Understanding the resilience of soil beneficials to combat apple replant disease (ARD).

Apple Replant Disease (ARD), caused by an accumulation of soil-borne fungal and oomycete pathogens in the soil, is an economically important disease of apples. Current management relies on the use of broad-spectrum chemical fumigation. Banning of chemical products has seen increased research into biological management strategies for ARD. This study aimed to test the efficacy of a number of commercially available biological soil amendments to improve the establishment of young apple trees in an attempt to minimise the detrimental effects of ARD. It also looked at changes in planting position and rootstock selection at planting to manage ARD and how climate change abiotic factors affect bulk apple soil microbiome communities. The efficacy of single species amendments was variety specific in the field. There was a increased rate of tree girth expansion in Gala trees amended pre-planting with Pseudomonas fluorescens but the same effect was not observed with Braeburn trees. The single species amendments did not increase the establishment of young apple trees either individually or in a consortium of amendments in semi-field conditions. In both field and semi-field conditions pre-plant amendment significantly altered the abundance of individual operational taxonomic units (OTUs) associated with both beneficial and pathogenic taxa of plants. The planting position in the inter-row alleyways and the genetic relationship of the new rootstock to the previously planted rootstock on the site were both identified to minimise ARD severity. In addition, a significant effect of CO₂ concentration and temperature increase on bulk soil microbiome communities was observed but this was not as significant as site management (organic vs conventional) effect. This research will aid with the development of management strategies for ARD by integrating single species biological amendments and cultural approaches with other management practices.