3.3. Classification of phenotypic variations in M2 mutants
A total of 1363 mutants were isolated from the M2 populations, and they were divided into four groups according to their phenotypes (Table 2): (1) mutations in the leaf morphology; (2) mutations in the stems; (3) mutations in the flowers; (4) mutations in the life cycle. Each category was subdivided into several sub-groups. Many mutants presented more than one phenotypic alteration. In such cases, classification was based on their most distinct features. For example, the mutant numbered #60 (Fig. 4) showed downward curled leaves in the early stages of growth, while later it displayed dwarfism, bushy lateral branches, and nearly complete sterility. Considering that the curled leaves could be observed through the whole life cycle, #60 was classified as one of the leaf mutants inTable 2. The phenotypic variations induced by carbon-ion beams mainly appeared in the leaves and in life-cycle alterations. The total mutation rate was 4.77%: the occurrence of leaf mutants and life cycle mutants was 2.33% and 1.57%, respectively, while that of stem and flower mutants was only 0.27 and 0.13%. In addition, the statistical analysis of pleiotropic phenotypes was performed (Fig. 5). In the 1363 mutant lines, 64% were displaying one conspicuous phenotype, 13.3% displayed two conspicuous phenotypes, and 13.1% showed at least three mutant traits. Fig. 6 and Fig. 7 show representative phenotypes from each group. These results demonstrate that carbon ions are effective mutagens for the induction of various mutants, especially mutants in leaves and life cycle (early maturing).