Chlorosis(redirected from greensickness)
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a plant disease in which the formation of chlorophyll in the leaves is disrupted and photosynthetic activity is decreased. Characteristic symptoms are premature yellowing and falling of leaves, formation of dwarf leaves, desiccation of shoot apices, and dying off of active roots. Among cultivated plants, fruit and berry crops and ornamentals are most often affected.
The causes of chlorosis are varied. Infectious chlorosis is caused by viruses (for example, raspberry chlorosis and apical chlorosis of tobacco and makhorka), fungi, and other microorganisms. Pests, such as thrips and aphids, are often the carriers of the causative agents of chlorosis. Noninfectious, or functional, chlorosis develops because of unfavorable soil or climatic conditions or because of inadequacy of cultivation practices. In most cases, fruit and berry crops (especially grapes) on carbonate soils suffer from ferrous or calcareous chlorosis. Zinc and magnesium chloroses also occur. A distinctive kind of yellowing occurs on diseased plants: spots appear, and at first yellowing appears only on the lower or upper leaves or only in the intervenous areas. Hereditary chlorosis of plants (variegation, gold-leafedness) is mutagenic and inherited; it is used in the selection of ornamental plants to develop variegated forms.
The prevention of chlorosis entails the application of mineral and mineral fertilizers. Carbonate soils are acidified, interrows of orchards are mulched and planted with ground cover, and pests that are carriers of infection are destroyed. Treatment of noninfectious chlorosis involves applying deficient nutrient elements close to the active zone of the root system and administering nonradical dressings and injections of solutions containing trace elements into the trunks, branches, and roots of fruit trees. Plants suffering from infectious chlorosis are removed.
REFERENCESDement’eva, M. I. Bolezni plodovykh kul’tur. Moscow, 1962.
Shpota, L. A. Khloroz rastenii v Chuiskoi doline i bor’ba s nim. Frunze, 1968.
Nakaidze, I. A. Pochvennye usloviia i khloroz vinogradnoi lozy v Gruzii. Tbilisi, 1969.
L. A. SHPOTA