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Preliminary location of some chlorina mutants in wheat1)
L.M.S. SEARS Department of Agronomy, University of Missouri, Columbia, Mo., 65201, U.S.A Chlorophyll mutants received from Dr. Calvin KONZAK (5 mutants) and from Dr. Horst GAUL (20 mutants) were grown in the greenhouse at Columbia, Missouri, and observed. Two of the Konzak mutants and nine of GAUL'S could be easily distinguished under our conditions. They were crossed into our test variety Chinese Spring for a varying number of generations. In the second and later generations, heterozygotes were used for the crosses. These were identified by checking that their selfed seed segregated the mutant phenotype. From a selfed generation, mutants were selected to be crossed with monosomics of Chinese Spring. Since these were all chlorina mutants, and previous work at Missouri and at the University of New South Wales had shown that three such mutants were located on chromosome 7A and one on chromosome 7D, they were crossed to monosomics of group 7 as a first approach to their location. Also, in the past it had been found that sometimes the absence of a homoeologous chromosome resulted in a more extreme phenotype. Thus whenever "super" (extreme) chlorinas were found among the F2, this was considered an indication that the gene was not on the chromosome tested but on one of its homoeologues. Table 1 lists the results obtained. For mutant 685 the analysis of the chlorina offspring placed this gene on chromosome 7B or 7D, but in the F2 of the cross with 7D there was a disomic green plant and also one superchlorina. This makes it unlikely that chromosome 7D is the critical one. Thus mutant 685 is most likely located on chromosome 7B. The same is true for mutant 691. Mutant 693 is almost certainly located on chromosome 7B, since disomics were found among green offspring of the crosses with 7A and 7D. Mutant 694 could be on chromosome 7A or 7B, but 7B seems more likely, so the mutant will first be checked against the others now believed to be on chromosome 7B. These four mutants will be crossed with each other to see whether the same locus in involved. Mutant 695 is being rechecked, since the results listed in the table were inconclusive. The fact that super chlorinas were found in the crosses with 7A and 7B would favor a location on chromosome 7D ; however, in the 7D F2 the one chlorina analyzed was monosomic, and one of the green seedlings was disomic. There is a strong possibility that monosomic shift caused these results. Mutant 679 is most likely on chromosome 7A. It will be crossed with one of the mutants that has been confirmed to be located on chromosome 7A. |
| 1) Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 7418 |