Diseases
Rhizopus stolonifer var.stolonifer (Ehrenb.) Vuill. - Dry Head Rot of Sunflower.
Systematic Position.
Kingdom Fungi, phylum Zygomycota, class Zygomycetes, order Mucorales, family Mucoraceae, genus Rhizopus.Synonyms:
Rhizopus stolonifer (Ehrenb.) Vuill, Rhizopus nigricans Ehrenb. (http: // www . SpeciesFungorum.org).Biological group.
Saprotroph.Morphology and biology.
The causative agent of Dry Head Rot of Sunflower is the fungus Rhizopus stolonifer var. stolonifer (Ehrenb.) Vuill., which is a polymorphic species. As a result, there are some questions concerning its systematic position. The fungus forms in its life cycle teleomorpha stage as zygospores (1000-2000 x 13-25 mkm) developing on overwintered mycelium (Kolte, 1985). Anamorpha stage is formed of spherical dark sporangia of 100-150 mkm in diameter. The fungus has abundant dark branched stolons and rhizoids. Sporangiophores are black, bunched, to 4 mkm in height. Spores are rounded, dark, 8-14 x 6-11 mkm in size (Tikhonov, 1975). The disease is shown after flowering as dark spots on the back side of sunflower heads. After a time, gray fungal mycelium appears on the upper side of heads between seeds. Here its tissue becomes hard. Sources of the infection are the affected residues and infected seeds.Distribution.
The disease is registered everywhere within sunflower area in the former USSR (Gorlenko, 1968; Tikhonov, 1975; Kukin, 1982).Ecology.
The Dry Head Rot of Sunflower is more intensively shown at dry and hot weather. The disease is depressed in conditions of optimum humidification (Kukin, 1982).Economic significance.
Affected heads of sunflower dry up. Seeds become puny and bitter. Reduction in yield and quality of sunflower caused by the disease can reach 20% (Tikhonov, 1975). Control measures are crop rotation, use less affected varieties and hybrids, presowing treatment seeds.Reference citations:
Gorlenko M.V. 1968. Diseases of sunflower. In: Agricultural Phytopathology. Moscow: Vysshaya shkola, p. 206 (in Russian).Kolte S.J. 1985. Diseases of annual edible oilseed crop. Vol.3: Sunflower, Safflower and Niegersed Diseases. Florida.
Kukin V.F. 1982. Diseases of sunflower and their control. Moscow: Kolos, 80 p. (in Russian).
Maric A., Camprag D. & Masirevic S. 1987. Sunflower diseases and pests and their control. Belgrade: Nolit, 379 p. (in Serbian).
Tikhonov O.I. 1975. Diseases of sunflower. In: V.S. Pustovoit, ed. Sunflower. Moscow: Kolos, p. 414-415 (in Russian).