The structure and formation of host-parasite pit connections between the red algal alloparasiteHarveyella mirabilis and its red algal hostOdonthalia floccosa

Summary Harveyella mirabilis is a colourless red algal alloparasite which grows on and within its photosynthetic hostOdonthalia floccosa. Cells ofHarveyella establish secondary pit connections (PCs) with other parasite cells and with cells of the host. Small, uninucleate conjunctor cells are produced by parasite cells and remain connected to them by PCs. Conjunctor cells may fuse with either an adjacent host or parasite cell, with the parasite-conjunctor cell PC becoming either a host-parasite or parasite-parasite secondary PC. Occasionally the conjunctor cell does not fuse with an adjacent cell (either host or parasite) and degenerates. The secondary pit plug which forms between a parasite cell and its conjunctor cell always develops with two structurally distinct surfaces characteristic of a host-parasite pit plug. Only if the conjunctor cell fuses with another parasite cell will the structure of the pit plug be altered to that of a parasite-parasite pit plug. Fungal hyphae also invade the region of infection, andHarveyella cells respond by producing nonfunctional conjunctor cells that grow towards adjacent hyphae. Evidence suggests that secondary PCs may be induced to form mechanically, by the physical presence of another cell, rather than in direct response to a message received from an adjacent cell. The mechanism of secondary PC formation described here is similar to that reported for the closely related alloparasiteHolmsella and may be common to a number of red algal parasitic associations. Helen Margaret Quirk, B. Sc. (Hons), M. Sc. (1953–1982), student, research assistant and friend, died after a long illness on October 24, 1982.     

Structure and Development of the Endophyte in the Parasitic Angiosperm <Emphasis Type="Italic">Cuscuta japonica</Emphasis>

The endophyte, that is, the haustorial part within the tissues of the host plant Impatiens balsamina, of the parasitic angiosperm Cuscuta japonica was studied with light and electron microscopy. The endophyte consisted mainly of vacuolated parenchymatous axial cells and elongate, superficial (epidermal) cells. Then the elongate, epidermal cells separated from each other and transformed into filamentous cells, called searching hyphae. The hyphae grew independently either intercellularly or intracellularly in the host parenchyma. The apical end of the hyphal cells was characterized by conspicuous, large nuclei with enlarged nucleoli and very dense cytoplasm with abundant organelles, suggesting that the hyphal cells penetrating host tissue were metabolically very active. Numerous osmiophilic particles and chloroplasts were noted in the hyphae. The osmiophilic particles were assumed to be associated with elongation of the growing hyphe. Plasmodemata connections between the searching hyphal cells of the parasite and the host parenchyma cells were not detected. Hyphal cells that reached the host xylem differentiated into water-conducting xylic hyphae by thickening of the secondary walls. A xylem bridge connecting the parasite and the host was confirmed from serial sections. Some hyphal cells that reached the host phloem differentiated into nutrient-conducting phloic hyphae. Phloic hyphae had a thin layer of peripheral cytoplasm with typical features of sieve-tube members in autotrophic angiosperms, i.e., parallel arrays of smooth endoplasmic reticulum, mitochondria, and plastids with starch granules. Interspecific open connections via the sieve pores of the host sieve elements and plasmodesmata of the parasite phloic hyphae were very rarely observed, indicating that the symplastic translocation of assimilate to the parasite from the host occurred.     

Schizophyllum commune Fr. as a destructive mycoparasite

Schizophyllum commune Fr. was shown, by light, scanning, and transmission electron microscopy, to be a destructive mycoparasite on several phytopathogenic and nematode-trapping fungi. The hyphae of S. commune coiled around host hyphae and fruiting structures and penetrated them by means of either unspecialized hyphae or by penetration pegs that developed from terminal appressoria. The host cell walls were usually chemically degraded after which the parasite grew through an electron-dense, papillate, reaction region and its underlying membrane(s) produce trophic hyphae inside the host cells.     

Antimalarial drug resistance and combination chemotherapy.

Antimarial drug resistance develops when spontaneously occurring parasite mutants with reduced susceptibility are selected, and are then transmitted. Drugs for which a single point mutation confers a marked reduction in susceptibility are particularly vulnerable. Low clearance and a shallow concentration-effect relationship increase the chance of selection. Use of combinations of antimalarials that do not share the same resistance mechanisms will reduce the chance of selection because the chance of a resistant mutant surviving is the product of the per parasite mutation rates for the individual drugs, multiplied by the number of parasites in an infection that are exposed to the drugs. Artemisinin derivatives are particularly effective combination partners because (i) they are very active antimalarials, producing up to 10,000-fold reductions in parasite biomass per asexual cycle; (ii) they reduce malaria transmissibility; and (iii) no resistance to these drugs has been reported yet. There are good arguments for no longer using antimalarial drugs alone in treatment, and instead always using a combination with artemisinin or one of its derivatives.     

Leaf curl disease of Almond caused byTaphrina deformans (Berk.) Tul.

Summary The host/parasite relationship ofTaphrina deformans (Berk.) Tul. on Almond,Prunus dulcis (Miller) D. A. Webb (=Prunus amygdalus Stokes), has been studied with the light microscope by clearing and sectioning infected leaves.A quantitative study of the host reaction shows that the presence of the fungus causes immediate cell division (hyperplasia) followed by cell enlargement (hypertrophy) and cell differentiation. The epidermal and bundle sheath cells in infected regions contain anthocyanin.The vegetative mycelium is located in intercellular spaces in three distinct leaf regions. The sub-epidermal and intercellular hyphae are morphologically similar, consisting of an irregularly branching network of cells separated by unusual septa. Sub-cuticular hyphae have a more regular shape and become short and wide during development of the disease.Infection margins illustrate changes in the healthy leaf caused byT. deformans and observations indicate that the fungus spreads in the upper leaf regions.     

干皮孔菌属的一个新种和三个组合种

本文报道了产自斯里兰卡的干皮孔菌属一个新种,该种的主要特征是具有平伏反卷或具菌盖的子实体,很小的孔口（每毫米8-10个）,菌丝系统二系,生殖菌丝覆盖有刺状结晶,骨架菌丝橙棕色,细腊肠状担孢子（2.7-3.4×0.5-0.8μm）。基于ITS和nLSU序列的系统发育分析表明该新种属于干皮孔菌属的一个明确的分支。此外,将毛孔菌属组合到干皮孔菌属中,并报道了3个组合种,白边干皮孔菌、印度干皮孔菌和萨彦干皮孔菌。     

Genetic variation in a host-parasite association: potential for coevolution and frequency-dependent selection

Abstract.— Models of host‐parasite coevolution assume the presence of genetic variation for host resistance and parasite infectivity, as well as genotype‐specific interactions. We used the freshwater crustacean Daphnia magna and its bacterial microparasite Pasteuria ramosa to study genetic variation for host susceptibility and parasite infectivity within each of two populations. We sought to answer the following questions: Do host clones differ in their susceptibility to parasite isolates? Do parasite isolates differ in their ability to infect different host clones? Are there host clone‐parasite isolate interactions? The analysis revealed considerable variation in both host resistance and parasite infectivity. There were significant host clone‐parasite isolate interactions, such that there was no single host clone that was superior to all other clones in the resistance to every parasite isolate. Likewise, there was no parasite isolate that was superior to all other isolates in infectivity to every host clone. This form of host clone‐parasite isolate interaction indicates the potential for coevolution based on frequency‐dependent selection. Infection success of original host clone‐parasite isolate combinations (i.e., those combinations that were isolated together) was significantly higher than infection success of novel host clone‐parasite isolate combinations (i.e., those combinations that were created in the laboratory). This finding is consistent with the idea that parasites track specific host genotypes under natural conditions. In addition, correspondence analysis revealed that some host clones, although distinguishable with neutral genetic markers, were susceptible to the same set of parasite isolates and thus probably shared resistance genes.     

Ovipositional response ofVenturia canescens (Grav.) (Hymenoptera: Ichneumonidae) to various host and parasite densities

Summary Ovipositional response inVenturia canescens (Grav.) parasitizingAnagasta kühniella (Zeller) is analyzed for all combinations of five parasite densities (2, 5, 10, 25, and 50), four host densities (25, 50, 100, and 200), and three floor area universe sizes (76 cm², 160 cm², and 345 cm²). Over this range, no mutual interference (as measured by decreasing parasite fecundity) was observed, althoughNicholson’s area of discovery decreased significantly with parasite density increase as a result of a non-Poisson distribution of parasite eggs; use of this parameter is therefore not a suitable means of determining if mutual interference is present. Other parameters studied, and for which significant correlations were obtained, include mean parasite eggs per host, percentage parasitization, percentage of parasite eggs wasted, and negative binomialk approximations. This study was conducted as part of a broad investigation into the processes operating in the dynamics of arthropod populations under a grant toC. B. Huffaker by the U.S. Public Health Service, National Institutes of Health.     

Development and Structure of the Haustorium of the Parasite Rhamphicarpa fistulosa (Scrophulariaceae)

Rhamphicarpa fistulosa (Hochst.) Benth. (Scrophulariaceae), a parasite of African cereals, develops secondary haustoria which penetrate the roots of the host plant. Light and electron microscopy have been used to study the structure and development of haustoria in this species, which, until now, have not been well characterized. Haustoria are initiated in the hypodermis of the parasite roots. A meristematic strand is developed between the parasite root stele and the host-parasite interface. From this strand, cells differentiate into xylem elements after penetration of the host root. Xylem differentiation follows an acropetal pattern. Mature haustoria are characterized by a continuous xylem bridge between water conducting elements of parasite and host. A detailed study of the hostparasite interface revealed the presence of collapsed and compressed host cells at the lateral interface (between parasite cells and host cortex), whereas the central interface between parasite cells and the host stele is almost devoid of host cell remnants. Implications of these observations for the penetration mechanisms are discussed.     

Nosema muris n. sp., a New Microsporidian Parasite of the White Mouse (Mus musculus L.)

SYNOPSIS. A microsporidian, Nosema muris n. sp., is described from laboratory white mice in Czechoslovakia. I t differs from Nosema cuniculi (Levaditi, Nicolau and Schoen, 1923) and other Microsporidia in mice in that it develops in the omentum and heart muscle, iorming large masses of schizonts and spores. The parasite is distributed to other tissues (liver, spleen, fat, peritoneal muscles, connective tissue and brain) by infected mononudear cells, and then forms localized cysts in them. Kidney, lungs, adrenal glands, pancreas and salivary glands are not infected. The parasite can be transmitted via the placenta, by feeding on infected tissues, or by experimental injection of ascitic fluid.     

Effect of synthetic combinations and tobacco root extract and the mixture of them on broomrape seed germination

Various types of broomrape (Orobanche cermua), such as parasitic weeds, live on the roots of many important crops. Different methods may be advised to eradicate this parasite. But the seed size is so tiny with high stability in the soil and having strong connection with the host, it is very difficult to eradicate this parasite and there is no useful and economic method has not been suggested in this regard yet. The seeds of all types of broomrape germinate in the soil only when they are exposed to the secretions of the host's roots, therefore, providing special combinations that cause the parasite's seeds germinate in the absence of the host, can be an effective way in controlling this parasite. The effect of the tobacco root's extract and the synthetic combinations as well as their mixtures with different concentrations on the germination of the seeds of Orobanche cermua Loefi were tested to introduce an effective combination that can be used in controlling this parasite. This experiment includes 28 treatments in three replications. The tobacco root's extract was derived from the tobacco roots planted in pots containing Perlit in different stages and were prepared in different concentrations. Synthetic combinations (including combinations 1, 2 and 3) were also prepared with concentration of 1, 2 and 3 parts per million (ppm), then these combinations were tested as treatments on Broomrape's seeds. At the end of experiment, it was concluded that all the combinations used in different concentrations in this experiment significantly differ from the control treatment in their effects in causing the Broomrape's seeds germinate. Among all the combinations examined, the following were the most effective ones in the process of the germination of the Broomrape's seeds: 1. combination 2 with the concentration of one part per million, 2. combination 2 with the concentration of two parts per million, and 3 tobacco root's extract in the third stage.     

Transfer of phloem-mobile substances from the host plants to the holoparasite Cuscuta sp

During the development of the haustorium, searching hyphae of the parasite and the host parenchyma cells are connected by plasmodesmata. Using transgenic tobacco plants expressing a GFP-labelled movement protein of the tobacco mosaic virus, it was demonstrated that the interspecific plasmodesmata are open. The transfer of substances in the phloem from host to the parasite is not selective. After simultaneous application of (3)H-sucrose and (14)C-labelled phloem-mobile amino acids, phytohormones, and xenobiotica to the host, corresponding percentages of the translocated compounds are found in the parasite. An open continuity between the host phloem and the Cuscuta phloem via the haustorium was demonstrated in CLSM pictures after application of the phloem-mobile fluorescent probes, carboxyfluorescein (CF) and hydroxypyrene trisulphonic acid (HPTS), to the host. Using a Cuscuta bridge (14)C-sucrose and the virus PVY(N) were transferred from one host plant to the another. The results of translocation experiments with labelled compounds, phloem-mobile dyes and the virus should be considered as unequivocal evidence for a symplastic transfer of phloem solutes between Cuscuta species and their compatible hosts.     

Mating type of isolates derived from the spermogonial state ofPuccinia coronata var.coronata

Hyphal confrontation between two haploid cultures originating from single basidiospores was used to determine the mating type ofPuccinia coronata var.coronata. Pairs of 15 single-basidiospore cultures were placed approximately 1 mm apart on the medium in all possible combinations. Hyphae of the pairs of colonies came into contact with each other in all combinations approximately two weeks after confrontations. When the nuclear number of hyphal cells in a contact zone was investigated one month after confrontation, monokaryotic hyphae were observed in selfing combination. On the other hand, dikaryotic hyphae were observed in 90.5% of crossing combinations between different cultures. Two isolates are considered compatible if dikaryotic hyphae are present in the contact zone but incompatible if they are absent. The mating type of the fungus was found to be characterized by multiple-allelomorphic tetrapolar incompatibility controlled by the “A” and “B” incompatible factors. Contribution No. 116, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba     

Corrigendum to Streicker et al. (2013) Differential sources of host species heterogeneity influence the transmission and control of multi‐host parasites

In a recent article, we described a conceptual and analytical model to identify the key host species for parasite transmission in multi‐host communities and used data from 11 gastro‐intestinal parasites infecting up to five small mammal host species as an illustrative example of how the framework could be applied. A limitation of these empirical data was uncertainty in the identification of parasite species using egg/oocyst morphology, which could overestimate parasite sharing between host species. Here, we show that the key results of the original analysis, namely that (1) parasites naturally infect multiple host species, but typically rely on a small subset of infected host species for long‐term maintenance, (2) that different mechanisms underlie how particular host species dominate transmission and (3) that these different mechanisms influence the predicted efficiency of disease control measures, are robust to analysis of a smaller subset of host–parasite combinations that we have greatest confidence in identifying. We further comment briefly on the need for accurate parasite identification, ideally using molecular techniques to quantify cross‐species transmission and differentiate covert host specificity from true host generalism.     

The gleba development of Langermannia gigantea (Batsch: Pers.) Rostk. (Basidiomycetes) compared to other Lycoperdaceae, and some systematic implications

The fruit body and in particular the gleba development of several species of Lycoperdaceae has been examined by light microscopic analysis of microtome sections of fruit body primordia in different ontogenetic stages. The gleba of Langermannia gigantea develops in a unique and previously unknown manner: the hymenium-forming palisade structures are borne on fan-like branches of hyphae. Hence the term of flabelloid glebal development is introduced. The other genera of Lycoperdaceae, including the genus Calvatia, are characterized by both lacunar and coralloid development of the gleba. Because these features cannot be distinguished clearly, this type of glebal development is referred to as coralloid-lacunar. Due to the peculiar ontogeny I suggest keeping the genus Langermannia separate from Calvatia.     

Macromolecular trafficking between Nicotiana tabacum and the holoparasite Cuscuta reflexa

Transgenic tobacco plants expressing green fluorescent protein (GFP) under the control of the companion cell-specific promoter, AtSUC2, were parasitized by the holoparasite Cuscuta reflexa (dodder). GFP, moving in the translocation stream of the host, was transferred to the Cuscuta phloem via the absorbing hyphae of the parasite. An identical pattern of transfer was observed for the phloem-mobile probe, carboxyfluorescein. Following uptake by the parasite, GFP was translocated and unloaded from the Cuscuta phloem in meristematic sink tissues. Contrary to published data, these observations suggest the presence of a functional symplastic pathway between Cuscuta and its hosts, and demonstrate a considerable capacity for macromolecular exchange between plant species.     

Specialized mycorrhizal colonization pattern in achlorophyllous Epirixanthes spp. (Polygalaceae)

Roots of the achlorophyllous Epirixanthes papunana and E. elongata were sectioned in complete series in order to reconstruct the three-dimensional mycorrhizal colonization pattern within their tissues. Hyphal morphology, vesicles, as well as the exclusively intracellular mode of colonization indicate a PARIS-type of arbuscular mycorrhiza showing a hitherto unknown colonization pattern: (1) the outer cortex is colonized by persistent straight-growing hyphae which branch in a cascading manner, (2) a specific layer (called layer 2) is inhabited by persistent hyphal coils, (3) in the cells of the anatomically distinct inner cortex parenchyma layer (called layer 1) the hyphae immediately degenerate, and (4) the layer outside to layer 2 (called layer 3) is either transitional layer 2 when penetrated from the outer cortex or the fungal material degenerates when colonized from the layer 2. This complex colonization pattern is a reasonable adaptation to the particular demands of Epirixanthes as a myco-heterotrophic plant. It not only allows a sustained benefit from the fungal symbiont but also provides a two-level distribution system of hyphae within the roots. The outer cortex hyphae function as a permanent intraradical resource of living fungi providing connection to the external mycelium as well as a coarse distribution of hyphae within the root. Layer 2 represents the fine scale distribution of hyphae, having access to all potentially digesting cells of the layers 1 and 3. Common structural features of mycorrhizae in myco-heterotrophic plants are pointed out in order to find putative prerequisites for their heterotrophic mode of life.     

Fruit-body production and mycelial growth ofTephrocybe tesquorum in urea-treated forest soil

Tephrocybe tesquorum is an ammonia fungus that forms reproductive structures successively on the forest floor after treatment of the soil with nitrogenous materials such as aqua ammonia and urea. Forest soil was treated with urea at the rates of 0, 5, 10 and 20 mg/g fresh soil for 5 d in the laboratory, then sterilized by gamma-irradiation. Vegetative hyphae ofT. tesquorum were inoculated into the sterilized soil, and the number and weight of fruit-bodies formed and the length of vegetative hyphae, were measured for 20 d after the inoculation. Only in the urea-treated soil did this fungus produce vegetative hyphae and fruit-bodies. Fruiting started 4 to 6 d after inoculation. The weight of fruit-bodies and the length of vegetative hyphae increased with the increase in the amount of urea added. These results indicate thatT. tesquorum develops vegetative hyphae and fruit-bodies when ammonium concentration, is high in soil.     

Lectin Binding Studies on the Cell Walls of Soybean Rust (Phakopsora pachyrhizi Syd.)

Walls of uredospores, infection structures, intercellular hyphae and haustoria of the soybean rust fungus (Phakopsora pachyrhizi) were studied by electron microscopy using gold-labeled wheat germ lectin (WGL) and Concanavalin A (ConA) as cytochemical probes. Receptors for WGL (probably chitin) were detected in all fungal walls included in this study. WGL-binding occurred throughout the entire walls (uredospores, appressorial cone, penetration hyphae, haustorial mother cells) or only to the inner wall layers (germ tubes, appressoria, intercellular hyphae).     

A mycorrhizal fungus changes microtubule orientation in tobacco root cells

Summary Cortical cells of mycorrhizal roots undergo drastic morphological changes, such as vacuole fragmentation, nucleus migration, and deposition of cell wall components at the plant-fungus interface. We hypothesized that the cytoskeleton is involved in these mechanisms leading to cell reorganization. We subjected longitudinal, meristem to basal zone, sections of uninfectedNicotiana tabacum roots to immunofluorescence methods to identify the microtubular (MT) structures associated with root cells. Similar sections were obtained from tobacco roots grown in the presence ofGigaspora margarita, an arbuscular mycorrhizal fungus which penetrates the root via the epidermal cells, but mostly develops in the inner cortical cells. While the usual MT structures were found in uninfected roots (e.g., MTs involved in mitosis in the meristem and cortical hoops in differentiated parenchyma cells), an increase in complexity of MT structures was observed in infected tissues. At least three new systems were identified: (i) MTs running along large intracellular hyphae, (ii) MTs linking hyphae, (iii) MTs binding the hyphae to the host nucleus. The experiments show that mycorrhizal infection causes reorganization of root MTs, suggesting their involvement in the drastic morphological changes shown by the cortical cells.