Effect of gibberellic acid (GA₃) on the internode elongation of some semi-dwarf hybrid rice (F₁)

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Four rice cultivars (2 semi-dwarf Indica/Japonica, one tall Indica and one tall Japonica) and their hybrids, when treated with the foliar application of exogenous gibberellic acid (GA₃) (10 and 50 ppm) around panicle initiation stage, showed the immediate effect on the total plant height elongation up to 14 days, and GA₃ did not affect the natural growing tendency during the effective period. The apperant additive, overdominance and complete dominance responses of the F₁ hybrids of the cross combinations of Early Tongil/HP736-3-3 and wx 126-12-13/HP 736-3-3, Early Tongil/Jinheung, and Jinheung/HP 736-3-3, respectively were not affected by the exogenous GA₃ in their total culm length. The first internode from the top was adversely affected in all the tested cultivars and their F, hybrids in length. 3rd and 4th internodes were elongated remarkably except in HP 736-3-3 in which 3rd internode was reduced and 5th and 6th ones were elongated. These elongated 5th and 6th internodes appeared as recessive in F₁ and GA₃ application did not show any adverse effect. Four different rice varieties and their F₁ hybrids were treated with gibberellic acid (GA₃) at 10 ppm and 50 ppm as the foliar application around panicle initiation stage. Observations were taken on plant height every 48 hours after GA₃ treatment up to 14 days. Culm length and internode length were measured at harvesting time. The results obtained were summarized as follows ; 1. All the tested rice varieties and their F₁ hybrids showed the immediate effect of GA₃ up to 14 days with maximum effect from 4 to 10 days after GA₃ treatment. The exogenous GA₃ did not affect the natural trend of growth within the effective period. 2. The apparant additive, over dominance and complete dominance gene responses of the F₁ hybrids of the cross combinations of Early Tongil/HP 736-3-3 and wxl26-12-13/HP 736-3-3, Early Tongil/Jinheung and wx126-12-13/Jinheung and Jinheung / HP 736-3-3 respectively were not affected by the exogenous GA₃ in their total culm length. 3. In all of the F₁ hybrids as well as parents, the first internode from the top has been reduced by the GA₃ treatment in length, and the lower 3rd and 4th internodes were elongated remarkably except in HP 736-3-3 in which 3rd internode was reduced, and 5th and 6th ones were elongated. 4. The 5th and 6th elongated internodes appeared as recessive genetically in F₁and the GA₃ application did not show any adverse effect on this.