Viruses - affects many plant species, symptoms are harder to identify as they are similar to certain nutritional deficiencies. They vary depending on the age of the plant and the time of infection. The main morphological changes are chlorosis (appearance of discolored or yellow spots on the green organs of the plant), mosaic (greenish, yellow spots alternating with normal colored tissue appear on the leaves of the diseased plant), necrosis (circular, ring-shaped, elongated yellow-brown or blackish-brown spots), deformities of the various organs (curling, twisting, asymmetry, atrophy of the leaves), dwarfism or dwarfing.