Asymbiotic germination and morphological studies of seeds of Atlantic Rainforest micro-orchids (Pleurothallidinae)

Abstract

The morphological and morphometric characters of seeds belonging to 11 species of the subtribe Pleurothallidinae using light and scanning electron microscopy were studied to understand the in vitro germination process. Qualitative data (color, shape, ornamentation) and quantitative ones were also evaluated in seeds and embryos (length, width, volume and air space percentage between the integument and the embryo). The viability of the seeds was evaluated by in vitro germination in woody plant medium (WPM), and by analysis of the developmental stages of protocorms until seedling formation (two to 24 weeks). Morphometric data showed variations within the genus Acianthera and between species of different genera. The best germination and protocorm formation responses occurred with Acianthera prolifera (92%) and Acianthera ochreata (86%), with the formation of seedlings after 12 and 16 weeks of sowing, respectively. The seeds and embryos of A. prolifera and A. ochreata were larger (length, width, and volume) with a structural polarity that may have facilitated their germination comparing to others studied species. Other characteristics of A. prolifera seeds that may have contributed to these results include the presence of a thin testa without ornamentation and a suspensor. The protocorms of Anathalis obovata, Dryadella liliputiana, and Octomeria gracillis developed slowly in the WPM, not reaching the seedling stage in 24 weeks of cultivation. This morphological and morphometric study contributes to the understanding of asymbiotic germination of some micro-orchid species.

Seed viability testing for research and conservation of epiphytic and terrestrial orchids

“…In many species, even when such impediments to germination is overcome, germination maybe very slow, requiring long-term germination monitoring. In the former case, it may not be possible to successfully germinate seeds (Yamazaki and Miyoshi 2006 ) and in the latter the time required to complete the germination test may exceed the standard test times (Koene et al 2020 ). This is true especially for orchids, which can take up to several years to complete germination compared to two to three weeks for agricultural and horticultural crops and eight weeks for woody species (Gosling 2003 ).…”

Developing Paraphalaenopsis labukensis (Shim, A. Lamb & C.L. Chan), an Orchid Endemic to Sabah, Borneo, Asymbiotic Seed Germination and In Vitro Seedling Development

“…Yet, the length and diameter of the capsule seed are not the most important parameters in evaluating seed maturity [44]. Moreover, orchid seeds differ in embryo morphometry, seed coat decoration, size, shape, and volume [45]. Consequently, knowledge of seed germination capabilities is necessary to determine the optimal germination conditions, which then could enhance the seed range that would most likely propagate [46].…”

Compuestos orgánicos en la propagación in vitro de Epidendrum falcatum Lindl orquídea endémica de México

“…Y tambien son más altos que los encontrados por Flores-Escobar et al, (2011), quienes reportan porcentajes de germinación de 48, 57 y 50% para las especies Oncidium stramineum, Brassia verrucosa y Encyclia adenocaula, respectivamente. Las bajas germinaciones en el cultivo in vitro de orquídeas de Oncidium stramineum, Brassia verrucosa y Encyclia adenocaula se pueden deber a factores propios de las semillas, como la baja viabilidad, embriones pequeños en relación a la testa, por lo que el volumen de la semilla puede estar ocupado por un 96% de aire y la humedad no llega al embrión (Koene et al, 2020), comparado con las semillas de E. falcatum, que presentaron mayor viabilidad y un estado de madurez óptimo de la capsula.…”