The diversity of plant aggressors is impressive since it includes cellular or
sub-cellular pathogens (fungi, bacteria, viruses, mycoplasmas), weeds, animals
(rodents, snails), and insects. Before starting a fight against plant disease, it is
necessary to identify the pathogen responsible and to know its ecology, its life cycle
and its mode of dissemination in the environment. The constant identification of new
taxa is continuously accompanied by a revision of the classifications thanks to the new
tools brought by molecular biology. In this chapter, the most recent knowledge on
classes of plant pathogens and plant pests in relation with their plant hosts is presented.
Keywords: Arthropods, Bacteria, Diversity, Fungi, Host range, Mycoplasmas,
Nematodes, Oomycetes, Pathogens, Parasitic Plants, Pests, Viruses, Viroids.
