| Inheritance of the sphaerococcum effect in tetraploid
wheat 1) J. W. SCHMIDT and V. A. JOHNSON 2) The sphaerococcum or shot-wheat kernel has been the distinguishing characteristic of the hexaploid wheat, Triticum sphaerococcum PERC.. SEARS (1947) has placed the hemizygous-ineffective recessive gene controlling this in chromosome 3D. Since then, SCHMIDT, et al. (1963) reported that a similar effect was produced by an incompletely dominant gene not allelic to the gene on chromosome 3D. This appeared as a mutant in common wheat. Because of sterility interactions in monosomic studies, the incompletely dominant gene could not be placed on a particular chromosome or in a genome. However, evidence that the sphaerococcum effect is not restricted to the D genome came from the report by SCHMIDT and JOHNSON (1963) of the same character in a tetraploid wheat. In all three of these sources expressions of the sphaerococcum effect is similar: (1) Awn length is reduced and a shortened kernel develops in nearly hemispherical glumes. (2) The rachis becomes strongly zigzag in shape. (3) Reduction in plant height occurs. (4) Flag leaves tend to be short and blunt. The sphaerococcum variant in the tetraploid wheat was crossed to the tetraploid population in which it was found (C. I. 8594, a durum introduction from China). The F1 resembled the normal parent although there was some expression of the sphaerococcum effect. More recent crosses show that the heterozygotes can probably be identified. An average of 54 F2 plants were grown from each of seven F1 plants. Since there appeared to be no significant deviation from the expected segregation ratio for any of the F2 populations, all F2 populations were combined. Of the 377 F2 plants, 285 were classified as non-sphaerococcum and 92 as sphaerococcum, a nearly perfect one-factor ratio. Classes were clearly defined. The presence of this sphaerococcum variant in a tetraploid wheat is evidence that the sphaerococcum effect is not restricted to the D genome in wheat. Furthermore, the heterozygote appears to show considerable heterotic effect in grain yield per head and possibly could have some plant-breeding value. The gene should be useful for linkage studies in tetraploid wheats. Small quantities of seed of the variant are available to those interested. References SCHMIDT, J. W., D. E. WEIBEL and V. A. JOHNSON. 1963. Inheritance of an incompletely dominant character in common wheat simulating Triticum sphaerococcum. Crop Sci. 3: 261-264. SCHMIDT, J. W. and V. A. JOHNSON. 1963. A sphaerococcum - like tetraploid wheat. Crop Sci. 3: 98-99. SEARS, E. R. 1947. The sphaerococcum gene in wheat. Genetics 32: 102-103. |
| 1) Contribution from the Department of Agronomy in
cooperation with the Crops Research Division, Agricultural Research Service,
U. S. Department of Agriculture. Published with the approval of the Director
as paper No. 1834a, Journal Series, Nebraska Agricultural Experiment Station,
Lincoln 2) Professor of Agronomy, University of Nebraska, and Research Agronomist, Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, Lincoln, Nebraska. |