Occurrence of Septoria species on cereals in Finland in 1971-1973.

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 sutiva 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 specieswas found to occur on all the cereals, being most commonly on wheat and two-rowed barley, moderately common on winter rye, very rare on sixrowed 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 —7O 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 6 10 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 Muller 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 per cent 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 1/4 of 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. avenue Frank f. sp. avenue 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 1/4 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-, Fusariumspecies and Erysiphe graminis DC. were observed to grow at the same time on the leaves of cereals.

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 -7O 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 6 10 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 Muller 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 per cent 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 1/4 of 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. avenue Frank f. sp. avenue 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. Introduction Several Septoria species are known to be serious causers of leaf spot diseases on cereals cultivated all over the world (Sprague 1950). Particularly S.nodorum (Berk.) Berk. & Br. has been found to cause large yield loss (Block 1959, Brönnimann 1968). On the other hand little is known of the occurrence and effect of several other Septoria species on cereals in many countries. In Scandinavia Septoria species have also been known since the last century (cf. Frandsen 1943, Jorstad 1967, but their significance has remained rather obscure (Leijerstam 1962, Kolk 1966, Hansen and Magnus 1969. In recent years, however, growing attention has begun to be attracted to Septoria species on cereals in Norway (Hansen and Magnus 1969), Denmark (Smedegärd Petersen 1974) and particularly in Britain (Hewett 1965, Holmes and Colhoun 1970, Richardson and Noble 1970, Richardson 1972, Williams and Jones 1972.
In Finland Septoria species has been rather insignificant to date. In recent years they have been found to be uncommon on barley and grasses (Mäkelä 1972(Mäkelä a, 1972. This study is part of a research project dealing with spot diseases on cereals and specifically with the pathogens causing these diseases (cf. Mäkelä 1972Mäkelä b, 1974Mäkelä , 1975. The purpose of the present study is to clarify the occurrence of Septoria species on cereals. The study is based on samples of cereals which were gathered in farmers' fields throughout the country over a three year period (1971)(1972)(1973).

Materials and Methods
The bulk of the cereals samples (Table 1) was gathered at a growth stage when the grain was milky ripe, chiefly from late July to early August. The samples of winter wheat and rye were gathered in May also.
The leaves were checked for diseases by occular examination on the basis of symptoms. Septoria and Leptosphaeria species were determined in the following way: 1. Diseased leaves were kept on moist blotter paper in Petri dishes for a few days, after which the pycnidia and conidia that had grown were examined with a stereomicroscope. 2. Identification of these fungi is not possible by the above procedure alone, therefore microscope slides were under illumination by day and at +7°+lo°C and in the dark by night for a period of 21 days. 5. The pycnidia and conidia of Septoria species grown on leaves were studied with a microscope.

Climate and Weather
The weather in summer in 1971, particularly in southern Finland, was characterised by low precipitation, except for part of August.
The weather during the growing seasons of 1972 and 1973 was exceptionally warm. Precipitation conditions varied greatly in different parts of the country. In 1972 there was little rain in May and June, whilst in August there was quite a lot of rain in southern and central Finland. During the entire growing season 1973 the amounts of precipitation were subnormal (Meteorol. Yearb. Finland 1971, 1973.  The formae speciales differ from each other in host range, symptoms and cultural characteristics (Johnson 1947, Shaw 1957.
The fungus is widespread (Frandsen 1943, Sprague 1950), but its economic importance varies with area and season (Noble andMontgomerie 1956, Shaw 1957 a). In Europe the fungus is a common seedling and leaf pathogen of oats in Scotland (Noble andMontgomerie 1956, Richardson andNoble 1970). It occurs in Germany, particularly in moist conditions (Muller 1963). In Scandinavia S. avenae on oats has been known in Denmark since 1898 (cf. Frandsen 1943) and in Norway (Jorstad 1930(Jorstad , 1945(Jorstad , 1967.
Nevertheless, the fungus is of little economic importance.
In this study S. avenue f. sp. avenue occurred rarely on oats in the southern parts of the country (Fig. 1) Helsinki, Viikki 6. 6. 1972, Snappertuna 24.5. 1972, Tuusula 20.11. 1972.  Pycnidia of the fungus were found on ripening and whithering leaves mostly in addition to Helminthosporium avenue Eidam (Mäkelä 1975 S. avenue f. sp. triticea causes a leaf blotch of wheat and, less commonly barley (Sprague 1950, Hosford et al. 1969. The fungus probably persists on stubble (cf. Shaw 1957 b). It has not been found in the seed samples (Kietreiber 1962, Richardson andNoble 1970).
The fungus has been found on wheat and, less commonly, on barley in Canada since 1943 (Johnson 1947). Today it is still common in Canada (Shaw 1957 b), as well as in the USA (Sprague 1950, Hosford et al. 1969. In Europe the fungus is found in Austria on wheat but is, however, of lesser significance than S. nodorum (Kietreiber 1962). On the other hand the fungus is found commonly in Scotland on wheat and barley (Richardson andNoble 1970, Richardson 1972). Richardson and Noble (1970) believe that S. avenue f. sp. triticea has long been known in Scotland but that it has been frequently misidentified as S. passerinii Sacc.
In Finland S. avenue f. sp. triticea was found in 5 % of the barley fields examined in 1970 and 1971 (Mäkelä 1972 b).
The fungus infects, besides wheat and barley, also oats, rye and certain grasses, paricularly the species Agropyron and Elymus (Johnson 1947Srpague 1950.
Barley Septoria avenue f. sp. triticea was encountered on barley throughout the country as far north as Inari, Lapland (Fig. 5). The disease occurred most commonly in the southwestern and southern parts of the country, which are the most important barley-growing areas ( Table 3). The fungus was found in the following localies: (1)   S. avenue f. sp. Irilicea was found in different years in an average 15 % (range 13-16%) of the fields (803 fields) examined (Table 1). The fungus was rather commoner in two-rowed varieties (21 -34%) than in six-rowed varieties (10-13%).
Pycnidia of the fungus were found in greatest abundance on maturing and whithering leaves, i.e. on brown necrotic lesions.
The perfect stage, L. avenaria, was found only twice on barley. The species has been divided into two formae speciales (Smedegärd Petersen 1974).
The fungus causes glume blotch on wheat, attacks all parts of the plant except the roots in all stages of its growth. Leaf lesions often coalescing to form a general leaf necrosis. The fungus is, however, primarily an ear pathogen (Weber 1922b, Frandsen 1934, Hopp 1957, Jorstad 1967, Brönnimann 1968). On barley the symptoms of the disease are redbrown spots which often continue in the form of chlorotic tissue along the leaf-ribs (Hansen andMagnus 1969, Smedegärd Petersen 1974).
S. nodorum occurs widespread in most of the world's wheat-growing areas (Sprague 1950, C.M.I. map no. 283). In Europe, the fungus was first observed by Berkeley in 1845 in the British Isles (Grove 1935). Today the fungus is very common on wheat (Hewett 1965, Richardson andNoble 1970) and occurs also on barley (Holmes andColhoun 1970, Richardson 1972). S. nodorum has been known to be common and destructive on wheat also in Germany (Hopp 1957, Block 1959, Bockmann 1963, Switzerland (Muller 1952, Brönnimann 1968), Austria (Kietreiber 1961(Kietreiber , 1962 and in the Netherlands (Becker 1955).
In Scandinavia S. nodorum has been known to blight wheat in Denmark (Frandsen 1943) and in recent years it has been widespread also on barley (Smedegärd -Petersen 1974). In Norway the fungus is found on wheat and berley. Only on wheat does it appear to be a parasite of economic importance (Jorstad 1930, 1945, 1967, Hansen and Magnus 1969. In Sweden S. nodorum is today quite Common on wheat (Leijerstam 1972) and also on rye (Kolk 1966). In Finland S. nodorum is apparently considered to be of negligible significance because up to now it has not attracted attention. In recent years, however, the fungus was found on barley (Mäkelä 1972 b), and on different grasses (Mäkelä 1972 a).
The perfect stage, Leptosphaeria nodorum has been found on wheat in Switzerland (Muller 1952) and in Britain (Lucas and Webster 1967) and on barley in Denmark (Smedegärd -Petersen 1974).

Wheat
In this study Septoria nodorum occurred on wheat in the southern parts of Finland, where most of the country's wheat is cultivated, occasionally turning up as far north as Inari, Lapland (Figs. 3 and 4). S. nodorum was more common than S. avenue f. sp. triticea both on spring wheat and winter wheat (Tables 1 and 2). S. nodorum was found in about 1/3 of the wheat fields studied as follows: Pycnidia of S. nodorum were found in greatest abundance on ripening and withering leaves, on brownish leafspot as well as on ears (Fig. 7). Pycnidia were yellow brown, measuring 90 300 //, mostly 157 pt in diam. Conidia were short, cylindrical, stright or bent, 10-29 X 1.5-4.5 pi, I-3-septa, mostly 19.7 X 3.0 pi, 1.8-septa (Figs. 6 and 7) (cf. Jorstad 1967).
In the inoculation tests (Table 4) it was found that the eleven isolates of S. nodorum which originated from spring and winter wheat and came from different localities, infected barley, wheat and rye, but did not infect oats. The perfect stage, L. nodorum, was found only a few times on spring wheat (Fig. 7). Septoria nodorum occurred on barley in the southern parts of the country, occasionally also as far north as Inari, Lapland (Fig. 5). S. nodorum was found to be moderately common on two-rowed barley in 1/3 of the fields studied, whilst on six-rowed barley it occurred only occasionally. The fungus was found in the following localities:  Pycnidia of S. nodorum were found in withering leaves on necrotic tissues. Pycnidia were light brown, measuring 70 234 p, mostly 138p in diam. Conidia were 12 -27 X 2 4.5 p, 0 3-septa, mostly 19.4 X 2.7 p, 1.6-septa (Figs. 6 and 7) (cf. Jorstad 1967).
In the inoculation tests (Table 4) it was found that the four isolates of S. nodorum, which originated from two-rowed and six-rowed barley and came from different localities, infected barley, wheat and rye, but did not infect oats.
The perfect stage, L. nodorum, was found only twice on barley.
In the inoculation tests (Table 4) it was found that the isolates of 5. nodorum which originated from winter rye, infected barley, wheat and rye, but did not infect oats. The perfect stage, L. nodorum, was found only twice on rye. The fungus causes leaf blotch on rye (Weber 1923, Frandsen 1943). The fungus is rarely encountered in the USA (Weber 1923, Sprague 1950 and Europe (cf. Frandsen 1943: 40); lately it has only been reported in Scotland (Richardson and Noble 1970). In Scandinavia S. secalis has been known in Denmark (Frandsen 1943) and Norway (Jorstad 1930(Jorstad , 1945(Jorstad , 1967.
The fungus has been reported only on rye and is considered to be econimically unimportant (Weber 1923, Jorstad 1930, Frandsen 1943.
In this study S. secalis occurred only on winter rye throughout the country as far north as Muhos and Hyrynsalmi (Fig. 8). The disease was observed to occur most commonly in the southwestern and southern parts of Finland, which are the country's main rye-cultivating areas (Table 2). 7 235 S. secalias was found in an average 26 % of the fields (341 fields) examined. In 1973 the fungus was found to be comparatively rarer than in 1972, apparently owing to weather conditions ( Pycnidia of S. secalis were found in greatest abundance on ripening and withering leaves, on brown necrotic spot. Pycnidia were brown, measuring 72-279 /x, mostly 155 fx in diam. Macroconidia were cylindrical, rounded at the ends 16.5-54 x 2.5 -5.0 fx, 2 5septa, mostly 34.4 x 3.2 /x, 3.0-septa (Figs. 6 and 9) (cf. Sprague 1950, Jorstad 1967).
The fungus has been mainly considered to be a foliar parasite. There have been no confirmed reports of the disease being seed borne (Jones andCooke 1971, Williams andJones 1972). It may overwinter on weed species and stubble (Jones and Odebunmi 1971) as well as on grasses (Williams and Jones 1973).
S. tritici is widespread and important, particularly in moist conditions (Frandsen 1943, Sprague 1950. In Europe the fungus is found in Britain (Grove 1935), also on spring wheat (Williams and Jones 1973) and in Scotland only rarely on winter wheat (Richardson and Noble 1970). In Scandinavia 5. tritici has been known in Denmark and Sweden since the last century (cf. Frandsen 1943) and in Norway since 1931 (Jorstad 1945(Jorstad , 1967.
Today the fungus is little known.

Discussion
This study is based on samples of cereals gathered during three growing seasons (1971 1973), except for wheat and rye samples, which were only gathered during two growing seasons (1972)(1973). The weather during the growing seasons of 1972 and 1973 was exceptionally warm and there was less precipitation than normal although rainfall varied greatly in different parts of the country (cf. p. 221). On the other hand it is known that epiphytotics of Septoria species have often occurred, particularly under moist and rainy conditions (Hopp 1957, Block 1959, Muller 1963, Scharen 1964, Jorstad 1967, Brönniman 1968). In any event this study has clarified the interrelationships of Septoria species on different cereals as well as their relation to other pathogens causing leaf-spot diseases, such as Helminthosporium species and Rhynchosporium secalis (Oud.) J. J. Davis (cf. Mäkelä 1974, 1975. Septoria species occurred most commonly on wheat and two-rowed barley, which are primarily cultivated in southern and southwestern Finland. It was in this area that the fungi were observed to thrive. On the other hand, on six-rowed barley, too, Septoria species were more common in southwestern Finland than in Ostrobothnia. The reverse held for the Helminthosporium species, which in the same samples of cereals were observed to be most abundant in Ostrobothnia (cf. Mäkelä 1975).
Septoria nodorum occurred on wheat, particularly as a foliar parasite. In some cases it was observed to affect the ears of spring wheat so severely that the field turned a dark grey colour (St: Vampula, Aug., 1973). Likewise S.
nodorum was found to occur according to the author very common and abundantly on ears of winter and spring wheat in many fields located in southwestern Finland in the exceptional rainy growing season 1974. The significance of the fungus in causing glume blotch of wheat can hardly be as large in Finland as it is in other countries (cf. Hopp 1957, Hewett 1965, Jorstad 1967, Brönnimann 1968, Richardson and Noble 1970. This is simply due to the small area in which wheat is cultivated. Of Finland's total field area (2 665 000 hectars), spring wheat occupies less than five per cent and winter wheat less than two per cent. The fungus also occurred on barley, particularly on tworowed varieties (cf. Jorstad 1967) but is apparently of little significance, as has been observed in other countries (Hansen andMagnus 1969, Richardson 1972). According to Smedegäd Petersen (1974), the fungus is an important pathogen on barley in Denmark.
The present study showed that S. nodorum occurred rather commonly not only on cereals but also on numerous cultivated and wild grasses (cf. Mäkelä 1972 a). This confirmes that S. nodorum occurs commonly in Finland. In other countries has also been known the occurrence of the species on grasses (Sprague 1950, Hopp 1957, Jorstad 1967, Teterevnikova Babayan and Bokhyan 1970, Williams and Jones 1973. The fungus is regarded as being a very weakly specialised species (Weber 1922b, Hopp 1957, Brönnimann 1968. This opinion is supported by the laboratory inoculation tests performed in this study, in which isolates of S. nodorum originating from different cereals infected not only their own host but also all other cereals except oats (cf. Holmes and Colhoun 1970). This conclusion runs counter to the results obtained by Smedegärd Petersen (1974). Septoria tritici occurred exclusively on winter wheat, especially in the spring of 1973, and caused severe seedling-leaf mortality. Similar observations have been made elsewhere (Sanderson 1964, Jorstad 1967, Richardson and Noble 1970. The fungus is held to be strictly a foliar parasite, though it is capable of infecting all parts of the plant (Jones and Cooke 1971). In the field, however, the fungus was not observed on spring wheat, on which it is known to occur in, for example, Britain (Jones and Odebunmi 1971, Williams and Jones 1972, 1973, nor was it observed on rye (cf. Weber 1922 b. Sprague 1950). In the laboratory inoculation tests, however, isolates of 5. tritici originating from winter wheat infected not only their own host but also spring wheat and rye.
Septoria avenae f. sp. triticea occurred rather commonly on wheat and barley. The fungus is apparently a pathogen of minor importance in Finland for it is considered to be a weak parasite (Johnson 1947, Shaw 1957. Similarly, on wheat it is considered to be of far less significance than S. nodorum (Kietreiber 1962).
This study has shown that besides occurring on cereals, S. avenae f. sp. triticea is also found on numerous grass species, apparently as a saprophyte (cf. Johnson 1947, Sprague 1950).
Septoria avenae f. sp. avenae is of quite negligible importance on oats owing to its sporadic occurrence. Similarly, S. secalis, which occurs to some extent on rye, is generally considered to be economically insignificant (Weber 1923, Jorstad 1930, Frandsen 1943).
The perfect stage (Leptosphaeria avenaris and L. nodorum) were found on all cereals and on numerous grasses, as were the corresponding Septoria species. The present study did not clarify the role these play in the surviving and transmission of fungi. In other countries there is also knowledge about the occurrence of the same Septoria species on cereals and grasses (Weber 1922b, Sprague 1950, Jorstad 1967, Teterevnikova-Babayn and Bokhyan 1970, Williams and Jones 1973.