Gibellina cerealis, an unusual pathogen of wheat

[ 653 ] Trans . Br . mycol, Soc. 84 (4), 653-659 (1985)

Primed in Great Britain

GIBELLINA CEREALIS, AN UNUSUAL PATHOGEN OF WHEAT By M. D. GLYNNE , B. D . L. FITT AND D. HORNBY Rothamsted Experimental Station, Harpenden, H erts. , ALS 2JQ The numbers of wheat plants infected by Gibellina cerealis in a long-term wheat and fallow experiment were recorded annually from 1935 to 1978 . Infected plants were few in number .an d generally widely separated. Overall, there were about twice as many infected plants after 3 years offallow as after 1 year. In an outside pot experiment, using soil amended with infected straw, wheat plants infected with G. cerealis, although rare, were more frequent after 4 or 5 years offallow than after 1-3 years offallow or continuous wheat. Similar lesions developed on wheat, barley, rye and triticale inoculated with G. cerealis, but not on oats or grass. Lesions developed on wheat grown in pots ofcompost inoculated with naturally infected straw collected a few months earlier, but not in pots with infected straw collected a year or more previously. Gibellina cerealis Pass. was first recorded on wheat near Parma (Passerini, 1886) and subsequently at several other sites in northern Italy (Cavara, 1893; Ferraris, 1930; Corte, 1969). In some years G. cerealis has been widespread, but in others it could not be found (Cavara, 1893). It has also occurred rarely in France (D elacroix & Maublanc, 1926), Bulgaria (T odorova, 1957) and Romania (Raicu & Avram, 1971) and has been widespread in northern China (Wang, Horng & Chow, 1956 ) and Georgia, USSR (E ndeladze, 1979 ). In Britain, it ha s been recorded only on the Rothamsted farm (G lynne, 1936). Little is known of the factors affect ing the sporad ic occurrence of this cereal pathogen . Passerini (1886) described the beaked perithecia, slender asci (100 x 15-22 ,urn) and light brown two-celled ascospores (20-22 x 7'5-9/lm) of G. cerealis but did not isolate the fungus. Larger ascospores (22-32 x 7'5-9,um and 28-34 x 7-10 ,urn) were reported by Cavara (1893) and Booth (1977), respectively. No conidial state is known (Booth, 1977). Gibellina is currently classified within the order Polystigmatales (H awksworth, Sutton & Ainsworth, 1983). Cavara (1893) could not induce ascospores to germinate but Wang et al. (1956) found that they germinated readily on wheat tissues. The symptoms of ' white straw disea se ' (F erraris, 1930 ) were first described by Cavara (1893). Infected plants were stunted and usually did not produce an ear. G. cerealis was confined to the leaf sheaths, causing elongated spots covered with felt-like stroma, within which perithecia (seen as dark spots ) developed. It did not infect the roots, as Passerini (1886) had stated. Some aspects of his

descriptions and illustrations are inaccurate because the plants he examined appear to have been infected by powdery mildew, Erysiphe graminis DC., which he wrongly thought was the imperfect stage of G. cerealis. Although G. cerealis is most common on wheat and can also infect barley (E ndeladze, 1979), its host range is unknown. This paper describes the occurrence of G. cerealis on a long-term wheat and fallow experiment on the Rothamsted farm, and pot experiments to investigate its survival and host range. MATERIALS AND METHODS

Field occurrence

The occurrence of G. cerealis on wheat in a long-term wheat and bare fallow experiment was recorded from 1935 to 1978. This experiment was begun on Hoosfield, Rothamsted in 1856. The land, a medium clay loam with flints, has received no manure or fertilizer since 1851. It is near the site of a Roman temple and fragments of Roman pots and tiles are comm on . Two parallel 0'2 ha strips (A and B), cropped alternately with wheat, had each been divided into four sections in 1932. When a strip was in wheat only three of the four sections were cropped, the fourth remaining fallow , so that each section had three years of fallow in turn on an 8 year cycle (T able 1). The nearest other crop of winter wheat was in a four-course rotation experiment on the sout hern edge of the wheat and fallow experiment. There were also two long-term spring barley experiments on Hoosfield (north and south of the wheat and fallow experiment). The winter wheat cultivars grown were Squarehead's Master (1935-62), Squarehead's Master and

Gibellina cerealis on wheat

654

Cappelle-Desprez (in strips) (1963, 1965), Squarehead's Master and Rothwell Perdix (1964), Rothwell Perdix and Cappelle-Desprez (1966) and Cappelle-Desprez (1967- 78). Winter wheat failed on the whole experiment in 1949 and on sections A3 and A4 in 1966 and was replaced by spring wheat (Fylgia in 1950, Kloka in 1967). Sowing rates were ca 200 kg ha" and herbicides were used on crops harvested in the years 1968-78. Further details of this experiment are given in two Rothamsted reports (Anon ., 1970, 1977). The numbers and positions of wheat plants infected by G. cerealis were recorded each year in late May and then at least three more times before harvest. Pot experiment, 1952-60 Wheat plants were grown in large pots (26 ern diam) containing soil (16'3 kg per pot) which had not been cropped to cereals previously. These pots were kept outside in a bird-proof cage. Infected straws bearing large numbers of G. cerealis perithecia were collected from the field, chopped coarsely and mixed into the top 5 em of soil in 43 of the pots in October 1952. Six unamended pots were used as controls. Each year from 1952 to 1959 pots were sown with winter wheat (cv. Squarehead's Master, 40 seeds per pot ) or grass (broadcast) in October or November, or left fallow (T able 2). Winter wheat sown in 1956 was killed by frost and the pots were resown with spring wheat, cv, AtIe, in March 1957. From 1956 to 1960 1 g of ammonium sulphate (in 50 ml water) was added to each pot of wheat every March. Each year all plants were removed at harvest and the numbers infected by G. cerealis recorded. Host range

In 1936 (during June-August) and 1937 (during January-July) nine winter wheat cuitivars (H oldfast, Hybrid 40, Juliana, Little Joss, Redman, Rivett, Squarehead's Master, Steel, Yeoman 2), four spring wheat cuitivars (April Bearded, Marquis, Red Marvel, Van Hoek), a six-rowed winter barley, five spring barley cuitivars (Chevalier, Kenia, Plumage, Plumage Archer, Spratt Archer), a winter rye and eight oat cuitivars (Eagle, Grey Winter, Golden Rain, Marvellous, Onward, Potato, Resistance, Victory) were tested. In 1952

(during June-August) two triticale cultivars (M untzing, Rimpav) and four grass species (cocksfoot , Italian ryegrass, perennial ryegrass and timothy) were tested. Pots (17'5 em diam) containing a mixture of Rothamsted soil (40 % ), sand (40 % ) and Kettering loam (20%) were each sown with twelve seeds and later thinned to 10 plants per pot. There were two pots per cultivar (four for triticale). About one week after sowing a 5 mm disc of G . cerealis, cut from a potato dextrose agar (PDA) colony, was placed against the base of each seedling stem and covered with a layer of loose soil. The pots were kept in an unheated glasshouse and watered twice daily until harvest when the numbers of plants infected by G. cerealis were recorded. Survival In November 1955 40 pots (11'5 em diam), filled with John Innes compost, were each sown with twenty seeds of winter wheat, cv. Squarehead's Master. Four weeks later chopped infected straw bearing perithecia from a collection made in 1955 was spread on the surface of the compost in 5 pots. Straw from earlier collections that had been kept dry in the laboratory was used to inoculate other pots as follows: 1939-49 collections, 23 pots ; 1953 collection, 3 pots; 1954 collection, 4 pots. Plants in a further 5 pots were inoculated with 5 mm discs of G. cerealis on PDA. The pots were placed in an unheated glasshouse and the numbers of plants infected with G. cerealis were recorded in July 1956.

OBSERVATIONS: THE PATHOGEN AND THE DISEASE

Gibellina cerealis Hyphae were hyaline, septate, developing polygonal cells when encountering hard surfaces, e.g , leaf sheaths or glass slides. Perithecia (315-600 x 258-570 pst»; average 432 x 395 /lm ) were pale, flask-shaped, with black, protruding beaks (F ig. 1 a) and contained numerous colourless paraphyses. Asci (90-125 x 13-18/lm; average were 8-spored. Ascospores 105 x 16 /lm ) (23- 36 x 7-11 /lm; average 30 x 9/lm) (F ig. 1 b) were biseriate, pale initially and becoming hazel or honey-coloured as they ripened, normally twocelled but occasionally two or three septate. The

Fig. 1. Gibellina cerealis. (a) Longitudinalsectionthrough a perithecium; (b) Ascospores in longitudinalsection of perithecium; (e) Infected plant with lesions on leaf sheaths; (d) Discrete and coalescent lesions on leaf sheaths; (e) Perithecia on leaf sheaths. (a) and (b), material collected in August (1969-71), stored in formyl acetic alcohol and embedded in wax for sectioning; (e) and (d), material collected in July and August 1964.

M. D. Glynne, B. D. L. Fitt and D. Hornby (a) (a)

\\ t ;' ..

:;., . . .J6>-' -.t.i!r!:,

(d)

(c) I

I

I

~

~

~

'A .~

(e)

Fig.

1.

For caption see opposite.

655

Gibellina cerealis on wheat

65 6 Table

1.

Occurrence of Gibellina cerealis on wheat in a wheat and fallow rotation experiment at Rothamsted, 1935-78 Number of plants infected

A (South)

1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 t 1951 1952 1953 1954 1955 1956 195TI: 1958* 1959* 1960* 1961 1962 1963§ 1964 1965 1966 11 1967 1968 1969 197° 1971 1972 1973 1974 1975 1976 1977 1978 Total No. of years of wheat Annual Mean

B (North)

1*

2

0

0

13

35

45

6

19

25

50

20

3

26

43

90

3

3

9

38

5

13

49

11

21

°

4

Total

0

0 93

67 33

65

39

250

°

3°

181

12

31

97

17

61

34

112

13

10

23

26

92

° 65 °

0

2

0

14

7

21

0

°

6

6

2

3

4

4

20

0

3

2

5

3

2

5

2

3

0 0 0

19

10

38

7

4

12

2

16

13 0

420

° 368

6 0 11

°

2 45

28

1106

22 16 16 17 17 25 23 15 5 5° * Western plot. - , Plot fallow. t Sown in spring. * 0·6 of each plot surveyed under wheat. winter-sown; A3 and A4 spring-sown.

Total

28

3 10

18

34 4

3

6

38

55 3

60

61

166

37

4°

1°5

77

188

19

92

°

14

60

1°4

119

188

411

+

+

+

7

16

+ 2

7

2

5

5

74

37

44

2

0

3

32

12

49

18

31

12 4°

132

23

67

76

166

72

369

587

542

1570

15 5

17 22

16 37

15 36

21 75

5

0 237

4

2

0 9

° 81

2

0

° °

14°

1*

177

§ G. cerealis present but not counted.

II At

M. D. Glynne, B. D. L. Fitt and D. Hornby Table

2.

657

In cidence of Gibellina cerealis on wheat in different wheat (w) and fallow if) sequences in pots 1953-60 Infected plants (mean per pot)*

Sequence w-w-w-w-w-w-w-w w-w-f-f-w-w-w-w w-f-w-f-w-f-w-w f-w-f-w-f-w-w-w f-f-w-w-f-f-w-w f-f-f-w-w-f-w-w f-f-f-f-w-w-w-w f-f-f-f-f-w-w-w

1953 0 0

1954 0 0

0

1955 0

195 6 0

0 0 0'75

0 0 0

1957 0 0 0'25 0 1'75

195 8

1959

0 '33 0 '33

0 '33 0

0 '5

0'75 0'75 0 0'25 4'5

0 2'0

1960 0 0 0 0'5 0 '25 0 0 0

* Plants grown in pots of soil amended with infected straw in 1952. Two, three or four pots per sequence, 40 wheat plants per pot.

colony on potato dextrose agar was fluffy, white, becoming pearl-white to grey and developing perithecia in ca 6 weeks at 20 °C . On wetting, perithecia ejected ascospores which could be collected on covers lips about 4 mm above the perithecia and germinated in drops of water. White straw disease G. cerealis infected the outer leaf sheaths of wheat, producing well-defined eye-shaped lesions with sharp brown edges, lighter interiors and central patches of dark plate-like mycelium (F ig. 1 c, d). Thin hyphae on each sheath surface developed pol ygonal cells before penetration. Penetration of successive sheaths as far as the culm was rapid so that infected areas were carried up the plant as sheaths elongated (Fig. 1 c). Discrete lesions (F ig. 1 d) may, therefore, have developed from a single infection site . Lesions normally appeared on leaf sheaths or blades and only rarely on the rachis or glumes. Infected plants were easily detected in May and June when the dark brown lesions contrasted strongly with surrounding green foliage. Thick, grey, felt -like stromata developed between the leaf sheaths and darkened as numerous perithecia developed (F ig. 1 e). By harvest, characteristically blackened tillers, with thin or no ears, had often lodged. RESULTS

Field occurrence

White straw disease was observed on wheat in the long -term wheat and fallow experiment on Hoosfield in every year from 1935 to 1977, except 1936 (T able 1). The incidence of infected plants was always small « 0 '5 % ) and numbers ranged from 1 (1950, 1968, 1970) to 411 (1961). On average there were 32 infected plants in plots where wheat followed 3

years of fallow but only 16 where wheat followed 1 year of fallow . White straw disease developed on all the winter wheat cultivars grown. When winter wheat failed, however, and was replaced by spring wheat, only one infected plant was recorded. Infected plants were scattered and did not occur in foci. In general, there were fewer infected plants in the western sections (A l, Br) than in the others. A total of eight infected wheat plants was recorded from Broadbalk field, about 0'5 km south-east of Hoosfield, from 1966 to 1981, in second to eleventh wheat crops. Infected plants were also observed, but not counted, on both the Hoosfield experiment and Broadbalk in 1984. G. cerealis has not been observed in other cereal experiments on Hoosfield, or elsewhere on the Rothamsted farm . Pot experiment, 1952-60 Less than 1 % of the wheat plants in pots with added inoculum developed lesions of white straw disease (T able 2). Most infected plants occurred after 4 or 5 years of fallow and very few after 1 .year of fallow or during continuous wheat. Only one plant developed lesions in the grass /wheat sequence (in 1959), in a first wheat after grass preceded by three wheat and two grass crops. Host range White straw disease developed on all nine winter wheat cultivars (56 % of plants infected), four spring wheat cultivars (40 % infected) and six barley cultivars (15 % infected) in the 1936 and 1937 experiments (T able 3). Rye failed in 1936 and one plant developed lesions in 1937. No oat plants developed white straw disease in either experiment. Both triticale cultivars developed white straw

Gibellina cerealis on wheat Table 3. Host range of G . cerealis Cultivars tested (no.) Winter wheat Spring wheat Winter barley Spring barley Oats Rye Triticale Grass

9 4 1 5 8

1

. 2

Plants inoculated (no.)

180 80 20 100 160 20 80 80

Plants infected (no.)

1936 102 32 9 24 o

.. 4 species: cocksfoot, Italian ryegrass, perennial ryegrass, timothy . - , Crop failed.

disease ( 12 ' 5 % infected). Lesions on perennial and Italian ryegrass were atypical and none developed on timothy or cocksfoot.

Survival Whereas 32 out of 98 plants inoculated with mycelium of G. cerealis on agar developed white straw disease, onl y 4 out of 97 plants developed lesions in pots inoculated with infected straw that had been stored for ca 3 months . None of 516 plants grown in pots inoculated with infected straw that had been stored from 1 to 16 years developed lesions . DISCUSSION

'White st raw disease' seems an inappropriate name for the symptoms of G. cerealis on wheat at Rothamsted, since by harvest the infected tillers are characteristically black; ' black straw disease' would be more appropriate . Although the black perithecial stroma (Fig. 1 e) is distinctive, earlier symptoms of the disease (Fig. 1 c, d) might be confused with those of eyespot (Pseudocercosporella herpotrichoides (Fron) Deighton) or sharp eyespot (Rhizoctonia cerealis van der Hoeven) (Sprague, 1937; Corte, 1969). Eyespot lesions, however, have a less distinctive margin and are usually confined to the base of the plant, while lesions of sharp eyespot, which are often carried up the plant during stem extension, generally coalesce into large multiple lesions, whereas those of G. cerealis do not. The occurrence of G. cerealis in the Hoosfield wheat and fallow experiment between 1935 and 1978 (T able 1) suggests that the fungus is able to survive in soil for several years in the absence of wheat crops. Since it can infect most cereals and some grasses (T able 3), it may also survive between wheat crops on alternative hosts. Results of the pot

1937 98

1952

32 4 11

o 1

10

2t t

Atypical symptoms.

experiment (T able 2), however, imply that G. cerealis can survive as stromata or perithecia on straw buried in soil for at least 5 years, although unable to survive dry storage in a laboratory for more than a few months. It is puzzling that the occurrence of G . cerealis should have been greatest after several years of fallow, both in the field and in pots. Most plant pathogens increase in the presence of their host, whereas G. cerealis appeared to be favoured by the absence of its main host, at least for several years . However, continuous wheat does not exclude the disease, since it also occurred on a few plants in continuous wheat sequences on Broadbalk. That there were fewest infected plants in plots on the prevailing upwind (west) side of the wheat and fallow experiment suggests that the inoculum may be wind-dispersed. If this experiment on Hoosfield provided the inoculum that infected a few plants on Broadbalk, then some inoculum can be dispersed over several hundred metres. On the basis of laboratory tests it seems likely that ascosp ores of G. cerealis are released from perithecia when infected straw is wetted. Thus we conclude that infection of winter wheat in the field by G. cerealis is initiated by air-borne, wind-dispersed ascospores. Wang et al. (1956) suggested that air-borne ascospores are the main agents spreading the disease in China. Although there may have been spore dispersal gradients away from sources of inoculum (F itt & McCartney, 1985), the absence of disease foci in the Hoosfield experiment suggests that the proportion of dispersed spores which initiated disease was very small. The scattered distribution of infected plants implies that there was little secondary disease spread. Ascospores were mature in August (F ig. 1) and plants were probably infected by spores dispersed in the autumn, since spring-sown wheat, though generally susceptible (Table 3), developed little disease either in the field or in pots

M. D. Glynne, B. D. L. Fitt and D. Hornby and no disease developed on neighbouring Hoosfield spring barley. Infections were active in the spring, when lesions were carried up elongating plants, and this may have been the resumption of activity after a latent period, or a ver y slow development, during the winter. It is surprising that G. cerealis, a pathogen with air-borne ascospores, is not more widespread on the Rothamsted farm and has not spread to other sites in the U.K. The Hoosfield wheat and fallow experiment is, however, unique ; its rotation is atypical ofcurrent farming practice in the U.K. and there are few other arable sites in Britain which have received no fertilizer for over 130 years. It may be that in many of the other areas where G. cerealis has been recorded, e.g, China (Wang et al., 1956); Italy (Corte, 1969); USSR (Endeladze, 1979), little fertilizer has been used and wheat crops have tended to be thin and low yielding. Perhaps G. cerealis is less able to infect plants in well-fertilized crops and only effectively survives competition with other organisms in poorly-fertilized crops. The origin of G. cerealis on this one site in the U .K. is a mystery. One possibility is that it was brought from northern Italy, where it is endemic (Cavara, 1893; Corte, 1969), by the Romans, perhaps on straw used to pack the tiles or pottery still found as fragments on the experimental site , and has been able to survi ve until the present day on grass and cereal crops. The assistance of J. Etheridge, R. J. Gutteridge, M . Holden, E. Lester, F . J. H . Moore, R. D . Prew, D. B. Slope and many others in recording G. cerealis at Rothamsted is gratefully acknowledged. REFERENCES

ANON. (1970). Details of the Classical and Long-term Experiments up to 1967. Harpenden : Rothamsted Experimental Station.

ANON. (1977). Details of the Classical and Long-term Experiments 1968-73. Harpenden : Rothamsted Experimental Station. BOOTH, C. (1977). Gibellina cerealis. C.M.I. Descriptions of Pathogenic Fungi and Ba cteria, no. 534. CAVARA, F . (1893). Ueber einige parasitische Pilze auf dem Getreide. Zeit schrift fur Pfianzenkrankheit en 3, 16--26. CORTE, A. (1969). La rizottoniosi del culmo del frumento ( = ' sharp eyespot ') in Italia. Rioista Patologia Vegetate, Pavia, S eries IV 5, 37--68. DELACROIX, G. & MAUBLANC, A. (1926). Maladies des Plantes Cultiuees; Maladies Parasitaires. Par is : J.-B. Bailliere. ENDELADZE, N . Y. (1979). [Study of the biology of Gibellina cerealis Pass. the root rot pathogen of wheat] (Ru .). Trudy Nauchno-lssledooatel'skogo Instituta Zashchity Rastenii Gruzinsko SSR 30,44-47. FERRARIS, T. (1930). Mal bianco degli steli di grano . Rioista Agricola 2.6, 407-408. FITT, B. D. L. & MCCARTNEY, H. A. (1985). Spore dispersal in relation to epidemic models . In Plant Disease Epidemiology, 1 (ed. K. J. Leonard & W. E. Fry). New York: Macmillan Publishing Company. (In the Press ). GLYNNE, M . D . (1936). Some new British records of fung i on wheat . Transa ctions of the British Mycological S ociety 2.0, 120-122. HAWKSWORTH, D . L., SUTTON, B. C. & AINSWORTH, G. C. (1983). Ainsworth & Bisby 's Dictionary of Fungi, 7th edn, Kew , Surrey : Commonwealth Mycological Institute. PASSERINI, G. (1886). Un'altra nebbia del frurnento. B ollett ino Comizion e di Agriculture, Parma 7 . RAICU, C. & AVRAM, M . (1971). Ciuperci din sol care produc putrezirea radacinilor si bazei tulipinii Ia Griu. Micr obiologia, Bucharest 2, 149-160. SPRAGUE, R. (1937). A further note on the fungus causing a white foot rot of wheat and oats . Phytopathology 27, 798--799. TODOROVA, V. (1957). [Foot rot and root rot of cereals] (Bul.) Bulletin of Plant Protection, Sofia 6, 15-28 . WANG,K-N .,HoRNG, S-V. &CHOW,C-P. (1956). On the ascospore germination of Gibellina cerealis Pass. Acta Phytopathologica Sinica z, 167-173.

(R eceiv ed for publication 27 September 1984)