The major contents of this course is to discuss the abiotic and biotic factors (including viruses, viroids, prokaryotic bacteria, mollicutes, fungi, parasitic higher plants , nematodes and protozoa) that caused crop diseases. The host-pathogen interaction relationship, pathogenesis, pathogenicity, and mechanisms of plant defense systems are explained in cases. The environmental factors influencing diseases development reveal the knowing of disease principles. The most important diseases of field crops, ornamental plant, fruit trees, vegetable and greenhouse plants would be discussed implicated with the principles of disease management.