A cytological study of Vilmorin’s unfixable dwarf wheat
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Vilmorin ever-splitting dwarf wheat plants give three main types of progeny: normals, dwarfs and pigmies. The pigmies are rare, the dwarfs and normals occur in varying ratios which approach 1:1 (Engledow and Wadham, 1926).
The dwarfs have 43 chromosomes, the normals 1–2 and the pigmies 44. The extra chromosome of the dwarfs is usually included in a trivalent association, but it may be univalent or be included in a quadrivalent or a quinquivalent.
Quadrivalents occur fairly frequently in “normal” segregates.
The chromosomes concerned are of two different lengths. One dwarf was found to have an extra “short” chromosome, and two an extra “long” one.
Since the different sized chromosomes can pair, many different chromosomal types of progeny are possible. The three main classes are determined by differences in chromosome number, but differences in the proportion of“long” and“short” chromosomes within each type are probably responsible for much of the variation noted by Engledow and Wadham.
The main genetic features of the problem are analogous to those of C-series speltoids or fatuoids and, as in these, are adequately accounted for by the cytological observations, but details require further study.
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