Pathogen

A pathogen is a biological infectious agent capable of causing plant diseases. Tomato pathogens include, among others, fungi, nematodes, bacteria, phytoplasmas, viruses, viroids, and parasitic nematodes; an example of a nematode is Phytophthora infestans. Not every exposure to a pathogen leads to the development of disease—much depends on the plant’s susceptibility and environmental conditions. Reducing the number of pathogens is the basis of prevention. In practice, this is achieved through the use of healthy nasiona and seedlings, clean tools, the removal of infected plant debris, and the mitigation of conditions conducive to infection.