Genetic diversity and host plant preferences revealed by simple sequence repeat and mitochondrial markers in a population of the arbuscular mycorrhizal fungus Glomus intraradices

Abstract

Summary• Arbuscular mycorrhizal fungi (AMF) are important symbionts of plants that improve plant nutrient acquisition and promote plant diversity. Although within-species genetic differences among AMF have been shown to differentially affect plant growth, very little is actually known about the degree of genetic diversity in AMF populations. This is largely because of difficulties in isolation and cultivation of the fungi in a clean system allowing reliable genotyping to be performed.• A population of the arbuscular mycorrhizal fungus Glomus intraradices growing in an in vitro cultivation system was studied using newly developed simple sequence repeat (SSR), nuclear gene intron and mitochondrial ribosomal gene intron markers.• The markers revealed a strong differentiation at the nuclear and mitochondrial level among isolates. Genotypes were nonrandomly distributed among four plots showing genetic subdivisions in the field. Meanwhile, identical genotypes were found in geographically distant locations. AMF genotypes showed significant preferences to different host plant species (Glycine max, Helianthus annuus and Allium porrum) used before the fungal in vitro culture establishment.• Host plants in a field could provide a heterogeneous environment favouring certain genotypes. Such preferences may partly explain within-population patterns of genetic diversity.

Relatedness among arbuscular mycorrhizal fungi drives plant growth and intraspecific fungal coexistence

“…Genetic and phenotypic differences among the isolates have already been shown (Koch et al, 2004(Koch et al, , 2006. The genetic distance among these isolates was already determined (Croll et al, 2008). We chose six isolates known as A1, A5, B2, B12, C2 and C5.…”

“…This was represented as a proportion, where 1 equals a different allele at all 13 loci and 0 represents identical alleles at all 13 loci. The loci are described in (Croll et al, 2008). There was one control treatment without AMF.…”

“…One aspect that has been largely overlooked is the effect on plant growth of several coexisting AMF from a population of the same species. This could be important ecologically because some AMF species such as Rhizophagus irregularis exhibit a high genetic diversity even at a small spatial scale (Koch et al, 2004;Croll et al, 2008;Bö rstler et al, 2010) and vary in their effects on plant growth (Munkvold et al, 2004;Koch et al, 2006). This means that several AMF of the same species, differing in their genetic relatedness and their effects on plant growth, have the opportunity to coexist in the same plant.…”

“…First, a set of appropriate markers now exists for distinguishing between AMF individuals and for measuring their relatedness (Croll et al, 2008). Second, quantitative techniques employing such markers can be used to measure relative frequencies of isolate-specific alleles in samples containing AMF DNA (Angelard et al, 2010).…”

“…Given that genetic variation is high in AMF populations (Koch et al, 2004;Croll et al, 2008;Bö rstler et al, 2010), we assume that a plant root must encounter AMF individuals that differ in their relatedness. AMF are thought to be clonal haploid organisms and their genetics is poorly understood .…”