The 2012 ASHS Annual Conference

The process leading to the development of new varieties involves the preservation of superior genotypes that perform well in the field. In vitro culture can regenerate important germplasm into a complete plant free of viral, bacterial or fungal diseases. An experiment was conducted to determine the effect of the size and shape of explants extracted from apical and axillary buds on their capacity to develop into plantlets following in vitro culture. A viable plantlet was defined as one with at least one root and one leaf, in both cases longer than 1 cm. The apical and axillary shoot buds were extracted, including some underlying tissue, and explants prepared using four types of cuts, namely, square, diametral, diamond, and transverse. With the exception of the transverse sectioning, for which length was 9 mm, each bud was left with underlying pith tissue measuring 3, 6, and 9 mm. Regardless of the size and shape of the explants, the plantlets derived from apical buds produced 4.2 times more leaves (P < 0.0001) and 2.7 times more roots (P < 0.0001) than those derived from axillary buds, resulting in 29% more explants producing viable plantlets (P < 0.0001) after 6 weeks on Murashige and Skoog medium. After two weeks of acclimation, the percentage of surviving, viable plantlets in relation to initial number of explants put into culture was higher (80%, P < 0.0001) from the 6-mm diamond-shaped explants than from the diametral-shaped (41% to 51%) and transverse-shaped (49%) explants, but not from the other diamond-shaped (71% to 76%) and the square-shaped explants (61% to 70%). Compared with other shapes, the reduced loss in viable plantlets during acclimation with diamond-shaped explants was associated with a higher root number to leaf number ratio prior to acclimation.