Diseases

Phoma lingam (Tode) Desm. - Black Leg of Cabbage, Phomosis

Systematic position.

Class Ascomycota, order Diaporthales, family Valsaceae, genus Phoma (=Plagiostoma).

Biological group.

Obligate parasite of crucifers.

Morphology and biology.

Phomosis atacks sprouts, adult plants, and seed cabbage. For the sprouts, pale indistinct spots with black pycnidia of fungus appear on cotyledons; bark lightens in lower part of stalk, becoming gray. Black pycnidia, as well as appreciable black points, appear on dried gray tissue later. Stalk dries up, becomes rotten, and the plant perishes. Disease continues its development in field on infected sprouts. Such plants lag in growth, becoming chlorotic and their lower leaves get a reddish-violet or bluish coloring. On adult plants the disease manifests itself on the radical part of stalk, on main and lateral roots, as grayish, slightly depressed spots. The spots darken later; numerous fine black convex pycnidia appear on their surface. Infested tissues of stalk and roots are gradually destroyed, and dry rot is formed. The disease can progress on roots of seed heads during storage, and stumps become dry, rotten, sometimes even hollow inside. In fields that are infected seed plants perish during flowering or formation of pods. Gray spots with pycnidia are also formed on pods, and they produce infected seeds. The seeds are somewhat smaller and dimmer than healthy ones. Such seeds produce diseased shoots with infected cotyledons. Imperfect fungus P. lingam is an agent of the disease. Fungal mycelium is distributed in an intercellular substance, and convex pycnidia are formed on surface of diseased tissues, merging and forming tubercles having a diameter up to 1 mm. Elongate-cylindrical or nearly ovoid, sometimes slightly bent, colorless conidia are formed in pycnidia and are 4-6 x 1.5-2 microns. The fungus penetrates into plant through tissues damaged by insects. This disease attacks cabbage, cauliflower and brussels sprouts, turnip, kohlrabi, garden radish, rutabaga, mustard and other species of cruciferous cultures.

Ecology.

Development of the disease is favored by high air humidity (60-80%) and temperatures of 20-24.C; incubatory period of the disease lasts 5-8 days. During the vegetative period the fungus can produce 5-8 generations. Infected seeds and plant residues are a source of the infection, and the infecting agent can be maintained for a period of 2-3 years in the form of pycnidia.

Distribution.

Disease registered for the first time in France in 1849. Then it spread everywhere throughout Europe, Australia, and America. In the former USSR data on its distribution in the Northern Caucasus and Krasnodar Territory and also in the Far East (Ussuri and Amur areas and Khabarovsk Territory), in Siberia and northwest areas of the former USSR appeared beginning in 1933. During damp years, Phomosis strongly develops in the Ukraine and Kazakhstan. In Byelorussia it is distributed everywhere, especially in southern and southwestern areas.

Economic value.

Phomosis is an extremely severe disease for stored parent and seed plants, attacking up to 100% of plants under favorable development conditions. Destruction of seed heads during storage reaches 77.8%, in fields up to 57.1% of seed plants are attacked, reduction of seed yield reaches 72%.

Control measures.

The main control measures include: crop rotation, fertilizers, use of resistant varieties, care of plants, growing of healthy seeds, destruction of plant residues, autumn plowing, seed dressing, removal of diseased sprouts, storing of only healthy parent plants, maintenance of the optimum mode of cabbage storage, selection of stumps before landing, plant protection against pests of cabbage, protective spraying of seed plants by fungicides.

Reference citations:

Bilai V.I., ed. 1988. Microorganisms . agents of plant diseases . Kiev: Naukova dumka. 550 p. (In Russian)
Hawksworth D.L., Kirk P.M., Sutton B.C., Pegler D.M. 1995. Ainsworth & Bisby.s Dictionary of the fungi. CAB International. 616 p.
Kvashnina E., Andreev N. 1935. Threat to yield of cabbage from Phomosis. Na zashchitu urozhaya (OGIZ-Sel.khozgiz, VIZR), 3: 20-22. (In Russian)
Mikhal.chuk N.V. 1984. Phomosis of Cabbage. Kartofel. i ovoshchi, 3: 26. (In Russian)
Peresypkin V.F. 1969. Agricultural Phytopathology. Moscow: Kolos. 479 p. (In Russian)
Sal.nikova A.F. 1952. Phomosis of Cabbage in conditions of the Far East and its control. PhD Thesis. Omsk. (In Russian)

© Khlopunova L.B.