| Awn inhibitor in Redman wheat K. TSUNEWAKI Laboratory of Genetics, Kyoto University, Kyoto, Japan Based on the F1 data of a series of crosses, Redman monosomics x Prelude, CAMPBELL and MCGINNIS (1958) concluded that a common wheat variety, Redman, carries two complementary genes for awn suppression on the chromosomes 5A (formerly IX ) and 1D (XVII). One of them located on chromosome 5A seems to be an allele of B1 gene. The other gene on chromosome 1D was designated as B3 by TSUNEWAKI and JENKINS (1961). In an attempt to establish isogenic marker lines in another common wheat variety, S-615, B3 has been chosen as a marker gene for chromosome 1D. In the course of transferring this gene from Redman to S-615, however, it was unexpectedly found that Redman carries only a single dominant gene instead of two complementary genes. Therefore, a further investigation has been made in order to reveal the gene system for awnlessness of Redman wheat. Redman and two other awnless varieties, Elgin and Jones Fife, which are known to carry only the B1 gene, were crossed to two awned varieties, Prelude and S-615. Data on the F2 segregation of those crosses are summarized in Table 1. Actual segregation ratios of all six crosses fitted the 1 : 3 ratio, disproving the 7 : 9 ratio of awned vs. awnless. Mono-5A of Redman, whose Seeds were kindly supplied by Dr. R. C. MCGINNIS, was crossed to S-615 as male parent. In the F1 generation, a cytological examination was made in order to distinguish disomic and monosomic hybrids. Their selfed progenies were tested for the segregation of awn types. Similarly to the result of CAMPBELL and MCGINNIS (1958), all disomic F1 plants were awnless, while F1 mono- 5A's were all awned. In the F2 generation of the disomics, however, 1 : 3 ratio of awned vs. awnless was obtained instead of 7 : 9 ratio expected from segregation of two complementary genes. No awnless plants were found in the offspring of F1 mono-5A. From these results it can be said that the gene system for awnlessness of Redman is not different from that of Elgin and Jones Fife, indicating only one dominant inhibitor, B1. PERSON (1956) has already pointed out that univalent shifts and other cytological changes may occur in monosomics due to occasional meiotic irregularities. Therefore, it is necessary to carry out a monosomic analysis, at least, to the F2 generation and compare the F1 record with the segregation data in F2. By such procedures a wrong conculsion due to occasional cytological change that occurred in a certain monosomic line may be avoided. |