Possible Breeding Tool

Press, Volume CI, Issue 29952, 13 October 1962, Page 6

Possible Breeding Tool

PJHROMOSOME substitution is a potentially important technique for wheat breeding. It may facilitate the transference of important characters between wheat plants in a more precise fashion than current methods of hybridisation. Dr. J. M. McEwan, who recently returned to the Crop Research Division at Lincoln after spending two years and a half in Canada studying this technique, is now producing a series of lines of both Aotea and Hilgendorf (1961), two of New Zealand’s most important wheats, which are deficient in specific chromosomes.

This work is preparatory to a study of the effect of the systematic replacement of certain chromosomes of these varieties in the hope that superior combinations may be obtained. The process, even using the growth chamber where production of generations is greatly speeded up, is a painstaking one. At Lincoln Dr. McEwan is using deficient lines in the Canadian variety. Rescue, to induce chromosome deficiency in the New Zealand wheats. The main lines are now at about the third or fourth generation stage. After the initial crossing of the Rescue line with the New Zealand wheat variety, the hybrid material must be backcrossed with the parent New Zealand wheat about eight times to ensure that the major characters of the New Zealand wheat are maintained.

At each generation microscopic examination of the plants is necessary to deter-

mine which is in fact monosomic or chromosome deficient and therefore due to be carried on.

While at present American material is being used as a base for this work, there is another possibility for the development of chromosome deficient lines. It has been reported that some wheat seeds have two embryos which give rise to twin seedlings and occasionally these are peculiar in genetic make-up in that they are haploid or have only half the usual number of chromosomes. This material eould thus be used in the building up of monosomic lines of Wheat, and was in fact the source of the original monosomic wheats developed in the United States. So far one such haploid wheat plant has been discovered at Lincoln in Asawa Twin seeds, or seeds with two embryos, although not necessarily Showing ahromosome deficiency, are found in A raws In the proportion of about one in 700 seeds examined, in Hilgendorf at one in 2500, and in Aotea as one tn 4000. The deficiency may show up In about one out of 20 twin seeds. Dr. McEwan Mtid that some chromosome deficient lines were of greater interest than others, and tor that reason they were being developed more rapidly than others Particular importance was attached to chromosomes which influenced such factors as protein quality in wheat. They were obviousiy of interest in possible wheat quality improvement