Early maturing mutations as germplasm stocks for barley breeding

A total of 102 early maturing mutations have been isolated after various treatments of seeds or plants with ionizing radiations or chemicals from a barley cultivar 'Chikurin Ibaraki 1' or its mutants. Fifty of them were evaluated as regards responses to internal physiological factors. The mutants were found to have a mutational alteration in vernalization and/or photoperiodic response. Earliness in a narrow sense was not noticeably changed. The original genotype is a winter and long-day type. By mutation four different degrees of change in vernalization requirement i.e. complete (V1) and incomplete (V2) spring habit and winter habit with reduced requirement to varying degrees (V3, V4) have been produced. Photoperiodic response was also changed into at least three types i.e. complete (P1) and incomplete (P2) loss of sensitivity to short photoperiod and a slight reduction in critical daylength for heading. P1 and P2 type mutants were all characterized by marked earliness in heading time in field. Thirty seven mutants were located in seven separate loci. Allelism test of the mutated genes to spontaneous ones revealed that the genes carried by P1 type mutants were all allelic to an earliness gene ea sub(k) on chromosome 5 and the gene involved in P2 type mutants to ea7 on chromosome 6. On the contrary, the gene commonly involved in all V1 type mutants and one V2 type mutant was not allelic to spring habit gene Sh2 or Sh3. It seemed likely that the gene was not allelic to, either, but closely linked with sh on chromosome 4. The diversity in terms of genetic and physiological properties of the early maturing mutants arising from common ancestry emphasizes the importance of induced mutation in broadening of germplasm of barley breeding. (author)