Effect of explant type and growth regulators on in vitro regeneration of apricot (Prunus armeniaca L.) Al-Amar rootstock

Apricot is a highly recalcitrant species for shoot regeneration in addition the plant regeneration capacity is strongly genotype - dependent. Thus, this study aimed to establish in vitro regeneration of the Egyptian Al-Amar apricot rootstock. Two explant types (Cotyledon and hypocotyl) were cultured on woody plant medium (WPM) supplemented with three concentrations of thidiazuron (TDZ) in combination with eight concentration of indole-3-butyric acid (IBA) or alpha-naphthalene acetic acid (NAA). The cotyledons showed direct somatic organogenesis as the explants formed buds directly on regeneration media. The highest percentage of cotyledons producing buds was 78.00% when cultured on WPM containing 13.62 mu M TDZ and 2.46 mu M IBA. In contrast hypocotyls expressed indirect somatic organogenesis, as the explants produced callus first before bud formation. The highest percentage was 96.87% in hypocotyls cultured on WPM fortified with 15.89 mu M TDZ and 1.61 mu M NAA. The shoot proliferation was achieved when buds from cotyledons and hypocotyls were cultured on Soot Regeneration Medium (SRM) supplemented with 8.87 mu M 6-Benzylaminopurine (BAP) and 0.54 mu M NAA. The highest shoot formation with an average of 6.4 shoots per explant was obtained from hypocotyls, while an average of 2.0 shoots per explants was achieved from cotyledons. The regenerated shoots were rooted on WPM including 9.80 mu M IBA. The results revealed that the regeneration of Al-Amar rootstock was more successful through hypocotyls and could therefore facilitate its genetic manipulation.