Synchytrium Solstitiale Sp. Nov. Causing a False Rust on Centaurea Solstitialis in France
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Mycologia, 96(2), 2004, pp. 407±410. q 2004 by The Mycological Society of America, Lawrence, KS 66044-8897 Synchytrium solstitiale sp. nov. causing a false rust on Centaurea solstitialis in France Timothy L. Widmer resin and 70% acetone, 4 h in a mixture of 50% resin and European Biological Control Laboratory, U.S.D.A. 50% acetone, then overnight in a mixture of 70% resin and Agricultural Research Service, Campus International 30% acetone. After an additional 8 h in 100% resin, the de Baillarguet, CS 90013, Montferrier sur Lez, 34988 samples were placed in molds, covered with fresh resin and St. Gely du Fesc CEDEX, France placed in an oven at 70 C for 16 h. Thick (5 mm) microtome sections were prepared by using a tungsten blade on a Leica RM 2145 microtome (Leica Abstract: A new species of Synchytrium, S. solstitiale, Microsystems, Nussloch, Germany). Sections were stained infecting leaves of Centaurea solstitialis in France, is with a solution of methylene blue-azure A and counter- described and illustrated. Synchytrium solstitiale caus- stained with a solution of basic fuchsin (Humphrey and Pitt- es development of orange to red galls on the leaves man 1974). The slides were observed under an Olympus Vanox microscope (Olympus, Tokyo, Japan). and petioles of living plants. It differs microscopically Zoospores were induced to release by placing segments from all previously described species of the genus of freshly collected infected leaves in a glass well containing mainly in having larger sporangia and zoospores and sterile distilled water plus 100 mg/L streptomycin. The well resting spores that are formed in succession without was placed in a glass Petri plate with moist ®lter paper in an evanescent prosoral stage. an incubator at 15 C with arti®cial light. After 6 h, zoo- Key words: Chytridiales, galls, systematics, yellow spores were observed and measured. starthistle TAXONOMY INTRODUCTION Synchytrium solstitiale Widmer sp. nov. FIGS. 1±5 Gallae in statu aggregato dihomeogallicae, in super®cie- In the search for biological control agents against the bus ambabus foliorum petiolorumque formantes, secus ven- noxious weed Centaurea solstitialis L. (yellow starthis- as abundantes, singulariter vel in gallas multiplices coales- tle) a new parasitic fungus was discovered in a single centes, aurantiacae vel atro-rubrae. Prosorus non visus. Sori locality in southern France. Plants were observed to solitares, sphaerici, cellulam hospitis penitus implentes, 96± be infected with a species of Synchytrium that caused 152 mm diametro (x 5 124 mm, n 5 29). Sporangia auran- orange galls to form on the leaves and petioles. The tiaca, ®gura irregulari, pro parte maxima polyhedrica, (22± taxon on C. solstitialis was compared to descriptions 72) 3 (18±56) mm diametro (x 5 54 3 37 mm, n 5 27), of species in Synchytrium and determined to be a new 5±25 per sorum. Sporae quiescentes sphaericae, laeves, oli- m 5 m species, which is described and illustrated below. vaceo- vel atro-brunneae, 34±48 m diametro (x 42 m, n 5 35). Zoosporae sphaericae, typice globulis aureis duo- bus, interdum unico vel tribus, 4±8 mm diametro (x 5 6 MATERIALS AND METHODS mm, n 5 40), ¯agello unico posteriore 8±16 mm longo (x 5 14 mm, n 5 20). Leaves of C. solstitialis with typical orange galls were col- Galls compositely dihomeogallic, forming on both lected in Cazevieille, France, (438439200 N; 038479420 E) and sides of the leaves and petioles, abundant along veins, immediately processed for sectioning. Symptomatic tissue was excised from the C. solstitialis leaf and immersed under occurring singly or coalescing to form compound vacuum for 4 h in 1 mL of 3% glutaraldehyde in 0.1 M galls, orange to dark red. Prosorus not observed. Sori potassium phosphate buffer, pH 7.2. The ®xative was re- solitary, spherical, ®lling host cell completely, 96±152 moved and the sample was rinsed two times with 0.1 M mm diam (x 5 124 mm, n 5 29). Sporangia orange, potassium phosphate buffer, pH 7.2. The samples were de- irregular in shape, predominantly polyhedral, (22± hydrated in a graded series of acetone (10, 20, 30, 50, 70, 72) 3 (18±56) mm diam (x 5 54 3 37 mm, n 5 27), 90 and 100%) for 10 min. in each wash. The samples then 5±25 per sorus. Resting spores spherical, smooth, ol- were washed three times in 100% acetone. The samples ive brown to dark brown, 34±48 mm diam, (x 5 42 were in®ltrated with Spurr's resin (Dawes 1994) by main- mm, n 5 35). Zoospores spherical, typically with two taining them 1 h at room temperature in a mixture of 30% gold globules, sometimes one or three globules, 4±8 m 5 m 5 Accepted for publication August 29, 2003. m diam (x 6 m, n 40) with single posterier E-mail: [email protected] ¯agellum 8±16 mm long (x 5 14 mm, n 5 20). 407 408 MYCOLOGIA FIG.1. Centaurea solstitialis plant showing typical symptoms of orange galls on a rosette leaf. Specimen examined. FRANCE. HEÂRAULT: Cazevieille-Pic average gall size was 194 mm diam (n 5 20). Some St. Loup, 438439200 N; 038479420 E, on leaves and petioles sori also were observed in the trichomes. Heavily in- of Centaurea solstitialis, 3 Nov 2000, T. Widmer, (HOLO- fected leaves often were distorted and curled. Nor- TY PE: BPI 842228). mally one or two layers of host cells surrounded the Etymology. From the Latin solstitiale, referred to gall. the plant species from which the species was collect- The genus Synchytrium (Chytridiales, Synchytri- ed. aceae) is characterized by a holocarpic thallus exog- Known distribution. France. enous to the zoospore cyst, which at maturity devel- Habitat. Parasitic on leaves and petioles of Centau- ops into a sorus, prosorus or resting spore (Barr rea solstitialis. 1980). The new species clearly belongs in Synchytrium Galls protruding from the surface of the leaves and because it lacks true mycelium and forms sporangia petioles of C. solstitialis were mostly singular but also and resting spores that release zoospores with a sin- coalesced together giving the appearance of rust pus- gle posterier ¯agellum. The majority of the species tules, hence the name of the disease ``false rust''. The in Synchytrium are assigned to two main groups on FIG.2. Synchytrium solstitiale sori and resting spore (low- FIG. 3. Single sorus of Synchytrium solstitiale embedded er right) embedded in tissue. Bar 5 100 mm. in tissue. Bar 5 50 mm. WIDMER: SYNCHYTRIUM SOLSTITIALE SP. NOV. ON CENTAUREA SOLSTITIALIS 409 4±4.8 4±5 m) 3 3 m 4±8 3±4 ( 3.5±4 1.5±2.2 Zoospore 3±4 3±3.2 m) m ( 32±48 50±80 40±70 50±200 80±270 60±170 Resting spores 25±38 37 m) 3 3 m 8±35 ( 45±80 17±35 14±20 57 Sporangia 62±78 FIG. 4. Two resting spores of Synchytrium solstitiale with- in the same host cell. Bar 5 50 mm. the basis of whether they are long-cycled, forming both sporangial sori and resting spores, or short-cy- cled, developing only sporangial sori or resting spores. Because S. solstitiale is long-cycled with the initial thallus transforming directly into a sorus and has digallic galls that are compositely dihomeogallic, this species is placed in the subgenus Synchytrium (Eusynchytrium). Karling (1964) reported two species compositely dihomeogallic compositely dihomeogallic compositely monogallic compositely monogallic compositely monogallic compositely dihomeogallic of Synchytrium, S. aureum and S. macrosporum, on spp. (Karling, 1964) Centaurea spp. but not on C. solstitialis. Unlike these two species, Synchytrium solstitiale is compositely di- homeogallic and has only 5±25 sporangia per sorus. Synchytrium aureum and S. macrosporum are compos- Synchytrium itely monogallic and have more than 100 sporangia per sorus. In addition, the resting spores of S. solsti- tiale are 32±48 mm diam while those of S. aureum with other Synchytrium (Eusynchytrium) Synchytrium (Eusynchytrium) Pycnochytrium (Chrysochytrium) Pycnochytrium (Chrysochytrium) Leucochytrium Mesochytrium Synchytrium solstitiale Species Subgenus Gall type I. Comparison of FIG. 5. Single zoospore of Synchytrium solstitiale. Bar 5 m ABLE 10 m. T Synchytrium solstitiale Synchytrium taraxaci Synchytrium aureum Synchytrium macrosporum Synchytrium globusum Synchytrium endobioticum 410 MYCOLOGIA and S. macrosporum are much larger, 50±200 mm and ACKNOWLEDGMENTS 80±270 mm, respectively. Other species of Synchy- trium occur on a wide range of hosts in the family The author wishes to thank Dr. Amy Rossman for her crit- ical review and suggestions for the improvement of this Asteraceae. However, all of those species, except S. manuscript and Dr. Patricia Eckel for the latin translation. taraxaci, differ in various characteristics such as being compositely monogallic or forming a prosorus, which place them in different subgenera (TABLE I). Synch- LITERATURE CITED ytrium taraxaci, the only other species fully known and placed with certainty in the subgenus Synchy- Barr, DJS. 1980. An outline for the reclassi®cation of the trium (Eusynchytrium), has larger resting spores (50± Chytridiales, and for a new order, the Spizellomyceta- 80 mm diam) and smaller zoospores (3.5±4 mm les. Can J Bot 58:2380±2394. diam) than S. solstitiale. Synchytrium endobioticum, Dawes, CJ. 1994. Introduction to biological electron mi- croscopy: theory and techniques. Burlington, Vermont: the causal agent of potato wart, differs from the new- Ladd Research Industries, Inc. 315 p. ly reported species in that the sorus of S. endobioticum Humphrey, CD. and Pittman, FE. 1974. A simple methylene forms above a prosorus, the sorus generally is smaller, blue-azure II-basic fuchsin stain for epoxy-embedded and the zoospores are smaller than those structures tissue sections. Stain Technol 49:9±14.