Fungal Death Research Articles

Meta-Analysis: The Efficacy of Strategies To Prevent Organ Disease by Cytomegalovirus in Solid Organ Transplant Recipients

Cytomegalovirus (CMV), the most common opportunistic viral infection in solid organ transplant recipients, is associated with substantial morbidity and mortality. To assess the efficacy of universal prophylaxis and preemptive approaches in preventing CMV organ disease and other complications in solid organ transplant recipients. Using no language restrictions, the authors searched the following databases from their inception through May 2005: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Evidence-Based Medicine. The authors also reviewed abstracts from scientific meetings and contacted experts and pharmaceutical companies. Randomized, controlled trials that evaluated antiviral strategies for preventing CMV and associated complications in solid organ transplant recipients were selected. Two reviewers independently extracted and assessed the data. The authors found 17 trials involving 1980 patients. Compared with placebo or no therapy, both universal prophylaxis (odds ratio [OR], 0.20 [95% CI, 0.13 to 0.31]) and preemptive strategies (OR, 0.28 [CI, 0.11 to 0.69]) reduced CMV organ disease. However, only universal prophylaxis seemingly reduced CMV organ disease in subgroups of patients at highest risk (donors with positive CMV serostatus and recipients with negative CMV serostatus and induction with antibodies). Both strategies reduced the rate of allograft rejection. Only universal prophylaxis statistically significantly reduced bacterial and fungal infections (OR, 0.49 [CI, 0.36 to 0.67]) and death (OR, 0.62 [CI, 0.40 to 0.96]). Both acyclovir and ganciclovir statistically significantly prevented CMV organ disease in the universal prophylaxis trials. Studies were of modest size, and few studies assessed all outcomes. Studies did not always provide data that discriminated between CMV organ disease and CMV syndrome or data about the timing of CMV organ disease. Universal prophylaxis and preemptive strategies are beneficial in preventing CMV organ disease in solid organ transplant recipients. Both strategies are associated with a reduction in allograft rejection, but current data suggest that only universal prophylaxis reduces bacterial and fungal infections and death. Acyclovir and ganciclovir are both effective for universal prophylaxis.

Tissue-specific localization of pea root infection by Nectria haematococca. Mechanisms and consequences.

Root infection in susceptible host species is initiated predominantly in the zone of elongation, whereas the remainder of the root is resistant. Nectria haematococca infection of pea (Pisum sativum) was used as a model to explore possible mechanisms influencing the localization of root infection. The failure to infect the root tip was not due to a failure to induce spore germination at this site, suppression of pathogenicity genes in the fungus, or increased expression of plant defense genes. Instead, exudates from the root tip induce rapid spore germination by a pathway that is independent of nutrient-induced germination. Subsequently, a factor produced during fungal infection and death of border cells at the root apex appears to selectively suppress fungal growth and prevent sporulation. Host-specific mantle formation in response to border cells appears to represent a previously unrecognized form of host-parasite relationship common to diverse species. The dynamics of signal exchange leading to mantle development may play a key role in fostering plant health, by protecting root meristems from pathogenic invasion.

The Pathogenesis of Fatal Outcome in Murine Pulmonary Aspergillosis Depends on the Neutrophil Depletion Strategy

Aspergillus fumigatus causes invasive disease in severely immunocompromised hosts but is readily cleared when host innate defenses are intact. Animal models for evaluation of therapeutic strategies to combat invasive aspergillosis that closely mimic human disease are desirable. We determined optimal dosing regimens for neutrophil depletion and evaluated the course of infection following aerosol infection in mice by determining survival, organ fungal burden, and histopathology in mice in which neutropenia was induced by three methods, administration of granulocyte-depleting monoclonal antibody RB6-8C5 (MAb RB6), administration of cyclophosphamide, and administration of both agents. Administration of either individual agent resulted in a requirement for relatively high conidial inocula to achieve 100% mortality in both BALB/c and C57BL/6 mice, although the infection appeared to be somewhat more lethal in C57BL/6 mice. Death following induction of neutropenia with MAb RB6 occurred when a relatively low fungal burden was present in the lung and may have been related to the inflammatory response associated with neutrophil recovery. In contrast, administration of both agents reduced the lethal inoculum in each mouse strain by approximately 1 log(10), and C57BL/6 mice that received both agents had a higher fungal burden and less inflammation in the lung at the time of death than BALB/c mice or mice of either strain that received MAb RB6 alone. Our data suggest that the relationship among fungal burden, inflammation, and death is complex and can be influenced by the immunosuppression regimen, the mouse strain, and the inoculum.

Ergosterol as a measure of living fungal biomass: persistence in environmental samples after fungal death

The membrane lipid ergosterol is found almost exclusively in fungi, and is frequently used by environmental microbiologists as an indicator of living fungal biomass, based on the assumption that ergosterol is labile, and therefore rapidly degraded after the death of fungal hyphae. We studied the degradation of ergosterol in environmental samples without living fungi. Under the conditions used in this study, ergosterol was very stable both when added as a pure compound and when associated with dead fungi. The decrease of ergosterol was at most 34% during 2 months when protected from sunlight. Presence of a natural bacterial assemblage did not enhance degradation over this time period, as compared to sterile controls. However, photochemical degradation was significant, and led to a 43% decrease of in ergosterol content during 24 h. These results suggest that ergosterol should be used cautiously as a biomarker for living fungi.

Selective destruction of microscopic fungi through photo-oxidation of ergosterol

Ergosterol is an important component of fungal membranes. This sterol can be easily transformed to peroxide of ergosterol by photo-oxidation with singlet oxygen. Cultures of Papalauspora immersa were grown on Czapeck agar medium, and subjected to the following conditions: 1) irradiation with daylight and quartz light (excluding UV light), 2) addition by diffusion of yellowish eosine (0.1 mg/mL), and 3) the control (no yellowish eosine, under darkness conditions). Fungal growth was completely inhibited after the treatment with quartz light (3 h) and yellow eosine, and no growth was observed in subsequent subcultures. These results suggested that plasma membrane components changed significantly by the transformation of ergosterol to peroxide of ergosterol leading to fungal death. To confirm this, a second experiment on a larger scale was carried out in which the fungus was grown on liquid medium in test tubes, treated, irradiated, and tested for peroxide of ergosterol by 1HNMR. This peroxide was only found in treated samples. These findings represent a new strategy for developing antifungal agents, based on ergosterol photo-oxidation which might probably be related to the disruption of the plasma membrane, instead of only preventing the ergosterol biosynthesis. The potential application of this strategy for the selective control or prevention of pathogenic fungi is considerable.

Low rate of Candida parapsilosis -relatedcolonization and infection in hospitalized preterm infants: a one-year prospective study

We determined the rate of Candida parapsilosis colonization in preterm neonates (NN) and the relationship between colonization and systemic infection through a prospective study in the Neonatal Intensive Care Unit of a university hospital. All NN born at a gestational age of 32 weeks or less were included. Specimens from rectum, mouth and retro-auricular skin were obtained at admission and weekly thereafter. All samples were inoculated on to Sabouraud agar, CHROMagar® and Dixon media. Candida species were identified using API Candida® and API 20C®. DNA analysis was performed using pulse field gel electrophoresis.Fifty-four patients were included (mean age: 30 ± 1.5 weeks; mean birthweight: 1347 ± 301 g; male: 40%). Fungal colonization was detected in 43 (79.6%). Causative agents were C. parapsilosis (N= 7);Malassezia furfur (N= 30);C. albicans (N= 21), C. guillermondii (N= 1). No sample was positive for two different yeasts at the same time. C. parapsilosis colonization included anal (N= 6), buccal (N= 1), and skin (N= 2). The average age at time of colonization was 17.8±9.8 days. Neither fungal septicaemia nor death were observed in colonized infants. Two central venous catheters were found to be colonized, one with C. parapsilosis and one with M. furfur. Logistic regression showed a link between colonization and gestational age alone. Three different DNA profiles were observed.This study suggests that in our units, the occurrence of C. parapsilosis colonization is low and bears no relation to systemic infection. The systematic identification of C. parapsilosis carriers for the purposes of isolation and preventive treatment does not appear to be warranted.

Phloem parenchyma cells are involved in local and distant defense responses to fungal inoculation or bark‐beetle attack in Norway spruce (Pinaceae)

The anatomical response of Norway spruce bark polyphenolic parenchyma cells (PP cells) to inoculation with the phytopathogenic fungus Ceratocystis polonica and attack by its bark-beetle vector Ips typographus was examined. Fungal inoculation on the periderm surface had no effect, while inoculation just below the periderm or halfway into the phloem (mid-phloem) generated detectable responses within 3 wk. The responses included increase in PP cell size and in periodic acid-Schiff's staining of PP cell phenolics, wound periderm initiation from PP cells, and cambial zone traumatic resin duct formation. Fungi were not seen in samples 3 wk after subperiderm or mid-phloem inoculation, but were found in some samples 6 and 9 wk after mid-phloem inoculation. In contrast, inoculations into the cambium resulted in partial (3 wk) or complete (6 and 9 wk) fungal colonization and death of tissue in the infected area. This indicates that PP cells have defenses capable of inhibiting fungal growth. Samples taken near bark-beetle galleries had similar anatomical responses as inoculated samples, validating the inoculation approach to studying defense responses in spruce. These results show that PP cells represent not only a constitutive defense system, but are also involved in local and remote inducible defenses against fungal and beetle attack.

Determinants of the efficacy of prophylactic granulocyte transfusions: a meta-analysis.

Cytokines that improve granulocyte collection yields have recently become available, and may lead to a new series of trials of granulocyte transfusion (GTX) therapy. We conducted a meta-analysis of studies of prophylactic GTX in order to identify the determinants of efficacy of this intervention, and to assist in the design of future trials of GTX for the treatment of patients with overwhelming infection. Randomized controlled trials of the efficacy of prophylactic GTX published in English in 1970-1995 were retrieved, and eight studies were eligible for analysis. Summary relative odds (RR) of bacterial or fungal infection, death, or death from infection in transfused patients vs. controls were computed for patient subsets defined on the basis of dose of granulocytes transfused, assessment of leukocyte compatibility, duration of neutropenia, and infection rate of controls. The random-effects method was used for all analyses. Assessment of leukocyte compatibility prior to the transfusion, dose of granulocytes transfused, and duration of neutropenia in enrolled patients could account, respectively, for the variation in findings across published reports in terms of all three, two, and one of the outcome measures studied. Transfusion of adequate doses of compatible leukocytes significantly reduced the relative risk (RR) of infection, death, and death from infection in transfused patients vs. controls (RR = 0.075, RR = 0.224, and RR = 0.168, respectively; P < 0.05). Two necessary elements in the design of future trials of therapeutic GTX should be the transfusion of high doses of granulocytes and the provision of leukocytes that are crossmatch-compatible with the recipient's serum.

Determinants of the efficacy of prophylactic granulocyte transfusions: A meta‐analysis

BACKGROUND Cytokines that improve granulocyte collection yields have recently become available, and may lead to a new series of trials of granulocyte transfusion (GTX) therapy. We conducted a meta-analysis of studies of prophylactic GTX in order to identify the determinants of efficacy of this intervention, and to assist in the design of future trials of GTX for the treatment of patients with overwhelming infection. METHODS: Randomized controlled trials of the efficacy of prophylactic GTX published in English in 1970–1995 were retrieved, and eight studies were eligible for analysis. Summary relative odds (RR) of bacterial or fungal infection, death, or death from infection in transfused patients vs. controls were computed for patient subsets defined on the basis of dose of granulocytes transfused, assessment of leukocyte compatibility, duration of neutropenia, and infection rate of controls. The random-effects method was used for all analyses. RESULTS: Assessment of leukocyte compatibility prior to the transfusion, dose of granulocytes transfused, and duration of neutropenia in enrolled patients could account, respectively, for the variation in findings across published reports in terms of all three, two, and one of the outcome measures studied. Transfusion of adequate doses of compatible leukocytes significantly reduced the relative risk (RR) of infection, death, and death from infection in transfused patients vs. controls (RR = 0.075, RR = 0.224, and RR = 0.168, respectively; P < 0.05). CONCLUSION: Two necessary elements in the design of future trials of therapeutic GTX should be the transfusion of high doses of granulocytes and the provision of leukocytes that are crossmatch-compatible with the recipient's serum. J. Clin. Apheresis 12:74–81, 1997. © 1997 Wiley-Liss, Inc.

Cellular mechanisms of callose deposition in response to fungal infection or chemical damage

Cellular mechanisms of callose deposition induced in cowpea (Vigna unguiculata) leaves by the living cowpea rust fungus (Uromyces vignae), boric acid, or the fungus killed by polyoxin D, were investigated by the use of chemical inhibitors. Effects of the inhibitors were observed in both a resistant and a susceptible cowpea cultivar. The effect of inhibitors differed depending on the type of callose-inducing stimulus and cultivar used. Inhibitors of transcription (actinomycin D) and protein synthesis (blasticidin S, cycloheximide) lowered the incidence of fungus-induced callose deposits in both cultivars. Inhibitors of protein synthesis also reduced deposits induced by boric acid or fungal death. Callose deposition induced by the living fungus in the resistant cultivar was reduced by inhibitors of protein glycosylation (tunicamycin, deoxynojirimycin) and microfilament function (cytochalasins B and E), but these inhibitors had no effect on callose deposition in the susceptible cultivar or on chemical or fungal death-induced deposition in either cultivar. No reduction in callose deposits was observed in plants treated with inhibitors of Golgi-associated vesicle transfer (brefeldin A, monensin) or microtubule polymerization (colchicine, oryzalin). The results suggest that the cellular processes involved in callose deposition differ with differing triggering stimuli and that callose deposition triggered by the living fungus in a resistant host cultivar is not a typical wound or damage response. Keywords: callose, infection, inhibitors, resistance, rust fungi.

Fluconazole versus amphotericin B as empirical antifungal therapy of unexplained fever in granulocytopenic cancer patients: a pragmatic, multicentre, prospective and randomised clinical trial

Amphotericin B, despite its intrinsic servere toxicity, is the most commonly used empirical antifungal therapy in cancer patients with unexplained fever not responding to empirical antibacterial therapy. The aim of this study was to show whether fluconazole was as effective as, and less toxic than, amphotericin, with no effort made to compare the antifungal activity of the two drugs. A group of 112 persistently febrile (> 38 °C) and granulocytopenic (< 1000 cells/mm 3) cancer patients, not receiving any absorbable antifungal antibiotic for prophylaxis, with a mean age of 27 years (range 1–73 years), undergoing chemotherapy for a variety of malignancies and with a diagnosis of unexplained fever after at least 96 h of empirical antibacterial therapy, were randomised to receive either fluconazole (6 mg/kg/day up to 400 mg/day) or amphotericin B (0.8 mg/kg/day) as empirical antifungal treatment. Patients were required to have normal chest X-rays at randomisation, no previous history of aspergillosis and negative surveillance cultures for Aspergillus. The intention-to-treat analysis showed defervescence and survival without treatment modification in 42 of 56 patients (75%) in the fluconazole group and in 37 of 56 (66%) in the amphotericin B group ( P = 0.4). Duration of therapy was 6 days (95% CI = 4–8 days) in both groups. Death occurred in 3 patients (5%) in the fluconazole and in 2 (4%) in the amphotericin B group. No fungal death was documented in either group. Adverse events developed in 18 of 56 patients (32%) in the fluconazole group and in 46 of 56 (82%) in the amphotericin B group ( P < 0.001). In the amphotericin B group, 5 patients had treatment discontinued because of toxicity, versus none in the fluconazole group, a difference which approached statistical significance ( P = 0.06). This study shows that fluconazole is by far less toxic than amphotericin B and suggests that it might be as effective as amphotericin B, in pragmatical terms and for this specific indication. However, numbers are too small to allow definitive conclusions about efficacy, and the use of fluconazole for this indication remains experimental. Future studies should try to identify patients more at risk of fungal infections, with the aim of individualising antifungal approaches.

Effect of fenpiclonil on phosphorylation of glucose in Fusarium sulphureum

AbstractThe phenylpyrrole fungicide fenpiclonil inhibited the metabolism of glucose in mycelium of Fusarium sulphureum Schlecht at a concentration which only slightly inhibited mycelial growth (EC15). At the same concentration, fenpiclonil also inhibited accumulation and, to a greater extent, phosphorylation of 2‐deoxy[U‐14C]glucose in starved mycelium loaded with unlabelled 2‐deoxyglucose. Fenpiclonil did not affect cell‐free phosphorylation of 2‐deoxyglucose or the ATP content of mycelium. Therefore, the primary mode of action of the fungicide may be based on inhibition of transport‐associated phosphorylation of glucose. This may cause a cascade of metabolic events which eventually lead to fungal growth inhibition and death. One major event affected by inhibition of transport‐associated phosphorylation is the accumulation of polyols, such as glycerol and mannitol, in mycelium. This was not observed in an osmotically sensitive, fenpiclonil‐resistant laboratory isolate of the fungus.

Systemic amphotericin B versus fluconazole in the management of antibiotic resistant neutropenic fever — preliminary observations from a pilot, exploratory study

A pilot exploratory study was undertaken to collect preliminary information relating to safety and overall outcome in using intravenous fluconazole (FLUC) for managing antibiotic resistant neutropenic fever (ARNF), with the objective of assessing feasibility of performing a larger prospective controlled study. Patients who were neutropenic from treatment for leukaemia or bone marrow transplantation, received either fluconazole (FLUC) or amphotericin B (AB). Eight of 16 patients (50%) on FLUC and 21 of 25 patients (84%) on AB defervesced; the mean time to defervescence was 11.0 +/- 10.0 days for FLUC compared to 7.7 +/- 6.3 days for AB, and a similar proportion in each treatment group defervesced within 5 days (50% vs. 52%), respectively. Six of 16 patients (37.5%) on FLUC and three of 25 patients (12%) on AB developed overt invasive fungal disease, including pulmonary aspergillosis (FLUC 4 cases, AB 2 cases) and invasive candidiasis (FLUC 2 cases, AB 0 cases). The mean time to these events was 19.5 +/- 13.4 (FLUC) and 9.0 +/- 3.6 (AB) days. The fungal related mortality rates were higher in the FLUC group: five of 16 patients (31%) vs. two of 25 patients (18%) died respectively; the time to fungal death was 43.2 +/- 18.2 (FLUC) and 25.0 +/- 18.4 (AB) days. This tendency towards a more favourable outcome in patients on AB may have been due to absence of prior fluconazole prophylaxis in patients subsequently receiving IV FLUC. Analysis of a small subgroup of patients who had all received prior prophylaxis with clotrimazole only, indicated that a greater number of patients subsequently receiving IV FLUC died from fungal disease (5/16 vs.0/6, P = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperinfection of strongyloides stercoralis

Strongylodiasis is universal in distribution but is most abundant in countries with a tropical climate. Although infestation by Strongyloides stercoralis is usually limited to the intestines, dessemination of this helminth in debilitated host can be lead to death with various clinical disorders, characterized by profound malabsorption, diarrhea, electrolyte imbalance, gram negative or opportunistic fungal sepsis, coma and death. Cell-mediated immunity contributing significantly to the control of helminthic infections, may be suppressed by carcinoma, immunosuppressive chemotherapy and use of corticosteroids. Diagnosis of Strongyloidiasis is achieved by an examination of samples of feces, duodenal aspirates and sputum of patients for Strongyloides stercoralis. Treatment of strongyloidiasis is twofold: correction of the immunosuppressive state by withdrawal of immunosuppressive drug, if possible, and vigorous treatment with thiabendazole. Testing for strongyloidiasis is especially recommanded before treating a patients should be monitored for infection by Strongyloides stercoralis and other opportunistic infection. We are reporting a case patient with Strongyloides stercoralis hyperinfection and pulmonary tuberculosis who had been used corticosteroid for persisting polyarthritis.

Chemoprophylaxis of Fungal Infections in Granulocytopenic Patients Using Fluconazole vs Oral Amphotericin B

Optimal chemoprophylaxis for fungal infection is not yet well defined. This study evaluates the respective roles of oral amphotericin B and fluconazole in granulocylopenic cancer patients. Fluconazole was better tolerated and had to be discontinued in only 1 of 30 patients compared with 5 of 29 patients receiving amphotericin B. The number of febrile episodes was similar in each group, but the median duration of prophylaxis prior to the first fever episode was longer in patients receiving fluconazole (8 days) than in those receiving amphotericin B (5 days). The number of patients requiring the initiation of intravenous amphotericin B was similar in each group. Documented fungal infections occurred in 4 patients receiving fluconazole and 6 receiving amphotericin B, including 2 patients in each group who developed fungaemia. No invasive candidiasis caused by Candida albicans was observed. Although the overall mortality was similar in each group, there was only one fungal death in the fluconazole group (due to aspergillosis) compared with 3 in the amphotericin B group (due to aspergillosis or trichosporosis).

Infection withFusarium species in two children with neuroblastoma

Two cases of Fusarium infection in children with neuroblastoma are reported. One of the patients had an overwhelming infection and the diagnosis was based on isolation of Fusarium moniliforme from blood and skin biopsy, and histological findings. The second patient developed chronic polyarthritis and Fusarium solani was cultured from synovial fluid samples taken from two different joints four months apart. No histological documentation of infection was obtained. The response to antifungal therapy was unfavourable. Both patients died, but in the second case the relationship between fungal infection and death was not established.

Effect of Fungal Death or Inhibition Induced by Oxycarboxin or Polyoxin D on the Interaction between Resistant or Susceptible Bean Cultivars and the Bean Rust Fungus

Effect of Fungal Death or Inhibition Induced by Oxycarboxin or Polyoxin D on the Interaction between Resistant or Susceptible Bean Cultivars and the Bean Rust Fungus

Indirect Interactions Between Temporally Separated Herbivores Mediated by the Host Plant

I tested the hypothesis that early season herbivory by leaf—chewing insects affects distribution, densities, and survivorship of late—feeding, leaf—mining insects; early chewing may physically and chemically alter quality of leaf miners on the shared host plant, Quercus emoryi. Proportions of intact leaves and leaves damaged by native leaf chewers on six control and six experimental trees were determined over two growing seasons. I manually damaged °50% of leaves on experimental trees to increase the total fraction of damaged leaves to °75%. Leaf—miner densities, distribution, survivorship, and mortality were monitored on control and experimental trees and in intact and damaged leaves within trees. Leaf miners occurred more frequently than expected by chance on intact than damaged leaves for both control and experimental trees. Leaf—miner densities did not differ between control and experimental trees. This result suggests ovipositing leaf miners did not discriminate between damaged and undamaged trees, but selected leaves within trees. More leaf miners survived intact than damaged leaves in both growing seasons. Survivorship was less in damaged leaves because of significantly increased rates of parasitism on these leaves. However, death from other causes (including bacterial and fungal death) was significantly less for leaf miners on damaged leaves. This positive effect did not compensate for overall lower survivorship of leaf miners in damaged leaves due to increased parasitism. Survivorship and mortality did not differ between control and experiment trees when damaged and intact leaves were pooled within treatments. However, in 1982—1983, survival was lower and parasitism greater for leaf miners in control—damaged leaves than experimental—damaged leaves. Survival and parasitism were not different between control—intact and experimental—intact leaves. These result suggest that (1) the effect of early season herbivory on leaf miners was inversely density dependent and, (2) occurrence of leaf miners on intact leaves may be caused by avoidance of damaged leaves rather than preference for intact leaves. Early season herbivory caused localized changes in phytochemistry within trees, and these chemical alterations were consistent with observed distributions and survivorship of leaf miners. Both early season herbivory and experimental damage resulted in higher levels of condensed tannins and lower protein content in damaged leaves within trees, but herbivory had no effect on between—tree chemistry differences. Leaf miner distributions correspond to these localized chemical changes: leaf miners avoided damaged leaves within trees but showed no between—tree preferences. Parasitism of miners on damaged leaves was higher, possibly because parasitoids used physical and chemical changes as cues to locate leaf—miner hosts, or because exposure of leaf miners to parasitoids was prolonged. However, when many leaves were damaged (experimental trees), the negative effect of parasites was mitigated because physical and chemical cues associated with damaged leaves were less effective. Lower leaf—miner mortality from other causes may be related to the bactericidal of fungicidal properties of increased tannins in damaged leaves. This study demonstrates that temporally separated guilds can interact subtly at low levels of herbivory through changes in the host plant. Current theories of within— and between—guild organization of phytophagous insects may need to be re—evaluated if such interactions are common.

Relationship Between Heat-Induced Fungal Death and Plant Necrosis in Compatible and Incompatible Interactions Involving the Bean and Cowpea Rust Fungi

Relationship Between Heat-Induced Fungal Death and Plant Necrosis in Compatible and Incompatible Interactions Involving the Bean and Cowpea Rust Fungi

Light and electron microscope studies of the interactions of host and non-host plants with cowpea rust— Uromyces phaseoli var. vignae

A comparison of infection of host plants and eight non-host angiosperm species by cowpea rust revealed that uredospores usually germinated equally well on hosts and non-hosts. On most of the latter, however, fewer germ tubes contacted stomata, apparently because of the reduced efficiency of directional growth. Compared with both resistant and susceptible host cultivars, at least twice as many hyphae in non-host leaves stopped growing during the very early stages of intercellular development. Nevertheless, the majority of infection hyphae continued to grow to the stage at which the first haustorial mother cell would be expected to form. However, further intercellular growth was rare and few, if any, infection hyphae formed haustoria. Ultrastructural investigation of four non-hosts suggested that haustorium formation could be inhibited by at least three mechanisms: deposition of osmiophilic material on adjacent non-host walls ( Phaseolus spp.), loss of contact between haustorial mother cell and non-host cell ( Vicia faba), or fungal death prior to haustorium initiation ( Pisum sativum). If haustoria were formed, the death of both haustorium and invaded cell rapidly followed although the initial response to the one haustorium observed ultrastructurally resembled that described previously for susceptible interactions. The diversity of cellular responses induced in resistant hosts and non-hosts by cowpea rust, described in this and earlier work, suggests that there are a number of stages during infection at which an interaction between this fungus and the higher plant can take place. It is proposed that each stage represents a “switching point” and that responses at each determine the subsequent progress of infection in both compatible and incompatible associations.