Number Of Germ Tubes Research Articles

The influence of temperature and vapour pressure deficit on conidia germination and germ tube production in an Australian Podosphaera xanthii isolate

Powdery mildew of cucurbits, caused by Podosphaera xanthii, is an economic constraint in cucurbit production worldwide. This study examined the influence of temperature and vapour pressure deficit (VPD) on the rate of conidial germination and the formation of germ tubes in an Australian P. xanthii isolate 12 – 48 h after inoculation. Two experiments were prepared by inoculating cucumber, cv. crystal salad, leaf-discs using a spore settling tower. The first experiment incubated inoculated cucumber leaf-discs at eight temperatures between 8 and 35 °C under saturated vapour pressure (SVP), the second compared 18 VPD conditions between 0.038 and 1.797 kPa, in six humidity chambers (33% – 99% relative humidity) and three temperatures (22 °C, 25 °C, 28 °C). Leaf-discs were cleared, stained and microscopically inspected for conidial germination and the number of germ tubes. The optimal temperature for germination was 28ºC at SVP, where more than 50% of conidia had germinated by 12 h, and 85% by 48 h. Fewer germinated conidia were recorded after 12 h at other temperature treatments between 17 °C and 31 °C. The germination percentage and germination rate were significantly lower when vapour pressure was between 0.13 and 2.5 kPa, with germination in response to VPD varying by approximately 10%, indicating difficulty associating conidial germination to VPD above 0.13 kPa. Germ tube production was highest between 25 ºC and 28 ºC at the lowest VPD treatment at near SVP, with more than 50% of the germinated conidia producing at least three germ tubes. Germination and formation of germ tubes significantly reduced when VPD increased. P. xanthii conidia were able to produce a primary germ tube under relatively dry conditions, such as 2.53 kPa, but these results show infection would be less likely and require longer incubation. This study provides the first crucial step in simulating powdery mildew infections on cucurbit plants and may lead to a model capable of providing risk forecasts or fungicide management decision support tools.

Effect of Legume Extracts on Germination, Seedling Health of Beans (Phaseolus vulgaris L.) and Soil Microorganisms

Application of undecomposed green manure has been reported to cause poor emergence and establishment of common beans in the field. Therefore, to understand the mechanisms’ contributing to the poor crop establishment, the effect of extracts from fresh and decomposed legume green manures on bean seed germination, fungal mycelial growth, spore germination and germ tube elongation were evaluated. The extracts were prepared in either ethanol or distilled water. Data was collected on percentage seed germination, seedling length, mycelial radial growth, spore germination and germ tube elongation. Ethanol extracts from fresh lablab inhibited bean germination by 56%, increased mean germination time to 8 days, and decreased germination index while ethanol extracts of groundnut and beans caused highest inhibition in bean shoot length and reduced biomass. Ethanol extracts from fresh green manures significantly inhibited fungal mycelial growth while the aqueous extracts from beans, groundnuts and soybean had significant level of antifungal activity while aqueous lablab extracts stimulated mycelial. Aqueous extract of lablab and soybean enhanced spore germination by over 70% with more pronounced effect on germ tube length and number of germ tubes by 8.0% and 13% respectively. The study comparatively reveals that the extract of lablab was inhibitory to common bean germination compared to other legume extracts and also stimulated the growth of root rot pathogens that may have resulted in poor establishment of beans.

Fruit maturity and post-harvest environmental conditions influence the pre-penetration stages of Monilinia infections in peaches

Brown rot caused by the fungi Monilinia laxa (Aderhold and Ruhland) Honey, M. fructicola (Winter) Honey, or M. fructigena (Aderhold and Ruhland) is a serious fungal disease of peaches. The fungal infection process begins when fungal conidia germinate on the fruit surface to produce germ tubes and/or appressoria, and the incidence of brown rot increases as fruit approaches maturity. The interaction between the fungal infection process, peach maturity, and the environmental conditions is not well understood. Accordingly, the objectives of this investigation were to investigate germ tube and appressorial formation by M. laxa and M. fructicola when they were exposed to peach skin from mature and immature fruit at various temperatures and relative humidities (RHs). The greatest number of germ tubes was found when M. laxa or M. fructicola was incubated in culture medium which contained a skin extract of mature peaches. In contrast, the greatest number of appressoria was found when M. laxa or M. fructicola was incubated in culture medium which contained a skin extract of immature peaches. Although M. fructicola produced the same number of germ tubes and appressoria at 4°C, M. fructicola produced more germ tubes than appressoria at temperatures higher than 10°C. M. laxa produced more germ tubes than appressoria at any temperature, except when it was incubated for 48h on culture medium which contained a skin extract of immature peaches at 10°C at 80% or 100% RH, or at 25°C at 60% RH. M. laxa conidia germinated better than M. fructicola conidia at low temperatures. Germ tube and appressorial formation by Monilinia spp. were influenced by fruit postharvest handling. The number of germ tubes that were formed by M. laxa conidia was significantly greater than that for M. fructicola when the conidia were incubated at 100% RH, and this number increased after 3days of refrigeration. The number of appressoria that were formed by both Monilinia spp. also increased after 3 consecutive days of refrigeration. Negligible or no germination of M. fructicola and M. laxa conidia occurred when the RH was 60%. We concluded that the dissimilar abilities of M. laxa and M. fructicola to germinate and form appressoria at low temperatures conferred a competitive advantage to M. laxa to survive during fruit postharvest refrigeration and cold storage at 4°C.

Identification and Characterization of Three Monilinia Species from Plum in China.

In total, 112 Monilinia spp. single-spore isolates were collected from plum fruit (Prunus salicina) symptomatic for brown rot disease from Yunnan, Hubei, and Zhejiang provinces and Chongqing municipality, China between 2012 and 2014. Three distinct colony morphologies (phenotypes) were observed on potato dextrose agar and two isolates per phenotype were selected for further analysis. Colony color, colony shape, conidia size, number of germ tubes per conidia, and pathogenicity on plum were investigated. The ribosomal internal transcribed spacer regions 1 and 2 as well as a polymerase chain reaction-based method that amplified fragments of the glyceraldehyde-3-phosphate dehydrogenase (G3PDH) and β-tubulin (TUB2) genes were used to identify the isolates to the species level. The three phenotypes were identified to be three different species: Monilinia fructicola, Monilia mumecola, and Monilia yunnanensis. Phylogenetic analysis based on G3PDH and TUB2 nucleotide sequences revealed that isolates within species clustered together regardless of host or geographical origin, suggesting that these factors did not play an important role for the evolutionary separation of the described species.

Histologische Aspekte der Resistenz von Cucumis melo PI 313970 gegenüber Podosphaera xanthii und Golovinomyces cichoracearum

Cucumis melo accession PI 313970 possesses numerous genes for race-specific resistance to powdery mildew incited by Podosphaera xanthii. It also exhibits resistant blister (RB) leaf reactions, characteristic for non-race-specificity, to several races of P. xanthii in California, U.S.A. Microscopic examination confirmed the presence of mycelia, conidiophores and conidia, and limited number of necrotic cells within and limited to RB tissue. PI 313970 was susceptible to inoculation with Czech isolates of P. xanthii and Golovinomyces cichoracearum on leaf discs. Frequency of conidial germination did not differ between pathogen species, or between PI 313970 and the susceptible cucumber cv. ‘Stela’ control, but number of germ tubes and appressoria, mycelial growth and conidial production of both pathogens through 144 hours post-inoculation were reduced in comparison with the susceptible control. Hypersensitive responses (HR) were not observed in ‘Stela’, but occurred to a limited extent in PI 313970 where = 3% of examined sites had necrotic spots. These responses indicate two different resistance mechanisms to these powdery mildew isolates in PI 313970. The first mechanism targets conidial germination and appressoria formation. The second mechanism reduces pathogen growth and reproduction with minimal or no HR involvement and may be influenced by the first mechanism. Resistant blisters, observed only on intact leaves evidence a third and non-race-specific mechanism to P. xanthii and G.cichoracearum in PI 313970, based on our histological study.

Virulence of extracellular phospholipase B of Candida albicans in rabbit experimental keratomycosis

To determine the virulence of extracellular phospholipase B (PLB) of Candida albicans in experimental keratomycosis. It was an experimental study. The PLB-deficient mutant strain of Candida albicans and its isogenic parental strain were used in this study. The effects of these two strains on the model of experimental keratomycosis in 48 New Zealand albino rabbits covered with contact lens was compared by observing the dynamic changes clinically and histopathologically. In vitro, these two strains were incubated with the corneal stromal cells separately (37 degrees C, 5% CO2). The influence of these two strains on monolayer keratocytes were detected by scanning electron microscopy (SEM), enzyme linked immunosorbent assay (ELISA), and flow cytometry with Annexin V/propidium iodide. The hyphae of these two strains grew perpendicularly to the corneal stromal lamellae. The difference of the hyphal invasion inoculated for 2 days by these two isogenic strains was statistically significant (P = 0.002), but at other intervals, no significant difference was found. The severity of the inflammation in parental keratomycosis was the same as that in PLB null strain at any time points (P > 0.05). Under SEM, the morphogenesis and the number of adherent germ tubes of these two isogenic strains appeared similarly (P > 0.05), but the number of germ tubes penetrating cell monolayer was significantly different (P = 0.009). Obviously more prostaglandin E2 (PGE2) was detected in the culture supernatants of parental strain group (65,466 +/- 5773) pg/ml than that of the null strain group (18,025 +/- 5232) pg/ml. The percentages of the cells with damaged cellular membrane in the parental group, the PLB null group and the control group, were 3.02%, 2.04% and 0.12%, respectively. The percentages of apoptosis cells in these three groups were 33.17%, 27.56% and 1.46%, respectively. The percentages of living cells were 63.81%, 70.40% and 98.41%, respectively. PLB shows virulent effects in triggering fungal invasion in cornea immediately following fungal adherence by decomposing membrane phospholipids and leading to cell lysis. However, its virulent effect does not appear to be critical as in the hematogenous model of disseminated candidiasis.

Nod factor induces soybean resistance to powdery mildew

Plants possess highly sensitive perception systems by which microbial signal molecules are recognized. In the Bradyrhizobium-soybean ( Glycine max (L.) Merr.) symbiosis, recognition is initiated through exchange of signal molecules, generally flavonoids from soybean and lipo-chitooligosaccharides (Nod factors) from the microsymbiont. Application of the Nod factor Nod Bj-V (C 18:1, MeFuc) induced soybean resistance to powdery mildew caused by Microsphaera diffusa. Addition of Nod factor (concentrations ranging from 10 −6 to 10 −10 M) to soybean root systems led to reductions in disease incidence. The lowest disease incidence was caused by Nod factor treatment at 10 −6 M. The effect of Nod factor application on fungal growth and development was measured at 4, 12, 48, and 96 h after inoculation. Colony diameter and number of germ tubes per conidium were decreased by 10 −6 M Nod factor. Phenylalanine ammonia lyase (PAL, EC.4.3.1.1.) is the first enzyme of the phenyl propanoid pathway, and is commonly activated as part of plant responses to disease. Treatment of soybean seedlings with Nod factor, through stem wounds, induced PAL activity; the most rapid increase followed treatment with 10 −6 M Nod factor. These data show that soybean plants are able to detect root applied LCO and respond by increased disease resistance.

Delineation of the three brown rot fungi of fruit crops (Monilinia spp.) on the basis of quantitative characteristics

The three Monilinia spp., known as the brown rot fungi of fruit crops, are usually distinguished from each other on the basis of (qualitative) colony characteristics. We linked these qualitative features to unambiguously defined, quantitative colony and germ tube characteristics. A wide collection of isolates of Monilinia fructicola (Winter) Honey, Monilinia laxa (Aderhold & Ruhland) Honey, and Monilinia fructigena (Aderhold & Ruhland) Honey was used to determine growth rate and sporulation intensity on potato dextrose agar (PDA) at 22°C under two light regimes (darkness, 12 h light : 12 h dark). The following germ tube characteristics were determined on water agar after incubation for 18 h at 22°C in darkness: length of the (leading) germ tube, distance to the first branch, and the number of germ tubes per conidium. Increase in colony diameter from day 3 to day 5 and sporulation intensity measured after 14 days was the highest in M. fructicola, whilst M. laxa and M. fructigena showed considerable overlap in these features. The length of the germ tube after 18 h incubation was shortest in M. laxa, ranging from 161 to 466 µm. In M. fructicola and M. fructigena these ranges were 465-851 and 307-806 µm, respectively. The occurrence of more than one germ tube per conidium was most prominent in M. fructigena. Discriminant analysis on the basis of different combinations of the quantitative characteristics measured, showed that the combination of growth rate on PDA and length of the germ tube was sufficient to delineate the three brown rot fungi. One of 11 M. fructicola isolates was misclassified, the same held for M. fructigena (one misclassification of nine isolates). No misclassifications occurred in M. laxa.Key words: brown rot fungi, growth characteristics, Monilinia spp., taxonomy.

Structural changes induced by glycine on Streptomyces antibioticus.

Germination and vegetative growth of Streptomyces antibioticus in liquid medium with different concentrations of glycine was examined. Both processes proved to be sensitive to the amino acid, being inhibited by 5 and 2.5% glycine, respectively. At concentrations of 5% or more, lysis of the vegetative mycelium occurred. Subinhibitory concentrations of glycine induced structural changes on germinating spores. These included an increase in the number of germ tubes produced by spore, in relation to the control. Moreover, soon after outgrowth the tubes bifurcate, giving rise to germinated spores with a characteristic aspect, and anomalous formation of cross-walls that appear both within the spores and in the newly formed germinative tubes, at or close to the region of outgrowth. The branching effect of glycine was also observed during vegetative growth of S. antibioticus.

Effects of ozone exposure and leaf age of wheat on infection processes of Septoria nodorum Berk.

The infection process of Septoria nodorum was studied on the flag and second leaves of wheat plants at the flag‐leaf emergence growth stage (GS 39), after pre‐inoculative fumigation with different doses of ozone (0, 80, 180 or 240 μg/m3) for 7 h daily over 7 days. On ozone‐treated plants, formation of appressoria occurred earlier, leading to a greater number and density of appressoria and faster growth of superficial infection hyphae than on plants grown without ozone amendment. Additionally, on leaves treated with 180 and 240 μg/m3 ozone, the percentage of papillae per appressorium was only half that on control plants. The number of germ tubes per conidium was not significantly affected by any treatment. Effects of increasing leaf age on the infection process were similar to those obtained with ozone. These results provide further evidence for similarities in the physiological effects of ozone and leaf ageing, which support the hypothesis that disease alterations due to ozone are strongly determined by the senescing effects of the pollutant.

Effect of prism generated discreet wavelengths of light on germination and post-germination development of Colletotrichum dematium var circinans (Berk.) v. Arx

Spores, harvested from 8 da old colonies ofColletotrichum dematium varcircinans (Berk.) v. Arx, were placed on slides under shimmed coverslips and subjected to 10 min irradiation with wavelengths of light ranging from 400 to 750 nm. Controls consisted of spores exposed to 10 min of fluorescent or tungsten light, or to continuous dark. Germination, and production of sessile and non-sessile appressoria, and germ-tubes was monitored. In addition position of germ-tubes on spores was noted and germination types were classified by numbers of germ-tubes and sessile and non-sessile appressoria produced. When compared to dark controls certain wavelengths, 400, 450, 600 and 650 nm, appeared to be inhibitory to germination and post-germination development, while others, 500, 550 and 750 nm, appeared to be stimulatory. Spores irradiated with some of the wavelengths (550, 700, 750 nm) that affected other responses produced the smallest percentage of sessile appressoria (approx. 10%). Placement of germ-tubes was not affected by treatment. More germ-tubes were produced from spore bottoms (53%) than tops (32%), and tips (15%). The fewest number of germ-tubes was produced from spore centers and from one tip. Thirteen germination types were noted. About 53% of spores germinated with one germ-tube, one non-sessile appressoria, and no sessile appressoria. The remaining 47% were distributed throughout the remaining 12 types, and ranged from 21% to less than 1% of the total. Treatments did not affect this distribution.

Banana black leaf streak disease ( Mycosphaerella fijiensis) in Western Samoa

The morphology of M. fijiensis and the pattern of sympton development in Western Samoa was similar to that found elsewhere. Rain, as little as 0.25 mm, was more important than dew in releasing ascospores of M. fijiensis from leaf tissue. In the laboratory ascospore release started within 10–15 min of wetting leaves and most spores were discharged within 3 h. When leaves were wetted on successive days more spores were released but the effect on total spore production was not determined. The midrib spotting infection pattern appeared to be caused by ascospore infections and could be simulated under defined conditions by weedkiller sprays. The tip spotting pattern found on most leaves in Samoan banana plantations indicated that ascospores were the major source of inoculum. Percentage germination, germ-tube growth, number of germ tubes and location of germ tubes on both ascospores and conidia were significantly affected by temperature, type of substrate and moisture.

Effect on germination and post-germination development of Colletotrichum dematium var circinans due to light and dark incubation and coverslip placement

Light regime was not a major factor in germination of spores of Colletotrichum dematium var circinans. Number of germ-tubes and appressoria formed were affected by incubation regime and coverslip placement. Most germ-tubes and appressoria were produced on spores under shimmed coverslips. Light incubation favored germ-tube production and dark incubation favored appressoria production. Predicted time to 100% germination was affected by treatments. Shortest times were predicted for light incubated spores under shimmed coverslips. Longest times were predicted for non-coverslipped spores. A significant number of appressoria were produced sessile on spores. Most sessile appressoria were produced on dark incubated spores. Approximately 56 % of all spores germinated, and approximately 60% of all germ-tubes and appressoria were produced on these spores which were situated closest to coverslip or droplet edges. Placement of germ-tubes on spores was not affected by treatments. However, percentages of germ-tubes, initiated from various areas of spores, were significantly different. This variation appears to be due to factors internal to spores.

Germinability of sclerotia of Macrophomina phaseolina

The germination of sclerotia of Macrophomina phaseolina from 3- to 20-day-old PDA cultures incubated at 32 °C and 24 °C varied from 98 to 25% and 75 to 30%, respectively. Germinability of sclerotia from cultures of all ages tested was rapidly lost during storage in desiccators for 24 h at 6 °C or in screw-top vials at room temperature for 30 days. Germination of sclerotia stored in screw-top vials at 6 °C for 30 days declined less rapidly. There was a linear relationship between the size of the sclerotium and the number of germ tubes emerging from it. The role of sclerotium size in survival and what factors may be responsible for loss of germinability with increasing age of source culture are discussed.

Effects of osmotic potential on germination of microsclerotia and growth of colonies of Verticillium dahliae

The influence of available water, expressed as osmotic potential (ψs), on germination of microsclerotia (MS) and expansion of colonies of Verticillium dahliae was studied in osmotically adjusted aqueous and agar media. In distilled water (ψs = 0 bar) at 25 °C, 64–70% of MS germinated within 36 h and the mean number of germ tubes per germinated MS (germination vigour) was 4.7. In aqueous solutions of KCl or NaCl percentage germination and germination vigour were increasingly inhibited as ψs was lowered, reaching 50% inhibition at −11 to −14 bar and 100% inhibition at < −98 bar. In aqueous sucrose solutions germination percentage and vigour were significantly higher (P = 0.05) than in salt solutions; maximum activity occurred at −4 bar, 50% inhibition occurred at −40 bar, and 100% inhibition occurred at < −114 bar. On corn meal dextrose agar (CMDA) amended with KCl, percentage germination at 25 °C was maximal at −9 bar, was reduced 50% at −40 bar, and was 0 at −90 bar. For a given ψs, germination percentages at 25 and 30 °C were significantly greater than at 20 and 15 °C. No germination occurred at 4 or 35 °C. Where ψs was adjusted with KCl, agar media were less inhibitory to germination than aqueous media between 0 and −50 bar. On CMDA media amended with KCl, colony expansion was progressively faster as ψs was lowered from −1.1 to −13 bar, then progressively slower as ψs was lowered further. Rates of colony expansion at 20 and 25 °C were significantly greater than at 4, 15 and 30 °C. At 25 °C growth was reduced 50% at −49 bar and was completely suppressed at −119 bar.

ROOT EXUDATES FROM RED PINE SEEDLINGS AND THEIR EFFECTS ON PYTHIUM ULTIMUM

The role of root exudates in interaction between pine roots (Pinus resinosa Ait.) and Pythium ultimum Trow was studied. By paper chromatographic methods three sugars and 13 amino acids were definitely identified in the root exudate. Gamma amino butyric acid was most abundant, although asparagine, glycine, serine, and alanine were also present in large amounts. Valine, leucine, glutamine, aspartic acid, glutamic acid and proline were detected in smaller quantities. Among the sugars, both glucose and fructose were abundant while traces of arabinose were detected. When supplied singly, all amino acids and sugars except serine, leucine and arabinose, stimulated growth of the pathogen and germination of sporangia. Mixtures of sugars or mixtures of three or four amino acids were very effective in stimulating mycelial growth and development of germ tubes. The kind of nutrient influenced the number of germ tubes per sporangium. Favorable nutrient combinations, viz. mixtures of sugars, mixtures of three or four amino acids or root exudate solution, produced two to nine germ tubes, while unfavorable ones, viz., glycine, arabinose and serine, etc., produced one or two germ tubes.