Efficiency of mycorrhizal fungi for seed germination and protocorms development of commercial Cattleya species (Orchidaceae)

Abstract

Orchidaceae is one of the largest plant families and stands out for its wide variety of flowers with ornamental and environmental importance. Cattleya is one of the main commercial genera, presenting a great diversity of species and hybrids that attract the attention of collectors, orchid enthusiasts, and consumers. In their natural environment, orchids associate with mycorrhizal fungi, which are responsible for providing carbon and other nutrients during seed germination. This study investigated the potential of mycorrhizal fungi isolated from the genus Cattleya for in vitro symbiotic germination of seeds from three contrasting Cattleya species, comparing them with non-symbiotic germination in a commercially used culture medium for orchid propagation. The isolated fungi were molecularly identified through phylogenetic analyses of DNA sequences using the ITS (Internal Transcribed Spacer) region. Three isolates obtained were identified as Tulasnella amonilioides, and through microscopic evaluations, the formation of monilioid cells was observed, a morphological characteristic previously unknown for this species. The T. amonilioides isolates were efficient in promoting seed germination of Cattleya bicolor, Cattleya walkeriana and Cattleya jongheana and accelerated the germination process when compared with the non-symbiotic commercial medium, showing to be promised for commercial seed production of these orchids species.

Keywords: Hadrolaelia; Laelia; Tulasnella; Mycorrhizal associaton; Orchidaceae; Taxonomy.

Fig. 1

Phylogenetic tree inferred by Bayesian analysis based on ITS region alignment. Posterior probability (PP) values ≥ 90 and maximum likelihood bootstrap support (ML) values ≥ 75, were placed next to each node (PP/ML). The clade belonging to the species Tulasnella amonilioides is within a green box. The isolates obtained in this study are highlighted in bold. The tree was rooted with the species Botryobasidium botryosum

Fig. 2

Tulasnella amonilioides (COAD 3519), a culture in PDA at 14 d, b culture in CMA at 14 d, c monilioid cells, d hyphae forming a 90º angle. Scale bars = 20 μm

Fig. 3

Germination of Cattleya bicolor. a Germination index at 30, 50 and 80 d after inoculation of isolates COAD 3517, COAD 3518 and COAD 3519 in modified oatmeal agar culture medium (OMA), and in axenic controls (OMA and commercial B&G culture medium). Comparisons between germination means were performed at each developmental stage (30, 50, and 80 days) using Duncan’s test at a 5% significance level. Protocorms at 50 days: b COAD 3517, c COAD 3518, d COAD 3519, e axenic OMA culture medium, f axenic B&G culture medium (white arrows point to protocorms). g Cluster of pelotons in the roots of symbiotically germinated orchid

Fig. 4

Germination of Cattleya walkeriana. a Germination index at 30, 50 and 80 d after inoculation of isolates COAD 3517, COAD 3518 and COAD 3519 in modified oatmeal agar culture medium (OMA), and in axenic controls (OMA and commercial B&G culture medium). Comparisons between germination means were performed at each developmental stage (30, 50, and 80 days) using Duncan’s test at a 5% significance level. Protocorms at 50 days: b COAD 3517, c COAD 3518, d COAD 3519, e axenic OMA medium, f axenic B&G medium (white arrows point to protocorms). g Cluster of pelotons in the roots of symbiotically germinated orchid

Fig. 5

Germination of Cattleya jongheana. a Germination index at 30, 50 and 80 d after inoculation of isolates COAD 3517, COAD 3518 and COAD 3519 in modified oatmeal agar culture medium (OMA), and in axenic controls (OMA and commercial B&G culture medium). Comparisons between germination means were performed at each developmental stage (30, 50, and 80 days) using Duncan’s test at a 5% significance level. Protocorms at 80 days: b COAD 3517, c COAD 3518, d COAD 3519, e axenic OMA medium, f axenic B&G medium (white arrows point to protocorms). g Cluster of pelotons in the roots of symbiotically germinated orchid