II.27. Induction of chlorophyll-deficient mutations in Steptoe by sodium azide.
R. A. Nilan and C. Sander, Program in Genetics and Department of Agronomy and Soils, Washington State University, Pullman, Washington 99163.
Washington bred Steptoe (CI15229) is a new high yielding, hulled, row, spring feed barley variety which appears to have a wide range of adaptation in the western USA. Although it possesses reasonably good straw strength, its yielding ability might be improved if it had shorter and stiffer straw and increased number of tillers per plant. To this end we have initiated a mutation breeding program with Steptoe using sodium azide.
As indicated in an accompanying abstract,* sodium azide has induced the highest frequency of chlorophyll-deficient mutations in barley than any other mutagen. It appears to be most efficient when the cell cycle is near or at S stage. The frequency of chlorophyll deficient M2 seedlings induced in Steptoe by azide is reported here.
Seeds of Steptoe were presoaked in aerated water at room temperature for 2 and 4 hours and then treated in a solution of 10-3 NaN3 at pH 3 for 4 hours and 2 hours, respectively. Each treatment was conducted in two replications.
M1 seedling growth was delayed about 30 hours due to the 2 hour azide treatment and about 35 hours by the 4 hour treatment. M1 plants were grown under isolation and for each time of presoaking about 10% of the plants exhibited chlorophyll-deficient stripes. Survival of M1 plants was 80-90%.
About 400 M1 spikes were harvested from about 400 plants from each presoaking time. The remaining spikes were harvested in bulk. The individually harvested spikes were cultivated in the greenhouse to determine frequency of M2 chlorophyll-deficient seedlings -- to give some prediction of the frequency of morphological, especially beneficial, mutants.
As seen from Table 1, the frequencies of mutations on an M1 spike basis were 52.9 and 53.7 for 2 hour presoak 4 hour azide and 4 hour presoak and 2 hour azide treatments, respectively. The differences in frequencies between presoaking times are not significant. As indicated in the accompanying abstract* increased frequencies might be realized with longer presoaking times. From these high chlorophyll-deficient mutation frequencies it is expected that many morphological mutants will be available for selection among M2 plants.
*Abstract not submitted to editors.
