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

Walnut blight is the major disease in the walnut orchards of Dauphine (Fran ce). The causal bacterium Xanthomonas campestris pv. juglandis can infect l eaves, catkins, buds and nuts and can induce important crop losses. Field o bservations have shown that the nature of the soil seems to play a prominen t role in crop losses. The hypothesis that soil may modify the amount of po lyphenols in walnut tissues and modify the natural resistance of fruits to necrosis has been assumed. We have shown that the nature of the soil, espec ially its permeability, induces variations in polyphenols in walnut tissues . Differences of susceptibility to walnut blight between the two cultivars studied, Franquette and Parisienne, may also be explained by different beha viours in relation to polyphenols. Moreover, the massive use of copper trea tments against walnut blight may induce an imbalance in polyphenol contents and could explain crop losses despite repeated copper sprays. ((C) Inra/El sevier, Paris.)