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The host range of four species of Olpidiopsis
Trans. Br. mycol. Soc. 49 (I), 69-72 (1966) Printed in Great Britain
THE HOST RANGE OF FOUR SPECIES OF OLPIDIOPSIS By G. C. SRIVASTAVA
Department of Botany, St Andrew's College, Gorakhpur, India A study of the host range of four species of Olpidiopsis has been made using eighteen species from six genera of Saprolegniaceae as possible hosts. O. saprolegniae var. saprolegniae (Braun) Cornu parasitizes species of Saprolegnia and Isoachlya anisospore var. indica Saksena & Bhargava but is incapable of infecting species of other genera. O.fusiformis Cornu can be described as a natural parasite of Achlya as it confines its host range to this genus only. The host range of O. varians Shanor is extended to Isoachlya anisospora var. indica though earlier its parasitism was reported to be confined to the genus Achlya. O. luxurians Barrett was formerly thought confined to to Aphanomyces laevis de Bary but its host range is now extended to A. helicoides Minden. The differences between the present observations and those of Shanor (1940) point to the occurrence of different physiological strains of Olpidiopsis. Except for species like O. varians, where a wide range of variation occurs in the exospore structure of resting spores, the identity of most species of Olpidiopsis may be based on the host range and the exospore structure of resting spores.
Shanor (1940) studied the host range of five species of Olpidiopsis and found that the host range of different species was limited. O. varians and O. fusiformis restricted their parasitism to Achlya, O. saprolegniae and O. incrassata Cornu were found to parasitize species of Saprolegnia and Isoachlya, and the host range of O. luxurians was confined to Aphanomyces laevis. Since then no other report of such work has been noticed in the literature. During the course of a study of the aquatic fungi of Gorakhpur, (Srivastava & Bhargava, 1963; Srivastava, 1964) four species of Olpidiopsis were encountered: O. saprolegniae var. saprolegniae, O.fusiformis, O. luxurians and O. varians. The last named was found parasitizing Isoachlya anisospore var. indica, contrary to the experience of Shanor (1940) with this host genus. This prompted a study of the host range of all the species collected at Gorakhpur. METHODS
Throughout the present study the techniques followed were the same as employed by Shanor (1940). Cultures of the host species were prepared on the lines suggested by Couch (1927) and Johnson (1956). Stock cultures of these were maintained on sterilized hemp seed halves in sterile distilled water. The cultures of the species of Olpidiopsis were maintained on their original hosts and these were frequently washed with sterile distilled water to eliminate bacterial contamination. When transferring the parasite from
7°
Transactions British Mycological Society
one host to the other, very young cultures of the hosts tested were used. Infected hyphae containing mature sporangia of the parasite were removed from the original culture and washed thoroughly in sterile distilled water before transfer to the host cultures. Sometimes the parasitized culture as a whole was placed in the Petri dish containing the young host cultures under test. At least three attempts were made to transfer any species of Olpidiopsis to each host tested. The host cultures were examined under a microscope after they had been exposed to the parasitized culture for 24 hr. If the cross-inoculation was successful, some hyphae of the host showed the characteristic swellings caused by the parasite. In those cases where no infection was found, the host under test was further exposed to the parasite and observations were made every 24 hr. for 4 days, after which the experiment was discontinued. In those cases oflate infection where only a few hyphae of the host were found parasitized, one of the hyphae containing an early infection was removed carefully from the culture, washed thoroughly in sterile distilled water and transferred to agar to obtain a pure culture. This was essential for ascertaining the identity of the host. The host species have been identified with the help of keys provided by Coker (1923), Coker & Matthews (1937),johnson (1956) and Scott (1961). The classification of parasitic species followed is that of Sparrow (1960). Table
1.
Host range offour species
Saprolegnia diclina Sc ferax Achrya dubia Coker A. proliferoides A. diffusa Harvey A. orion A. prolifera A. americana Humphrey A. klebsiana A. .flagellata A. conspicua Coker Isoachlya anisospora var, indica I. luxurians Dictyuchus sterile Coker D. monosporus Leitgeb. Aphanomyces laeois A. helicoides Leptolegnia sp. Original host, H; susceptibility
+ ; no
infection -
EXPERIMENTAL RESULTS
The results of experiments conducted to study the host range of the four species of Olpidiopsis are given in Table I. O. saprolegniae var. saprolegniae found parasitizing Saprolegnia diclina Humphrey was easily transferred to S.ferax (Gruith.) Thuret and Isoachlya
Olpidiopsis. G. C. Srivastava
71
anisospora var. indica. It could not be transferred to speCIes of Achlya, Dictyuchus, Leptolegnia and Aphanomyces. The host range of O. fusiformis was restricted to species of Achlya only. Most vigorous infection of this parasite was noted in Achlya klebsiana Pieters, the original host, and in A. jlagellata Coker. The infection in A. prolifera C. G. Nees was poor and could be induced only after several exposures to the parasite. O. varians was originally collected on two hosts, Achlya proliferoides Coker and Isoachlya anisospora var. indica, from the same water sample. It also caused infection in Achlya orion Coker & Couch and A. jlagellata when tested experimentally. Attempts to transfer it from either of the two original hosts to species of Saprolegnia, Dictyuchus, Leptolegnia, Aphanomyces and one other species of Isoachlya were unsuccessful. O. luxurians confined its host range to Aphanomyces laevis and A. helicoides only and the species from other genera tested seemed immune to this parasite. The morphology of the walls of sporangia, companion cells and resting spores of the parasites was studied in all hosts supporting growths of these four species of Olpidiopsis. In O. varians variation in the size, spininess and shape of sporangia and resting spores was noted not only in different hosts but in the same host as well. The exospores of resting spores in this species have been observed to assume different configurations and show a wide range of variation (Srivastava, 1964). In the remaining three species only slight or almost no variation of this nature was noted when the parasites were grown in different hosts. DISCUSSION
The two main characteristics, considered together, for the identification of the species of Olpidiopsis are: the identity of the host and the morphology of the exospore of the resting spores. The host specialization exhibited by the parasites studied here emphasizes the importance of the host in identifying the species of Olpidiopsis. The host range for any species of Olpidiopsis seems to be restricted. The natural parasitism of O. saprolegniae var. saprolegniae to species of Saprolegnia is evident from the results shown in Table I. This fungus could not be transferred to species of other genera except those of Saprolegnia and one species of Isoachlya. Olpidiopsisfusiformis has a host range restricted to species of Achlya and so it can be described as a natural parasite of this host. The present observations differ from those of Shanor (1940) who was unsuccessful in his attempts to transfer this parasite to Achlya jlagellata. Shanor (1940) did not succeed in transferring O. varians to any species of Isoachlya. The present isolate was found naturally infecting Isoachlya anisospora var. indica as well as Achlya proliferoides, and could be transferred to both the hosts experimentally thus enlarging its host range. It is evident from these observations that the present isolates of O.fusiformis and O. varians are of different physiological strains than those of Shanor (1940). A similar situation has been described by Sparrow (1960, p. 940) in the case of O.incrassata. Olpidiopsis luxurians can be described as a natural parasite of the genus
72
Transactions British Mycological Society
Aphanomyces as it could not be transferred to the members of other genera. This confirms the experience of previous workers (Barrett, 1912; Shanor, 1940). Variations in the structure of the exospore of resting spores of O. saprolegniae var. saprolegniae, O.fusiformis and O. luxurians have not been noteworthy and a wide range of variation has been observed only in O. varians. Therefore; in most cases the character of the exospore of resting spores can be relied upon in identifying the species of Olpidiopsis. However, this cannot be considered a suitable diagnostic character for species like O. varians which present marked variability in the exospore structure of the resting spores. Similar observations have been made by McLarty (1941) for O. achlyae McLarty. The author has much pleasure in expressing his gratitude to Prof. K. S. Bhargava, Head of the Botany Department, University of Gorakhpur, for his kind guidance and criticism. This work forms part of a thesis for the Ph.D. degree of Gorakhpur University. REFERENCES
BARRETT, J. T. (1912). Development and sexuality of some species of Olpidiopsis, (Cornu) Fischer. Ann. Bot. 26, 209-238. COKER, W. C. (1923). The Saprolegniaceae, with notes on other water molds. Chapel Hill: University of North Carolina Press. COKER, W. C. & MATTHEWS, V. D. (1937). Saprolegniales. N. Am. Flora, 2 (I), 15-67. COUCH, J. N. (1927). Some new water fungi from the soil, with observations on spore formation. J. Elisha Mitchell scient. Soc. 42, 227-242. JOHNSON, T. W. (1956). The genus Achlya: morphology and taxonomy. Ann Arbor: University of Michigan Press. McLARTY, D. A. (1941). Studies in the family Woroninaceae. I. Discussion of a new species including a consideration of the genera Pseudolpidium and Olpidiopsis. Bull. Torrey bot. Club, 68, 49-66. SCOTT, W. W. (1961). A Monograph of the genus Aphanomyces. Tech. Bull. Va agric. Exp, Stn. no. 15 I. SHANOR, L. (1940). Studies in the genus Olpidiopsis. III. Some observations on the host range of certain species. J. Elisha Mitchell scient. Soc. 56, 165-176. SPARROW, F. K. (1960). AquaticPhycomycetes, 2nd ed. Ann Arbor: University of Michigan Press. SRIVASTAVA, G. C. & BHARGAVA, K. S. (1963)' Observations on Indian aquatic fungi. I. Three species of Olpidiopsis from Gorakhpur. Indian Phytopath, 16, 271-274. SRIVASTAVA, G. C. (1964). Observations on Indian aquatic fungi. II. Occurrence of Olpidiopsis varians Shanor at Gorakhpur. Indian Phytopath. 17, 249-253.
(Accepted for publication 12 May 1965)
THE HOST RANGE OF FOUR SPECIES OF OLPIDIOPSIS By G. C. SRIVASTAVA
Department of Botany, St Andrew's College, Gorakhpur, India A study of the host range of four species of Olpidiopsis has been made using eighteen species from six genera of Saprolegniaceae as possible hosts. O. saprolegniae var. saprolegniae (Braun) Cornu parasitizes species of Saprolegnia and Isoachlya anisospore var. indica Saksena & Bhargava but is incapable of infecting species of other genera. O.fusiformis Cornu can be described as a natural parasite of Achlya as it confines its host range to this genus only. The host range of O. varians Shanor is extended to Isoachlya anisospora var. indica though earlier its parasitism was reported to be confined to the genus Achlya. O. luxurians Barrett was formerly thought confined to to Aphanomyces laevis de Bary but its host range is now extended to A. helicoides Minden. The differences between the present observations and those of Shanor (1940) point to the occurrence of different physiological strains of Olpidiopsis. Except for species like O. varians, where a wide range of variation occurs in the exospore structure of resting spores, the identity of most species of Olpidiopsis may be based on the host range and the exospore structure of resting spores.
Shanor (1940) studied the host range of five species of Olpidiopsis and found that the host range of different species was limited. O. varians and O. fusiformis restricted their parasitism to Achlya, O. saprolegniae and O. incrassata Cornu were found to parasitize species of Saprolegnia and Isoachlya, and the host range of O. luxurians was confined to Aphanomyces laevis. Since then no other report of such work has been noticed in the literature. During the course of a study of the aquatic fungi of Gorakhpur, (Srivastava & Bhargava, 1963; Srivastava, 1964) four species of Olpidiopsis were encountered: O. saprolegniae var. saprolegniae, O.fusiformis, O. luxurians and O. varians. The last named was found parasitizing Isoachlya anisospore var. indica, contrary to the experience of Shanor (1940) with this host genus. This prompted a study of the host range of all the species collected at Gorakhpur. METHODS
Throughout the present study the techniques followed were the same as employed by Shanor (1940). Cultures of the host species were prepared on the lines suggested by Couch (1927) and Johnson (1956). Stock cultures of these were maintained on sterilized hemp seed halves in sterile distilled water. The cultures of the species of Olpidiopsis were maintained on their original hosts and these were frequently washed with sterile distilled water to eliminate bacterial contamination. When transferring the parasite from
7°
Transactions British Mycological Society
one host to the other, very young cultures of the hosts tested were used. Infected hyphae containing mature sporangia of the parasite were removed from the original culture and washed thoroughly in sterile distilled water before transfer to the host cultures. Sometimes the parasitized culture as a whole was placed in the Petri dish containing the young host cultures under test. At least three attempts were made to transfer any species of Olpidiopsis to each host tested. The host cultures were examined under a microscope after they had been exposed to the parasitized culture for 24 hr. If the cross-inoculation was successful, some hyphae of the host showed the characteristic swellings caused by the parasite. In those cases where no infection was found, the host under test was further exposed to the parasite and observations were made every 24 hr. for 4 days, after which the experiment was discontinued. In those cases oflate infection where only a few hyphae of the host were found parasitized, one of the hyphae containing an early infection was removed carefully from the culture, washed thoroughly in sterile distilled water and transferred to agar to obtain a pure culture. This was essential for ascertaining the identity of the host. The host species have been identified with the help of keys provided by Coker (1923), Coker & Matthews (1937),johnson (1956) and Scott (1961). The classification of parasitic species followed is that of Sparrow (1960). Table
1.
Host range offour species
Saprolegnia diclina Sc ferax Achrya dubia Coker A. proliferoides A. diffusa Harvey A. orion A. prolifera A. americana Humphrey A. klebsiana A. .flagellata A. conspicua Coker Isoachlya anisospora var, indica I. luxurians Dictyuchus sterile Coker D. monosporus Leitgeb. Aphanomyces laeois A. helicoides Leptolegnia sp. Original host, H; susceptibility
+ ; no
infection -
EXPERIMENTAL RESULTS
The results of experiments conducted to study the host range of the four species of Olpidiopsis are given in Table I. O. saprolegniae var. saprolegniae found parasitizing Saprolegnia diclina Humphrey was easily transferred to S.ferax (Gruith.) Thuret and Isoachlya
Olpidiopsis. G. C. Srivastava
71
anisospora var. indica. It could not be transferred to speCIes of Achlya, Dictyuchus, Leptolegnia and Aphanomyces. The host range of O. fusiformis was restricted to species of Achlya only. Most vigorous infection of this parasite was noted in Achlya klebsiana Pieters, the original host, and in A. jlagellata Coker. The infection in A. prolifera C. G. Nees was poor and could be induced only after several exposures to the parasite. O. varians was originally collected on two hosts, Achlya proliferoides Coker and Isoachlya anisospora var. indica, from the same water sample. It also caused infection in Achlya orion Coker & Couch and A. jlagellata when tested experimentally. Attempts to transfer it from either of the two original hosts to species of Saprolegnia, Dictyuchus, Leptolegnia, Aphanomyces and one other species of Isoachlya were unsuccessful. O. luxurians confined its host range to Aphanomyces laevis and A. helicoides only and the species from other genera tested seemed immune to this parasite. The morphology of the walls of sporangia, companion cells and resting spores of the parasites was studied in all hosts supporting growths of these four species of Olpidiopsis. In O. varians variation in the size, spininess and shape of sporangia and resting spores was noted not only in different hosts but in the same host as well. The exospores of resting spores in this species have been observed to assume different configurations and show a wide range of variation (Srivastava, 1964). In the remaining three species only slight or almost no variation of this nature was noted when the parasites were grown in different hosts. DISCUSSION
The two main characteristics, considered together, for the identification of the species of Olpidiopsis are: the identity of the host and the morphology of the exospore of the resting spores. The host specialization exhibited by the parasites studied here emphasizes the importance of the host in identifying the species of Olpidiopsis. The host range for any species of Olpidiopsis seems to be restricted. The natural parasitism of O. saprolegniae var. saprolegniae to species of Saprolegnia is evident from the results shown in Table I. This fungus could not be transferred to species of other genera except those of Saprolegnia and one species of Isoachlya. Olpidiopsisfusiformis has a host range restricted to species of Achlya and so it can be described as a natural parasite of this host. The present observations differ from those of Shanor (1940) who was unsuccessful in his attempts to transfer this parasite to Achlya jlagellata. Shanor (1940) did not succeed in transferring O. varians to any species of Isoachlya. The present isolate was found naturally infecting Isoachlya anisospora var. indica as well as Achlya proliferoides, and could be transferred to both the hosts experimentally thus enlarging its host range. It is evident from these observations that the present isolates of O.fusiformis and O. varians are of different physiological strains than those of Shanor (1940). A similar situation has been described by Sparrow (1960, p. 940) in the case of O.incrassata. Olpidiopsis luxurians can be described as a natural parasite of the genus
72
Transactions British Mycological Society
Aphanomyces as it could not be transferred to the members of other genera. This confirms the experience of previous workers (Barrett, 1912; Shanor, 1940). Variations in the structure of the exospore of resting spores of O. saprolegniae var. saprolegniae, O.fusiformis and O. luxurians have not been noteworthy and a wide range of variation has been observed only in O. varians. Therefore; in most cases the character of the exospore of resting spores can be relied upon in identifying the species of Olpidiopsis. However, this cannot be considered a suitable diagnostic character for species like O. varians which present marked variability in the exospore structure of the resting spores. Similar observations have been made by McLarty (1941) for O. achlyae McLarty. The author has much pleasure in expressing his gratitude to Prof. K. S. Bhargava, Head of the Botany Department, University of Gorakhpur, for his kind guidance and criticism. This work forms part of a thesis for the Ph.D. degree of Gorakhpur University. REFERENCES
BARRETT, J. T. (1912). Development and sexuality of some species of Olpidiopsis, (Cornu) Fischer. Ann. Bot. 26, 209-238. COKER, W. C. (1923). The Saprolegniaceae, with notes on other water molds. Chapel Hill: University of North Carolina Press. COKER, W. C. & MATTHEWS, V. D. (1937). Saprolegniales. N. Am. Flora, 2 (I), 15-67. COUCH, J. N. (1927). Some new water fungi from the soil, with observations on spore formation. J. Elisha Mitchell scient. Soc. 42, 227-242. JOHNSON, T. W. (1956). The genus Achlya: morphology and taxonomy. Ann Arbor: University of Michigan Press. McLARTY, D. A. (1941). Studies in the family Woroninaceae. I. Discussion of a new species including a consideration of the genera Pseudolpidium and Olpidiopsis. Bull. Torrey bot. Club, 68, 49-66. SCOTT, W. W. (1961). A Monograph of the genus Aphanomyces. Tech. Bull. Va agric. Exp, Stn. no. 15 I. SHANOR, L. (1940). Studies in the genus Olpidiopsis. III. Some observations on the host range of certain species. J. Elisha Mitchell scient. Soc. 56, 165-176. SPARROW, F. K. (1960). AquaticPhycomycetes, 2nd ed. Ann Arbor: University of Michigan Press. SRIVASTAVA, G. C. & BHARGAVA, K. S. (1963)' Observations on Indian aquatic fungi. I. Three species of Olpidiopsis from Gorakhpur. Indian Phytopath, 16, 271-274. SRIVASTAVA, G. C. (1964). Observations on Indian aquatic fungi. II. Occurrence of Olpidiopsis varians Shanor at Gorakhpur. Indian Phytopath. 17, 249-253.
(Accepted for publication 12 May 1965)