Investigations were carried out in order to clarify the effect of gibberellic acid (GA
3) on the flowering, inflorescence morphology, and pollen germination in 6 triploid cultivars: ‘Egu-imo’; ‘Hasuba-imo’; ‘Ishikawa-wase’; ‘Oyazeme’; ‘Taikoban’; ‘Daikichi’, 2 diploid cultivars: ‘Tono-imo’; ‘Takenoko-imo’, and colchicineinduced tetraploids from ‘Takenoko-imo’ of taros (
Colocasia esculenta Schott) cultivated in Japan.
GA
3 was applied either by soaking apical buds in the seed corms of 8 cultivars in each aqueous solution of 0, 250, 500, and 1000ppm for 2 hours a day before planting, or by dropping 1-2ml of 500ppm on the bases of petioles of the young plants in ‘Takenoko-imo’ and its induced tetraploids four times at intervals of 2, 5, 7 days commencing with the 3-leaf stage.
Among the 8 cultivars and induced tetraploids treated, flowering occurred in 6 cultivars except in ‘Hasuba-imo’ and ‘Tono-imo’, in the induced tetraploids, and the untreated ‘Egu-imo’. There were differences in the reaction to the three concentrations of GA
3 among cultivars.
The percentage of plants flowered was 100% both in ‘Takenoko-imo’ and its induced tetraploids treated by dropping, and 6.7-84.6% in 6 cultivars treated by soaking. The number of inflorescences per plant was about one in ‘Ishikawa-wase’, ‘Oyazeme’ and ‘Taikoban’ with a lower percentage of plants flowered, and was more than 2.5 in ‘Egu-imo’ and ‘Daikichi’ with a higher percentage of plants flowered, while it was 14.5 in ‘Takenoko-imo’ and 7.4 in its induced tetraploids treated by dropping.
The earliest inflorescence development was observed in ‘Takenoko imo’ treated by soaking after 10 weeks from treatment, while the latest was recorded in ‘Ishikawa -wase’ and ‘Oyazeme’ after 13 weeks. Treated ‘Egu-imo’ produced inflorescences more than 3 weeks ahead of the untreated ones. The duration of inflorescence flowering was 1-4 weeks in 3 cultivars and was about 9 weeks in 2 cultivars and both ‘Takenoko-imo’ and its induced tetraploids.
In ‘Egu-imo’ the inflorescences which were produced on treated plants at almost the same time as those on untreated plants were similar in both the length of floral parts and the number of florets. The early-produced inflorescences, however, were fewer in the number of florets, compared with those of the late-produced inflorescences. All treated cultivars except ‘Hasuba-imo’ and ‘Tono-imo’ also gave rise to a number of bract-like deformities with no spadaces.
Triploid cultivars: ‘Ishikawa-wase’, ‘Oyazeme’ and ‘Taikoban’ did not extrude any pollen at all, while the pollen sheddings from triploid cultivars: ‘Egu-imo’ and ‘Daikichi’, a diploid cultivar ‘Takenoko-imo’ and its induced tetraploids were inconsistent. Percentage of pollen germination of their triploid cultivars was very poor and none of the pollens of their early-produced inflorescences germinated. On the other hand, the pollens of diploid ‘Takenoko-imo’ germinated more than those of triploid cultivars, giving 24.7% in germination percentage.
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