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diseases of plants— such as aster, celery, and peach yellows; witches’-broom of delphinium; purple top wilt of potato; and big bud— caused chiefly by mycoplasma-like organisms and by viruses.
Diseased plants are stunted and chlorotic, with many lateral shoots pressed to the main stem. The flowers have elongated sepals, deformed corollas that turn green, and an ovary that germinates into leaflets. Yellows attack many plants (potato, clover, onion, carrot, ornamentals). The reservoirs of the causative agents are weeds such as dandelion and field sow thistle. The disease is transmitted by various species of cicadas after the incubation period of the causative agent in their bodies and also by aphids. Yellows decrease the yields of greens, fruits, and seeds and impair the ornamental qualities of flowering plants. Some yellows (for example, cabbage yellows) are caused by fungi. The symptoms of these yellows are yellowing, wilting of leaves, and premature death of the plant. Control measures include crop rotation, cultivation of resistant varieties, removal of diseased plants, and control of weeds and disease carriers.
REFERENCESSmith, K. Virusnye bolei.nl rastenii. Moscow, 1960. (Translated from English.)
Ryzhkov, V. L., and A. E. Protsenko. Atlas virusnykh bolcznei rastenii. Moscow, 1968.
Ploaie, P., R. G. Granados, and K. Maramorosch. “My coplasma-like Structures in Periwinkle Plants With Crimean Yellows, European Clover Dwarf, Stolbur, and Parastolbur.” Phytopathology, 1968, vol. 58, no. 8, p. 1063.
A. E. PROTSENKO