Analysis of libraries of 'Micro-Tom' tomato mutations induced by heavy-ion bombardment

Fruit setting, development, and ripening are complex, genetically programmed processes. Identifying the factors that control these processes is important for understanding the mechanisms of reproductive development. We induced mutations in the tomato cultivar 'Micro-Tom' by irradiation with accelerated heavy ions (HII), recently established as an effective method for inducing mutations in plants, and constructed mutation libraries. 'Micro-Tom' showed lower sensitivities to higher HII doses. The survival rate of 'Micro-Tom' was about 50% with both ions. Screening 6,814 M1 plants, we found various mutations, including those affecting the sizes of plants, leaves, or fruit, and one conferring a broccoli-like inflorescence. This M1 mutant resembles tomato anantha mutant,in which the development of floral primordia is blocked before organogenesis. Because we could not obtain seeds from this mutant, inheritance and segregation of the trait are unknown, but anantha was reported, caused by a recessive mutation. The isolation of monogenic homozygous recessive mutants in the M1 generation has not commonly been described in other mutational studies using many plant species, although our group isolated such mutants in sweet pepper by M1 plant selection in HII mutational studies. To date, we have visually phenotyped 1,175 M2 families (five sibs per line) in the field, and found 262 plants differing from the wild type in one or more characteristics. These results suggest that such mutation libraries could be powerful tools to explain the reproductive development of plants. (author)