| Results and Discussion Combining the colchicine, DMSO and cold treatments resulted in the production of 59.8% fertile alloploid triticales from surviving plants among hexaploids and 12.3% among octoploids (Table 1). Twenty five percent of another group of hybrids between hexaploid wheat and diploid rye, not recorded in Table 1, produced selfed amphiploid seed when treated with this technique. The mortality rate undoubtedly could have been reduced by additional care to prevent leakage of colchicine from the vials and elimination of weak plants from the experiment. No explanation is known for the lower percentage of fertile plants among octoploid hybrids but it is possible that plants with higher chromosome numbers require additional or more concentrated applciations of the alkaloid. The lower success rate may reflect the unfavorable balance of three wheat genomes (A, B, D) to one rye genome (R). Both colchicine and low temperature are known to allow chromosome multiplication while inibiting cell division (TILNEY 1971; INOUE 1952). Our results suggest that low treatment and shortened days may stimulate the development of new tillers from polyploid cells. Additional experiments are in progress to devise a means of treating crown meristems while the seedlings are still in culture tubes and the roots are protected by submersion inagar medium. Such a procedure has been used successfully to double chromosome numbers of barely haploids (K. KASHA, personal, communication). Results were inconclusive in various attempts to combine colchicine with growth regulators such as kinetin and gibberellin. Acknowledgment Financial aid for this study was provided by the Rockefeller Foundation. Literature Cited BELL, G.D.H. 1950. Investigations in the Triticinae. I. Colchicine techniques for chromosome doubling in interspecific and intergeneric hybridization. J. Agric. Sci. 40 : 9-18. INOUE, S. 1952. Effect of temperature on the birefringence of the mitotic spindle. Biol. Bull. 103 : 316. JENSON, C.J. 1974. Chromosome doubling techniques in haploids. Proc. First Int. Symp. Haploids in Higher Plants. Univ. of Guelph. Ontario. Canada. pp. 153-190 LARTE, E.N,. T. TSUCHIYA and L.E. EVANS 1968. Breeding and cytology of triticale. Proc. 3rd Int. Wheat Gent Symp., Austral. Acad. Sci., Canberra, pp. 213-221. NORSTOG, K. 1973. New synthetic medium for the culture of premature barley embryos. In Vitro 8 : 307-308. SIDDIQI, K.A. 1971. Induction of polyploidy in multigeneric hybrids in the group Triticeae. Hereditas 67 : 191-203. TILNEY, T.G. 1971. Origin and continuity of cell organelles. 2 : 222-231. |
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