| Homoeologous chromosome recombination in Triticum
aestivum C. N. LAW Plant Breeding Institute, Cambridge, England The absence chromosome 5B in Triticum aestivum results in non - homologous pairing and recombination (RILEY 1960). Evidence is also available which indicates that non - homologous exchanges are confined largely to chromosomes within, rather than between, the seven homoeologous groups of T. aestivum (RILEY and KEMPANNA 1963). These two facts imply that, by the use of suitable chromosome techniques, strictly homologous recombination can be extended so as to involve the, presumably, genetically more diverse homoeologues. It has been suggested by RILEY (1960) that the application of such techniques may allow a repatterning of the genetic architecture of wheat in ways which may be economically beneficial. Thus, it may be envisaged that the duplication or the removel of certain genes or regions of a chromosome may improve the genetical behaviour of wheat in a desired way. Indeed, this method of plant breeding is already being attempted in Hordeum vulgare. (HAGBERG, PERSSON and WIBERG 1963). As a first step in exploiting this aproach it is necessary to demonstrate that variation as a result of homoelogous recombination can be achieved from within a pure breeding line of hexaploid wheat. An experiment was consequently undertaken in which material, deficient for chromosome 5B and tetrasomic for chromosome 5D, in the variety Chinese Spring (obtained from Dr. E. R. SEARS) was multiplied so that sufficient seed for a small field experiment was available. Moreove, of obvious importance to this experiment, a number of generations have elapsed since the nullisomic - tetrasomic material was first formed, so that the results of homoeologous recombination may reasonably be expected to have appeared. Progenies from twelve plants taken at random amongst the stock material were studied. To eliminate changes in chromosome number, root - tip counts were carried out on each plant. Where departures from 2n = 42 occurred, the deviant plants were discarded. As a result observations were confined to plants having the hexaploid number of chromosomes only. The layout of the experiment consisted of two randomised blocks in which each plot contained five plants, spaced twelve inches apart. Measurements were made on each plant and the mean effects taken over blocks and plots are shown in the accompanying table 1. Analysis was carried out on the mean effect of the five plants per plot. |
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