Fusarium–orchid interactions under greenhouse conditions

Abstract

Orchids reveal a complexity of interactions with their microbial partners, particularly with mycorrhizal fungi. Orchid roots are also colonized by a number of associated endophytic fungi, whose activity and role is as yet insufficiently known. Here we studied the relations between two epiphytic orchids, Dendrobium moshatum and D. nobile, and several strains of the genus Fusarium – two pathogenic, F. fujikuroi (IMI58289) and F. proliferatum (NRRL 62905), and an orchid-associated, Fusarium proliferatum ET1. Recent reports indicate that F. proliferatum shows a high phenotypic variation in causing symptoms on one or different hosts. In this study, in contrast to the pathogenic species, an orchid-associated F. proliferatum ET1 strain showed its neutral endophytic lifestyle strategy towards the host-orchids. Despite an invasive and aggressive distribution of both phytopathogens, causing the root and leaf symptoms, the moderate colonization of F. proliferatum ET1 did not cause any negative effects on the adult plants during the experimental period. The quantitative characteristic of the fungal growth assessed by counting colony forming units confirmed the results of the bioassay, supporting the strain-specificity of the orchid-fungal interactions and a pattern of balanced relations with the non-mycorrhizal endophytic Fusarium isolate.