Is it feasible to use mixed orchards to manage apple scab?

Abstract

Apple scab, caused by the fungus Venturia inaequalis, is one of the most damaging diseases of cultivated apples (Malus x domestica) worldwide. It results in huge losses as it diminishes fruit quality and impacts tree growth. Current management revolves around the application of fungicides, however the number of sprays required per season is unsustainable and expensive. Further to this, populations of V. inaequalis have developed fungicide resistance. Breeding new cultivars with higher levels of resistance to scab is a priority, however, this process is long, so introducing mixed cultivar orchards may be a faster solution. We reviewed the general principles of using mixtures to manage plant diseases, and then considered specifically using mixed cultivars to manage apple scab in commercial production. Limited field studies have demonstrated the potential of using mixture to suppress apple scab development; but scab super-races that could emerge from mixture can pose a significant risk in commercial production. However, recent research on population genetics of apple scab in monoculture and mixed orchards suggests that the risk of super-race emergence is probably over-stated, because assortative mating among lesions on the same leaves is likely to occur, rather than commonly assumed random mating. Thus, we conclude that cultivar mixtures can contribute towards sustainable scab management, particularly in commercial cider apple production.

Keywords

• apple scab
• venturia inaequalis
• mixed cultivar culture
• disease management