Relationships between Oak powdery mildew incidence and severity and commensal fungi

Abstract

Oak (Quercus robur) powdery mildew is a common and damaging fungal disease. In a local survey at Reading, UK, oak powdery mildew was common on trees of all height classes but was most common on trees of 3-9 m. A variety of other fungal species were commonly found growing in association with oak powdery mildew colonies. The abundance of such fungi was estimated through stratified sample surveys for 2.5 years. The taxa most commonly associated with oak powdery mildew were Acremonium sp., Trichoderma sp., Ampelomyces/Phoma sp. and Leptosphaerulina australis. Nearly 90% of mildew colonies were associated with L. australis, which is not generally considered as a mycoparasite or antagonist, in contrast with the other three fungi. Abundance varied between June and October surveys. Acremonium sp. abundance was greater in summer samplings, whereas L. australis and Trichoderma sp. abundances were greater in autumn samplings. Ampelomyces/Phoma sp. was never observed in the absence of powdery mildew. Relationships between the mildew-associated fungi and oak powdery mildew appeared curved and differed significantly between sampling years. L. australis was positively correlated with the other three associated fungi studied when powdery mildew was also present. The variety and high population densities of the mildew-associated fungi suggest that they may be important in determining the final density of oak mildew and the damage caused by it.

Enhancing identification accuracy for powdery mildews using previously underexploited DNA loci

“…Amplification, sequencing, and species discrimination success varied greatly across genes, perhaps due to low quantity and quality of environmental PM DNA. Those which were unsuccessful were characterised by weak reads, resulting in little or no sequence data, or messy reads, potentially contaminated with more than one PM species or with mycoparasitic fungi (Pintye et al, 2015;Topalidou & Shaw, 2016) and other phylloplane community members (Berendsen et al, 2012;Topalidou, 2014;Franco et al, 2017). Amplification of multiple products in certain accessions was also evident and may indicate that the primer combination is not 100% specific to PMs; amplifying mycoparasitic fungi as well as the targeted PM.…”

Mutual interplay between phytopathogenic powdery mildew fungi and other microorganisms

“…Mycoparasites co‐occur with powdery mildews in natural settings, as, for example, reported for the oak powdery mildew pathogen (Topalidou et al. , ). Such intimate fungal associations may also include species that are seemingly not mycoparasitic (Topalidou et al.…”

“…Such intimate fungal associations may also include species that are seemingly not mycoparasitic (Topalidou et al. , ). The tritrophic interaction between plant hosts, powdery mildew fungi and their mycoparasites serves as an interesting example of plant and fungal ecology (Parratt et al.…”

Urbanization affects oak–pathogen interactions across spatial scales

“…This negative, year‐dependent impact contrasts with the positive effects of leaf litter shown for herbivorous insects on urban oaks (Herrmann et al 2012, Barr et al 2021), where leaf litter possibly increased overwintering survival by providing an insulative layer. Instead, leaf litter may alter the microclimate of the tree, such as humidity levels, which could impact powdery mildew performance (Sayer 2006), or affect the survival of specialist and opportunistic fungi that attack powdery mildew (Topalidou and Shaw 2016). Since an effect of leaf litter was only detectable in one year, the strength and direction of this effect might be dependent on the specific climatic conditions within a given year.…”