The infestations of nematodes are an increasing problem due to the disappearance of conventional chemical disinfectants. These soil inhabitants attack the roots causing deformations and galls, but symptoms are extremely visible on the aerial parts of the plant: wilting, yellowing, loss of vigour, rotting.
Also of special note are infections caused by fungi, bacteria or viruses. The virulence of these infectious agents is determined, to a large extent, by the plant’s level of resistance and by the conditions in which it finds itself.