Heterodera avenae Wollenweber - Cereal Cyst Nematode
Systematic position.Type Nemathelminthes, class Nematoda, subclass Secernentea, order Tylenchida, family Heteroderidae, genus Heterodera. Probably, the Cereal Cyst Nematode represents a group of sibling species, including Heterodera filipjevi (Madzhidov) (Subbotin et al., 1999).
Biological group.Obligate parasite.
Morphology and biology.Coelelminth of microscopic size. It is characterized by sexual dimorphism; female rounded, white (930 x 680 microns); male vermiform, transparent (1300 x 40 microns). Eggs oval (143 x 50 microns); vermiform larvae of I and II instars develop there. The larvae of II instar are mobile (moving distances of up to 30 cm) and able to search for and invade roots. Larvae develop in roots, growing into the sedentary bottle-like larvae of III instar and rounded ones of IV instar. The latter larvae turn into females or males. Swollen body of the nematode breaks off bark of root; males penetrate ground, and the hind end of females becomes accessible for insemination. Majority of eggs (as many as several hundred) remain inside female body. The female turns into a brown cyst by the end of vegetation season, as her external cover hardens and her internal parts die. Within the cyst, the larvae remain in anabiosis for several years in the absence of host-plants (wheat, barley, oats, cereal grasses, wild oat, couch-grass). Cysts of the nematode spread with grain or ground. Visual signs of infection include weakened plants and shredded plant roots.
Distribution.The Cereal Cyst Nematode distribution area coincides with the zone of grain cultivation. There are different distribution regions allocated within Russia: the nematode is absent in the Northern Caucasus; high population density and aggressive pathotype C occur in the Middle Volga region, CIS-Urals, Western Siberia, and the Central-Chernosem region; low population density and common pathotype A is found in Northwestern European Russia. In Byelorussia, the Baltic States, and Poland, the situation is similar to that in the Russian Northwest. In Ukraine, the zone of high population density includes areas adjoining the Central-Chernosem region. The nematode is found in some areas of Kazakhstan, Armenia and Tajikistan.
Ecology.The species is ecologically flexible, distributed throughout both maritime and continental climate zones. Damp, warm springs and summers (growing degree days. temperatures total is 1154°C; hydrothermic coefficient must be at least 1) are favorable for its development. Porous soils are preferable. The species is more prevalent in areas that grow susceptible cultures, i.e., wheat and oats in the Volga region and CIS-Urals, wheat and barley in Siberia, and oats and barley in the Northwest.
Economic significance.This pest is associated with the reduction of grain yield, as it oppresses plants by damaging their roots. Thresholds of harmfulness depend on the pre-sowing population density of the nematode, which differs among various cultures and varieties and depends on weather conditions and regions of cultivation. In Bashkortostan, the presence of 300-400 larvae per 100 cm╕ of ground reduces wheat yield by 5%; in Western Siberia, 200 larvae causes the same loss in yield, and 1000 larvae per 100 cm╕ reduces yield by 30%. In the Northwest region, the nematode is occasionally harmful, emerging as a pest after pathogen accumulation in the ground during years of favorable weather. The area affected by the Cereal Cyst Nematode covers about 1 million hectares, and losses of grain yield may be significant. Control measures include crop rotation with grain cultures not exceeding 20% of plantings; the use of black fallows; deep autumn plowing; and the use of resistant varieties of barley.
Related references:Gus.kova L.A., Karlik F.A., Saulich M.I., Sergeeva L.S. 1991. Cereal Cyst Nematode in Leningrad Region. In: Nesterov P.I., ed. Nematode plant diseases. IX All-Union Conf. Kishinev: Inst. zool. Moldova, p.9 (in Russian).
Kir.yanova E.S. & Krall. E. L. 1971. Parasitic plant nematodes and their control. V. 2. Leningrad: Nauka, 522 p. (in Russian).
Polyakov I.YA., Terent.eva T.G., Gus.kova L.A., Antonova V.V. 1979. Distribution of nematodes - parasites of agricultural crops in the USSR. Moscow: VNIITEISKH, 32 p. (in Russian).
Popova M.B. 1972. Heterodera avenae (Wollenweber, 1924) Filipjew 1934 in the Volga region and Cis-Urals and biological bases of their control. PhD Thesis, Moscow: All-Union Inst. Helminthology, 21 p. (in Russian).
Shiabova T.N. 1982. Factors of harmfulness of Cereal Cyst Nematode. In: Ivanov O.A., ed. Ecology of pests of agricultural crops. Novosibirsk: SibNIIZKHim, p. 32-36 (in Russian).
Subbotin S.A., Waeyenberge Z., Molokanova J.A., Moens M. 1999. Identification of Heterodera avenae group species by morphometrics and DNA-RFZPs. Nematology 1(2): 195-207
Tikhonova L.V. 1972. Problem of heteroderosis of grain crops in the USSR. In: Ershov V.S., ed. Nematode diseases of agricultural crops and their control. Abstracts of workshop. Moscow: All-Union Inst. Helminthology, p.25 (in Russian).
Tikhonova L.V. 1986. Ecological bases of regulation of numbers of especially dangerous nematodes on grain crops and preventive measures of phytohelminthoses. DSc Thesis, Moscow: All-Union Inst. Helminthology, 48 p. (in Russian).