Expanded, young leaf blades of Begonia Tuberhybrida Group 'Clips Yellow' were cut into four pieces radially from the junction with the petiole; each piece was inserted in various media in nursery trays. The surviving percentage of the leaf pieces, grown in rockwool beds, was higher than in other media; about half of them formed adventitious buds. When the leaf piece was cut into the proximal and distal halves, several adventitious buds were formed on the former, but only a few on the latter. Many leaf pieces, inserted in April, May, and October formed adventitious buds, but only a few leaf pieces inserted in July, did. The optimum temperature for adventitious bud formation was around 15-20°C. The results suggest that the adventitious bud formation is affected by temperature rather than day length.
We studied the effects of the type of leaf cuttings, 6-benzylaminopurine (BA) application, and the section position and orientation of leaf pieces on adventitious bud formation in leaf cuttings inserted in rockwool beds, using expanded young leaf blades of Begonia Tuberhybrida Group 'Tenella'. In BA absence, 73% of whole leaf blades with petioles formed adventitious buds, whereas none of the 2 × 1.5 cm leaf pieces did at all. The percentages of surviving and adventitious bud formation of 2 × 1.5 cm leaf pieces without petioles were 47% and 0%, respectively. When these small leaf pieces were inserted in rockwool beds containing 0.25-2 ppm BA, the percentages of surviving and adventitious bud formation were 100% and 80%, respectively. In BA presence, the percentage of adventitious bud formation became lower from the base towards the tip of the leaf, and the leaf pieces at positions 2 cm away from the leaf bases did not form adventitious buds at all. When they were placed horizontally and vertically inverted, the percentages of adventitious bud formation were 60% and 80%, respectively.
Begonia x tuberhybrida is propagated mainly by seed, because vegetative propagation by cuttings or tissue culture is difficult. However, seedlings generally exhibit a wide range of variation due to their high level of heterozygosity, and also the pollination period is limited. An adequate technique of vegetative propagation of B. x tuberhybrida if established, would be useful for commercial production. Therefore, we investigated the propagation characteristics of the stem and leaf cuttings, and influence of BA and NAA on adventitious bud formation in leaf cuttings of B. x tuberhybrida. Stems (2 cm in length) with 5 cm of basal part of leaf blades but with axillary buds removed, and leaf pieces (2.5 x 2.5 cm) cut from young expanded leaves were planted in a mixture of vermiculite and perlite on a bench in a glasshouse controlled at 25/17°C (DT/NT). Both of the stems and the leaf pieces formed only roots or calli, but none of them formed any adventitious buds. Effects of plant growth regulators on adventitious bud formation were examined by planting leaf pieces (2 x 1.5 cm) on agar medium containing NAA (0-0.5 or 1 ppm) and/or BA (0, 0.5 or 1 ppm) at 23°C. When leaf pieces were planted on agar medium without plant growth regulators, the leaf piece did not form adventitious buds. On the medium with BA, adventitious buds were formed. The leaf pieces planted on the medium with 1 ppm BA formed adventitious buds in 25% and callus in 31% of them. Most leaf pieces in the medium containing NAA died. BA may be effective for inducing adventitious bud formation in leaf cuttings of B. x tuberhybrida.
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