Mutation induction by gamma irradiation of in vitro cultured shoot-tips of banana and plantain (Musa cvs).

Vegetative shoot apices composed of a meristematic dome with two pairs of leaf primordia were excised from in vitro-cultured shoots of seven clones of dessert banana (AA, AAA and AAAA), plantain (AAB) and bluggoe cooking banana (ABB). The mutation induction experiments were carried out with 60Co gamma irradiation of 15, 30, 45 and 60 Gy at a dose rate of 8 Gy min-1. Radiosensitivity was assessed by determining the relative increase of fresh weight of cultures and by the rates of shoot differentiation. Musa clones exhibited differences in radiosensitivity and post-radiation recovery. These differences were dependent on ploidy level and hybrid constitutions by genomes A (acuminata) and B (balbisiana). Considerable phenotypic variation was observed among plants regenerated from in vitro shoot-tips after mutagenic treatment. An early-flowering putative mutant plant of Grand Nain (GN-60 Gy/A) was selected in the glasshouse in the M1V4 generation. The mutant plant was micropropagated and its vegetative progeny was planted for field testing in a tropical environment. Leaf protein electrophoresis provided evidence of an altered genetic nature of the mutant plant in comparison with the original clone. The mutant GN-60 Gy/A showed a less densely staining protein of about 33 kDa Mwt and lacked three other proteins. In addition, two bands of esterase isozymes, characteristic for the original Grand Nain, were not detected in extracts of GN-60 Gy/A. The potential of induced mutagenesis for genetic improvement of banana and plantain is discussed and a scheme of in vitro mutation breeding is outlined.