Effect of 1,2-benzisoxazole-3-acetic acid on adventitious shoot regeneration and in vitro rooting in apple

The effect of 1,2-benzisoxazole-3-acetic acid (BOA), compared to 1-naphthaleneacetic acid (NAA), on adventitious shoot formation in leaf portions acid compared to indolebutyric acid (IBA), on in vitro rooting in the apple (Malus domestica Borkh) cultivars McIntosh and Gals, and one rootstock, Jork 9, was investigated. BOA at 43.0 mu m or 2.7 mu m at NAA in combination with 17.8 mu m benzyladenine (BA), induced the highest number of explants to produce adventitious shoots in Jerk 9. In Gala, the combination of 21.5 mu m BOA with 1.0 mu m thidiazuron (TDZ) or with 22.0 mu m BA induced the highest regeneration percentages, 58 and 54%, respectively, giving more satisfactory results than NAA (where only 42% of leaf explants exhibited shoot formation). In McIntosh, the highest percentage of regeneration was obtained with 1.3 mu m NAA and 22.0 mu m BA, while 51% was the highest response obtained with the BOA treatment. The combination of BOA with TDZ completely inhibited regeneration activity in leaf portions of this cultivar. The shoots of all the genotypes obtained with the most morphogenetic NAA or BOA treatments were excised, multiplied and successfully rooted and hardened. The results demonstrate that the synthetic auxin BOA is active in inducing shoot regeneration from leaf explants of apple and that the activity of BOA in plant regeneration is genotype dependent. When BOA was used to induce rooting in apple microcuttings, lower rooting percentages were obtained than with IBA, showing that the effect of BOA in inducing root formation is very low and that it cannot be used routinely to replace IBA in the in vitro rooting of microcuttings.