Anchoring the species Rhizophagus intraradices (formerly Glomus intraradices)

Abstract

The nomenclatural type material of Rhizophagus intraradices (basionym Glomus intraradices) was originally described from a trap pot culture established with root fragments, subcultures of which later became registered in the INVAM culture collection as FL 208. Subcultures of FL 208 (designated as strain ATT 4) and a new strain, independently isolated from the type location (ATT 1102), were established as both pot cultures with soil-like substrate and in vitro root organ culture. Long-term sampling of these cultures shows spores of the species to have considerable morphological plasticity, not described in the original description. Size, shape and other features of the spores were much more variable than indicated in the protologue. Phylogenetic analyses confirmed earlier published evidence that sequences from all R. intraradices cultures formed a monophyletic clade, well separated from, and not representing a sister clade to, R. irregularis. Moreover, new phylogenetic analyses show that Rhizoglomus venetianum and R. irregularis are synonymous. The morphological characters used to separate these species exemplify the difficulties in species recognition due to the high phenotypic plasticity in the genus Rhizophagus. Rhizophagus intraradices is morphologically re-described, an epitype is designated from a single-spore isolate derived from ATT 4, and R. venetianum is synonymised with R. irregularis.

Rhizophagus irregularis, the model fungus in arbuscular mycorrhiza research, forms dimorphic spores

“…In this context, to capture all the intraspecific morphological variability, Walker et al . (2021) emphasized the importance of characterizing new species based on analyses of multiple cultures grown long enough and the need for intermittent redescriptions of species in the Glomeromycotina, as type specimens may represent only a subset of the phenotype based on variation in anatomical/histochemical characters.…”

“…It is thus plausible that biotic and/or abiotic factors induce the production of spores with two divergent morphologies primarily in vivo, but not under the very stable in vitro conditions commonly used for the propagation of the strain DAOM 197198 of R. irregularis. In this context, to capture all the intraspecific morphological variability, Walker et al (2021) emphasized the importance of characterizing new species based on analyses of multiple cultures grown long enough and the need for intermittent redescriptions of species in the Glomeromycotina, as type specimens may represent only a subset of the phenotype based on variation in anatomical/histochemical characters.…”

“…Rather, up to 10 rRNA genes with distinct sequences (pairwise similarity = 92.6–100% for the partial SSU‐ITS‐LSU regions) are present within the R. irregularis DAOM 197198 genome and are located on four chromosomes (Yildirir et al ., 2022; Sperschneider et al ., 2023). This intragenomic rDNA heterogeneity can mislead molecular identification; a situation well‐illustrated by the description of R. venetianum (Turrini et al ., 2018), which was described as a new species based on only one of the multiple ribotypes of R. irregularis (Walker et al ., 2021). Thus, phenotypic plasticity, dimorphism, and intragenomic rDNA heterogeneity make AMF taxonomy, species recognition, and inoculum purity a challenging endeavour.…”

The Metabolic Profile of Anchusa officinalis L. Differs According to Its Associated Arbuscular Mycorrhizal Fungi

“…Despite the widely accepted fact that different AMF genera could affect plant metabolome differently [ 52 ], one of the main observations of the present study is that AMF species belonging to the same genus may induce similar, but not strictly identical, metabolomic responses in A. officinalis plants, without being strongly related phylogenetically. Indeed, the latest updates regarding the phylogenetic classification of under-investigated AMF strains showed that R. irregularis is phylogenetically more closely related to R. clarus than to R. intraradices [ 53 ]. Therefore, the outcome of the association in terms of, e.g., plant growth promotion and metabolites enhancement, is highly specific to the identity of the AMF symbiont [ 2 , 54 , 55 ].…”

Arbuscular Mycorrhizal Fungi and the Need for a Meaningful Regulatory Plant Protection Product Testing Strategy

“…In these studies, continuous in vitro root production can be achieved, enabling mycorrhizal colonization, without the need for aboveground plant tissues (Bécard & Fortin, 1988; Danesh et al, 2006; Srinivasan et al, 2014). Wan et al (1998) used Ri T‐DNA–transformed Daucus carota roots associated with Glomus intraradices (now Rhizophagus intraradices [Walker et al, 2021]) to show that this system could be used to detect dose responses of reductions in percentage of root colonization following exposure to increasing concentrations of copper sulfate, glyphosate, and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid, with no effects observed for benomyl, chlorothalonil, and dimethoate. Both Zocco et al (2008) and Campagnac et al (2008) examined mycorrhization of D. carota by R. intraradices following exposure to the fungicides fenpropimorph and fenhexamid, with Zocco et al (2008) reporting no effects and Campagnac et al (2008) reporting significant declines driven by fenpropimorph only.…”