OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XI. A PHYSODERMA ON AGROPYRON REPENS

Sparrow , Frederick K. (U. Michigan, Ann Arbor), Joyce E. Griffin , and Robert M. Johns . Observations on chytridiaceous parasites of phanerogams. XI. A Physoderma on Agropyron repens. Amer. Jour. Bot. 48(9): 850–858. Illus. 1961.—A Physoderma has been found in Michigan on Agropyron repens, which produces dark-brown, non-erumpent streaks up to 20 mm (usually 4–6 mm) in length by 0.5 mm in width and very local discoloration of the leaf blades and sheaths. There is no systemic infection, and plants parasitized are normal in size and bear flowers. Resting spores upon germination produce zoospores which may develop either into the endobiotic, poly-centric, resting spore-bearing thallus or into monocentric, epibiotic, ephemeral sporangia. The latter bear either colorless or orange globuled zoospores. These zoospores may give rise to new epibiotic sporangia, or, apparently without fusing in pairs, to the endobiotic system. Comparison with other congeneric fungi reported on Agropyron repens reveals the Michigan fungus to be distinct from them. Whether it can be embraced within Physoderma graminis (Büsgen) de Wild. or other described taxa on grasses awaits the results of future cross-inoculation studies.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XXVII. A FURTHER STUDY OF PHYSODERMA HYDROCOTYLIDIS VIÉGAS AND TEIXEIRA

A further study of Physoderma hydrocotylidis from California on its host Hydrocotyle ranunculoides gives further details on its structure and development. EM micrographs reveal that the notably thin wall of the resting spore consists of an outer, an intermediate, and an inner layer. The complete wall thickness from measurements of these EM preparations is only 0.5 μm, the thinnest of any known Physoderma resting spore. Such resting spores germinate readily in 2–5 h by the dehiscence of a broad cap and formation of a protruding endosporganium. Zoospores from the latter infect epidermal host cells and produce either the endobiotic, polycentric rhizoidal system with tenuous filaments, turbinate cells and eventually resting spores, or a hitherto unknown epibiotic, monocentric, rhizidiaceous sporangial stage. Zoospores from the latter may all bear colorless lipid globules or all faintly orange-colored ones.     

MORPHOLOGICAL AND ECOLOGICAL STUDY OF PHYSODERMA DULICHII

A new species of aquatic Phycomycete, Physoderma dulichii Johns, parasitic on the aquatic sedge Dulichium arundinaceum (L.) Britt., is described from northern Michigan. This parasite infects and kills the upper epidermal cells of the host leaves. Macroscopically, infection by P. dulichii is indicated by striking brown bands with irregular margins, at intervals on the upper surfaces of the leaves. Like other species of Physoderma, this organism's development includes two distinct phases, an epibiotic monocentric phase producing asexual zoospores and an endobiotic polycentric phase bearing thick-walled resting spores that germinate after an extensive period of maturation at low temperature to form zoospores. The morphology and development of the two phases and of resting spore germination are reported in detail. Only the immature leaves of the host are susceptible to infection, which may be initiated by the introduction of mature resting spores, zoospores from germinated resting spores, or zoospores from epibiotic sporangia. Resting-spore zoospores may also produce the endobiotic stage directly. Initiation of infection in nature requires that the terminal cluster of immature leaves on the host plant be submerged, but infection of subsequently formed leaves of emergent culms can be accomplished through the agency of zoospores from epibiotic sporangia on older leaves. The relation of infected stands of hosts to their environment is discussed and the importance of standing water to infection noted. The geographical distribution of the parasite shows correlation with the drainage basins of the Great Lakes, the St. Lawrence River, and the northern Atlantic Coastal Plain     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XIV. PHYSODERMA CALAMI

Physoderma calami, a chytrid (Phycomycetes), has not been studied or apparently even collected in Europe since 1895 and has never been recorded in this hemisphere. Material widely distributed in herbaria indicated it was a Physoderma but no details save color, shape, and size of resting spores were known. A study of living material from Vermont indicates resting spore germination occurs by dehiscence of a lid and production of a sporangium with zoospores. The latter may form either an epibiotic or “ephemeral” sporangial stage and zoospores, or an endobiotic one, with extensive polycentric thallus bearing turbinate cells along the rhizoids, and, as outgrowths of these turbinate cells, straw-colored, thick-walled resting spores. The latter stage produces dark-brown spots on infected parts of the host.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XX. RESTING SPORE GERMINATION AND EPIBIOTIC STAGE OF PHYSODERMA BUTOMI SCHROETER

The development and morphology of Physoderma butomi Schroeter on Butomus umbellalus L., found in Michigan, is followed from germination of the resting spore through formation of epibiotic and endobiotic stages, to resting spore. No evidence for sexuality was found.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XIX. A PHYSODERMA ON EURASIAN WATER MILFOIL (MYRIOPYLLUM SPICATUM)

A Physoderma was found on Myriophyllum spicatum in Michigan. This is the first recorded on this host from this hemisphere. It differs from the Danish P. myriophylli Rostrup in not producing galls on the host and in several aspects of its endobiotic stage. It more closely resembles a Swedish fungus attributed to Physoderma hippuridis by Lagerheim occurring on the same species of host.     

Observations on chytridiaceous parasites of Phanerogams

Summary A reexamination of Physoderma maculare Wallroth the type species of the genus, on Alisma, confirms Clinton's (1902) account of the production of an epibiotic stage from resting spore zoospores. The latter on mature host tissue may also give rise to the endobiotic stage which bears resting spores. On seedlings, however, resting spore zoospores produce only epibiotic sporangia. The fungus could not successfully infect Sagittaria, a closely related host.Contribution No. 1152     

DEVELOPMENT AND CYTOLOGY OF THE ENDOBIOTIC PHASE OF PHYSODERMA PULPOSUM

Lingappa , Yamuna . (U. Michigan, Ann Arbor.) Development and cytology of the endobiotic phase of Physoderma pulposum. Amer. Jour. Bot. 46(4): 233–240. Illus. 1959.—The contents of the zygotes of Physoderma pulposum pass into the epidermal cells of the host and become incipient primary turbinate organs. The latter develop into resting sporangia in 3 different ways: (1) Occasionally, they may become thick walled as sporangia in their entirety. Such monocentric development of the endobiotic thalli is described for the first time in Physoderma; (2) usually, however, the contents of primary turbinate organs undergo centripetal cleavage; or (3) their contents may be cleaved tangentially. As a result, several uni- or multinucleate segments are formed which give rise to tenuous hyphae. The swollen distal end of each tenuous hypha develops into a secondary turbinate organ which in turn gives rise to hyphae and tertiary turbinate organs. Thus, the polycentric organization of the rhizomycelium is maintained. During this process, buds, which develop in the axils of the apical tufts of haustoria of turbinate organs, enlarge into resting sporangia. Nuclear divisions in turbinate organs and of resting sporangial initials are mitotic, and 4 chromosomes are evident on the equator of the intranuclear spindles. As the resting sporangia are inoperculate, the endosporangia protrude through irregular openings in the exospores.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. VIII. UROPHLYCTIS (PHYSODERMA) PLURIANNULATUS AND U. MAJUS

Sparrow , Frederick K. and Yamunga Lingappa . (U. Michigan, Ann Arbor.) Observations on chytridiaceous parasites of phanerogams. VIII. Urophlyctis (Physoderma) pluriannnlatus and U. majus. Amer. Jour. Bot. 47(3): 202—209. Illus. 1960.—Urophlyctis pluriannulatus, an obligate parasite of Sanicula spp., has an endobiotic phase which is strongly polycentric and produces small crateriform galls on the petioles and blades of the host leaves. The agent accomplishing infection is not known but is probably a zygote. The first cell of the parasite established in the host is the so-called “primary turbinate organ.” This becomes multinucleate, is somewhat pyriform and becomes multicellular by 2 methods: (1) by cleavage into peripheral segments; or (2) by division into cells, each with its own cell wall. Replication of the thallus is accomplished by the production of nucleated outgrowths bearing haustoria which elongate, become ribbon-like, somewhat roughened and lumened, and produce distally turbinate organs of a second order. Tertiary, etc. turbinate organs are produced in like manner. Resting spores usually form at the tip of an extremely short outgrowth from the apex of a turbinate organ. These bear a supra-equatorial crown of 7—10 branched haustoria. Rarely, monocentric thalli are formed, in which a single turbinate organ becomes converted into a resting spore. All nuclear division figures were intranuclear. The fungus produced marked enlargement of infected host cells and their nuclei, and caused division of neighboring cells. As development continues, lysis of the surrounding host walls takes place and a large cavity bearing a dense symplast and numerous host nuclei is formed, within which is the thallus of the parasite. At maturity, all traces of symplast and of fungus, except for resting spores, disappear. Urophlyctis majus, a parasite on leaves of Rumex orbiculatus, hitherto known only from its resting spore stage, has a pattern of development strikingly similar to that of U. pluriannulatus. Here, however, turbinate cells only form peripheral segments. Furthermore, the “hyphae” are smooth and without a lumen. Aside from size differences, the mature thallus with resting spores, unbranched (not branched) haustorial tufts, etc. is like that of the Sanicula parasite. The galls produced were compartmentalized, dark red to black, usually surrounded by a reddish zone, and early dropped from the leaf. No undoubted evidence of the epibiotic gametangial phase was found in either species.     

Observations on chytridiaceous parasites of phanerogams

Host symptoms and morphology of the endo-and epibiotic stages of a Physoderma on Phalaris arundinacea L. are described. It is considered identical with a Physoderma on Agropyron repens earlier described. Both are referred to Physoderma gerhardti Schroeter found in 1883 by Gerhardt from near Liegnitz, Schlesien.     

THE DEVELOPMENT AND CYTOLOGY OF THE EPIBIOTIC PHASE OF PHYSODERMA PULPOSUM

Lingappa , Yamuna . (U. Michigan, Ann Arbor.) The development and cytology of the epibiotic phase of Physoderma pulposum. Amer. Jour. Bot. 46(3) : 145-150. Illus. 1959.—Physoderma pulposum, a chytrid parasite on Chenopodium album L. and Atriplex patula L., has a zoosporangial epibiotic phase. The latter consists of extramatrical sporangia and intramatrical bushy rhizoids, both enclosed in large protruding galls. The sporangia are subspherical, up to 350μ in diameter, and may produce hundreds of planospores. If planospores settle on the host surface, they develop narrow germ tubes which penetrate the epidermal cells and develop into rhizoids. The planospore body, however, remains on the host surface and develops into a mature epibiotic sporangium in about 20-25 days at 16°C., 12-15 days at 20-25°C., or 6-8 days at 30°C. During development, its nucleus and daughter nuclei divide mitotically with intranuclear spindles until the sporangium contains several hundred nuclei. This is followed by progressive cleavage which delimits the planospore rudiments. When mature sporangia are placed in fresh water, the planospores are quickly formed within 1 hr. at 25°C. and begin to swarm within the sporangia. They escape in large numbers through an opening formed by the deliquescence of a papillum in the sporangial wall. The planospores are subspherical or elongate, 3-5 × 4-6 μ, and each has an eccentric orange-yellow refractive globule and a flagellum 18-22 μ in length. The electron micrographs of the flagella indicate that the flagella are absorbed from tip backward during encystment of the planospores. By periodic inoculation of the host plants with planospores from epibiotic sporangia, as well as from germinating resting sporangia, generation after generation of epibiotic sporangia have been obtained for 4 years. This proves the existence of a eucarpic, epibiotic, ephemeral zoosporangial phase in P. pulposum. Field observations on the duration and sequence of development of the fungus indicate that the endobiotic resting sporangial phase always follows the epibiotic phase. The results of infection experiments also indicate that the epi- and endobiotic phases belong to one and the same fungus, P. pulposum.     

Observations on chytridiaceous parasites of phanerogams

Summary Resting spores of the chytrid parasite of Claytonia virginica or Spring Beauty, Physoderma claytonianum var. sparrowii, were overwintered in plastic containers buried at the site of collection near Ann Arbor, Mich., USA. Germination took place in the field in early March. The process was followed in the laboratory and involved dehiscence of an operculum, protrusion of an endosporangium, zoospore formation and discharge. Resting spore zoospores were repeatedly placed in contact with young Claytonia plants but there was no evidence that they ever developed into epibiotic, ephemeral sporangia. Rather, in all instances within 36 hours the endobiotic, polycentric thallus was established inside the host. Both observational evidence and the speed with which the endobiotic thallus first appeared pointed to the complete lack of an epibiotic stage in our material.Paper No. 1131, Department of Botany, University of Michigan. Acknowledgement is made to the National Science Foundation for financial support of this project.     

Observations on chytridiaceous parasites of phanerogams

Summary A hitherto unnoted species of Physoderma on the basal leaves of Juncus pelocarpus Mey. is described. The fungus produces light brown irregularlyplaced spots on the outermost leaves. The endobiotic system is composed in addition to rhizoids of non-septate or 1–2 septate turbinate cells, resting spores and ovate haustorial-bearing cells. Resting spores germinate by dehiscence of a lid and protrusion of a finger-like zoosporangium. No epibiotic stage has as yet been seen. The host range of the fungus has not as yet been studied. This is the first account of a Physoderma on a member of the Juncaceae.Acknowledgement is made to the National Science Foundation for support of this project.     

A Physoderma species parasitic on bulrush

A Physoderma species selectively parasitic in the ovaries of bulrush (Scirpus articulatus L.) is described and named as Physoderma thirumalacharii Pavgi & Singh.     

Resting spore formation in the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo

Summary The resting spore morphology of the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo are described. Both species form endogenous resting spores. The spore valve of C. furcatus differ from those of the vegetative cells primarily by (i) a greater convexity and (ii) a coarser and more distinctly fasciculated areolation. This resting spore is identical to the diatom traditionally identified as C. stellaris var. symbolophorus (Grunow) Jørgensen in the Antarctic. The resting spore of T. australis differs from the vegetative cells by (i) a lack of clusters of strutted processes in a modified ring on valve face, (ii) a coarser areolation and tangential rows of areolae and (iii) a narrower and more simply structured girdle. The resting spore valve of T. australis has been described as belonging to a separate species, Actinocyclus excentricus Peragallo.     

OBSERVATIONS ON CHYTRIDIACEOUS PARASITES OF PHANEROGAMS. XXV. PHYSODERMA JOHNSII SPARROW,A PARASITE OF CALTHA PALUSTRIS L.

The morphology of the endobiotic and epibiotic stages of Physoderma johnsii Sparrow on Caltha palustris is described. Highly characteristic of the endobiotic stage is the formation of numbers of large, narrowly pyriform cells with a tuft of rhizoids at the broader (distal) end. Early developmental features are not included since germination of the resting spore has not as yet been achieved. Reasons for maintaining this taxon distinct from older ones on Caltha palustris are given.     

Interaction of vascular plants and vesicular-arbuscular mycorrhizal fungi across a soil moisture-nutrient gradient

Summary Abundance and distribution of vascular plants and vesicular-arbuscular mycorrhizal (VAM) fungi across a soil moisture-nutrient gradient were studied at a single site. Vegetation on the site varied from a dry mesic paririe dominated by little bluestem (Schizachyrium scoparium) to emergent aquatic vegetation dominated by cattail (Typha latifolia) and water smartweed (Polygonum hydropiperoides). Plant cover, VAM spore abundance, plant species richness, and number of VAM fungi represented as spores, had significant positive correlations with each other and with percent organic matter. The plant and VAM spore variables had significant negative correlations with soil pH and available Ca, Mg, P and gravimetric soil moisture. Using stepwise multiple regression, Ca was found to be the best predictor of spore abundance. Test for association between plant species and VAM fungal spores indicated that the spores of Glomus caledonium are associated with plants from dry, nutrient poor sites and spores of gigaspora gigantea are positively associated with plants occurring on the wet, relatively nutrient rich sites. Glomus fasciculatum was the most abundant and widely distributed VAM fungus and it had more positive associations with endophyte hosts than the other VAM fungi. We found no relationship between beta niche breadth of plant species and the presence or absence of mycorrhizal infection. However, our data suggest that some plant species may vary with respect to their infection status depending upon soil moisture conditions that may fluctuate seasonally or annually to favor or hinder VAM associations.     

Effect of bongkrekic acid on growth and metabolism of filamentous fungi

The antifungal activity of bongkrekic acid against 17 tested molds was determined. Bongkrekic acid prevented spore germination and mycelial proliferation of Aspergillus niger, Rhizopus oryzae and Penicillium italicum. The action of bongkrekic acid was fungicidal. Under these conditions, the incorporation of ¹⁴C-leucine and ¹⁴C-uracil into the perchloric acid insoluble material of germinating A. niger conidia was significantly reduced by bongkrekic acid. Respiratory activity of resting spores was not affected by bongkrekic acid. Respiratory activity of germinated spores was inhibited by bongkrekic acid to the extent of 30 to 60% of controls for A. niger, R. oryzae and P. italicum. It has been concluded that operation of adenine nucleotide translocation in mitochondria of tested fungi is obligatory both for normal spore germination and fungal growth.     

Comparing two methods for quantifying soil-borne Entomophaga maimaiga resting spores

To improve usability of methods for quantifying environmentally persistent entomophthoralean resting spores in soil, we modified and tested two methods using resting spores (azygospores) of the gypsy moth pathogen Entomophaga maimaiga. Both methods were effective for recovering resting spores at concentrations >100 resting spores/g dry soil. While a modification of a method originally described by Weseloh and Andreadis (2002) recovered more resting spores than a modified method based on Percoll density gradients, the ability to estimate true densities from counts was similar for both methods. Regression equations are provided for predicting true resting spore densities from counts, with R² values for both methods ?0.90.