Diseases

Peronospora pisi Sydow. - Downy Mildew of Peas

Systematic posicion.

Class Oomycetes, order Peronosporales, family Peronosporaceae, genus Peronospora.

Biological group.

It is a biotroph.

Morphology and biology.

Infected seeds and vegetation residues with wintering oospores are the source of initial infection. The disease can be found in two forms, diffusive and local. Local infection appears on leaves, stipules, and sepals as yellowish or brown spots. On the lower side of spots the grayish-violet bloom of conidial sporulation of the fungus is formed. On beans the infected tissue becomes colorless, and then develops a dark brown tint. Dwarfism of plants and gradual change of coloring are characteristic attributes of the diffusive forms of the disease. Usually such plants dry up and do not produce beans. Conidiophores are brown-violet, dichotomously ramified; conidia yellowish, ellipsoid, 18-28 x 17-22 microns in size. The fungus also forms sexual cells of sporulation, or oospores. These are spherical, yellowish-brown, with thick folded coat, 30-35 microns in size.

Distribution.

P. pisi is distributed throughout Europe, India, Northern America, Africa and New Zealand. In the territory of the former USSR the disease is recorded in all areas of pea cultivation. The greatest harm the disease causes is in Non-Chernozem zone, Baltic States, Kaliningrad Region, at foothills of the Northern Caucasus, in western areas of Central Chernozem zone, in Ukraine, Byelorussia, Georgia, Azerbaijan.

Ecology.

Damp cool weather promotes the development of the Downy Mildew of Peas. Cold nights and plentiful dews favorably influence the disease development.

Economic significance.

The disease can infect Pisum elatius Bieb in addition to Pisum sativum L. With strong development of the disease the yield losses of grain can reach 25-75%; green weight and hay are reduced by 15-20%. Weak development of the disease is promoted by maintenance of crop rotation, early terms of sowing, seed dressing, spraying of crops by fungicides, destruction of vegetation residues.

Reference citations:

Cherepanova N.P. 1987. Species of Peronospora as parasites of higher plants. Leningrad: Leningrad University. 124 p. (In Russian)
Krivchenko V.I., ed. 1975. Diseases of Fodder leguminous cultures in Non-Chernozem zone of Russia. Methodical instructions. Leningrad: VIR. 154 p. (In Russian)
Makasheva R.Kh. 1973. The pea. Leningrad: Kolos. 312 p. (In Russian)
Starostin S.P., Kotova V.V., Tsvetkova N.A., Borisenko L.A. 1988. Pests, diseases and weeds on peas and their control. Zashchita rastenii, 3: 14-15. (In Russian)

© Kungurtseva O.V.