Diseases

Peronospora aestivalis Sydow - Downy mildew of Lucerne.

Sytematic position.

Division Oomycota, order Peronosporales, family Peronosporaceae, genus Peronospora.

Synonym.

Peronospora trifoliorum de Bary f. medicaginis-sativae Thuem.

Biological group.

These are biotroph parasites.

Morphology and biology.

Spots on the upper leaf surface are light green, then turn pale, indistinct. Gray-violet layer of conidiophores is located on the lower surface. The parasite is distributed on all organs; leaves become bright-yellow, ribbon-lengthened, braided, with abundant bloom of conidiophores on the lower surface; plants lag behind in growth and development, internodes are shortened. Conidiophores are repeatedly ramified 4-7 times dichotomously or treelike, 200-510 x 4-12 microns. Apical branches are located at right angles, short, straight. Conidia are yellow-brown, widely elliptic, 12-37 x 9-27 microns, with a papilla at top. Oogonia round, 33-35 microns in diameter. Oospores are spherical, yellow-brown, with smooth or verrucose coat, 20-31 microns in diameter. In the winter period the fungus is maintained on wintering stalks and leaves as oospores, and also in wintering buds at root neck and in seeds as mycelium. The greatest damage is caused in the spring. From the middle of July to the middle of August the disease ceases development owing to high temperatures and a lack of moisture; in autumn under favorable conditions it may appear to a lesser degree.

Distribution.

Baltic States (Latvia, Lithuania, Estonia), Leningrad, Novgorod, Pskov, Moscow, Belgorod, Voronezh, Kursk, Orel, Tambov, Tula, Astrakhan Regions, Bashkiria, Krasnodar and Stavropol Territories, Alania, Kabardino-Balkaria, Dagestan, Azerbaijan, Georgia, Armenia, Ukraine, Byelorussia, Moldova, Western Siberia (Novosibirsk, Omsk Regions), Altai, Eastern Siberia (Krasnoyarsk Territory), Buryatia, Uzbekistan, Turkmenistan, Kazakhstan, Kyrgyzstan.

Ecology.

The best conditions for disease development are moderate temperatures and increased humidity. The disease develops intensively at a daily average air temperature of 18-20 .C and relative humidity levels of 48-53% over a week. Higher temperature or a decrease in humidity stops the disease development. The parasite has begun to adapt to conditions of droughty areas and is sometimes found to a small degree during the hot dry period (June through the beginning of July)

Economic significance.

Mainly the spring hay harvest of lucerne suffers from the disease. As for the rest of the season, the disease has a limited distribution, damaging individual leaves. First-year crops of lucerne suffer the most. The disease causes a restriction of growth and development, and full destruction of plants is sometimes observed. With the average disease severity the yield of seeds is reduced by 40.7%, the protein content in green weight decreased by 11.5%. With high disease severity the protein content is reduced by 15%. Control measures include spraying of fungicides, removal of plants with diffuse lesions, early spring haying of lucerne, spatial isolation of lucerne crops of different sowing years, sowing of lucerne under cover of cereal cultures.

Reference citations:

Assaul B.D. 1973. Peronosporosis of Lucerne in irrigation conditions. Zashchita rastenii, 10: 24. (In Russian)
Berdysh Yu.I. 2004. Distribution of the main pests and diseases of crops in Krasnodar territory in 2003 and the forecast of their occurrence in 2004. Krasnodar: STAZR. 35 p. (In Russian)
Ermalavichute-Stanyavichene S. 1970. Peronosporosis of leguminous plants in Baltics. In: Dambrose I.P, Zherbele I.Ya., Michene M. Ya., Mikheeva R.I., Peterson L.P. Diseases of agricultural and wood plants and its control. Materials of 7th Baltic meeting on plant protection. Yelgava: Agricultural Academy of Latvia. 45-48 p. (In Russian)
Faizieva F. 1968. To a question on the false mildew of lucerne in Uzbekistan. Uzbek biological magazine, 5: 13-15. (In Russian)
Hawksworth D.L., Kirk P.M., Sutton B.C., Pegler D.N. 1995. Ainsworth and Bisby's Dictionary of the fungi. 8th edition. Kew, Surrey: Commonwealth Mycological Institute. 616 p.
Kalinina I.G., Krivko V.I., Parshikov A.T., Anyutina L.R., Shirokov A.I., Ionin P.F. 1985. Forecast of pests, diseases and weeds distribution in crops of Omsk Region for 1985 and its control. Omsk: Omsk Publishing House. 20 p. (In Russian)
Karimov M.A. 1961. Fungal parasites of Lucerne. Tashkent: Ministry of agriculture of Uzbekistan. 208 p. (In Russian)
Mamytova D.M. 1990. Peronosporosis of lucerne in Kirgizia. In: Guseva O.G., Kapten Yu.L., Ivanova O.S., Sokolova Yu.Ya., Susoi O.V., Shvedov A.N., eds. Ecological problems of plant protection. Proceedings of conference of young scientists; 1990 Nov 21-24; Leningrad: VIZR. 94 p. (In Russian)
Nazemnov A.S., Yakushev E.I., Mirova N.I. 1978. Distribution of pests and diseases of crops in 1977 year. Forecast of its distribution in 1978 year in Penza region. Penza: Privolzhskoe publishing house. 22 p. (In Russian)
Novotelnova, N.S. & K.A. Pystina. 1985. Order Peronosporales. Flora of sporous plants of the USSR, V. XI, Fungi (3). Leningrad: Nauka. 238-239 p. (In Russian)

© Gasich E.L.