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Light and electron microscope studies on Cladosporium tenuissimum, mycoparasitic on poplar leaf rust, Melampsora larici-populina
Notes and brief articles producing lysine or ornithine decarboxylases. None produced levan or indole, grew at 42° or elicited a hypersensitive response in tobacco. A comparison of the differentiating charact eristics of the unknown isolate, P. tolaasii and P . agarici is shown in Table 1. The absence of arginine dihydrolase activity in the causal pseudomonad differentiates it convincingly from P. tolaasii, P. gingeri and the mummy disease-causing organism. P . agarici and the isolated pseudomonad possess several unique characteristics in common, especiaUy black pigment production on sodium benzoate, hydrogen sulphide production and weak fluorescence; however, the ability of the new pseudomonad to rot potato tissue, reduce nitrate and hydrolyse gelatin allows a clear separation to be made. Using the determinative scheme of LeUiott, Billing & Hayward (1966) the pseudomonad is characterized as LOPAT - + + - -. This does not faU within the present groupings, and a new subdivision of group III would be required to accommodate it. A new species designation may have to be made . REFERENCES
FAHY, P. C. & HAYWARD, A. C. (1983). Media and methods for isolation and diagnostic tests. In Plant Bacterial Diseases (ed . P . C. Fahy & G . J. Persley), pp . 337-378. Sydney: Academic Pre ss. KING, A. & PHILLIPS, I. (1985). Pseud omonads and related bacteria. In Isolation and Identification of
12 5
Micro-organisms of M edical and Veterinary Importance (ed . C. H . Collins & J . M . Grange), pp. 1-12. London: Academic Press. KING, E. 0 ., WARD, M . K . & RAl'oo"EY, D. E . (1954). Two simple media for the demonstration of pyocyan in and fluore scin. Journal of Laboratory and Clinical M edicine 44, 301-3 0 7. KODAKA, H ., ARMFIELD, A. Y., LOMBARD, G . L. & DOWELL, V. R. JR (1982). Practical procedure for demonstrating bacterial flagella. J ournal of Clinical . Microbiology 16, 948-952. LELLJOTT, R . A., BILLING, E . & HAYWARD, A. C. (1966). A determinative scheme for the fluorescent plant pathogenic pseudomonads. Journal of Applied Bacteriology 29, 470-489. PAINE, S . G . (1919). Studies in bacteriosis. II. A brown blotch disease of cultivated mushrooms. Annals of Applied Bi ology 5, 206-219· SCHISLER, L. C., SINDEN, J. W. & SIGEL, E. M . (1968). Etiology of mummy disease of cultivated mushrooms. Phytopathology 48, 944-948. WONG, W. c., FLETCHER, J. T., UNSWORTH, B. A. & PREECE, T . F. (1982). A note on ginger blotch, a new disease of the cultivated mushroom, Agaricus bisporus. Journal of Applied Bacteriology 52, 43-48. YOUNG, J. M . (1970). Drippy gill: a bacterial disease of cultivated mushrooms caused by Pseudomonas agarici n .sp . N ew Zealand Journal of Agricultural Research 13, 977-99 0. ZARKOWER, P. A., WUEST, P. J ., ROYSE, D . J. & MYERS, B. (1984). Phenotypic traits of fluorescent pseudomonads causing bacterial blotch of Agaricus bisporus mu shrooms and other mushroom-derived fluore scent pseudomonads. Canadian Journal of Mi crobiology 30, 360-367·
LIGHT AND ELECTRON MICROSCOPE STUDIES ON CLADOSPORIUM TE NUISSIMUM , MYCOPARASITIC ON POPLAR LEAF
RUST, MELAMPSORA LARICI-POPULINA BY 1. K. SHARMA
Australian National Botanic Gardens, P.O. Box 1777, Canberra, ACT
2601,
Australia
AND W. A. HEA THER
Department of Forestry, Australian National University, P.O. Box 4, Canberra, ACT
2601,
Australia
Cladosporium tenuissimum is recorded as a destructive mycopara site of uredinia and germinating urediniospores of Melampsora larici-populina in vitro . With the exception of echinules , the entire urediniospore is destroyed. C. tenuissimum also exhibits antibiosis towards germinating urediniospores.
In the field, certain Cladosporium spp. colonize uredinia of Melampsora medu sae Thurn. and M. larici-populina Kleb., the causal organi sm of leaf rust in Populus spp. in Australasia (Sharma & Heather, 1978). Among species of Cladosporium tested in vitro , C. tenuissimum Cooke has been Trans. Br , mycol. Soc. 90 (1), (1988)
shown to be the most antagonistic to production of uredinia by various races of M. larici-populina and was also the most exten sive colonizer of the uredinia produced (Sharma & Heather, 1981 b, 19 82 ). Antibiosis by conidia of C. tenuissimum towards urediniospore germination in M. larici-populina,
Prim ed in Grear Brita in
N otes and brief articles
126
Fig.
Fig .
2.
1.
SEM of erurnpent uredinium of M . larici-populina.
SEM of uredinium of M . larici-populina colonized by C. tenuissimum .
and dir ect parasitism of germinating urediniospores (Sh arma & Heather, 1981 a), are likely bases for this ant agonism. Further details of th e morph ology and histology of para sitism of ure dinio spores and germ -tubes by C. tenuissimum are descr ibed here for the first time. C. tenuissimum (IM I 249464), origi nally isolated from uredinia of M. larici-populina in th e field, was cultured on malt extract agar for 17 d at 25 °C. Conidia and supe rficial myceliu m were harvested by lightly scraping the culture surface with a scalpel, dri ed over silica gel for 2 d at 25°, and th en macerated to produce a powder y mass referr ed to hereafter as 'conidia ' . T rans. B r. mycol. Soc. 90 ( 1), (1988)
Urediniospores (5 mg mixture of races A, D and E, Chandrashekar & Heather, 1980) of M . laricipopulina wer e released in a spore-settling tower (Sharma, H eath er & Win er, 1980), and dep osited on 50 leaf disks ( 15 rnrn diam ) of P op ulus x euramericana cv. 1-488, and on 10 coverglasses ( 12 mm diam ). T went y-five leaf disks and five coverg lasses (to serve as controls) were rem oved from the tower and subsequently 5 mg of conidia of C. tenuiss imum were deposited on th e remain ing disks and covcrglasses . After rem oval from th e sett ling tower, all coverglasses (with or witho ut coni dia), were inverted over sepa ra te humidit y cham bers (Omar & H eath er, 1978), and incubat ed
Printed in Great B ritain
Notes and brief articles
127
'-
12·9 p m
Fig. 3. Lysis of germinated urediniospore (V ) of M. larici-populina following penetration by mycelium of C. tenuissimum (C) (after 48 h) .
o
o
-
12·9 pm
• Fig. 4. Penetration of germ-tubes (G) of urediniospore (disintegrated) by haustorium-like structures (arrows) developed by mycelia (C) of C. tenui ssimum.
at 20° in the dark for 48 h. Some coverglasses were examined under phase contrast and Nomarski interphase contrast microscopes, while others were prepared for scanning electron microscopy . Leaf disks were placed on plastic foam saturated with 10 p.p .m. gibberellic acid (Singh & Heather, 1981 ) in glass Petri dishes and incubated at 20°, 100 liE m" S- 1 light intensity, 16 h photoperiod, for 15 d. Following incubation and the recording of uredinia numbers, small pieces ( eQ 4 rnrn") of leaf tissue carrying uredinia were cur from selected leaf disks. These, together with the coverglasses Trans. Br , mycol. S oc. 90 ( 1), (1988)
previously prepared, were placed in a Dynavac tissue freeze drier for 24 h. Specimens were coated with 20-30 nm of gold and examined in a Cambridge Stereoscan 180 scanning electron microscope at 30 kV voltage . In the absence of C. tenuissimum, numerous uredinia erupted on leaf disks (F ig. 1). By contrast, with conidia of C. tenuissimum, the number of uredinia produced per leaf disk (U L D) was reduced by about 50 % . On the latter disks, few uredinia were erumpent and most were overgrown by C. tenuissimum mycelium (F igs 2, 7). When similarly
Printed in Great Britain
Notes and brief articles
128
M
. ~-
o
12·9 1lm
Fig. 5. C. tenuissimum (C) reproducing on rust mycelium (M ).
Fig. 6. SEM showing fruiting of C. tenuissimum (C) on an isolated lysed urediniospore (D) of M. lar icipopulina. Arrows indicate outline of hyphae within the disintegrating spore. inoculated disks were incubated for 20 d, boreholes and cracks were evident in the urediniospores (F ig. 8), whilst after incubation for 22 d some urediniospores had collapsed completely (F ig. 10). Hyphae of C. tenuissimum formed infection pegs which ent ered the spore and , after proliferating , emerged to sporulate (Figs 6, 9)· When ur ed iniospores and conidia were deposited on coverglasses and incubated for 48 h, tho se conidia attached to echinules of th e urediniospores germinated rapidly and develop ed long germtubes, in contrast with th ose separated from the spore (Fig. 11 ). Occasion ally the conidial germtube penetrated the urediniospore and spread T rans. Br . my col. Soc. 90 (1), (1988)
within it before the latter germinated ; while sometimes mycelium of the mycoparasite penetrated an already-germinated rust spore (F ig. 3). Following extensive development of Cladosporium , the urediniospore disintegrated to a mass of echinules and the mycoparasite fruited on the remnants (F ig. 6). In addition to parasitizing indi vidual urediniospores, C. tenuissimum also penetrated th eir germ-tubes (F ig. 4). M ycelium grew along th e tubes, inserted minute haustor ialike struc tur es (podia ; Figs 4, 5) and subsequently emerged and spo rulated at these centres of penetration (Fig. 5). Cladosporium spp. are recognized as facultative
Print ed in Great B ritain
Notes and brief articles
12 9
Fig. 7. SEM showing fruiting of C. tenuissimum (C) on a urediniospore (U) of M. larici-populina within a uredinium (15 d after simultaneous inoculation).
Fig. 8. SEM, 20 d after simultaneous inoculation; colonization of urediniospores of M. larici-populina by C. tenuissimum. Lysed urediniospores (UD) and the presence of bore-holes (E).
parasites (Preece & Dickinson, 1976). However, Powell (1971) recorded an unknown species subsequently identified as C. gallicola Sutton (Sutton, 1973), colonizing aeciospores of Cronartium comandrae Pk, while Tsuneda & Hiratsuka (1979) reported C. gallicola, parasitizing the galls of Endocronartium harknessii J. P. Moore, on Pinus contorta Doug!. var. latifolia Engelm., and P. banksiana Lamb. In the present investigation, lysis of urediniospores of M. larici-populina by Cladosporium (Fig. 9) was commonly recorded, thus confirming the observations of Sharma & Heather Trans. Br. mycol. Soc. 90 (1), (1988)
(1978, 1981). Whilst C. tenutsstmum grew and fruited prolifically on uredinia, development on those areas of the leaf surface not occupied by uredinia was insignificant. Hulea (1939) has suggested that similar localized growth with Sphaerellopsis filum (Biv.-Bern.: Fr.) Sutton, on various rusts results from the release of substrates from the leaf at erumpent uredinia. Swendsrud & Calpouzos (1972) proposed that an unidentified substance released from urediniospores of Puccinia recondita Rob. ex Desm. could account for colonization of uredinia by S. filum. In the present
Printed in Great Britain MYC90
Notes and brief articles
Fig . 9. SEM, penetration of a urediniospore (U) within a uredinium by a haustorium (H) developed from mycelium of C. tenuissimum (C) (15 d after simultaneous inoculation).
Fig.
10.
SEM showing collapse and disintegration of uredinia of M . larici-populina by C. tenuissimum (2 2 d after simultaneous inoculation).
investigations, rapid germination and growth from conidia attached to echinules of urediniospores of M. larici-populina (F ig. 11) is consistent with this suggestion. Mycoparasitism by C. tenuissimum of single urediniospores may either involve killing of the latter prior to penetration or penetration of the living urediniospore as reported for Verticillium hemileiae Zimm. on Hemileia uastatrix Berk . & Br. (L occi, Ferrante & Rodrigues, 1971) and for C. gallicola on Endocronartium harknessii J. P. Moore (T suneda & Hiratsuka, 1979). In addition, C. Trans. Br . mycol. Soc. 90 (1), ( 19 88)
tenuissimum penetrates the mycelium produced by germinating urediniospores (F ig. 4). Disintegration of the urediniospore wall, adjacent to entry points (F ig. 8) suggests at least the partial involvement of enzymic processes. The potential impact of C. tenutsstmum on epidemiology of M . larici-populina is twofold. The presence of the mycoparasite can reduce the number of uredinia produced on leaves . Additionally, under the conditions of incubation of this experiment, rust and mycoparasite sporulated simultaneously, with the latter overgrowing ure-
Prim ed in Grear Britain
Notes and brief articles
131
Fig. 11. Nomarski interphase contrast micrograph demonstrating enhanced germination of conidia of C. tenuissimum when attached to a urediniospore of M. larici-populina (after 48 h).
dinia and its conidia attaching to urediniospores. Thus on dispersal of the latter the mycoparasite would also be distributed, and this might reduce the potential build-up of rust population over successive generations. We wish to thank the Nell and Hermon Slade Trust and the Australian Orchid Foundation for their support. REFERENCES
CHANDRASHEKAR, M. & HEATHER, W. A. (1980). Reactions of poplar clones to physiological races to Melampsora larici-populina Kleb. Euphytica 29, 401-407· HULEA, A. (1939). Contribution a la connaissance des champignons commensaux des uredinea. Bulletin de la Section Scientifique de l 'Academie Bucharest, Roumanie 22, 1-19. LOCCI, R., FERRANTE, G. M. & RODRIGUES, C. J. (1971). Studies by transmission and scanning electron microscopy In the Hemileia vastatrix- Verticillium hemileiae association. Revue de Pathologic Vegetale et d' Entomologie 4, 127-140. OMAR, M. & HEATHER, W. A. (1978). A simple humidity chamber for germinating spores. Bulletin of the British Mycological Society 12, 128-129. POWELL, J. M. (1971). Fungi and bacteria associated with Cronartium comandrae on lodgepole pine in Alberta. Phytoprotection 52, 45-51. PREECE, T. F. & DICKINSON, C. H. (Eds) (1976). Ecology of Leaf Surface Micro-organisms. London: Academic Press. SHARMA, J. K. & HEATHER, W. A. (1978). Parasitism of
Trans. Br. mycol. Soc. 90 (1), (1988)
uredospores of Melampsora larici-populina Kleb. by Cladosporium sp. European Journal of Forest Pathology 8,4 8-54. SHARMA, I. K & HEATHER, W. A. (1981a). Hyperparasitism of Melampsora larici-populina Kleb. by Cladosporium herbarum (Pers.) Link and Cladosporium tenuissimum Cooke. Indian Phytopathology 34, 395-397. SHARMA, I. K & HEATHER, W. A. (1981b). Antagonism by three species of Cladosporium to three races of Melampsora larici-populina Kleb. Australian Forest Research 11, 283-293. SHARMA, 1. K. & HEATHER, W. A. (1982). Temperature sensitivity of the antagonism of Cladosporium species to races of Melampsora larici-populina Kleb. on cultivars of Populus x euramericana (Dode) Guinier. Phytopathologische Zeuschri]t 105, 61-70. SHARMA, J. K, HEATHER, W. A. & WINER, P. (1980). Effect of leaf maturity and shoot age of clones of Populus species on susceptibility to Melampsora laricipopulina. Phytopathology 70, 548-554. SINGH, S. J. & HEATHER, W. A. (1981). An improved method for detached leaf culture of Melampsora leaf rust of Populus sp. Transactions of the British Mycological Society 77, 435-436. SUTTON, B. c. (1973). Hyphomycetes from Manitoba and Saskatchewan, Canada. Mycological Papers (C.M.I.) 132. SWENSRUD, D. P. & CALPOUZOS, L. (1972). Effect of inoculation sequence and humidity on infection of Puccinia recondita by the mycoparasite Darluca filum. Phytopathology 62, 931-932. TSUNEDA, A. & HIRATSUKA, Y. (1979). Mode of parasitism of a mycoparasite, Cladosporium gallicola on Western gall rust, Endocronartium harknessii. Canadian Journal of Plant Pathology 1,31-36.
Printed in Great Britain 5-2
FAHY, P. C. & HAYWARD, A. C. (1983). Media and methods for isolation and diagnostic tests. In Plant Bacterial Diseases (ed . P . C. Fahy & G . J. Persley), pp . 337-378. Sydney: Academic Pre ss. KING, A. & PHILLIPS, I. (1985). Pseud omonads and related bacteria. In Isolation and Identification of
12 5
Micro-organisms of M edical and Veterinary Importance (ed . C. H . Collins & J . M . Grange), pp. 1-12. London: Academic Press. KING, E. 0 ., WARD, M . K . & RAl'oo"EY, D. E . (1954). Two simple media for the demonstration of pyocyan in and fluore scin. Journal of Laboratory and Clinical M edicine 44, 301-3 0 7. KODAKA, H ., ARMFIELD, A. Y., LOMBARD, G . L. & DOWELL, V. R. JR (1982). Practical procedure for demonstrating bacterial flagella. J ournal of Clinical . Microbiology 16, 948-952. LELLJOTT, R . A., BILLING, E . & HAYWARD, A. C. (1966). A determinative scheme for the fluorescent plant pathogenic pseudomonads. Journal of Applied Bacteriology 29, 470-489. PAINE, S . G . (1919). Studies in bacteriosis. II. A brown blotch disease of cultivated mushrooms. Annals of Applied Bi ology 5, 206-219· SCHISLER, L. C., SINDEN, J. W. & SIGEL, E. M . (1968). Etiology of mummy disease of cultivated mushrooms. Phytopathology 48, 944-948. WONG, W. c., FLETCHER, J. T., UNSWORTH, B. A. & PREECE, T . F. (1982). A note on ginger blotch, a new disease of the cultivated mushroom, Agaricus bisporus. Journal of Applied Bacteriology 52, 43-48. YOUNG, J. M . (1970). Drippy gill: a bacterial disease of cultivated mushrooms caused by Pseudomonas agarici n .sp . N ew Zealand Journal of Agricultural Research 13, 977-99 0. ZARKOWER, P. A., WUEST, P. J ., ROYSE, D . J. & MYERS, B. (1984). Phenotypic traits of fluorescent pseudomonads causing bacterial blotch of Agaricus bisporus mu shrooms and other mushroom-derived fluore scent pseudomonads. Canadian Journal of Mi crobiology 30, 360-367·
LIGHT AND ELECTRON MICROSCOPE STUDIES ON CLADOSPORIUM TE NUISSIMUM , MYCOPARASITIC ON POPLAR LEAF
RUST, MELAMPSORA LARICI-POPULINA BY 1. K. SHARMA
Australian National Botanic Gardens, P.O. Box 1777, Canberra, ACT
2601,
Australia
AND W. A. HEA THER
Department of Forestry, Australian National University, P.O. Box 4, Canberra, ACT
2601,
Australia
Cladosporium tenuissimum is recorded as a destructive mycopara site of uredinia and germinating urediniospores of Melampsora larici-populina in vitro . With the exception of echinules , the entire urediniospore is destroyed. C. tenuissimum also exhibits antibiosis towards germinating urediniospores.
In the field, certain Cladosporium spp. colonize uredinia of Melampsora medu sae Thurn. and M. larici-populina Kleb., the causal organi sm of leaf rust in Populus spp. in Australasia (Sharma & Heather, 1978). Among species of Cladosporium tested in vitro , C. tenuissimum Cooke has been Trans. Br , mycol. Soc. 90 (1), (1988)
shown to be the most antagonistic to production of uredinia by various races of M. larici-populina and was also the most exten sive colonizer of the uredinia produced (Sharma & Heather, 1981 b, 19 82 ). Antibiosis by conidia of C. tenuissimum towards urediniospore germination in M. larici-populina,
Prim ed in Grear Brita in
N otes and brief articles
126
Fig.
Fig .
2.
1.
SEM of erurnpent uredinium of M . larici-populina.
SEM of uredinium of M . larici-populina colonized by C. tenuissimum .
and dir ect parasitism of germinating urediniospores (Sh arma & Heather, 1981 a), are likely bases for this ant agonism. Further details of th e morph ology and histology of para sitism of ure dinio spores and germ -tubes by C. tenuissimum are descr ibed here for the first time. C. tenuissimum (IM I 249464), origi nally isolated from uredinia of M. larici-populina in th e field, was cultured on malt extract agar for 17 d at 25 °C. Conidia and supe rficial myceliu m were harvested by lightly scraping the culture surface with a scalpel, dri ed over silica gel for 2 d at 25°, and th en macerated to produce a powder y mass referr ed to hereafter as 'conidia ' . T rans. B r. mycol. Soc. 90 ( 1), (1988)
Urediniospores (5 mg mixture of races A, D and E, Chandrashekar & Heather, 1980) of M . laricipopulina wer e released in a spore-settling tower (Sharma, H eath er & Win er, 1980), and dep osited on 50 leaf disks ( 15 rnrn diam ) of P op ulus x euramericana cv. 1-488, and on 10 coverglasses ( 12 mm diam ). T went y-five leaf disks and five coverg lasses (to serve as controls) were rem oved from the tower and subsequently 5 mg of conidia of C. tenuiss imum were deposited on th e remain ing disks and covcrglasses . After rem oval from th e sett ling tower, all coverglasses (with or witho ut coni dia), were inverted over sepa ra te humidit y cham bers (Omar & H eath er, 1978), and incubat ed
Printed in Great B ritain
Notes and brief articles
127
'-
12·9 p m
Fig. 3. Lysis of germinated urediniospore (V ) of M. larici-populina following penetration by mycelium of C. tenuissimum (C) (after 48 h) .
o
o
-
12·9 pm
• Fig. 4. Penetration of germ-tubes (G) of urediniospore (disintegrated) by haustorium-like structures (arrows) developed by mycelia (C) of C. tenui ssimum.
at 20° in the dark for 48 h. Some coverglasses were examined under phase contrast and Nomarski interphase contrast microscopes, while others were prepared for scanning electron microscopy . Leaf disks were placed on plastic foam saturated with 10 p.p .m. gibberellic acid (Singh & Heather, 1981 ) in glass Petri dishes and incubated at 20°, 100 liE m" S- 1 light intensity, 16 h photoperiod, for 15 d. Following incubation and the recording of uredinia numbers, small pieces ( eQ 4 rnrn") of leaf tissue carrying uredinia were cur from selected leaf disks. These, together with the coverglasses Trans. Br , mycol. S oc. 90 ( 1), (1988)
previously prepared, were placed in a Dynavac tissue freeze drier for 24 h. Specimens were coated with 20-30 nm of gold and examined in a Cambridge Stereoscan 180 scanning electron microscope at 30 kV voltage . In the absence of C. tenuissimum, numerous uredinia erupted on leaf disks (F ig. 1). By contrast, with conidia of C. tenuissimum, the number of uredinia produced per leaf disk (U L D) was reduced by about 50 % . On the latter disks, few uredinia were erumpent and most were overgrown by C. tenuissimum mycelium (F igs 2, 7). When similarly
Printed in Great Britain
Notes and brief articles
128
M
. ~-
o
12·9 1lm
Fig. 5. C. tenuissimum (C) reproducing on rust mycelium (M ).
Fig. 6. SEM showing fruiting of C. tenuissimum (C) on an isolated lysed urediniospore (D) of M. lar icipopulina. Arrows indicate outline of hyphae within the disintegrating spore. inoculated disks were incubated for 20 d, boreholes and cracks were evident in the urediniospores (F ig. 8), whilst after incubation for 22 d some urediniospores had collapsed completely (F ig. 10). Hyphae of C. tenuissimum formed infection pegs which ent ered the spore and , after proliferating , emerged to sporulate (Figs 6, 9)· When ur ed iniospores and conidia were deposited on coverglasses and incubated for 48 h, tho se conidia attached to echinules of th e urediniospores germinated rapidly and develop ed long germtubes, in contrast with th ose separated from the spore (Fig. 11 ). Occasion ally the conidial germtube penetrated the urediniospore and spread T rans. Br . my col. Soc. 90 (1), (1988)
within it before the latter germinated ; while sometimes mycelium of the mycoparasite penetrated an already-germinated rust spore (F ig. 3). Following extensive development of Cladosporium , the urediniospore disintegrated to a mass of echinules and the mycoparasite fruited on the remnants (F ig. 6). In addition to parasitizing indi vidual urediniospores, C. tenuissimum also penetrated th eir germ-tubes (F ig. 4). M ycelium grew along th e tubes, inserted minute haustor ialike struc tur es (podia ; Figs 4, 5) and subsequently emerged and spo rulated at these centres of penetration (Fig. 5). Cladosporium spp. are recognized as facultative
Print ed in Great B ritain
Notes and brief articles
12 9
Fig. 7. SEM showing fruiting of C. tenuissimum (C) on a urediniospore (U) of M. larici-populina within a uredinium (15 d after simultaneous inoculation).
Fig. 8. SEM, 20 d after simultaneous inoculation; colonization of urediniospores of M. larici-populina by C. tenuissimum. Lysed urediniospores (UD) and the presence of bore-holes (E).
parasites (Preece & Dickinson, 1976). However, Powell (1971) recorded an unknown species subsequently identified as C. gallicola Sutton (Sutton, 1973), colonizing aeciospores of Cronartium comandrae Pk, while Tsuneda & Hiratsuka (1979) reported C. gallicola, parasitizing the galls of Endocronartium harknessii J. P. Moore, on Pinus contorta Doug!. var. latifolia Engelm., and P. banksiana Lamb. In the present investigation, lysis of urediniospores of M. larici-populina by Cladosporium (Fig. 9) was commonly recorded, thus confirming the observations of Sharma & Heather Trans. Br. mycol. Soc. 90 (1), (1988)
(1978, 1981). Whilst C. tenutsstmum grew and fruited prolifically on uredinia, development on those areas of the leaf surface not occupied by uredinia was insignificant. Hulea (1939) has suggested that similar localized growth with Sphaerellopsis filum (Biv.-Bern.: Fr.) Sutton, on various rusts results from the release of substrates from the leaf at erumpent uredinia. Swendsrud & Calpouzos (1972) proposed that an unidentified substance released from urediniospores of Puccinia recondita Rob. ex Desm. could account for colonization of uredinia by S. filum. In the present
Printed in Great Britain MYC90
Notes and brief articles
Fig . 9. SEM, penetration of a urediniospore (U) within a uredinium by a haustorium (H) developed from mycelium of C. tenuissimum (C) (15 d after simultaneous inoculation).
Fig.
10.
SEM showing collapse and disintegration of uredinia of M . larici-populina by C. tenuissimum (2 2 d after simultaneous inoculation).
investigations, rapid germination and growth from conidia attached to echinules of urediniospores of M. larici-populina (F ig. 11) is consistent with this suggestion. Mycoparasitism by C. tenuissimum of single urediniospores may either involve killing of the latter prior to penetration or penetration of the living urediniospore as reported for Verticillium hemileiae Zimm. on Hemileia uastatrix Berk . & Br. (L occi, Ferrante & Rodrigues, 1971) and for C. gallicola on Endocronartium harknessii J. P. Moore (T suneda & Hiratsuka, 1979). In addition, C. Trans. Br . mycol. Soc. 90 (1), ( 19 88)
tenuissimum penetrates the mycelium produced by germinating urediniospores (F ig. 4). Disintegration of the urediniospore wall, adjacent to entry points (F ig. 8) suggests at least the partial involvement of enzymic processes. The potential impact of C. tenutsstmum on epidemiology of M . larici-populina is twofold. The presence of the mycoparasite can reduce the number of uredinia produced on leaves . Additionally, under the conditions of incubation of this experiment, rust and mycoparasite sporulated simultaneously, with the latter overgrowing ure-
Prim ed in Grear Britain
Notes and brief articles
131
Fig. 11. Nomarski interphase contrast micrograph demonstrating enhanced germination of conidia of C. tenuissimum when attached to a urediniospore of M. larici-populina (after 48 h).
dinia and its conidia attaching to urediniospores. Thus on dispersal of the latter the mycoparasite would also be distributed, and this might reduce the potential build-up of rust population over successive generations. We wish to thank the Nell and Hermon Slade Trust and the Australian Orchid Foundation for their support. REFERENCES
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