Diseases

Plasmopara halstedii (Farl.) Berl. et de Toni - Downy Mildew of Sunflower.

Systematic position.

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

Synonyms.

Peronospora halstedii Farl., Rhysotheca halstedii (Farl.) G.W.Wilson, and Plasmopara helianthi Novot. f. helianthi.

Biological group.

Obligate parasite.

Morphology and biology.

The life cycle of P. halstedii has both sexual and asexual development. In sexual development, oospores are formed, providing for the preservation, and reproduction of the causal agent. Asexual reproduction is characterized by a number of generations of zoosporangiums with numerous mobile biflagellate zoospores. The zoospores infect sunflowers at the early stages of development and during vegetative stage. Seeds are also a source of infection. Inside the infected tissue the fungus forms endophytic, nonseptate, colorless or light-yellow mycelium. The affected plants have an underdeveloped root system, broken heliotropism; are dwarf, having extremely connivent internodes, and fine crimped leaves bearing P. halstedii on underside. Upon flowering and later in development the disease can be found on separate stalks with such symptoms as dark green indistinct spots, sporification on leaves or heads, spots of dried out disk flowers; appearing also on the reverse side of head, where tissue hardens and becomes fragile. A line of physiological races is identified in P. halstedii. In the countries of the former USSR they are found in Russia only.

Distribution.

Downy Mildew is spread through out Russia and other countries of the former USSR on sunflower everywhere.

Ecology.

High humidity and low air temperatures promote mass infection of sunflower with the fungus P. halstedii, intensive development of the disease, and the accumulation of inoculum. Germination of oospores in soil occurs when humidity is about 95% and temperature range from 12.C to 14.C. Zoospores release from zoosporangia happens most intensively under moist conditions at temperatures from 15.C to 18.C. Zoosporangia lose their viability at temperature less than 2.C or more than 26.C.

Economic significance.

Losses of sunflower yield caused by Downy Mildew can reach 30% and more. The greatest damage of the disease is observed in the northern part of the Central Black Soil Zone and in the foothill areas of the Northern Caucasus of Russia, in the northern part of forest-steppe in western Ukraine, and in the northern part of Moldova. Control measures against Downy Mildew include optimal crop rotation, the use of resistant varieties and hybrids, and seed dressing prior to sowing.

Reference citations:

Gulya T.J., Sackston W.E., Viranyi F., Maserevic S., Rachid R.Y. 1991. New Races of the Sunflower Downy Mildew Pathogen (Plasmopara halstedii) in Europe and North America. Phytopathology 132:303-311.
Novotelnova N.S. 1966. Downy mildew of sunflower. Taxonomy and biology of the causal agent, pathogenesis of disease. Nauka: Moskow. 150 pp. (In Russian).
Tikhonov O.I. 1975. Diseases of sunflower. In: Pustovoit V.S., editor. Sunflower. Moskow: Kolos. 401-409 pp. (In Russian)
Tourvieille de Labrouhe D., Gulya T.J., Masirevic S., Penaund A., Rashid Kh.Y., Viranyi F. 2000. New nomenclature of races of Plasmopara halstedii (Sunflover downy mildew). 15th International Sunflower Conference, 12-15 June 2000, Toulouse-France. T.2: 1-66.
Yakutkin V.I. 2001. Diseases of sunflower in Russia and their control. Zashchita i karantin rastenii N.10: 26-29. (In Russian)
Yakutkin V.I., Akhtulova E.M. 2002. Physiological races of the causal agent of Downy mildew on sunflower in Russia. Modern Mycology in Russia (Abstract). First Congress of Russian Mycologists. Russia. 7: 217-218. (In Russian)
Yakutkin V.I., Aleksandrova L.I., Akhtulova E.M. 1995. Peronosporosis of sunflower in Central Black Soil Zone of Russia and a problem of breeding for resistance to disease. In: All Russian Congress of Plant Protection. St. Petersburg. 275-276 pp. (In Russian)
Yakutkin V.I., Tavolzhanskii N.P. 1999. Disease control on sunflower in Russia. In: Research progress in plant protection and plant nutrition. Agro annual meeting China 99. China Agriculture Press. Beijing. 214-218 pp.
Zimmer D.E. 1974. Physiological specialization between races of Plasmopara halstedii in America and Europe. Phytopathology 64:1465-1467.

© Yakutkin V.I.