| Adding individual rye chromosomes to wheat Ralph RILEY Plant Breeding Institute, Cambridge, England Experience with interspecific and intergeneric crosses in the Triticinae has indicated that some manipulation of the raw amphidiploid will almost certainly be necessary before agriculturally useful forms can be obtained (Bell, Lupton and Riley 1955). It has been proposed that lines of wheat disomic for the addition of a single pair of chromosomes of a diploid species might incorporate useful features of the diploid with the minimum alteration of the basic phenotype of wheat. Because of their balanced chromosome constitutions such lines might be expected to be true-breeding and of normal fertility. Six of the seven possible disomic additions of the chromosomes of Secale cereale, King II, to Triticum vulgare, Holdfast, have been obtained. Each rye chromosome produces a more or less characteristic alteration to the phenotype of Holdfast. The chromosome added may thus be recognised by its phenotypic effect and also, in certain additions, by the morphology of the chromosome itself. Most alterations to the phenotype of wheat are quantitative. The characters which mainly distinguish rye - the narrow single nerved glume, long hairs on the keel of the lemma, exposed grain and the absence of a terminal spikelet - do not appear in the addition series. The only distinguishing character transferred is "hairy neck" ccntrolled in this material, as in that of O'Mara (1951), by a factor on chromosome I, and by a factor of less pronounced effect, and of limited penetrance, on chromosome II (Chapman and Riley 1955). Certain complementary effects result in expressions shown by neither the rye nor the wheat. Thus three addition lines have red grains although those of Holdfast are white and those of King II grey. One addition line has branched ears. Of more practical potentiality is the resistance to both rye and wheat races of mildew developed by two addition lines. The resistance to wheat mildew introduced by chromosome II is shown to be controlled by a factor on the non-satellited arm, by the behaviour of the telocentrics for each arm. There is usually a phenotypic expression of the dose difference between monosomic and disomic additions. The characters which distinguish monosomic additions from Holdfast are generally further exaggerated in disomic additions. |
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