No Indication of Strict Host Associations in a Widespread Mycoparasite: Grapevine Powdery Mildew (Erysiphe necator) Is Attacked by Phylogenetically Distant Ampelomyces Strains in the Field

Abstract

Pycnidial fungi belonging to the genus Ampelomyces are common intracellular mycoparasites of powdery mildews worldwide. Some strains have already been developed as commercial biocontrol agents (BCAs) of Erysiphe necator and other powdery mildew species infecting important crops. One of the basic, and still debated, questions concerning the tritrophic relationships between host plants, powdery mildew fungi, and Ampelomyces mycoparasites is whether Ampelomyces strains isolated from certain species of the Erysiphales are narrowly specialized to their original mycohosts or are generalist mycoparasites of many powdery mildew fungi. This is also important for the use of Ampelomyces strains as BCAs. To understand this relationship, the nuclear ribosomal DNA internal transcribed spacer (ITS) and partial actin gene (act1) sequences of 55 Ampelomyces strains from E. necator were analyzed together with those of 47 strains isolated from other powdery mildew species. These phylogenetic analyses distinguished five major clades and strains from E. necator that were present in all but one clade. This work was supplemented with the selection of nine inter-simple sequence repeat (ISSR) markers for strain-specific identification of Ampelomyces mycoparasites to monitor the environmental fate of strains applied as BCAs. The genetic distances among strains calculated based on ISSR patterns have also highlighted the genetic diversity of Ampelomyces mycoparasites naturally occurring in grapevine powdery mildew. Overall, this work showed that Ampelomyces strains isolated from E. necator are genetically diverse and there is no indication of strict mycohost associations in these strains. However, these results cannot rule out a certain degree of quantitative association between at least some of the Ampelomyces lineages identified in this work and their original mycohosts.

A hyperparasite affects the population dynamics of a wild plant pathogen

“…Furthermore, amplification worked well for the six selected strains tested, despite high genetic variability in their ITS sequences (Pintye et al 2012), suggesting Prevalence of Ampelomyces Fraction of plants infected Fig. 3 The impact of the prevalence of the hyperparasite Ampelomyces in autumn 2011 on the overwintering success (fraction of infected plants in July 2012) of its powdery mildew host Podosphaera plantaginis at a small spatial scale (1-m 2 quadrat).…”

“…The reverse primer (AQ-R462, 5 0 -GCT GCCAATTGCTTTGAGAT-3 0 ) is located in a hypervariable region; however, it presents 60% identity with ITS sequence of the host plant and the powdery mildew fungal host. This partial overlap of the Ampelomycesspecific AQ-F264/AQ-R462 primers and the ITS sequence of P. plantaginis could not be avoided due to the diversity of ITS sequences determined in different Ampelomyces lineages (Pintye et al 2012). However, the qPCR method developed in this work did reliably distinguish the Ampelomyces-specific amplifications from false-positive results by setting up a proper cut-off value (see below).…”

“…As the within-species diversity of Ampelomyces within Aland has not yet been studied, we assessed the generality of our detection method by testing six different Ampelomyces strains (A1, AQ10, B124-a, GYER, TP1 and Vitis32, see details in Table S1, Supporting information) belonging to four different lineages of the five described to date (Pintye et al 2012). These strains were grown on Czapek-Dox medium supplemented with 2% malt.…”

First Report of Ampelomyces quisqualis from Sycamore and Crape Myrtle and Its Potential as a Mycoparasite of Powdery Mildew

“…At present, a few Ampelomyces isolates have already been registered as biocontrol agents of powdery mildews, e.g. AQ10 biofungicide is commercially used for the biocontrol of grape powdery mildew [10].Recent research on the phylogenetic analysis based on the internal transcribed spacer (ITS) rDNA sequences revealed that the species could be classified into five different genetic clades, showing that different physiological forms exist within genetically diverse strains of the species [11]. P. occidentalis is widely planted as a street tree distributed in South Korea and is useful in the rehabilitation of various sites with saturated soils.…”

“…Bootstrap values are shown above/below branches supported by more than 50% from 1,000 replications. Each clade was made based on the previous phylogenetic system constructed by Pintye et al [11]. fungi (Biopact Corp., Daejeon, Korea).…”