The experiment was conducted to study the effect of growth regulators on plantlet regeneration and bulbing of onion in vitro. Results from the experiment showed that both plantlet regeneration and bulbing were greatly affected by growth regulators or their combinations. It was found that shoot induced from twin scale in 0.1 mg/l NAA was with a percentage of 93% and per explant shoot rate of 0.84. A combination of 0.1 mg/I NAA + 2 mg/I 4PU 30 induced 89% shoot regeneration from twin scale. The highest per explant shoot (1.25), however, was observed in 0.1 mg/I NAA + 1 mg/I 4PU 30. There was no significant difference between the effect of combining NAA+BA and NAA+4PU 30 on shoot production. The highest root percentage (89%) in twin scale was obtained with a combination of 0.1 NAA+3 mg/I BA, and highest per explant root (1.06) was observed in 0.1 mg/I NAA+1 mg/1 BA treatment. The effect of 4PU 30 and sucrose on inducing bulb formation independently was also studied. The highest bulb percent (84%) was induced in 0.8 mg/I 4PU 30. The mean bulb circumference at the same concentration was 2.6 cm after six weeks of culture. In sucrose treatment, the highest bulb percentage (81%) was observed in 100 g/I sucrose. Apparently, a slightly higher (2.9 cm) mean bulb circumference was observed compared to 4PU 30. There was, however, no significant difference in bulb circumference between the two treatments.

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