| Transfer of D genome from common wheat to durum
wheat E.G. ZHIROV and T.K. TERNOVSKAYA Krasnodar Lukyanenko Research Institute of Agriculture, 350012, Krasnodar, USSR One of the most important events in wheat evolution was the transition of genome constitution from a tetraploid level to hexaploid one by addition of wild Aegilops tauschii (Coss.) Schmal. genome to cultivated Triticum dicoccum (Schrank.) Schuebl. (MCFADDEN & SEARS 1946). The consequence of such a transition has been studied at various points and provided evidence for drawing a general outline of the origin and evolution of common wheat. These investigations were mainly carried out when using natural wheats and their relatives. However, there are many details left that cannot be clarified in experiments with only these wheat forms. It is necessary to develop some particular genetic material. Thus, for detailed study of D genome of common wheat those forms are needed, which differences can be converged to differences of their D genomes. This report concerns developing these particular forms. The objective was to substitute A and B genomes of common wheat (AABBDD, 2n = 42) by the similar genomes of durum wheat (AABB, 2n = 28) while retaining D genome inchanged. This substitution was realized with a series of 5-6 backcrosses of the hybrids between the two species (AABBD, 2n = 35) to durum wheat as a recurrent parent. Spring cultivar Triticum aestivum L. var. ferrugineum (Alef) Mansf. "Kalyansona" and winter cultivar T. aestivum L. var. lutescens (Alef) Mansf. "Kavkaz" were used as a D genome donor. The recipient for them was a winter line Triticum durum Desf. var. muticitalicum Dorof. & A. Filat. "MI". Pentaploid hybrids, which contained 14 bivalents, belonging to A and B genomes and 7 univalents coming from D genome, were backcrossed as female parents to MI. Random distribution of 7 univalents to eggs bring about segregation of the backcross progenies for chromosome number from 28 to 35. As only 35-chromosome plants contain a complete complement of unpaired D genome chromosomes they were selected for the production of the successive generation. Unfortunately, while carring out this procedure, the share of pentaploid plants in backcross progenies proved to be insufficient (1.2% for Kalyansona and 0.7% for Kavkaz) for continuous backcrossing. The attemps to take advantage of a possible increase in the share at the expense of the preferential functioning more viable 21-chromosome male gametes from pentaploid when pollinating the tetraploid parent with its pollen was not a success because the seeds from such a cross were shrunken and produced no healthy seedlings. Therefore, begining from the first backcross for Kavkaz and the second one for Kalyansona to enlarge the number of plants carring a complete set of D genome chromosomes, the transition to each following backcross was realized after selfing 35-chromosome plants from the previous backcross and selecting 35-42-chromosome plants. It was found that the share of such plants markedly decreased in the progenies of the second and the successive backcross pentaploids in comparison with the first one (see table). Without a doubt this drop was caused by the substitution of ineffective in retaining D genome chromosomes of durum wheat gene/genes for effective common wheat alleles. |
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