Effects of a cultivar mixture on scab control in apple orchards

The impact on apple scab of a cultivar mixture including the cvs Melrouge (low susceptibility to scab) and Pitchounette (Rvi6 resistant) was assessed in two experimental orchards: an organic apple orchard located in Rhône Valley (Drôme, France) and an IPM orchard in Loire Valley (Maine-et-Loire, France). Each cultivar represented 50% of the trees mixed within the row. In the organic orchard, the resistance of Rvi6 gene was effective since the orchard plantation in 2004. In this context, the cultivar mixture showed a good efficiency to decrease the scab incidence on leaves and fruits of Melrouge, during two consecutive years. In the IPM orchard, Pitchounette resistance was overcome in 2008, and the level of disease on Melrouge was very important in 2009; no significant difference between the pure stand and the mixture was observed for scab incidence on fruit at picking in this context. The cultivar mixture enhanced scab control as long as Rvi6 resistance was not overcome and the level of disease not too high. Anglai