Trans. Br. mycol. Soc. 72 (1) 145-146 (1979)

[ 145 ]

Printedin Great Britain

EFFECT OF LIGHT QUALITY ON GROWTH AND SPORULATIONIN VERTICILLIUM AGARICINUM

By MOHAMED OSMAN AND L. R. G. VALADON

Department of Botany, Royal Holloway College, University of London, Egham Hill, Egham, SurreyTW20 oEX, England

Growth and sporulation of Verticillium agaricinum were studied under various wavelengthsbetween 300 and 750 nm. The fungus produced spores under all wavelengths tested as wellas in the dark. Of all lights used only actinic blue 320-450 nm (max 370 nm) markedlyincreased sporulation and retarded growth. The whole process can be considered as light-variable and not light-dependent. Mycochrome which may be involved in sporulation incertain fungi is not operative in this system.

Micro-organisms respond to light in differentways: by changed growth, spore production,and pigment formation (Carlile, 1965, 1970).Aspergillus fiavus (Muntanjola-Cvetkovic & Nesk-ovic, 1968) and Trichoderma viride (Gressel &Galun, 1967) were found to produce abundantconidia only after exposure to light. Hill (1976)found that light induces conidiation and inhibitsgrowth in Aspergillus ornatus. Several earlyobservations, reviewed by Smith (1936), Page(1952), Snyder & Hansen (1941) and Harter(1939), confirmed that light retards mycelialgrowth. Zentmyer & Ribeiro (1977) found thatPhytophthora cinnamomi produced sporangia atall wavelengths and intensities tested, and indarkness, and concluded that sporangial productionis light-variable. Tan & Epton (1973) foundthat sporulation of Botrytis cinerea was stimulatedby near-u.v. light and was slightly affected byinfrared, red and yellow light, but blue and greenwere ineffective. They observed also that contin-uous black light retarded linear growth.

Carotenogenesis in Verticillium agaricinum isphoto-dependent and near-u.v. light is veryeffective. The near-u.v. light effect is reversedby blue light but the photoreceptor is not myco-chrome (Osman & Valadon, 1979). Furthermore,this fungus does not behave in the same way asother fungi in response to light (Valadon &Mummery, 1973; Mummery & Valadon, 1973).

The object of the present paper is to studythe effect of light on growth and sporulation inV. agaricinum and to compare it with other fungi.

MATERIALS AND METHODS

The fungus V. agaricinum (Lk) Cda was used inthis study. Malt extract-agar medium (20 ml)was poured into Petri dishes (8-5 em diam).

Spore suspension was prepared from 7-daycultures of the fungus. A loopful was placed inthe centre of each dish, which was then incubatedin the dark and under different lights for 5 daysat 24-25 DC. The lights used were white, black,actinic blue, blue, yellow and red (Table 1).Linear growth of the developed colonies wasmeasured. The spores were counted using ahaemocytometer. The light intensity was 95 flWcm-2 for white and actinic blue light, and 10 flWem -2 for the other lights, between 300 and 750 nm.

RESULTS AND DISCUSSION

Linear growth was markedly affected by actinicblue (near-u.v.) light (Table 1) and the colonyappeared to be wrinkled and very deep-orangein colour. Carotenoids are greatly increasedunder near-u.v, light (Osman & Valadon, 1978)and this was reflected by the appearance of thecultures. Linear growth (6 em) under black lightwas also inhibited compared with cultures in thedark (8-2 em), and it is also known that carotenoidproduction is more than doubled under blacklight compared to white light (Osman & Valadon,1978). Growth under all other lights used did notdiffer significantly from dark controls. The coloniesunder black light appeared flat and were light-orange in colour; under white light the appearancewas again flat and slightly orange coloured; whilstunder all other lights and in the dark there wasno trace of colouration and the cultures were allwhite and fluffy.

The spores under near-u.v, light were variablein size and shape in comparison with those grownin the dark (Osman & Valadon, 1979). As canbe seen from Table 1, the average numberof spores was 6-8 x 105 ml - 1 which was signi-ficantly different from dark-grown spores or

0007-1536/79/2828-483° $01.00 © 1979 The British Mycological Society

Photobiology of Verticillium

Table 1. Effect of light quality on linear growth, sporulation and appearance of colonies of V. agaricinum

Linear SporeTransmittance growth Number Character of

Light quality (nm) (ern) ml '! x 10-5 ColoniesDark 8'2 4'5 Fluffy and whiteWhite Visible spectrum 8'0 5'2 Flat and slightly orangeBlack 300-420 (peak 355) 6'0 5'5 Flat and light-orangeActinic blue (near-u.v.) 320-450 (peak 370) 1'0 6·8 Wrinkled and deep-orangeBlue 380-525 (peak 475) 8'1 5'4 Fluffy and whiteYellow 545-620 (peak 570) 7'9 4'9 Fluffy and whiteRed 625 and above 8'1 5'4 Fluffy and white

spores under any other kind of light. Althoughthere is an increase of approximately 40 % innumber of spores under near-u.v., on the wholesporulation in V. agaricinum is not photo-depen-dent, but continuous near-u.v, light retardsgrowth and increases sporulation. Black light,on the other hand, inhibits linear growth butdoes not affect sporulation, so we are in disagree-ment with a number of reviewers in that lightdoes not inhibit growth in V. agaricinum.

Kumagai et al. (1976) have proposed the termmycochrome for their photoreceptor system, inwhich near-u.v. caused sporulation, and this isreversed by blue light. They proposed the actionof mycochrome as follows:

Bmycochrome (MB)~ mycochrome (M:01uv)

N-UV

Irradiation with near-u.v. light will convert theM N UV form to the M B form which is active inconidiation. In our case near-u.v. increasedsporulation by about 40 % but blue light had noeffect, i.e. blue light cannot reverse the effect ofnear-u.v. light. We have already shown thatmycochrome cannot operate in V. agaricinum(Osman & Valadon, 1979) and that the pigmentsystem must be new. This conclusion is rein-forced by the results above. Since there is a highirradiance reaction involved in carotenogenesisin this fungus (Osman & Valadon, 1979), phyto-chrome must also be involved.

REFERENCES

CARLILE, M. J. (1965). The photobiology of fungi.Annual Review of Plant Physiology 16, 175-202.

CARLILE, M. J. (1970). The photoresponses offungi. InPhotobiology of Micro-organisms, pp. 309-344. NewYork: Wiley-Interscience.

GRESSEL, J. & GALUN, E. (1967). Morphogenesis inTrichoderma: Photoinduction and RNA. Develop-mental Biology 15, 575-598.

HARTER, L. L. (1939). Influence of light on the lengthof the conidia in certain species of Fusarium. Ameri-canJournal of Botany 26, 234-243.

HILL, E. P. (1976). Effect of light on growth andsporulation of Aspergillus ornatus, Journal of GeneralMicrobiology 95, 39-44·

KUMAGAI, T., YOSHIOKA, N. & aDA, Y. (1976). Furtherstudies on the blue and near ultraviolet reversiblephotoreaction with an intracellular particulate frac-tion of the fungus, Alternaria tomato. Biochimica etBiophysica Acta 421, 133-140.

MUMMERY, R. S. & VALADON, L. R. G. (1973). Theeffect of antimycin A on carotenogenesis in Verticil-lium agaricinum. Planta (Berlin) 109, 353-356.

MUNTANJOLA-CVETKOVIC, M. 1.& NESKOVIC, M. (1968).Studies on the effect of some substances as possiblesubstitutes of light in the sporulation of Aspergillusflaous 28-A. Bulletin de l'Institut et du Jardin Bota-nique de l'Unioersite de Belgrade 3, 35-41.

OSMAN, M. & VALADON. L. R. G. (1978). Effect oflightquality on the photoinduction of carotenoid synthesisin Verticillium agaricinum. Microbios 18, 229-234.

OSMAN, M. & VALADON, L. R. G. (1979). Studies onthe near u.v. effect on carotenogenesis in Verticilliumagaricinum. Microbios. (In the press.)

PAGE, R. M. (1952). The effect of nutrition on growthand sporulation of Pilobolus. American Journal ofBotany 39, 731-739.

SMITH, E. C. (1936). In Biological Effects of Radiation(ed. B. M. Dugger), pp. 889-918. New York:McGraw-Hill.

SNYDER, W. C. & HANSEN, H. N. (1941). The effect oflight on taxonomic characters in Fusarium. Mycologia33, 580-591.

TAN,K. K. & EpToN, H. A. S. (1973). Effect of light onthe growth and sporulation of Botrytis cinerea.Transactions of the British Mycological Society 61,147-157.

VALADON, L. R. G. & MUMMERY, R. S. (1973). Effectof certain inhibitors of carotenogenesis in Verticil-lium agaricinum in response to nicotine and toCPTA. Microbios 10A, 97-104.

ZENTMYER, G. A. & RIBEIRO, O. K. (1977). The effectof visible and near-visible radiation on sporangiumproduction by Phytophthora cinnamomi. Phytopatho-logy 67, 91-95.

(Accepted for publication 30 June 1978)