Inhibitor of fungal polygalacturonase. It is an important factor for plant resistance to phytopathogenic fungi. Substrate preference is polygalacturonase (PG) from A.niger >> PG of F.oxysporum, A.solani or B.cinerea. Not active on PG from F.moniliforme. Mutation of Lys-253 confers the ability to inhibit the F.moniliforme PG. Belongs to the polygalacturonase-inhibiting protein family. It is uncertain whether Met-1 or Met-10 is the initiator.