Seed Micromorphology, In Vitro Germination, and Early-Stage Seedling Morphological Traits of Cattleya purpurata (Lindl. &amp; Paxton) Van den Berg

Miriam Bazzicalupo,Jacopo Calevo,Laura Cornara,Annalisa Giovannini,Andrea Copetta,Martino Adamo

doi:10.3390/horticulturae7110480

Abstract

In the context of a symbiotic plant-fungus interaction study concerning Cattleya purpurata, we focused on some aspects of seed morphology and biology, and the early stages of seedling development. Seed morphology was characterized using light and scanning electron microscopy. In vitro seed germination capability was evaluated, comparing symbiotic and asymbiotic methods. The morphology of the seeds was overall comparable to that of other congeneric species, showing classical adaptations related to the aerodynamic properties and to the wettability of seeds, but calcium oxalate druses were identified inside the suspensor cells. Asymbiotic seed germination was successful in all tested media (17.1–46.5%) but was higher on 1/2 Murashige & Skoog. During symbiotic interaction with the fungal strain MUT4178 (Tulasnella calospora), germination rate was significantly lower than that obtained with the best three asymbiotic media, suggesting a low fungal compatibility. Seedling morphology was in line with other taxa from the same genus, showing typical characteristics of epiphytic species. Our observations, in particular, highlighted the presence of stomata with C-shaped guard cells in the leaves, rarely found in Cattleyas (where usually they are reniform), and confirm the presence of tilosomes in the roots. Idioblasts containing raphides were observed in both roots and leaves.

Highlights

Orchidaceae, with about 28,000 species and new ones being discovered every year, is one of the largest families of flowering plants [1]
Almeida et al [26] indicated Tulasnellaceae as the main possible fungal symbionts for this orchid group; our results, which report the first attempt of symbiotic germination for C. purpurata may indicate that the fungal strain used, isolated from an European terrestrial orchid, might not be the most appropriate or the dominant symbiont for this species, even if we demonstrated its colonization of roots
Seedling morphology was comparable with other congeneric species, showing typical characteristics of epiphytic orchids such as root velamen with 2–3 cells layers

Summary

Introduction

Orchidaceae, with about 28,000 species and new ones being discovered every year, is one of the largest families of flowering plants [1]. The great majority of species is native to tropical or sub-tropical areas, but the family can be considered cosmopolitan, being spread over the five continents, with a distribution range that extends from the Arctic. Among the Epidendroideae subfamily, the subtribe Laeliinae is strictly neotropical and comprises about 50 genera with about 1500 species [7,8]; it is one of the largest subtribes in the family after Pleurothallidinae and Oncidiinae [9]. Horticulturae 2021, 7, 480 over the last few decades; in this subtribe, Dressler [7] included the genera Cattleya Lindl., Laelia Lindl., Schomburgkia Lindl., and Sophronitis Lindl. Van den Berg et al [9,10], thanks to a phylogenetic analysis on ITS regions and considering the hybridization capability within

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Discussion

Conclusion