Relationship between the Growth of Current Shoot and the Development of Inflorescence and Vegetative Buds in Oncidesa Gower Ramsey ‘Honey Angel’ Leaf Axils

Abstract

The flowering control of Oncidesa Gower Ramsey ‘Honey Angel’ is important and in-demand by the industry. Therefore, an understanding of the development of inflorescence and vegetative shoot from the leaf axils on the current shoot is required. The internode of a young Oncidesa current shoot between the 0th (at the base of the pseudobulb) and 1st (immediately above the pseudobulb) nodes can enlarge to form a pseudobulb, and the axillary bud on the 0th or -1st (immediately below the 0th node) node can differentiate into an inflorescence bud. The axillary buds on the lower nodes (-2nd to -4th nodes) can remain vegetative. In this study, we investigated the growth and anatomical features of axillary buds at various stages during the growth of the current shoot. We sampled the axillary buds on the 0th to -4th nodes from the current shoots when they were 10, 15, 20, 25, and 30 cm in length for sectioning and anatomical observations. Vegetative buds on the -2nd to -4th nodes grew faster and had more nodes than the inflorescence bud when the current shoot grew from 10 to 25 cm. However, when the current shoot elongated from 25 to 30 cm, the length and node number in the inflorescence bud on the 0th node increased and the inflorescence branch primordia were observable. The length and node number of the inflorescence bud became the same as that of the vegetative buds, which had no further growth, whereas the current shoot grew from 25 to 30 cm. The pseudobulb began to emerge from the leaf sheath (unsheathing) when the current shoot had reached 30 cm in length. Therefore, the time when the pseudobulb started to unsheathe from its subtending leaf was critical for the reproductive growth of Oncidesa Gower Ramsey ‘Honey Angel’ when growth acceleration of the inflorescence bud occurred. Evaluating the current shoot length can be a nondestructive method of estimating the developmental stage of the inflorescence bud.