Chromosome doubling of Allium fistulosum x A-cepa interspecific F-1 hybrids through colchicine treatment of regenerating callus

Regenerating calluses of Allium fistulosum x A. cepa interspecific F-1 hybrids were treated in vitro with colchicine. A factorial experiment was designed to test the effects of colchicine concentration and time on the recovery of tetraploid plants from in vitro-colchicine-treated calluses. Shoot production of regenerating calluses following in vitro colchicine treatment decreased with increasing colchicine concentration and treatment time. Cytological analyses of root tip cells from regenerated plantlets showed that chromosomes of control plantlets (not treated with colchicine) were not doubled. Chromosome number of some plantlets regenerated from in vitro-colchicine-treated calluses were doubled, resulting in tetraploids. Calluses treated with 0.1 or 0.2% colchicine in BDS liquid medium for 48 or 72 hours yielded the highest numbers of tetraploid plantlets. Chromosome bridges at anaphase or early telophase were observed in diploid and tetraploid plants; their potential use is discussed. These results demonstrate that in vitro-colchicine treatment of regenerating calluses of interspecific F-1 hybrids is effective in recovering tetraploid plants.