Diseases

Rhynchosporium secalis (Oudem.) J. Davis - Rye scald.

Classification.

Class Deuteromycetes, Order Hyphomycetales, Family Dematiaceae, Species Rhynchosporium secalis (Oudem.) J. Davis (Ainsworth, 1971).

Biological group.

Hemibiotroph.

Morphology and biology.

Scald is an important disease of rye, barley and others wild grasses, particularly species of Bromus (Ishkova et al., 2002). Scald on rye presents oval to lens-shaped or elongated spots (lesions) 0.5-2 x 0.1-0.5 up to 1-2 x 5-7 cm, surrounded by straw-colored borders which develop mostly on the leaves and leaf sheaths. A fungus develops a superficial, loose stroma on which transparent conidias are produced from short cells. The conidia has one or two unequally sized cells of 12-20 x 2.3-5.4 um. The terminal cell hooks into a beak. The fungi overseasons as mycelia on dead or living leaves of infected plants and on other crop debris. The scald fungi may infect seeds and can be carried on the seed (Nazarova et al., 1998). A sexual stage has not been observed in nature. During prolonged periods of cool, moist weather in the spring, the scald fungi resumes growth and produce large amounts of conidia. Spores produced on infected leaves are transported to other plants by rain drops and wind. Under favorable conditions disease develops in 14-15 days (Nazarova et al., 1998).

Distribution.

Where rye is cultivated in Europe, Asia, America and Australia. In Russia it is found in all regions where rye is cultivated (Ishkova et al., 2002).

Ecology.

Scald is an important fungus in cool, humid, temperate climates. Disease develops only when the weather is cool (optimal - 10 to 21 .C) and the leaves are wet for a long time. Spore production and infection occurs repeatedly during cool, moist, humid periods that last at least 12 hours in the spring and early summer, and continue until the crop ripens. Scald is checked during hot, dry, summer weather. New infections occur in the fall when cool, damp weather returns. Infection of winter crops may be carried out in autumn by spores from debris of wild plants (Nazarova et al., 1998).

Economic value.

Starting in 1980, scald infestation has increased in European countries including Russia (Nazarova et al., 1998); (Buga et al., 1997). Severe attacks of scald have caused yield losses as high as 20 percent in cultivated crops. Attacks at the late boot or early heading stage reduce the size of the grain and the number of kernels formed per head. Control measures: crop rotation of at least one year with a non-host crop, application of seed-treatment and foliar fungicides

Reference citations:

Ainsworth G.C., ed. 1971. Ainsworth and Bisby's Dictionary of the fungi. CAB International. 660 pp.
Buga S.F., Ushkevich L.L., Bojarchuk V.E., Padyna A.A. 1997. Harmfulness of rye scald. Actual problems of phytovirology and plant protection. Minsk: BelNIIZR 57-58 pp. (In Russian)
Ishkova T.I., Berestetskaya L.I., Gasish E.L., Levitin M.M., Vlasov L.Iu. 2002. Diagnostics of the main fungus diseases of cereal crops. St. Petersburg: VIZR. 76 pp. (In Russian)
Nazarova L.N., Devjatkina G.A., Poljakova T.M., Jokhova T.P. 1998. Method of Rhynchsporium secalis(Oudem.) Davis inoculum reception for artificial infectious background. Mycology and Phytophatology 32(6): 83-88. (In Russian)
Nazarova L.N., Polyakova T.M. 1996. Rye protection against scald. Plant protection and quarantine 6: 20-21. (In Russian)

© Dmitriev A.P.