I have crossed a number of lines to Nebraska Stiff Stalk Synthetic (NSSS) to obtain material which is better adapted to the Nebraska environment. Among these lines were several stocks which were testers for transposable elements. NSSS was crossed as the female by lines carrying bz2-m or a-m-1 and two or three ears of the resultant F1 were selfed. The bz2-m allele could be followed by the bronze phenotype while the a-m-1 allele was followed by the linked sh2 marker. In the case of the a-m-1 allele, no dots or sectors of color were seen on shrunken kernels, indicating an absence of Spm activity. Only ears which were segregating 3:1 for colored, plump vs. colorless, shrunken kernels were considered. In the case of bz2-m, seven different crosses were done. The ears resulting from the self pollination of two of these crosses showed mutability of the bronze phenotype. The mutability is expressed as sectors and dots of color. This suggests the presence of an Ac like activity. With the small sample size, no conclusion can be drawn about the copy number of the element.
This Ac element could be resident in either the NSSS or the bz2-m line. In the first case, the cross to the tester served to indicate the presence of an active element while in the second case an active element was generated by outcrossing to the NSSS. Crosses with other Ds-induced alleles in different genetic backgrounds would be necessary to support one model over the other. It is possible that the Ac element is resident in the NSSS. Peterson and Salamini (Maydica 31:163, 1986) have shown the presence of the Uq and Mrh systems in Iowa Stiff Stalk Synthetic. Tests for the presence of five other transposable element systems failed to show any positive results but did not rule out the possibility that these elements existed in the material. NSSS, originally derived from Iowa Stiff Stalk Synthetic, is a composite of two sub-populations which were selected for high grain yield. The presence of an Ac element in this breeding population lends support to the idea that transposable elements provide diversity which can be used in selection.
John C. Osterman
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