The garden strawberry, Fragaria × ananassa is a very popular and important fruit crop grown worldwide in various climates . In places with short seasons, it is increasingly common to cultivate strawberry in greenhouses and plastic tunnels. Despite the benefits of a prolonged season and the more controlled environment they provide, this type of cultivation can lead to economic losses due to higher disease pressure from certain pathogens . Protected culture systems have ideal conditions for the fungal pathogen Podosphaera aphanis which thrives in rain free, dry, and warm environments . P. aphanis is an obligate biotrophic parasite that causes strawberry powdery mildew, one of the most significant strawberry diseases .
The current main treatment of strawberry powdery mildew is to use fungicides. However, fungicides overuse has led to development of fungicide resistant pathogens and a growing concern for fungicide residues on the fruits. In addition, many commercial strawberry cultivars are especially susceptible to the pathogen . Thus, there is a demand for new disease management strategies. An approach that can facilitate disease management is to characterize the pathogen population structure. This can reveal valuable information and be a useful complement to development of alternative treatments and resistance breeding .
Investigating the genetic diversity of specific pathogen populations can clarify the complexity of powdery mildew and give suggestion for the most effective breeding approach for a particular area based on its pathogen type. If the pathogen diversity is high, it will be necessary to develop cultivars with broad resistance . Knowledge of the population structure can also facilitate treatment applications by adapting them to the local pathogen population .
Currently nothing is known about the genetic structure and potential genetic differences of P. aphanis populations in Norway. This study aims at investigating genetic variation of Norwegian P. aphanis by using a newly developed method based on amplicon sequencing (AmpSeq). The method is cheap and well adapted for obligate biotrophic organisms like powdery mildew species where high DNA quantity is difficult to obtain and a reference genome is lacking . AmpSeq has been used to determine origin, mating types and genetic differences within and between populations of organisms causing powdery mildew in hops and grape .
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