Compositions and methods for controlling phytopathogenic infections

A method for preventing, controlling or treating a fungal infection by a phytopathogenic fungal strain on a plant organ, said method comprising the steps of applying on the plant organ a composition comprising at least one UPR (Unfolded Protein Response) inhibitor, in an in vitro sub-effective concentration being a concentration equal or inferior to a non-fungicidal concentration C1 of said inhibitor against the phytopathogenic fungal strain:

• wherein the non-fungicidal concentration C1 is determined by comparing the growth of the phytopathogenic fungal strain cultures in contact with increasing concentrations of said at least one UPR inhibitor, with the growth of a control culture of the phytopathogenic fungal strain, in the absence of said at least one UPR inhibitor;
• the last concentration of the increasing concentrations of the at least one UPR inhibitor resulting in the same fungal culture growth as the control culture being retained as the non-fungicidal concentration C1 of said at least one UPR inhibitor;
• wherein the at least one UPR inhibitor is at least one xanthone of formula I:
• wherein:
• R2=R8:
• prenyl, R1=R3=R6=R7:
• OH, and R4=R5:
• H (γ-mangostin);
• R1=R3=R5:
• OH, R2=R6=R7=R8:
• H, and R4:
• prenyl (1,3,5 trihydroxy-4-prenylxanthone);
• R1=R3=R5:
• OH, R4=R6=R7=R8:
• H, and R2:
• prenyl (1,3,5 trihydroxy-2-prenylxanthone);
• R1=R5=R6:
• OH, R2=R3=R4=R8:
• H, and R7:
• prenyl;
• R8:
• geranyl, R1=R3=R6=R7:
• OH, and R4=R5:
• H (demethylrubraxanthone);
• and
• R1=R3=R4=R5:
• OH, R6=R7=R8:
• H, and R2:
• prenyl, wherein the R2 and R3 moieties form a 2,3,3-trimethyltetrahydrofuran ring,
• wherein the compound of formula (I) inhibits the UPR cellular development and environmental adaptation in the phytopathogenic fungal strain, once they have been exposed to the plant defense molecules expressed by the plant organ.