Classification of pathogens: bacteria, fungi, nematodes, parasitic plants, and viruses
There are five different groups of pathogens that typically cause disease in trees. Four of these belong to four different kingdoms (the first four below). Viruses, the fifth group, are so small that they cannot be seen with a light microscope, and are self-replicating, often pathogenic infectious agents. The origin of viruses in the evolutionary history of life is unclear. Further information on these five groups of pathogens and links to specific pathogens within these groups can be found by clicking on the groups below: