The potato crop is exposed to infection with many fungal diseases including late blight, caused by Phytophthora infestans. The control of late blight disease requires an integrated management approach represented in cultivation control, plant resistance, and fungicide control. The citrus plants are infected by Phytophthora nicotianae that is causing root rot disease in Egypt. Three species of Phytophthora responsible for infection of citrus plants; P. nicotianae, P. citrophthora, and P. palmivora. Other pathogens associate P. nicotianae and form complexes or coinfection that release different diseases for citrus plants such as gummosis, Phytophthora–Diaprepes complex (PDC), and Huanglongbing syndrome (HLBS).