| Chromosome substitutions, genetic recombination and
the breeding of hexaploid triticale A. MERKER swedish seed Association, S-268 00 Svalov, Sweden During the passed 15 years increasing attention has been paid to triticale as a potential cereal crop. This is mainly the result of the successful breeding efforts in several countries such as Hungary, Canada, Mexico and the USSR. These programs have shown that triticale has many agronomically valuable properties such as high yield potential, good nutritional quality, good disease resistance, drought resistance and winter-hardiness. The breeding has so far led to the release of varieties in some countries e.g. Canada, USA and Spain. In Hungary triticales have been in practical cultivation for several years. CIMMYT of Mexico counts on practical cultivation of triticale within some years. Early triticale breeding programs were restricted to octoploid lines from breadwheat and rye. This material usually could not compete with wheat and rye. The selection of improved hexaploid lines from crosses between octoploid and hexaploid triticales was reported by PISSAREV (1963) and by KISS (1966). JENKINS (1966), and ZILLINSKY and BORLAUG (1971) reported the same thing from crosses between hexaploid triticale and bread wheat. These results underlined the importance of Triticum aestivum germplasm in the breeding of hexaploid triticale. Among triticale breeders, 42-chromosome triticales that have Triticum aestivum in their genetic background are referred to as secondary hexaploids (KISS 1966). The superiority of secondary hexaploids has been explained along three different lines : genic, cytoplasmic and chromosomal. Most probably all three explanations are valid and the superior performance of secondary hexaploids is the result of an interaction between factors on the genic, chromosomal as well as cytoplasmic levels. The genic explanation (PISSAREV 1963, MUNTZING 1972, THOMAS and KALTSIKES 1972) is based on the assumption that the A and B genomes of hexaploid and tetraploid wheats are not genetically identical, because they have had a long period of separate evolution behind them. The A and B genomes of bread wheat are supposed to be better adapted to the presence of a third genome. This should make them cooperate better with the rye genome in the triticales. By means of reciprocal triticale F1 hybrids LARTER and HSAM (1973) have shown that triticales with cytoplasm from hexaploid wheat in several respects are superior to those with cytoplasm from tetraploid wheat. This indicates that the incorporation of bread wheat cytoplasm is of importance in the breeding of triticale. The substitution of rye chromosomes by D genome chromosomes is the basis of the chromosomal explanation of the superiority of secondary hexaploids. ZILLINSKY and BORLAUG (1971), on plant morphological and physiological grounds, presumed that the Armadillo triticales were the result of a spontaneous outcross between triticale and bread wheat. GUSTAFSSON and ZILLINSKY (1973) proved the presence of the 2D chromosome in an Armadillo line. The F1 between this line and the ditelo 2D of Chinese Spring wheat showed a heteromorphic bivalent in the first meiotic metaphase. Based on the meiotic pairing in the F1 between the Armadillo and bread wheat they concluded that the 2D had replaced the 2R. |
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