R H I Z O P U S H O M O T H A L L U S - - A N O T A B L E A D D I T I O N T O I N D I A N S O I L M U C O R A C E / E

BY J. N . RAI AND J. P. TEWARI (Microbiology Laboratory, Botany Department, Lucknow University, Lucknow)

Received Janualy 2, 1962

(Communicated by Prof. S. N. Das Gupta, r.A.Sc.)

INTRODUCTION

DURING the course of taxa-ecological studies on Soil Fungi of fertile soils (both cultivated and uncultivated) of Uttar Pradesh, India, the authors have recorded Absidia butleri Lendner, Rhizopus nigricans Ehrenberg, R. arrhizus Fischer, R. nodosus Namyslowski, Circinella muscce (Sorokine) Berlese and de Toni, Mucor hiemalis Wehmer, M. plumbeus Bonorden, M. jansseni Lendner, and M. bacil~formis Hesseltine. Rai and Mukerji (1961) have recorded Circinella muscce and Mucor bacilliformis from virgin soils (Usar) and as being new records from Indian soils.

A fungus, isolated from Lucknow soils and resembling the genus Zygorhynchus Vuillemin in certain features, was sent to Dr. C. W. Hesseltine for his advice, who informed (personal communication) it to be the second isolation of a very interesting homothallic species of Rhizopus and that he has also prepared a description of another isolate of this organism for publica- tion, which was isolated from desert soil in Guatemala in 1956. Dr. Hesseltine has named it as R. homothallus Hesseltine.

Total number of species of genus Rhizopus is rather very much confused. Zycha (1935) recorded eight main species based on fifty-four mentioned in the literature. Naumov (1939) lists about twenty-eight species. Hesseltine (1955) remarked that although many species of Rhizopus have been reported, the exact number is uncertain. In a recent monograph on this genus based on a study of 77 identified strains Kockov~i-Kratochvilovfi and Palkoska (1958) have resolved the genus into five species. While omitting the zygospore morphology from their study, they have followed certain novel criteria for determining the species.

MATERIALS AND METHODS

Samples of soil were collected under aseptic conditions from a depth of 3-6" and were plated on Czapek-Dox agar + 0"5~o yeast using methods 302

Rhizopus homothaUus 303

outlined by Waksman and Fred (1922) and Warcup (1950). pH determination of the soil was done by means of B.D.H. pH paper and Universal Indicator.

DESCRIPTION

A short taxonomic description of R. homothallus is given below:

Colonies on Czapek-Dox agar + 0.5~o yeast at 27 4- 1 ° C. fast spreading, about 0.5-1.0 cm. high, with rather strong white aerial mycelium and very abundant black zygospores. Sporangia produced in extremely low numbers from the point of origin of rhizoids generally in groups of 1-2, almost globose, with a diffluent wall, 48.0-51.2/zx48.0-52.8t . borne on sporangiophores which are light brownish, smooth, 168.0-705.5#x3.2-8.8/z (Figs. 1-4). Columellm dome-shaped to variously shaped, generally with a pronounced apophysis, indehiscent and not forming " b y collapse, an organ of the shape of the pileus of a mushroom" (Gilman, 1957), collar absent, 9.6-28.8 tzx 11.2-32.0/z (Figs. 1-5). Sporangiospores globose to oval, smooth, hyaline, 3-2-4.8 t~ x 2.424 • 0/~ (Fig. 6). Rhizoids very poorly to moderately deve- loped, frequently branched and septate, hyaline (Figs. 1-3, 7, 8). Stolons present but very poorly developed (Figs. 1-3, 7, 8). Zygospores produced in large numbers on the aerial mycelium, suspensors very unequal and arising from branches of the same or different hyph~e (Figa. 9-19), the larger ones collapsing from the side and remaining attached to the zygospore even in old specimens, the smaller ones perishing as a whole (Fig. 20). Zygospores almost spherical .(Figs. 18, 19), 48-0--91-2ta in diameter including the spines, exospore almost hyaline when young (Figs. 13-17), deep brown at maturity (Figs. 18-20), with coarse spines united in plates (Fig. 18), apparently lacking at the point of contact of the suspensors, gradually thinning out towards the suspensors, endospore hyaline, thick, with simple warts (Fig. 20), development delayed, mesospore not investigated. Chlamydospores formed (Fig. 21).

In rare cases the smaller suspensor was found to be lacking (Fig. 21). Several young stages were also suggestive of such a development (Fig. 22). Such a state may arise by a tendency of the whole initial of one side (the smaller one) functioning directly as a gametangium.

A subculture has been deposited in ARS Culture Collection Investigations, Fermentation Laboratory, U.S. Department of Agriculture, Peoria, Illinois, under lyophil number A-10, 901.

Table I presents some general information about the isolation and ecology of this form.

304 J . N . RAt A~a) J. P. TEWARI

:~ ~::i ~

FIGs. 1-23. Rhizopas homothallus. Figs. 1-3. Habit, x 111. Fig. 4. Sporang]um, ×444. Fig. 5. Columella, x444. Fig. 6. Sporangiospores, x 444. Figs. 7-8. Rhizoidal

systems with stolons, x 444. Figs. 9-19. Stages in zygospore development, × 296. Fig. 20. A zygosporo with exospore ruptured to show the endospore, x 296. Fig. 21. Young and old chlamydospores, × 444. Figs. 22-23. Abnormal development of zygospores, x 296.

In our studies the frequency occurrence of R. homothallus decreased significantly on advent of rains (Table I). It was also the most dominant

Rhizopus homothalluS 305

form in a sample of river (Gomti) bank soil which was very sandy and would not encourage any water-logging. Although the study was not conducted on a large scale, the results indicate that this species of Rhizopus may be a natural inhabitant of porous soils with low moisture content. Isolation of this form from desert soils of Guatemala by Dr. Hesseltine (personal communi- cation) confirms these observations.

Rhizopus homothallus closely approaches R. microsporus van Tieghem in sporangiospore morphology.

TABLE I*

Locality

University Botany Laboratory, Farm s oil

Juue

No. o~ No. from which soil [ isolated

samples pH xamiue S2

12 6.7- 6 4 6.9

No., of [ soil [

samples ~amined

July

No. from which isolated pH

Sp. Sd.

No. of soil

samples ~xaminec

August

whNc~, from pH . _ _ isolated

Sp. Sd.

5 .5 0 0

Sp., Soil plate m~thod (Warcup, 1950). Sd., Soil dilution method (Waksman and Fred, 1922).

* Rains were very late in 1960, the year in which study was conducted.

SUMMARY

Rhizopus homothallus Hesseltine, a homothallic species of Rhizopus Ehrenberg, has been isolated from cultivated and river bank soils of Lucknow. Preliminary investigations indicate it to be a natural inhabitant of sandy soils with low moisture content.

ACKNOWLEDGEMENT

The authors are grateful to Dr. C. W. Hesseltine, Head, ARS Culture Collection Investigations, U.S. Department of Agriculture, for his help in the identification of the form described and to Dr. Anna Kockov~i- Kratochvilov~ of Slovak Technical University, Bratislava, for helping us with the literature. Thanks are also due to the Council of Scientific and Industrial Research, New Delhi, for the award of a Fellowship to the junior author during the tenure of which this work was done.

306 J. N. R ~ AND J. P. T~wmna

l ~ c E s

Gilman, J .C. ..

Hesseltine~ C.W. ..

Kockov~i-Kratochvilov~l, A. and Palkoska, V.

Naumov, N.A. ..

Rai, J. N. and Mukerji, K. G.

Waksman0 S. A. and Fred, E. B.

Warcup, J. H.

Zycha, H.

A Manual of Sotl Fungi, The Iowa State College Press, Ames., Iowa, U.S.A., 1957.

"Genera of Mueorales with notes on their synonymy," Mycologia, 1955, 47, 344-63.

"A taxonomic study of the genus Rhizopus Ehrenberg 1820," Preslia, 1958, 30, 150-64.

Clds des Mucorindes (Mucorales), Encyclopddie Mycologique, Paul Lechevalier, Paris, 1939.

. . "New records of microfungi from Usar soils of India,', Curr. Sci., 1961, 30, 345.

"A tentative outline of the plate-method for determining the numbers of micro-organisms in the soil," Soil Sci., 1922, 14, 27-28.

.. "The soil plate method for isolation of fungi from soil," Nature, Lend., 1950, 166, 117.

.. Pilze 11 (Mucorinea¢) Kryptogamenflora tier Mark Bran. denburg. Verlag yon Gebriider Borntraeger; Leipzig, 1935.