Colchicine Treatment Of Seedlings Research Articles

Colchicine Alternatives for Chromosome Doubling in Maize Haploids for Doubled‐Haploid Production

In vivo production of doubled‐haploid (DH) lines in maize (Zea mays L.) routinely involves artificial chromosome doubling by colchicine treatment of seedlings. Because colchicine is a hazardous chemical, replacing it by less‐toxic alternatives would be highly desirable. Our objectives were to (i) test the efficacy of various herbicides alone or in combination with other herbicides or phytohormones as chromosome doubling agents, (ii) evaluate the efficacy of application of these chemicals for different durations and methods of delivery to meristems, and (iii) compare colchicine treatment with the most promising alternative treatment under economic aspects. Several antimitotic herbicides with different modes of action and two phytohormones were tested in various combinations and concentrations in four experiments for survival rate (SR) of germinated seedlings, reproduction rate (RR) measured as the proportion of D0 plants with seed set, and overall success rate (OSR) measured as the proportion of D1 ears with seed set obtained from the germinated seedlings. Amiprophos‐methyl (APM) and pronamid, applied with the seedling soaking method, outperformed all other alternative treatments tested and reached almost the same OSR as colchicine. Cost comparison between the best treatment, containing APM and pronamid, and the colchicine control showed that the total production cost per D0 plant with seed set was about 10% higher than for colchicine as a result of slightly lower OSR. In conclusion, APM combined in an optimum dosage with pronamid is a promising alternative to colchicine in view of the lower toxicity and similar rate of chromosome doubling in maize.

EVALUATING MUTATION BREEDING METHODS TO FAST-TRACK THE DOMESTICATION OF TWO AUSTRALIAN NATIVE CALANDRINIA SPECIES FOR ORNAMENTAL HORTICULTURE

There are about 50 Calandrinia (Portulacaeae) species native to Australia. These annual or perennial herbaceous succulents occur mainly in semi-arid regions. They tend to have attractive flowers. We are conducting plant improvement research on two Australian Calandrinia species with anticipated potential as ornamental flowering pot plants. Calandrinia sp. nov. (not yet fully classified) has large flowers (ca. 7 cm diam.) featuring concentric coloured ring patterns of bright violet, red, orange, and yellow in each flower. Calandrinia balonensis selections have smaller (ca. 4 cm diam.) pink/purple and sometimes white flowers. Being succulents, both species have relatively low water requirements. They are floriferous throughout the year. Neither species is currently available in the ornamentals industry. To enhance variation in our parent germplasm, the mutation breeding techniques of induced polyploidy by in vitro colchicine treatment of seedlings, and gamma irradiation of vegetative cuttings are being applied. These tools have demonstrated potential to quickly introduce desired horticultural traits, such as compactness, multiple branching, novel flower form, and brighter flower colours.

A synthetic wheat with 56 chromosomes derived fromTriticum turgidum andAegilops tauschii

By colchicine treatment of hybrids between Triticum turgidum and Aegilops tauschii (as seedlings), a fertile wheat plant (SHW-L2) carrying 56 chromosomes was artificially synthesized. At metaphase I of 50 pollen mother cells, the 56 chromosomes of the new wheat SHW-L2 showed a mean pairing configuration of 2.82 univalents, 6.18 rod bivalents, 19.39 ring bivalents, 0.5 trivalents, and 0.14 quadrivalents. Cytological analyses suggested that SHW-L2 had additional 7 pairs of chromosomes from the A and D genome besides the 42 chromosomes of common wheat. The special chromosome constitution of SHW-L2 may be derived from the chromosome doubling by the colchicine treatment of seedlings and then spontaneous doubling of gametes.

Cytogenetics of Lolium perenne

A number of diploid inbred lines of Lolium perenne were treated with colchicine at the early seedling stage to induce chromosome doubling. In each inbred line the colchicine-treated undoubled diploids were kept as controls, as well as the normal untreated diploids. Comparisons of vegetative growth and development, involving the three treatments within each line, revealed that colchicine treatment of seedlings has long-lasting effects upon plant growth and development independent of chromosome doubling, and that for certain characteristics the effects of chromosome doubling are confounded with other effects of the treatment used to produce tetraploids. This colchicine induced variation in the diploids is transmitted through the seed generations in at least one of the inbred lines. The variation appears to be non-random and also shows a strong genotypic component. In so far as the effects of chromosome doubling could be determined, they showed the usual gigas response but were again strongly influenced by genotype.

‘Grasslands Kara’ cocksfoot (Dactylis glomerataL.)

Abstract ‘Grasslands Kara’ is a 19-parent synthetic. It was bred from hybrids made by the late Dr P. C. Barclay between ‘Grasslands Apanui’ cocksfoot and 2 Portuguese populations of the diploid subspecies lusitanica that grew vigorously during the winter at Palmerston North. A tetraploid population of the Portuguese lines was made in 1962 by colchicine treatment of seedlings. Thirty tetraploid plants were pair-crossed to Apanui in 1965, and the hybrid progeny evaluated as spaced plants, especially for greater seasonal spread of growth. The most promising genotypes were back-crossed to Apanui and selected in the field for rust resistance, yield, and improved amount and uniformity of flowering. The resulting 72 genotypes were progeny-tested during 1972—75, and 19 of them were retained. These were then cloned and inter-pollinated and the seed was used for sward trials under the code name ‘G16’. G16 was approved for certification by the Ministry of Agriculture and Fisheries in 1980, and was then re-named ‘Grasslands Kara’. Grasslands Division maintains the parent plants at Palmerston North, to provide nucleus seed.

Classes of True-Breeding Diploid Mutants Obtained After Colchicine Treatment of Sorghum Line, Experimental 3

Colchicine treatment of seedlings of sorghum line, Experimental 3, has resulted in the production of true-breeding mutant lines which fall into specific types. Nine classes (two with subclasses based on variation in a single character) have been set up. Non-recurrent mutant lines (some resembling certain classes to a degree and others distinctly different) have also been obtained. Further work would be expected to produce both additional lines and additional classes. The composite nature of the mutants, the presence of classes, and the relationships between different classes and between certain classes and non-true-breeding mutants, all suggest that major chromosome changes are involved in their formation. These results contribute to the hypothesis that the mutants result from chromosome substitution (Sanders and Franzke, 1964).

Somatic Reduction of Tetraploid Sorghum to Diploid Mutants following Colchicine Treatment

COLCHICINE treatment of seedlings of certain sorghum lines has resulted not only in the expected polyploids, but also in diploid plants which are mutant for many characters. Some of these diploid mutants breed true immediately while others give segregating progenies1–3. The original hypothesis to explain their appearance suggested that a somatic reduction of the chromosomes (similar to that observed by Huskins4) occurred and was followed by duplication. These mechanisms could result in the concentration of chromatin from ancestors of a putative allopolyploid. However, investigations have produced either no or little cytological evidence for duplication or relocation of chromatin5,6. In addition, mutant characters which have been studied have shown Mendelian inheritance7–10. The alternative hypothesis was then proposed that, in addition to a balanced somatic reduction of the chromosomes after application of colchicine, mutations at many loci also occurred prior to duplication back to the diploid number.