Maintaining cultures of ectomycorrhizal and plant pathogenic fungi in sterile water cold storage.

Mycelial cultures of 64 isolates of 14 species of ectomycorrhizal fungi and 27 isolates of 15 species of plant pathogenic fungi were grown on agar medium in Petri dishes. Mycelial discs, 8 mm in diameter, were removed from the cultures and stored in sterile distilled water in test tubes at 5 degrees C. Sixty-four, 61, and 41 isolates of the symbiotic fungi were viable after 1, 2, and 3 years storage respectively. Only 19, 10, and 8 isolates of the pathogenic fungi were viable after 1, 2, and 3 years storage, respectively. Time in pure culture before water storage did not affect viability of any fungal species following water storage. After 3 years storage, four fungi (three symbionts and one pathogen) were tested and found to have retained their original growth rates and root-infecting abilities on pine seedlings. The same four isolates, however, maintained on agar slants at 5 degrees C and subcultured every 4 to 6 months, grew slower and did not infect as many feeder roots of pine as the water-stored isolates.     

AN IMPROVED METHOD FOR OBTAINING AXENIC CLONES OF PLANKTONIC BLUE-GREEN ALGAE1,2

Axenic clones from 5 isolates of Anabaena flosaquae, 1 isolate of Microcystis acruginosa, and 1 isolate of Aphanizomenon flos-aquae were obtained by a combination of steps that provided a 1000-fold reduction in the bacteria-algae ratio and permitted bacteria-free filaments or cells to be isolated and grown from agar pour plates. The first step consisted of the addition of phenol to a dark-treated culture to selectively reduce the numbers of actively growing bacteria while leaving the resting algal cells viable. The next steps involved washing the treated algal suspension on a Millipore filter pad or membrane followed by plating in washed agar containing buffered mineral medium plus vitamins and soil extract. The final steps consisted of incubating the agar pour plates, coring bacteria-free filaments or cells, culturing the agar cores in a buffered mineral medium, and rigorously testing the resulting cultures for bacteriological contamination. Between 50 and 90% of the cores grew, and of these about 50% were judged axenic. The method, with appropriate adaptations, should be suitable for obtaining axenic clones of other freshwater and marine algae.     

Examination of Potential Virulence Factors of <Emphasis Type="Italic">Candida tropicalis</Emphasis> Clinical Isolates From Hospitalized Patients

Candida tropicalis has been reported to be one of the Candida species which is most likely to cause bloodstream and urinary tract infections in hospitalized patients. Accordingly, the aim of this study was to characterize the virulence of C. tropicalis by assessing antifungal susceptibility and comparing the expression of several virulence factors. This study was conducted with seven isolates of C. tropicalis from urine and blood cultures and from central venous catheter. C. tropicalis ATCC 750 was used as reference strain. Yeasts adhered (2 h) to epithelial cells and silicone and 24 h biofilm biomass were determined by crystal violet staining. Pseudohyphae formation ability was determined after growth in fetal bovine serum. Enzymes production (hemolysins, proteases, phospholipases) was assessed by halo formation on agar plates. Susceptibility to antifungal agents was determined by E-test. Regarding adhesion, it can be highlighted that C. tropicalis strains adhered significantly more to epithelium than to silicone. Furthermore, all C. tropicalis strains were able to form biofilms and to express total hemolytic activity. However, protease was only produced by two isolates from urine and by the isolates from catheter and blood. Moreover, only one C. tropicalis (from catheter) was phospholipase positive. All isolates were susceptible to voriconazole, fluconazole and amphotericin B. Four strains were susceptible-dose dependent to itraconazole and one clinical isolate was found to be resistant.     

Studies in the differentiation between Microsporum ferrugineum Ota and Trichophyton soudanense Joyeux

A study, conducted with 20 isolates of Microsporum ferrugineum and 12 isolates of Trichophyton soudanense, revealed that some of the discrepancies in the literature regarding their characteristics and differentiation were due to methodology, strain variation and the use of an insufficient number of isolates. We found all isolates of T. soudanense to be urease negative and gelatinase positive (usually by the first week); to produce brown to black colonies on Lowenstein-Jensen medium; to rapidly decompose casein and more slowly tyrosine; to grow well or better at 37°C as compared to room temperature; to produce reflexive branching on cornmeal Tween agar and abundant microconidia on casero medium and to exhibit no sexual reaction with either mating type of Arthroderma simii. All but one isolate demonstrated restricted growth on lactose agar and only three isolates perforated hair.In contrast, we found 18 of 20 isolates of M. ferrugineum to be urease positive in urea broth (most isolates were negative on urea agar); all produced light-colored colonies on Lowenstein-Jensen medium; spreading colonies on lactose agar and failed to perforate hair in vitro or to produce reflexive branching. Most isolates manifested poorer to no growth at 37°C compared to room temperature and all but one failed to decompose casein and tyrosine. A few strains produced macroconidia and/ or microconidia on casero medium and some reacted sexually with A. simii (a) or (–) mating type. Gelatin hydrolysis was variable.We suggest the following key tests to differentiate M. ferrugineum from T. soudanense: urease activity in urea broth; colony color on Lowenstein-Jensen medium; growth on lactose agar; growth at 37° C compared to room temperature; presence of reflexive branching on cornmeal Tween agar.     

Identification and characterization of Francisella species from natural warm springs in Utah, USA

Aims: To characterize Francisella isolated from two natural warm springs in Utah and compare them to a strain isolated from a patient with probable exposure to one of the springs in 2001. Methods and Results: A total of 39 presumptive Francisella isolates were obtained from two springs, Wasatch Hot Spring and Hobo Warm Spring, just north of Salt Lake City, Utah. All isolates were characterized by a combination of biochemical and molecular analyses, including novel PCR/electrospray ionization‐mass spectrometry (ESI‐MS) typing assays. Thirty‐one were identified as F. philomiragia, while the remaining eight were identified as F. tularensis ssp. novicida. Phylogenetic analysis of the 16S rRNA sequences revealed 27 isolates, which clustered with F. philomiragia, albeit into two distinct clades. The remaining isolates clustered along with other F. tularensis strains including the Utah clinical isolate. Testing with the PCR/ESI‐MS assays confirmed the identities of the isolates, but both yielded DNA signatures distinct from that of the clinical isolate. Conclusion: We were successful in isolating several Francisella strains from natural warm springs; however, none appeared to genetically match the original 2001 clinical isolate. Significance and Impact of the Study: This work highlights the presence of viable, potentially pathogenic Franscisella species living in the unique environmental niche of natural warm springs.     

Trichoderma harzianum and its Metabolite 6-Pentyl-alpha-pyrone Suppress Fusaric Acid Produced by Fusarium moniliforme

The interaction of the pathogen Fusarium moniliforme and two antagonistic Trichoderma harzianum isolates was studied especially with respect to their secondary metabolites fusaric acid (FA) and 6‐pentyl‐alpha‐pyrone (6PAP). Among 10 isolates of F. moniliforme screened for FA production on maize kernels, the isolate 8 accumulated the highest amount of FA (678 μg/g). Mycelial growth and production of FA by isolate 8, determined in different liquid media revealed that the highest biomass and FA were produced in Czapek Dox Broth (CDB) followed by Richard’s solution. The amount of FA per gram mycelial dry weight reached its maximum in CDB and Richard’s solution after 14 days of incubation. Mycelial growth and conidia production of both Trichoderma isolates (T16 and T23) were retarded by increasing concentrations of FA in agar medium. At FA concentration of 300 mg/ml the radial mycelial growth of the isolates T16 and T23 were retarded by 32.5% and 45%, respectively. Conidia production was diminished in a similar extent as mycelial growth. Both T. harzianum isolates were capable to degrade FA in potato dextrose broth medium, particularly when lower doses of FA were present. In the presence of 50 mg/ml FA in the culture medium, the isolates T23 and T16 reduced FA by 51.4% and 88.4%, respectively, 9 days post‐inoculation. The antifungal metabolite 6PAP, isolated from T. harzianum T23 cultures, was introduced at different concentrations into 2‐day‐old cultures of F. moniliforme. After further 5 days of incubation of F. moniliforme in the presence of 6PAP, the FA contents per gram mycelial dry weight were significantly decreased compared to control cultures where 6PAP was absent. Dosages of 300 and 400 mg/l of 6PAP in the cultures retarded FA accumulations by 62.5% and 77.2%, respectively. The current results, however, provided the first evidence for activity of 6PAP, as a Trichoderma secondary metabolite, on degrading/synthesis suppression of the Fusarium toxin FA.     

Mating behaviour of Microsporum equinum with Nannizzia otae

Twelve isolates of Microsporum equinum and nine monoascospore cultures of Nannizzia otae were studied on Sabouraud dextrose agar, polished rice grain, and on Pablum cereal agar for their gross morphology and micromorphology. The urease activity of each isolate was determined on Christensen's urea broth, and the in vitro hair perforation test was performed according to Ajello and Georg's technique. The 12 M. equinum isolates were paired with nine tester strains of N. otae (108 crosses) and with five M. canis isolates that were nonfertile with N. otae (60 crosses). The M. equinum isolates were also paired with each other in all possible combinations (78 crosses) on soil-hair medium, Pablum cereal agar, and oatmeal salts agar.Whereas most of the macroconidia produced by the M. equinum isolates were smaller than those of N. otae, some were in the size range of the latter species. Both species hydrolyzed urea within 8 to 14 days. Although N. otae isolates perforated hair consistently, none of the M. equinum isolates perforated hair in vitro. The crosses between N. otae and M. equinum cultures, between isolates of M. canis (that were incompatible with N. otae) and the isolates of M. equinum, and between M. equinum isolates among themselves were nonreactive. These differences strongly support the view that M. equinum is a distinct species and should not be treated as a synonym of M. canis (N. otae).     

Cultural, morphological, pathogenic and molecular variability amongst tomato isolates of Alternaria solani in India

Early blight (Alternaria solani) is an important disease causing severe damage in tomato. The eleven isolates of A. solani designated as So, Dh, Sh, Va-5, Ka, Ma, Hy, Ba-1, My, Va-3 and Mi were collected from different agroclimatic conditions and these isolates were characterized for cultural, morphological, pathogenic and molecular variations. The pigmentation varied from yellow, brown, black, brownish to greenish black in isolates of A. solani on potato dextrose agar medium. In general, radial growth of all isolates ranged between 14.9 mm and 32.2 mm on PDA and 24.3 mm to 53.7 mm on three selective media i.e., ASM, V-8 juice agar and V-8 juice agar (synthetic) on the fourth day. The fastest radial growth was recorded in the So isolate and slowest in the Ka isolate on PDA, while isolates Dh, Ba-1 and Va-3 were recorded to be faster in growth on ASM, V-8 juice agar and V-8 juice agar (synthetic) medium. The thickness of conidiogenous hyphae varied between 1.17 μ and 9.56 μ, with maximum in the Va-5 and Ma isolates. Most of the isolates showed smooth mycelial growth with circular and irregular margin and without concentric zonation. Sporulation was not found in any of the isolates on four different nutrient media, whereas conidiogenous hyphal length was observed in V-8 juice agar medium only. Based on the pathogenicity, isolates of A. solani were rated as virulent or less virulent based on percentage disease incidence data. Molecular variability studies were also done to find out the best annealing temperature and eighty-six primers were screened to select for maximum polymorphism of DNA. The best annealing temperature was recorded between 32.5 °C and 34.0 °C for the pathogen, and most efficient amplification and polymorphism of DNA was found with random primer 5′-CGCGTTCCTG-3′.     

Biocontrol activity of salt tolerant Streptomyces isolates against phytopathogens causing root rot of sugar beet

Biological control of fungi causing root rot on sugar beet by native Streptomyces isolates (C and S2) was evaluated in this study. The dry weight and colony forming unit (CFU) of S2 and C increased when 300 mM NaCl was added to medium. The in vitro antagonism assays showed that both isolates had inhibitory effect against Rhizoctonia solani AG-2, Fusarium solani and Phytophthora drechsleri. In dual culture, Streptomyces isolate C inhibited mycelial growth of R. solani, F. solani and P. drechsleri 45%, 53% and 26%, respectively. NaCl treatment of medium increased biocontrol activity of soluble and volatile compounds of isolate C and S2. After salt treatment, growth inhibition of R. solani, F. solani and P. drechsleri by isolate C increased up to 59%, 70% and 79%, respectively. To elucidate the mode of antagonism, protease, chitinase, beta glucanase, cellulase, lipase and α-amylase activity and siderophore and salicylic acid (SA) production were evaluated. Both isolates showed protease, chitinase and α-amylase activity. Also, biosynthesis of siderophore was detectable for both isolates. Production of siderophore and activity of protease and α-amylase increased after adding salt for both isolates. In contrast, chitinase activity decreased significantly. Production of SA, beta glucanase and lipase by isolate S2 and biosynthesis of cellulase by isolate C were observed in presence and absence of NaCl. Soil treatment with Streptomyces isolate C inhibited root rot of sugar beet caused by P. drechsleri, R. solani and F. solani. Results of this study showed that these two Streptomyces isolates had potential to be utilized as biocontrol agent against fungal diseases especially in saline soils.     

Phenotypic characteristics of root-nodulating bacteria isolated from Acacia spp. grown in Libya

Thirty isolates of root-nodulating bacteria obtained from Acacia cyanophylla, A. karroo, A. cyclops, A. tortilis (subsp.raddiana), Faidherbia albida and Acacia sp., grown in different regions of Libya, were studied by performing numerical analysis of 104 characteristics. Three fast- and one slow-growing reference strains from herbaceous and woody legumes were included. Five distinct clusters were formed. The fast-growing reference strains were separated from the isolates whereas the slow-growing was included in cluster 4. With the exception of one cluster, the majority of clusters were formed regardless of the host plant or site of origin. Based on plant tests, generation times, acid production and carbon utilization the isolates were diverse (fast and slow-growing isolates). Like slow-growing isolates, most of the fast-growing isolates appeared to be non-specific, nodulated many species from the same genus notably F. albida, known to nodulate only with slow-growing strains. Most clusters grew at temperatures 35 °C and 37 °C; some grew at temperatures above 40 °C. The majority of isolates grew at acid and alkaline pH and only one isolate grew below pH 4. Most isolates were able to utilize many amino acids as nitrogen sources and to reduce nitrate. Urea was hydrolysed by all clusters. Monosaccharides and polyols were used by slow and fast-growing isolates as the only carbon sources whereas assimilation of disaccharides varied: Some isolates, like slow-growing isolates, failed to utilize these carbon sources. Most isolates were unable to utilize polysaccharides. Regarding tolerance to NaCl on agar medium, the majority of isolates were unable to grow at a concentration of 2% NaCl, but some were highly resistant and there was one isolate which grew at 8% NaCl. Most isolates were resistant to heavy metals and to antibiotics.     

Mycotoxins produced by toxic Fusarium isolates obtained from agricultural and nonagricultural areas (Arctic) of Norway

Twenty-five isolates of F. acuminatum, 38 of F. avenaceum, 1 of F. culmorum, 31 of F. oxysporum and 56 of F. sambucinum were obtained in 1983, 1984 and 1986 from cereal grains and soil from various parts of Norway. The isolates were grown on an autoclaved Uncle Ben's parboiled rice medium and examined for production of trichothecenes and other toxins and for toxicity in rat feeding tests. F. culmorum N46C(2) and Fusarium sambucinum 45-86-A produced zearalenone (F-2) 864 and 665 ppm, respectively and caused uterine enlargement in rats. Most of these isolates produced no known trichothecene mycotoxins that could account for the toxicity that was demonstrated in the rat feeding tests. All but F. avenaceum N26B produced fusarin C (1.5 ppm) but caused no toxic effects in rat feeding test. None of the isolates produced fusarochromanone (TDP-1). Thirteen isolates of F. acuminatum, 16 of F. avenaceum, 14 of F. oxysporum and 3 of F. sambucinum produced a cytotoxic factor which we named HM-8. One isolate of F. avenaceum, 12 of F. oxysporum and 46 of F. sambucinum produced a hemorrhagic factor which we named H-1 (wortmannin). Twenty isolates of F. acuminatum, 22 of F. avenaceum, 17 of F. oxysporum and 1 of F. sambucinum produced moniliformin. Four isolates of F. acuminatum, 9 of F. avenaceum, 25 of F. oxysporum and 52 of F. sambucinum caused death to rats. Three isolates of F. avenaceum, 19 of F. oxysporum and 47 of F. sambucinum induced hemorrhage in various organs. All isolates caused decreased weight gain, relative to the control diets.     

Wheat-infectingFusarium species in Poland — their chemotypes and frequencies revealed by PCR assay

ThreeFusarium species:F. graminearum, F. culmorum andF. cerealis were identified in laboratory cultures and in sporodochia from spikelets of scabby wheat. SCAR (sequence characterized amplified region) primers were used to identifyFusarium species and nivalenol (NIV) and deoxynivalenol (DON) chemotypes within species in laboratory cultures and field collected heads harvested in 2006. Results from PCR analyses confirmed preliminary identifications of species on the basis of examination of macroconidia under a light microscope and identification of cultures on agar media. NIV and DON (3Ac-DON and 15Ac-DON) chemotypes were identified using PCR assay. Among samples and isolates ofF. graminearum, the 15Ac-DON chemotype dominated, and among those whereF. culmorum was identified, the 3Ac-DON chemotype prevailed. Only 5 of the 41 isolates ofF. graminearum tested, displayed the NIV chemotype. An increase in the frequency ofF. graminearum and a decrease in the frequency ofF. culmorum were found during 1998 to 2006.     

Chemical and physiological characterization of taxa in theFusarium sambucinum complex

Forty-one isolates ofFusarium sambucinum sensu lato were screened for production of secondary metabolites in agar cultures. Of 16 strains ofF. sambucinum sensu stricto all but two strains produced diacetoxyscirpenol and two unidentified metabolites, TB1 and TB2 respectively. The two remainingF. sambucinum strains produced T-2 toxin, TB1 and TB2.Fusarium venenotum (6 strains) produced diacetoxyscirpenol and an unidentified metabolite BB.Fusarium torulosum (8 strains) produced wortmannin and antibiotic Y. The three species could be differentiated by their pattern of identified and unidentified metabolites detected by agar plug TLC combined with chemical data from HPLC-diode array detection of fungal extracts, and data on growth rates on potato sucrose agar and tannin sucrose agar.     

The Selection of an Isolate of the Hyphomycete Fungus,Metarhizium anisopliae,for Control of Termites in Australia

Ninety-three isolates ofMetarhizium anisopliae,mostly derived from a survey of termite material, were screened for activity againstNasutitermes exitiosusandCoptotermes frenchiorC. acinaciformisusing a grooming assay technique. Twenty-six of the most promising isolates were further evaluated by bioassay againstN. exitiosusandC. acinaciformis.All isolates were pathogenic withCoptotermesspp. being more susceptible thanN. exitiosus.A group of nine isolates, chosen for their level of pathogenicity for one or other genus of termites and to represent a genetically diverse group, was finally compared in a minicolony test using termite colonies in 1 liter jars. The isolate, code-named FI-610 (derived from nest-mound material ofC. lacteusin SE New South Wales), was one of the most effective isolates against termites from both of the two colonies tested. This isolate also grew relatively well on agar plates at 36°C. FI-610 was thus selected for field trials and was found to be effective in killing colonies ofC. acinaciformiswhen 10 g (=3 × 10¹¹conidia) or more of conidial powder was blown into the center of the large mound colonies.     

Cultural and physiological characteristics of Stemphylium lycopersici causing leaf blight disease on vegetable crops

During 2011–2012, an extensive leaf spot disease caused by Stemphylium lycopersici was observed on vegetable crops including, tomato, eggplant, pepper and lettuce in major vegetable-growing regions of Malaysia. Four isolates of S. lycopersici obtained from each vegetable crop were used to determine cultural and physiological characteristics. The variations were found in colony colour (pale to light grey or light as well as the brown), texture (cottony or mycelium flat), shape (regular with concentric growth rings or irregular) and pigmentation (yellow or deep red) of the cultures. The optimum temperature for the conidial germination and mean radial growth of the isolates was 25?°C, and the radial growth of the isolates was maximal on V-8 juice agar followed by potato carrot agar. The maximum sporulation of S. lycopersici isolates was observed on V-8 juice agar media under 12/12 h light/darkness photoperiod at 25?°C.     

Guttation droplets of <Emphasis Type="Italic">Penicillium nordicum</Emphasis> and <Emphasis Type="Italic">Penicillium verrucosum</Emphasis> contain high concentrations of the mycotoxins ochratoxin A and B

Eight of eleven ochratoxigenic isolates of Penicillium nordicum and Penicillium verrucosum produced guttation droplets when grown on Czapek yeast extract (CYA) agar for 10–14 days at 25°C. Parallel cultivation of one strain each of P. nordicum and P. verrucosum on malt extract agar demonstrated that higher volumes of exudate are produced on this agar. However, HPLC analyses revealed higher concentrations of ochratoxin A (OTA) and B (OTB) in droplets originating from cultures on CYA. For quantitative determination of the mycotoxin contents, triplicates of three isolates each of P. nordicum and P. verrucosum were grown as single spot cultures on CYA for up to 14 days at 25°C. Guttation droplets were carefully collected between day 11 and 14 with a microliter syringe from each culture. Extracts from exudates and corresponding mycelia as well as fungal free agar were analyzed by HPLC for the occurrence of ochratoxin A (OTA) and B (OTB). Mean concentrations ranging between 92.7–8667.0 ng OTA and 159.7–2943.3 ng OTB per ml were detected in the guttation fluids. Considerably lower toxin levels were found in corresponding samples of the underlying mycelia (9.0–819.3 ng OTA and 4.5–409.7 ng OTB/g) and fungal free agar (15.3–417.0 ng OTA and 12.7–151.3 ng OTB/g). This is the first report which shows that high amounts of mycotoxins could be excreted from toxigenic Penicillium isolates into guttation droplets.     

Growth and mycotoxin production by <Emphasis Type="Italic">Chaetomium globosum</Emphasis>

Chaetomium globosum, the most common species within this genus, produces chaetoglobosins A and C when cultured on building material. Relatively low levels of these compounds have been shown to be lethal to various tissue culture cell lines. This study had two major objectives: (1) to determine the frequency at which Chaetomium species are isolated in water-damaged buildings and (2) to examine the production of chaetoglobosins A and C in isolates of C. globosum obtained from different buildings. Out of 794 water-damaged buildings, Chaetomium species were isolated in 49% of these structures. C. globosum ATCC 16021 was grown on four different media: oatmeal agar (OA), potato dextrose agar (PDA), corn meal agar (CMA), and malt extract agar (MEA). After 4 weeks, fungal growth was evaluated based on colony diameter and the quantity of spores produced on agar plates. In addition, production of chaetoglobosin A and C was monitored using high performance liquid chromatography. Colony diameter, spore production, and mycotoxin production by C. globosum were the highest on OA. Out of 30 C. globosum isolates cultured on OA for 4 weeks, 16 produced detectable amounts of chaetoglobosin A and every isolate produced chaetoglobosin C.     

Taxonomic studies on Filobasidiella species and their anamorphs

The taxonomy of Filobasidiella neoformans Kwon-Chung and F. bacillispora Kwon-Chung and their anamorphs were reinvestigated. Although the cross between the type cultures of the two species failed to produce viable basidio-spores, another pair of isolates did yield viable basidiospores. The segregation of phenotypic markers among the tetrads isolated from this interspecific cross proved that meiosis had occurred. On the basis of other previously known differences and the present genetic study, the two species are now considered to be two varieties of the species, F. neoformans. The anamorph of F. neoformans var. neoformans grew well at 37°C in vitro and produced fatal infection in mice while that of F. neoformans var. bacillispora grew poorly at 37°C and failed to produce fatal infection in mice. Cryptococcus bacillisporus Kwon-Chung et Bennett is regarded as a synonym of C. neoformans var. gattii Vanbreuseghem et Takashio.     

First morphogenetic identification of <i>Fusarium solani</i> isolated from orange fruit in Egypt

Losses due to postharvest decay may occur at any time during postharvest handling, from harvest to consumption affecting the produce quality and quantity. Accurate identification of the pathogen causing postharvest disease is essential to the selection of an appropriate disease control approach. Nine isolates of Fusarium recovered from orange fruit were identified as Fusarium solani. The fungus is involved with fruit decay. The obtained cultures were purified and grown on potato-dextrose agar (PDA), malt yeast agar (MYA), and Czapek's nutrient media (CNM) under light for identification. A pathogenicity test was carried out to fulfil Koch's postulates. The pathogen could only enter ripe orange fruit through wounds and cracks causing the rot disease. The identification of the fungal isolates was confirmed to be F. solani by DNA sequencing, which was 99 to 100% homologous to those deposited in the Gen- Bank. The identity of nine fungal isolates was confirmed to be F. solani by DNA sequencing of the internal transcribed spacer (ITS) rDNA region (GenBank Accession Nos. DQ486874 to DQ486881 and KC758879). To our knowledge, this is the first morphogenetic identification of F. solani isolated from orange fruit in Egypt.     

Effect of temperature and water activity on spore germination and mycelial growth of three fungal biocontrol agents against water hyacinth (Eichhornia crassipes)

Aims: To determine the effect of water activity (a_w = 0·880–0·960) and temperature (15–35°C) on the percentage of viable conidia and mycelial growth of three biocontrol agents effective against water hyacinth in Mali: Alternaria sp. isolate Mlb684, Fusarium sacchari isolate Mln799 and Cadophora malorum isolate Mln715. Methods and Results: The fungi were grown in vitro on plates containing potato dextrose agar medium at different a_w values (glycerol being added to adjust the a_w). The percentage of viable conidia and radial growth rate decreased with decreasing water activity. Statistical analysis showed a significant effect of a_w, temperature and the a_w × temperature interaction on mycelial growth (P < 0·0001). Water activity emerged as the factor exerting the greatest influence. Differences were observed between the fungi tested, the C. malorum appearing more tolerant to low a_w and the F. sacchari more tolerant to high temperature (35°C). Growth models predicting the combined effect of a_w and temperature were developed and response surfaces generated, showing fairly good agreement with the experimental values. Conclusions: Our results confirm the previous finding that a_w has a greater influence than temperature on fungal growth. Under most conditions, variation of environmental factors has a detrimental influence on the percentage of viable conidia and mycelial growth rate of fungal isolates. Significance and Impact of the Study: The developed models may contribute to predicting the best environmental conditions for use of these fungi as effective biocontrol agents against water hyacinth.