Department of Plant Pathology, University of Helsinki, Viikki, Helsinki 71, Finland
This study was carried out on Septoria species found on cereals: spring and winter wheat (Triticum aestivum L.), spring barley (Hordeum vulgare L.), winter rye (Secale cereale L.) and oats (Avena sativa L.). The objective was to ascertain their distribution and general significance in Finland. The results were obtained from samples of cereals gathered in 2 040 fields all over the country during the growing season 1971-1973. The fungi in all the samples were examined by microscope and cultures and inoculation tests were used as well in laboratory. One of the Septoria species was found to occur on all the cereals, being most commonly on wheat and two-rowed barley, moderately common on winter rye, very rare on six rowed barley and only sporadic on oats. Septoria species were observed to occur most commonly in the southwestern and southern parts of the country, whereas they were very rare in the middle parts of the country and Ostrobothnia. The imperfect stages of the fungi (Septoria) occurred dominantly, whereas at all times the perfect stages (Leptosphaeria) were found only occasionally. The following Septoria species were found to occur on cereals: Septoria nodorum (Berk.) Berk. & Br. was found to occur as the most common species on spring and winter wheat and was moderately common on two-rowed barley. The fungus was found on wheat in 60—70 per cent, and on barley, in about 40 per cent of the localities and for both cereals in 1/3 of the fields that were studied. On the other hand the fungus was found to be very rare on six-rowed barley and winter rye in 610 per cent of the localities and only 2—4 per cent of the fields studied. Also in the inoculation tests it was found that S. nodorum isolates, which originated from different cereals, infected not only their own host but all the other cereals with the exception of oats. The perfect stage, Leptosphaeria nodorum Müller was found only a few times on spring wheat, spring barley and winter rye. Septoria avenue Frank f. sp. triticea T. Johanson was found to be the most common on two-rowed barley in about 45 percent of the localities and in about 1/3 of the fields studied; on wheat in about 35—40 per cent of the localities and in nearly 1/4of the fields studied. The perfect stage of the fungus, Leptosphaeria avenaria Weber f. sp. triticea T. Johnson was found only a few times on spring wheat and barley. S. avenae Frank f. sp. avenae Shaw was found to occur only occasionally on oats in nearly 10 per cent of the localities and only in 3 per cent of the fields studied. The perfect stage of the fungus, L. avenaria Weber f. sp. avenaria Shaw was found a few times also on oats. Septoria tritici. Rob. ex Desm. was found to occur only on winter wheat in about 1/2 of the localities and in about 40 per cent of the fields studied. The fungus was found only in the spring (May to early June). It sometimes attacked fields in great profusion. In the inoculation tests it was found that the S. triticis' isolate originated from rye weakly infected not only rye but also spring wheat and winter rye. Septoria secalis Prill. & Delacr. was found to occur only on winter rye, being moderately common in 1/2 of the localities and in about ¼ of the fields studied. On the basis of this study not much can be said about the magnitude or economic importance of the damages caused by the Septoria species. In addition to Septoria species, several other parasitic fungi such as Helminthosporium-, Puccinia-, Fusarium-species and Erysiphe graminis DC. were observed to grow at the same time on the leaves of cereals.
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