| Dosage effect of 5A chromosome or the long arm in a
Japanese wheat variety, Shinchunaga S. ICHIKAWA Laboratory of Genetics, Kyoto University, Kyoto, Japan In the progenies of gamma-ray irradiated Shinchunaga, a Japanese variety of common wheat, numerous kinds of mutants were found. Among these radiation-induced mutants, many speltoid and compactoid mutants were included. Through the cytogenetical analyses on the speltoid and compactoid mutants, it has been proved that there are several speltoid mutants which are missing the whole or the long arm of 5A chromosome, and that some compactoid mutants have 5A chromosome or the long arm excessively. The dosage effect of 5A chromosome or the long arm observed in the present case, however, differs from that in Chinese Spring ever reported. Namely, zero, one, two, three, four, and five dosages of 5A or the long arm made the plants homozygous speltoid, heterozygous speltoid, normal, squareheaded, sub-compactoid, and compactoid, respectively, in Shinchunaga wheat. On the other hand, it has been shown by several authors that disomics, trisomics, and tetrasomics of 5A chromosome in Chinese Spring are squareheaded, sub-compactoid, and compactoid, respectively. This difference may be attributable to the different genetic effects of the Q gene locating on the long arm of 5A chromosome and/or the allelic genes on 5B and 5D chromosomes, or it may relate to a gene on the short arm of 5A, loss of which makes the plants squareheaded. Actually, the spikes of normal Shinchunaga are non-squareheaded, whereas those of normal Chinese Spring are squareheaded. At any rate, this difference is a new evidence of the differentiation accomplished between these two varieties. |