Stigmasterol-driven enhancement of the in vitro multiplication rate for the marubakaido apple rootstock

The treatment of in vitro-grown shoots of the marubakaido apple rootstock with 0.5 mu g stigmasterol, an end-pathway sterol of the bifurcated sterol biosynthetic pathway, in 5 mu L acetone per shoot led to a significant (p a parts per thousand currency sign 0.05) enhancement of the multiplication rate (MR) from 5.1 (shoots treated with 5 mu L acetone only) to 10.3. This increase in the MR was due to a significant enhancement of the number of newly formed main shoots suitable for micropropagation purposes (measuring at least 15 mm in length) from 2.6 to 3.3 per explant, and of the number of newly formed primary lateral shoots from 2.2 to 5.0 per explant as well. Shoots treated with stigmasterol at 0.5 and 2.5 mu g per shoot presented primary and secondary lateral shoots with significantly (p a parts per thousand currency sign 0.05) longer length compared to shoots treated with acetone only. These results provide an insight into the morphological responses of the marubakaido rootstock shoots to the treatment with an end-pathway sterol. To the best of my knowledge, this is the first report on the successful use of stigmasterol for the improvement of a micropropagation system. These results also demonstrate that stigmasterol-induced shoot proliferation is a low-cost and effective way to enhance the in vitro MR for the apple rootstock.