Molecular phylogeny of the arbuscular mycorrhizal fungiGlomus sinuosumandSclerocystis coremioides

Celebrating INVAM: 35 years of the largest living culture collection of arbuscular mycorrhizal fungi

The International Culture Collection of (Vesicular-) Arbuscular Mycorrhizal Fungi-INVAM-the largest living culture collection of arbuscular mycorrhizal fungi (AMF) celebrated its 35th year in 2020. The authors record here the mission and goals of INVAM, its contribution as a living culture collection, some historical aspects of INVAM, and describe the advances in mycorrhizology and AMF systematics after INVAM moved to West Virginia University. This commentary emphasizes the importance of a living culture collection to preserve germplasm and to educate and assist researchers in mycorrhizal science.

Loss of arbuscular mycorrhizal fungal diversity in trap cultures during long-term subculturing

Long-term successional dynamics of an inoculum of arbuscular mycorrhizal fungi (AMF) associated with the maize rhizosphere (from traditionally managed agroecosystems in Los Tuxtlas, Veracruz, Mexico), was followed in Bracchiaria comata trap cultures for almost eight years. The results indicate that AMF diversity is lost following long-term subculturing of a single plant host species. Only the dominant species, Claroideoglomus etunicatum, persisted in pot cultures after 13 cycles. The absence of other morphotypes was demonstrated by an 18S rDNA survey, which confirmed that the sequences present solely belonged to C. etunicatum. Members of Diversisporales were the first to decrease in diversity, and the most persistent species belonged to Glomerales.

Evolutionary ecology of mycorrhizal functional diversity in agricultural systems

The root systems of most agronomic crops are colonized by diverse assemblages of arbuscular mycorrhizal fungi (AMF), varying in the functional benefits (e.g. nutrient transfer, pathogen protection, water uptake) provided to hosts. Little is known about the evolutionary processes that shape the composition of these fungal assemblages, nor is it known whether more diverse assemblages are beneficial to crop productivity. In this review we aim to identify the evolutionary selection pressures that shape AMF diversity in agricultural systems and explore whether promotion of AMF diversity can convincingly be linked to increases in agricultural productivity and/or sustainability. We then ask whether farmers can (and should) actively modify evolutionary selection pressures to increase AMF functioning. We focus on three agriculturally imposed selection regimes: tillage, fertilization, and continuous monoculture. We find that the uniform nature of these practices strongly selects for dominance of few AMF species. These species exhibit predictable, generally non-beneficial traits, namely heavy investment in reproduction at the expense of nutrient scavenging and transfer processes that are beneficial for hosts. A number of focus-points are given based on empirical and theoretical evidence that could be utilized to slow down negative selection pressures on AMF functioning, therein increasing crop benefit.

Morphology and molecular diversity of arbuscular mycorrhizal fungi in wild and cultivated yew (Taxus baccata)

Taxus baccata L. roots collected from two sites in southern Germany were heavily colonized by arbuscular mycorrhizal fungi (AMF). The colonization pattern was of the Paris type. The diversity of the colonizing AMF species was investigated using polymerase chain reaction based molecular techniques. The internal transcribed spacer (ITS) region of the DNA from AMF within the roots was amplified using Glomeromycota-specific primers and then cloned and sequenced. Phylogenetic analysis using a data set of 5.8S rDNA sequences from a wide range of glomeralean taxa as well as data sets of partial ITS2 sequences from glomeralean subgroups indicated root colonization by four sequence types of Glomus and one sequence type of Archaeospora. These sequence types are distinct from any previously published sequences and differed between the two study sites.Key words: arbuscular mycorrhiza, Paris-type AM, molecular diversity, ribosomal internal transcribed spacers, Taxus baccata.