The influence of soil nature on polyphenols in walnut tissues. A possible explanation of differences in the expression of walnut blight

Abstract

Walnut blight is the major disease in the walnut orchards of Dauphin (France). The causal bacterium Xanthomonas campestris pv. juglandis can infect leaves, catkins, buds and nuts and can induce important crop losses. Field observations have shown that the nature of the soil seems to play a prominent role in crop losses. The hypothesis that soil may modify the amount of polyphenols in walnut tissues and modify the natural resistance of fruits to necrosis has been assumed. We have shown that the nature of the soil, especially its permeability, induces variations in polyphe- nols in walnut tissues. Differences of susceptibility to walnut blight between the two cultivars studied, Franquette and Parisienne, may also be explained by different behaviours in relation to polyphenols. Moreover, the massive use of cop- per treatments against walnut blight may induce an imbalance in polyphenol contents and could explain crop losses despite repeated copper sprays. ( © Inra/Elsevier, Paris.) Juglans / walnut blight / polyphenols / soil Rsum -Influence de la nature du sol sur la composition en polyphenols des tissus de noix. Une explication possible des diffrences observes dans l'expression de la bactriose du noyer. La bactriose est la principale maladie des noyers dans les vergers du Dauphin (France). La bactrie responsable de cette maladie, Xanthomonas campestris pv. juglandis, infecte les feuilles, les chatons, les bourgeons, les fruits et peut causer d'importantes pertes de rcolte. Des observations de terrain ont montr que la nature du sol semblait influencer l'importance des pertes de rcolte. L'hypothse que la nature du sol puisse modifier la composition en polyphnols des tissus et ainsi modifier la rsistance natu- relle des fruits la ncrose a t faite. Nous avons montr que la nature du sol, spcialement sa permabilit, induit des Communicated by Grard Guyot (Avignon)