Aiming to optimize plant growth of the apple rootstock cultivar Marubakaido (Malus prunifolia) in greenhouse, one-year old plants coming from in vitro cultivation were sprayed once, twice and three times in a 7-day interval with gibberellic acid (GA3). The concentrations of 0, 50, 100, 200, 400, 800 and 1,600 mg L-1 were used. Plant growth was evaluated every two weeks during two months. Internode length, number of buds and the dry mass of the aerial part were also evaluated at the end of the experiment. Three sprays of GA3 at 800 mg L-1 was the best treatment providing the largest rate of plant growth (912% against 114% of non-treated plants) in relation to their initial height, besides providing larger internode length and higher dry matter of aerial parts. Plants sprayed once did not present significant response to GA3 for none of the studied variables. These results suggest that the use of GA3, in apple plants coming from micropropagation, improves the growth, although a number of at least three applications, associated with high concentrations, is necessary to improve the efficiency of this regulator.
Malus prunifolia; in vitro culture; adaptation; dormancy
