. Instead, the embryos grew from sporophytic tissue of the anther wall. The embryos failed to develop further when subcultured to root and shoot induction medium due to a high frequency of hyperhydration. Morphogenesis was detected but shoots and roots developed poorly. This investigation also revealed that proline could be used as a biochemical indicator for early detection of embryogenesis. Since the induction of polyploidysation will only be effective if the treatment is given during the active vegetative stage, the conversion from vegetative to reproductive growth in S. formosa was investigated with particular emphasis on the effect of different photoperiods. Although photoperiod affected the time required for first flower initiation, the number of nodes before the plant entering the reproductive stage was not affected by photoperiod and presumed to be set genetically. It was found that under artificial photoperiods of 16, 12 and 8 hours the 12th and 11th nodes were the critical nodes for the main and side stems, respectively. Meanwhile the 10th and 8th nodes were found to be critical for main and side stems of plants grown under natural photoperiods ranging from 12 to 16 hours during their life cycle. Histological examination indicated that when the plants were grown under 12 – 16 hours photoperiods the first floral bud formation was initiated within 56 – 60 days after germination, thus this period was considered as the critical time for the conversion from vegetative to reproductive growth in S. formosa. Following from the previous experiments, polyploidy induction using antimitotic chemicals was carried out as early as possible in the life cycle of the plant. However, seed treatment with colchicine was found to be detrimental and resulted in no polyploid induction. Seedlings, in contrast, were found to be more responsive to either colchicine or oryzalin application. Unfortunately, the rate of conversion was very low. It was also noted that the ployploidysation in S. formosa was unstable. Reversion to diploid characteristics in F1 generation has become a major problem in obtaining plants with stable tetraploid chromosomes. Some new findings relating to the breeding aspects of S. formosa are reported here although the induction of haploid and triploid plants was unsuccessful. These results can, however, be used as a valuable reference for future work on breeding programmes to create quality flowers in S. formosa.

Type: Thesis (S3)
Subjects: S Agriculture > SB Plant culture
Depositing User: Zulkarnain
Date Deposited: 27 Dec 2017 00:50
Last Modified: 27 Dec 2017 00:50

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