7/30/2019 Seras Ah

1/7

Journal of' General Microbiology (1 986), 132, 1 18 1-1 187. Printed in Great Britain

Water Potential, Growth and Cellulolysis of Fungi Involved inDecomposition of Cereal ResiduesBy N . M A G A N * A N D J . M . L Y N C H

Glasshouse Crops Research Institute, Littlehampton, West Sussex BNI 7 6 L P , U K(Received 29 October 1985; etised 1 December 1985)

1181

The effect of water potential and temperature on growth and cellulolysis of 10 soil fungi whichcolonize cereal crop residues was determined in tlitro. On 2 % (w/v) milled straw agar all speciesgrew in the range - .7 to - -0 MPa at both 10 and 20 "C. Growth rates differed depending onthe solute type used to control water potential. In general, but with the exception of thePenicillium spp., growth decreased with decreasing water potential. Hyphal growth on sterilestraw internode segments was much less than that on 2 % straw agar. Fusarium culmorum andTrichoderma harzianum colonized straw pieces best at high potential ( - 0.7 MPa) while only F .culmorum and the Penicillium spp. grew at low potential (-7.0 MPa). Trichoderma spp.,Gliocladium spp. and Chaetom ium globosum cleared cellulose agar most rapidly, depth of clearingdecreasing with water potential in the range -0.7 to -2.8 MPa at 20 "C. The relationshipbetween dry weight loss of inoculated cellulose filter paper and water potential was morevariable.

I N T R O D U C T I O NCereal straw residues remaining after harvest are colonized by a wide variety of fungi often

classified as primary 'sugar' fungi and secondary cellulose and lignin decomposers (Garrett,1970). As cellulose and hemicellulose are the major components of straw, contributing up to 75%of the dry matter (Harper & Lynch, 1981), those species able to utilize these constituents play aparticularly active role in decomposition. The major abiotic factors which determine bothprimary and secondary colonization and rate of decomposition are the water potential of thesubstrate, temperature and perhaps pH and gas composition (Griffin, 1972; Swift et al., 1979).

Fungi colonizing wheat straw have been shown to belong predominantly to the generaFusarium, Mucor and Penicillium with species of Trichoderma, Gliocladium, Aspergillus, Pyt hiu mand Cephalosporium among others isolated (Sadavisan, 1939; Walker, 1941). More recentlyHarper & Lynch (1985) studied a range of fungi which colonize straw and found thatTrichoderma spp., Sordaria alcina and Chaetomium globosum were particularly active incolonizing straw and decomposing cellulose in vitro. However, in all these studies, the waterrelations of the soil/straw system and the influence these may have on growth and cellulosedecomposition were not considered. This is particularly important in understanding the possibleinteraction between groups of fungi competing for the straw substrate. Some Penicillium speciesgrow optimally at slightly reduced water potentials down to - .8 MPa (Hocking & Pitt, 1979)while Aspergillus species, e.g. the A . glaucus group, grow optimally at - 7.0 to - 4-0MPa(Ayerst, 1969; Magan & Lacey, 1984~). hese groups of fungi may therefore under somecircumstances dominate the substrate (Chen & Griffin, 1966). More attention has perhaps beengiven to the water relations of plant pathogens such as Fusarium culmorum and Cephalosporiumgramineum, which colonize and survive on crop residues, than to those involved indecomposition (Cook & Duniway, 1981).

Although water potential and temperature have been shown to affect the rate ofdecomposition of milled straw (Bartholomew& Norman, 1946; Sain & Broadbent, 1975;Roper,0001-30430 986 SGM

7/30/2019 Seras Ah

2/7

1182 N . M A G AN A N D J . M . L Y N C H

Water potential (-MPa)Fig. 1. Relationship between water potential and water content (adsorption) for wheat straw (cvNorman) previously dried at 45 "C.

1985), little information is available on the effect these factors may have on the ability ofdifferent soil fungi to grow on straw substrates and to utilize cellulose. This paper presentsinformation on the effect of water potential and temperature on growth and cellulolysis of arange of soil fungi in uitro.M E T H O DS

Fungal isola tes. The isolates used in this study were isolated from decomposing crop residues in soil and wereAcremonium persicinum (Nicot) G ams (IM I 284720), Chaetomium globosum Kun ze ex Stend. (I M I 286935),Gfiocfadiu m oseum Bain (R190), Gliocfadiumuirens Miller (R193), Fusarium culmorum (W . G . Sm.) Sacc. (R191),Penicilfium anthinellum Biourge (IMI 284724), P. hordei Stolk ( P . hirsutum Dierckx) (IM I 284723), Trichodermaharzianum Rifai (IM I 275950),T .hgibrachiatum Rifai (IM I 284728), and T . viride Pers. :Fr. (IM I 298375). Thosecultures with IMI numbers are held by the Commonwealth Mycological Institute (CMI) and those with Rnumbers are in the GCRI culture collection.

Waterpotentialandgrowth.Freshly harvested straw (winter wheat cv. Norm an, C :N ratio 130: 1) was milled topass through a 0.5 mm m esh and used to prepare 2% straw agar (2% , w/v, milled straw an d 2%, w/v, technical agarno. 3: Oxoid) modified osmotically with glycerol (Dallyn & Fox, 1980)and KCl (Campbell & Gar dner, 1971) n thewater potential range -0.7 to - 14.0 MP a. Straw agar (p H 5.5) in 9 cm Petri dishes was inoculated cen trally with4 mm discs of test fungi, taken from the m argins of 7-10-d-old colonies on po tato dextrose agar. Peniciffium pp.were inoculated as a fine loop ofspo re suspension (Pi tt, 1979).Plates were stacked and sealed in clean polyethylenebags and then incubated a t 10 and 20 "C for 7-28 d depending on the water potential. Grow th was measured alongtwo diameters at right angles to each other, usually at daily intervals. Experiments were done twice with threereplicates on each occasion. Radial growth rates in mm d -' at different com bination s of water potential an dtempe rature w ere calculated for each test species. The standard errors of mean radial growth rates were calculated.Internode sections of straw (cv. No rman , 5-3cm long and 2.5-3 mm w ide) were cut carefully to avoid splittingand dried at 45 "C to constant weight (approx. 2.5% water content, wet weight basis). Known amounts of strawwere autoclaved a t 121 "C for 30 min. K now n volumes of sterile distilled water were carefully added to groups ofsterile straws in 250 ml flasks, as calculated from a straw-water adsorption curve (Fig. 1) to obta in water potentialsof -0-7, -2.8 and -7.0 MPa. Flasks were sealed and kept at 5 "C for 24 h with regular mixing to allowequilibration. Sterile straw internodes were placed carefully in three compartments of a 9 cm Petri dish dividedinto four sections. The fourth contained 2% water agar modified with KC l to the same water potential a s the strawto help maintain an accurate potential. A 4 mm disc, 0.5-1 mm thick, of a test fungus was inoculated onto theupper surface of one end of the straw segment. Petri plates were sealed with masking tape or Parafilm andincubated at 20 "C . The Pe tri dishes were examined daily for 7 d and th en as required for a maximum of 14 d.Grow th w as measured along the length of the straw segments using a dissecting microscope. For e ach species theexperiment was done with five replicate Petri plates for each water potential (total of 15 straw segments). Thestandard error of the mean growth achieved was calculated.

Water potential and celfulofysis.Th e ability of fungi to utilize cellulose was examined by two meth ods. (a)T heclearing of 2% ball-milled cellulose powder (W hatman C F 11, 72 h) in a m ineral salts medium (Dalton & Postgate,1969) modified with glycerol to -0.7, - 1.4 and -2.8 MP a. Th e medium was adjusted to pH 6 with 0.1 M-HCI.

7/30/2019 Seras Ah

3/7

Water relations of'soil fungi 1183

-4 - P. anthinellum P.hordei

1 -I I I I I I I I I I I I I2.8 5 .6 8 .4 11.2 2 .8 5 .6 8.4 11.2

Water potential (-MPa)Fig. 2. Effect of water potential on radial g rowth (mm d-I) of Trichoderma harzianum, Chaetomiumglobosu m, Penicillium janthinellum an d P . hordei on 2% (w/v) straw agar. Water potential was controlledosmotically with glycerol (a) nd KCl (0).ars represent SE.

Th e depth of clearing of the cellulose agar in test tubes (15 x 1.5 cm) was determined a fter incubation at 20 "C fo rfour weeks. Th e experimen t was done twice with three replicates on each occasion. (b )Loss in dry w eight of filterpaper (five Whatman no. 3, 7.5 cm) by the method of Garrett (1963) as modified by Fo rbes & Dickinson (1977).The water potential of the mineral salts medium was altered to -0.7, - -4 and -2.8 MPa with NaCl (Scott,1957). Glycerol was substituted with N aCl in this experiment to maintain a C :N ratioof 180,as used originally byGarrett (1963).The m edium was adjusted to pH 6 as before. Th e filter papers in 250 ml flasks were inoculated with4 mm agar plugs from the margin of growing fungi. The flasks were incubated at 20 "C for four weeks. Wads offilter papers were then dried t o constant w eight at 80 "Cand com pared with tha t of control wads of the same waterpotential. The experiment was done twice with three replicates per fungus at each water potential.

Wa ter potential measurement. The water potentials of agar media, mineral salts solutions and straw samples, todetermine the moisture adsorption curve, were all checked with a 100 channel automated thermocouplepsychrometer (Stevens & Acock, 1976) for high water potentials and a Sinascope (Sina, Switzerland) at low w aterpotentials.

R E S U L T SFig. 2 shows the effect of water potential on the growth of four of the test fungi. Somedifferences in growth were app aren t between m edia with the w ater potential am ended byglycerol and KCI. Growth was slightly greater when KCl was used as solute at high waterpotentials while at low water potentials growth on glycerol-amended media was greater.

7/30/2019 Seras Ah

4/7

1184 N . M A GA N A N D J . M . L Y N C HTable 1. Relationship between water potential and radial growth rate at I0 and 20 "C on

2% (wl u) straw agar modiJied with glycerolRadial growth rate (mm - ' )

f

Water 10 "C 20 "Cpotential A > I A \( - M P a ) . . . 0.7 2.8 7.0 9.8 14.0 0.7 2.8 7- 0 9.8 14.0Species

A . persicinumC. globosumF . culmorumG . roseumG . uirensP . hordeiP . anthinellumT. harzianumT . longibrachiatumT . r?iridePooled SE

2.3 1.7 0.31.7 1.4 0.22-9 2.3 1.01.2 0.3 0.11.3 0.9 0.11.2 1.7 1.01.1 1.4 0.23.5 2.4 0.62.6 1.5 0.73.2 1- 4 NG0.23 0.20 0.15

NGNG0.4NGNG0. 80.2NGNGNG0.08

NGNGNGNGNG0.60-NGNGNG

0-03

4.9 3.5 0.7 0.44.6 3.5 0.7 0.17.8 4.8 1.7 0-83.0 1.6 0.2 NG2.4 1-4 0.3 0.32.9 2-7 2.0 1.61.7 1.9 1-4 0.311.5 7.2 1.9 0.89.3 6.1 1.4 0.28.4 4.6 0.6 0.10.67 0.68 0.41 0-10

NGNG0.2NGNG1.00.2NGNGNG

0.07NG. N o growth.

Table 2. Efect of water potential on colonization of sterile internode straw segments after 14 dat 20 "C with, in parentheses, mean growth rates in mm d-'Water Colonization (mm SE)potential r A .( - M P a ) . . . 0.7 2.8 7.0Species

A . persicinumC. globosumF . culmorumG . roseumG . virensP . hordeiP . anthinellumT . harzianumT , longibrachiatumT , viride

9.7 f 0.7 (0.7) 3.0 f .7 (0-2) 1.0 (0.1)23.9 f 2.2 (1.7) 7.2 f 1.3 (0.5) NG98.5* f 10.9 (7.0) 36.0 f .4 (2.6) 6.3 f .5 (0.5)8.5 f 1.8 (0.6) 3.7 f 0.8 (0.2) NG6.2 f 0.1 (0.4) 2.8 f 0.7 (0.2) NG22.2 f 1.7 (1.6) 18-0 f 1-O(l.3) 10.9 +_ 0.7 (0.8)29.4 f 2.9 (2.1) 18.1 f 3.1 (1.3) 3-5 f 0.3 (0.3)71*0*f 10.5 (5.1) 5.5 f .3 (0.4) 1.0 (0.1)32-8 f 1.6 (2-3) 4.9 f 1.3 (0.4) 1.0 (0.1)20.1 f 1.0 (1.4) 6.0 f 1.0 (0.4) 0.4 (< O *l )NG, N o growth.* By extrapolation.

Chaetomiumglobosum was an exception to this. All species grew in the range - -7 o - .0 M Paat both 10 and 2 0 C on 2 % straw agar (Table l), the growth rate usually decreasing withdecreasing water potential. The Trichoderma spp. had the highest growth rates of all speciestested between -0.7 and -2.8 MPa. The exceptions were Penicillium hordei (10 "C) and P .janthinellum (10 and 20 "C) where optimum growth occurred at -2.8 M Pa when glycerol wasused as solute. Growth of all species at 10 "C was less than 50% of that at 20 "C, especially a t-0.7 and -2.8 MPa.Growth on sterile straw segments where water potential was controlled matrically was notdirectly correlated w ith growth on 2 % straw agar (Table 2). Optimum growth was at - .7 MP abut w as significantly reduced at a water p otential of - .8 MP a. Only F . culmorum,P. hordei andP . anthinellum grew at a water potential of -7.0 MPa.Th e cellulose clearing test favoured fungi able to produce extracellular cellulases, for exam pleTrichoderma spp., Gliocladium spp. and C. globosum. Depth of clearing decreased withdecreasing water potential (Table 3 ) . Penicillium spp. and F . culmorum demonstrated pooractivity in th e clearing test over a period of four weeks. Dry weigh t loss of cellulose filter pa pe r in

7/30/2019 Seras Ah

5/7

Water relations o f soil ungi 1185Table 3. EJect of water potential on cellulolysis measured by clearing of ' cellulose agar and lossin dry weight offi lte r papers afier 4 weeks incubation at 20 "C

Water Clearing (mm ) Weight loss (mg)potential ( r-*-( - M P a ) . . . 0.7 1.4 2.8 0.7Species

A . persicinurnC. globosumF . culmorumG . roseumG . cirensP. hordeiP . janthinellumT . harzianumT. longibrachiatumT. tliridePooled SE

5.0 3.5 -9.0 6-5 5.56.0 4.0* 2*0*9.0 3.5 1-O*

11.5 8.0 2*5*6.0 5- 0 1-5*5.5 3*5* -9.5 7.5 5.010.0 8.5 2.57.5 4.5* 2*0*

1.0 0.9 0.6* Partial clearing.

170220220120264240200601943428.9

1.42304060201702401005016045

16.5

2.8154012420

1002608064

1804713.7

relation to water po tential was more variable. C. globosurn, F . culmorum,G . virens and P . hordeicaused greatest loss in weight of filter paper at -0.7 M Pa w hile at the lowest water po tentialtested, -2.8 MPa, P. hordei, T. longibrachiatum an d F . culmorum were most active.

D I S C U S S I O NFungal colonization and decomposition of crop residues in soil occurs over a much widerrange of water potential than that permitting crop growth, which becomes limited at about

- .5 M Pa, the so-called perman ent wilting point (Griffin, 1972). Some decom position of cerealstraw has been detected at between - 19.6 and -28.0 M Pa although active decompo sition ofrice straw occurred a t - 4.0 M Pa (Bartholomew & Norman, 1946; Sain & Broadbent, 1975).Most of the fungal species examined in this study grew optimally a t a water potential of - .7to - .4 MP a at b oth 10 and 20 "C, growth being markedly reduced below -2.8 MPa.Interactions between reduced water potential a nd tem perature resulted in the greatest reductionin growth rate. In natural environments such interactions often determine the microbialcomm unities colonizing the straw substrate. The higher growth rates obtained when KCl ratherthan glycerol was used to control water potential have been previously observed (Brownell &Schneider, 1984) and may be due to K + ons in the medium being accumu lated by the microbialcells and perhap s serving as a com patible solute to assist in adjusting to w ater stress. However,high concen trations of the salt (low water p otentials) can inhibit en zyme activity, e.g. isocitratedehydrogenase, in some fungi (Luard, 1983). Th e glycerol in am ended m edia m ay also have beenutilized by som e of the test fun gi to help overcome water stress. Polyols, particularly glycerol,have been shown to function as compatible solutes, being accumulated by yeasts such asSaccharomyces rouxii (Brown, 1978) and by filamentous fungi such as Penicillium chrysogenumand Chrysosporium firstidium (Luard , 1982), conferring protection to enzym es at low waterpotentials.Much narrower ranges for growth of C. globosum and T . viride (minim a of -8.4 and- .6 MPa respectively) were obtained on clean glass than were obtained in this study on 2 %straw agar (Ko uyeas, 1964). Nutrient status may influence the w ater potential ran ge for growth(Griffin, 1972) and the latter m edium is perhaps a more realistic in vitro substrate. Moreinformation is available on F. culmorum isolates causing seedling diseases and ear blight ofwheat, growth occurring down to - .3 to - 11.2 MPa and - 14-0 M Pa, respectively (Cook etaf.,1972; Magan & Lacey, 19843) and for P. hordei and P. janthinellum, which can grow overmuch wider ranges of water potential down to -21.0 M Pa an d lower (Pitt, 1973 ; M agan &

7/30/2019 Seras Ah

6/7

1186 N . M A G A N A N D J . M . L Y N C HLacey, 1984a). Very little information is available on the water relations of the other fungiexamined in this study (Domsch et al., 1980).The importance of considering growth in vitro on substrates as close as possible to thatencountered in the natural environment was emphasized by the results obtained on the waterrelations of growth on sterile straw segm ents. Grow th of most test species was considerably lessthan that obtained on straw agar, although competition from the natural microflora whichwould normally occur on the straw was absent. This may partly be d ue to the water p otential instraw segments b eing controlled m atrically while that in straw agar is controlled osmotically.The matric water potential range for growth of pathogens such as Alternaria alternata andPhytophthora cinnamomi in soil is less than the osmotic w ater potential range (A debayo & Harris,1971) while Cook et al. (1972) found little difference for I ; . culmorum. Again, only P. ulmorumand the Penicillium spp. grew on straw segments at a water po tential of - .0 M Pa. Although thePenicillium spp. often grow relatively slowly at high water p otential (-0 .7 MP a), at slightlyreduced substrate water potential they may be at a competitive advantage.Although the cellulose clearing test suggested that optimum cellulolysis by Trichoderma,Gliocladium spp. and C. globosum occurred at a water potential of -0.7 M Pa, the loss in dryweight of cellulose filter paper sugge sted tha t so me fun gi, particularly Penicillium spp., may bejust as active a t slightly reduced water potentials. Although the effects of some env ironm entalfactors such as temperature, gas composition and pH on cellulolysis of some fungi has beendetermined (Walsh & Stewart, 1971; Forbes & Dickinso n, 1977), inform ation on the effect ofwater availability is scarce. Aspergillus terreus hydrolyses cellulose best a t its maxim um waterholding capacity, 400%, while at 300-100% cellulolysis is slower (Kundu et a/., 1983).Unfo rtunately, the relationship between w ater content an d water po tential of the cellulose wasnot determine d in their study. Penicillium and Aspergillus spp . have the ability to degrade plan tresidues with a large cellulose/hemicellulose com pone nt (Chatterjee & Nandi, 1981). Theytherefore may be important components of the microbial community colonizing cereal straw(Kouyeas, 1964).

Ga rrett (1975) suggested that successful saproph ytic colonization of straw by a fungal speciesis depen dent on the growth rate (metabolic activity) an d ability to degrade cellulose while othershave suggested that pectinase and xylanase activity may be just as important (Boothby &Magreola, 1984). Growth, nutrient utilization and competition between species may bemarkedly influenced by interaction between water potential and tem perature (Ma gan & Lacey,1 9 8 4 ~ ) .ndividual species may be affected in different ways, influencing the colon ization of thestraw substrate. Although in vitro studies cannot alone satisfactorily explain th e role of differentspecies in decomposition, knowledge of interactions of these factors, growth and nutrientutilization may assist in understanding their ecological role.We are grateful to Dr R . I . Grange for advice and use of the thermocouple psychrometer and to Nin a Jenk ins for

technical assistance.

R E F E R E N C E SADEBAYO, . A . & HARRIS,R. F. (1971). Fungalgrowth responses to osmotic as compared to matricwater potential. Proceedings. Soil Science Society o f'America 35, 65-469.AYERST, . (1969). The effects of water activity andtemperature on spore germination and growth insome mould fungi. Journal of' Stored ProductsResearch 5 , 127- 141 .BARTHOLOMEW,. V. & NORM AN, . G . (1946). Th ethreshold moisture content for active decomposition

of some mature plant materials. Proceedings. SoilScience Society of' America 11, 270-279.BOOTHBY,. & MAGR EOLA,. D. (1984). Prod uction ofpolysaccharide degrading enzymes by Cochliobolussatitlus and Fusarium culmorum growth in liquid

culture. Transactions of' the British MycologicalSociety 83, 275-280.BROWN, . D. (1978). Comp atible solutes and extremewater stress in eukaryotic micro-organisms. A d -cances in Microbial Physiology 17, 18 1-242.BROWNELL,. H . & SCHNEIDER,. W . (1984). Rolesofmatric and osmotic components of water potentialand their interaction with temperature in the growthof Fusarium oxysporum in synthetic media and soil.Phytopathology 75, 53-57.CAMPBELL, . S. & G A R D N E R , . A. (1971). Psychro-metric measurement of soil water potential: tem-perature and bulk density effects. Proceedings. SoilScience Society of' America 35, 8-1 2.CHATTERJEE,. K . & N A N D I , . (1981). Role of some

7/30/2019 Seras Ah

7/7

Wa ter relations oj' soil jun gi 1187mesophilic micro-organisms in rice stubble degrada-tion. International Biodeterioration Bulletin 17, 133-139.C H E N ,A. W. & GR I FFI N, . M. (1966). Soil physicalfactors and the ecology of fungi. V . Furth er studies inrelatively dry soils. Transactions y j ' the BritishMycological Societjy 49, 4 19-426.COOK,R . J . & D U N I W A Y ,. M. (1981). Water relationsin the life cycles of soil borne plant pathogens. InWater Po ent i d Relations in Soil Microbiology,pp. 97-1 18. Edited by J. F. Parr, W. R. G ardn er &L. F. Elliot. Madison: Soil Science Society ofAmerica.COOK,R . J., PAPENDICK, . I. & GR I FFI N,D. M.(1972). Grow th of two root-rot fungi as affected byosmotic and matric water potentials. Proceedings.Soil Science Societj. yf ' America 36, 78-82.DALLYN, . & Fox, A . (1980). Spoilage of material ofreduced water activity by xerophilic fungi. InMicrobial Growth and Sur riral in E.utremes uj'Enciron-ments. Edited by G. H. Could & J . E. L. Corry.Society of' Applied Bacteriology Tech nical Series no.1.5,pp. 129-139. L ond on: Academic Press.DALTON, . & POSTGATE,. R. (1969). Effect of oxygenon growth of Azotobacter chroococcum in batch andcontinuous culture. Journal uf 'General Microbiologj

DOMSCH, . H., CAM S,W . & ANDERSON,. H . ( 1 980).Compendium of'soil Fungi. London Academic Press.FORBES, . S . & DICK INSO N, . H . (1977). Effect oftempera ture, pH and nitrogen on cellulolytic activityof Fusarium acenaceum. Transactions of the BritishMycological Society 68, 229-235.GAR R ETT,. D. (1963). Soil Fungi and Soil Fertility.Oxford : Pergamon Press.GARRETT,S. D. (1970). Pathogenic Root-infectingFungi. Cambridge : Cambridge University Press.GARRETT, . D. (1975). Cellulolysis rat e an d com peti-tive saprophytic colonization of wheat straw by foot-rot fungi. Soil Biology and Biochemistry 7, 323-327.GR IFFIN , . M. (1972). Ecology ofSoil Fungi. London:Chapman & Hall.HAR PER ,. H. T . &LYNC H,. M . (1981). The ch emicalcomposition and decomposition of wheat strawleaves, internode s and nodes. Journa lof'Science Foodand Agriculture 32, 1057-1062.HAR PER ,. H. T. & LYNCH, . M. (1985). Colonisationand decom position of straw by fungi. Transactions ofthe British Mycological Society 85, 655-66 1 .HOCKING, . D. & PITT, . I. (1979). Wa ter relatio ns ofsome Penicillium spp. at 25 "C. Transactions of' heBritish Mycological Society 73, 141- 45.KOUYEAS,V . (1964). An approach to the study ofmoisture relations of soil fungi. Plant and Soil 20,KUNDU, . B., GHOSH,B. S ., GHOSH,B. L. & GHOSE,S. N . (1983). Role of water in the hydrolysis of

54 , 463-473.

35 1-363.

cellulose in a solid state. Journal yJ FermentationTechnology 61, 185-188.LUAR D,E. J . (1982). Accumulation of intracellularsolutes by two filamentous fungi in response togrowth at low steady state osm otic potential. Journaloj'General Microbiologj 128, 2563-1574.LUAR D. . J . (1983). Activity of isocitra te dehydrogen-ase from three filamentous fungi in relation toosmotic an d solute effects. Archires u j 'Microbiology

MAGAN,N . & LACEY,J . (1 98 4~ ). The effect oftemperature and pH on the water relations of fieldand storage fungi. Trunsactions uf' the British Myco-logical Society 82, 71-81.MAGAN, . & LAC EY, . (1984b). Wa ter relations ofsome Fusarium spp. from infected wheat ears andgrain. Transactions y j the British Mycological SocietyMAGAN, . & LAC EY,. (19 84 ~) . he effect of wateractivity, temperature and substrate on interactionsbetween field and storage fungi. Transactions 91' heBritish Mycological Society 82, 83-93.PITT, J. I . (1973). An appraisal of identificationmethods for Penicillium spp. - novel taxonomiccriteria based on temperature and water relations.Mycologia 65, 1 135- 1 157.PITT, J. I . (1979). The Genus Penicillium and itsTeleomorphic States Eupenicillium and Talaromyces.London : Academic Press.ROPER , M. M. (1985). Straw decomposition andnitrogenase activity: effects of soil moisture andtemperature. Soil Biology and Biochemis try 17,65-7 1.SADAVISAN,. S. (1939). Succession of fungi deco mpos -ing wheat straw in different soils, with specialreference to Fusarium culmorum. Annals of' AppliedBiology 26, 497-508.SAIN, P. & BROADBENT, . E. (1975). Moistureabsorption and m ould growth an d decomposition ofrice straw at different relative humidities. AgronomyJournal 67, 759-762.SCOTT,W. J . (1957). Water relations of food spoilagemicro-organisms. Adcances in Food Research 7, 83-127.STEVENS, . F. & ACOCK,B. (1976). A thermocouplepsychrometer with rapid automatic scanning anddigital printout of 100channels. Journal qf'Scien ttjcInstruments 9, 1058- 1062.SWIFT,M. J . , HEAL,0. W . & ANDERSON,. M. (1979).Decomposition in Terrestrial Ecosystems. London 1Blackwell Scientific Publications.WALKER,A. G. (1941). The colonization of buriedwheat straw by soil fungi with special reference toFusarium culmorum. Annals of Applied Biology 28,WALSH,J . H . & STEWART, . S. (1971). Effect oftemperature, oxygen and c arbon dioxide on cellulaseactivity of some fungi. Transactions of' the BritishMycological Society 57, 75-84.

134, 233-237.

83, 281-285.

333-350.