Meiotic Defects and Premature Tapetal Degeneration Are Involved in the Low Fertility of Oncidesa Gower Ramsey, an Important Cut-flower Orchid

Abstract

The dancing-lady orchid, Oncidesa Gower Ramsey, is an important cultivar for cut-flower production, but it has low pollen fertility in breeding programs. In this study, we compared the pollen germination in vitro, sporad type, and pollinia development of Oncsa. Gower Ramsey and a diploid species, Oncidium sphacelatum Lindl (one of its grandparents). In Oncsa. Gower Ramsey, the pollen germination in vitro was lower as compared with those in Onc. sphacelatum. In addition, the frequency of abnormal sporads in Oncsa. Gower Ramsey was higher than those in Onc. sphacelatum. In Oncsa. Gower Ramsey, the middle layer and the tapetum were disorganized before meiosis, and subsequently they degenerated at the early tetrad stage. In contrast, the middle layer and the tapetum of Onc. sphacelatum began to degenerate at the early tetrad stage and fully disappeared at the bicellular pollen stage. These results suggested that the abnormal meiosis caused by unbalanced genomes and the premature degeneration of the middle layer and the tapetum could probably result in the abnormal pollen development and the low fertility of Oncsa. Gower Ramsey.