Studies on Relationship between Embryogenesis and Germination in Orchidaceae

Abstract

The ability of seeds of 47 orchid species, collected at differnt stages of embryo development, to germinate was studied.
1. Most immature seeds collected when the embryos were pretetrad through the intermediary stages germinated poorly and grew slowly. They had a tendency to require longer developmental periods before they germinated.
2. The highest % germination (rate) was attained when embryos were between the octant stage and completion of embryogenesis. Most orchid species attained maximum germination rates after completion of embryogenesis except in Cypripedium japonicum and Cephalanthera falcata. The maximum % germination (rate) ranged between 0.8%100 %; seeds of all species developed well after germination except those of Cypripedium japonicum.
3. No close relationship was recognized among embryos collected at the earlist developmental, intermediate and mature stages versus the developmental stage of the ovary at anthesis.
4. Orchids were grouped into 4 types with respect to their % germination (rate) after attaining maximum.
Type a : The highest germination rate was observed at final stage just before yellowing and dehiscence of ovary.
Type b : The highest germination rate was attained at final stage and the germination rate has possibility to change according to the progress of developmental stage.
Type c : Germination rate decreased as embryogenesis progressed.
Type d : The germination rate continued at maximum until the embryo matured.
The largest number of species was categorized as Type c.
5. The days between sowing and germination ranged from 3 to 305 depending on the stage of embryogenesis and species. Based on the relationship between the days from sowing date to germination and developmental stages of the harvested embryos, the species were grouped into two types : a, the interval before germination was shortened with increasing embryo age or b, the period became prolonged with embryo age.
Much more species were classified as Type a than Type b.
6. Among the media tested, Hyponex medium was suitable for embryo culture, but the Murashige and Skoog medium resulted in better % germination (rate) and seedling growth for Gastrodia elata and Cymbidium hosai.
7. No common characteristics of subfamily were recognized among the 47 species with respect to embryogenesis and seed germination.