Phacidiopycnis washingtonensis--a new species associated with pome fruits from Washington State

A new species of Phacidiopycnis associated with pome fruits is described. The fungus causes fruit rot on apples during storage and is associated with a twig dieback and canker disease of crabapple trees and dead twigs of pear trees. To characterize the biology of the fungus and compare it with Ph. piri, the type species of the genus, effects of nine media and light on mycelial growth and pycnidial production, mycelial growth in response to temperature and mode of conidial germination in response to nutrient were determined. Apple-juice agar, pear-juice agar, prune-juice agar, potato-dextrose agar (PDA) and malt-extract agar, Czapek-Dox agar and oatmeal agar (OMA) favored mycelial growth. Cornmeal agar (CMA) did not favor mycelial growth. Light effect on pycnidial formation was medium dependent. Abundant pycnidia with mature conidia formed in 14 d old PDA and OMA cultures at 20 C, regardless of light, whereas none or very few pycnidia formed on other media in the dark. Fluorescent light stimulated formation of pycnidia except on CMA. The fungus grew at -3-25 C, with optimum growth at 15-20 C. Conidia germinated either by forming germ tubes or less often by budding. Budding of conidia occurred in 1 and 10% pear-juice solutions but not in 100% pear-juice solution. Six isolates of Ph. washingtonensis from different species of pome fruits had identical ITS sequences. The sizes of the ITS region were the same for both Ph. washingtonensis and Ph. piri, and four polymorphic nucleotide sites were found in the ITS region between Ph. washingtonensis and Ph. piri. The similarity in ITS sequences between these two taxa is confirmatory evidence for the erection of the new species of Phacidiopycnis associated with pome fruits we describe here.     

Characterization of Growth and Conidia Production of Exserohilum monoceras on Different Substrates

On agar media the maximum conidia production of Exserohilum monoceras occurred on V-8 juice agar (VA) or centrifuged V-8 juice agar, whereas the optimal radial mycelial growth occurred on Czapek-Dox agar. The optimal temperatures for radial mycelial growth and conidia production were 28 and 27°C respectively. Light prohibited E. monoceras conidia production. The best sporulation occurred under continuous dark conditions. Echinochloa leaf decoction significantly increased conidia production on potato dextrose agar (PDA) and VA, and significantly increased germ tube length on PDA, lima bean agar and VA, but did not affect conidia germination. No conidia were produced in liquid media. Of 22 agricultural-based products evaluated as solid substrates, the most abundant sporulation (1.8 × 10⁶ conidia g^-1 of dry weight) occurred on corn leaves. The conidia production of E. monoceras on corn leaves was affected by incubation period, moisture content and substrate quantity. There were no differences in germination rate, germ tube length and virulence of conidia produced on agar media or corn leaves.     

Characterization of Sporulation of Alternaria alternata f. sp. sphenocleae

Studies were conducted on agar media to characterize the factors for the optimization of sporulation of Alternaria alternata f. sp. sphenocleae , a fungal pathogen being evaluated as a biological control agent for Sphenoclea zeylanica (gooseweed). A. alternata f. sp. sphenocleae conidiation was affected by nutrition, temperature, light conditions, and moisture. On all agar media tested, except for half-strength potato dextrose agar (½ PDA) and V-8 juice agar (VJA), exposure to different light conditions did not have any significant effect on conidia production. However, when comparing ½ PDA and VJA, sporulation under constant near-ultraviolet (NUV) light at 28 o C increased markedly on VJA, but decreased substantially on ½ PDA. This trend, however, was opposite under dark conditions since ½ PDA produced the greatest number of conidia whereas a 75% reduction in conidia production occurred on VJA in the dark. On all the standard agar media evaluated, the most virulent conidia were obtained on ½ PDA at 28 o C under constant NUV incubated for 4 weeks. Sporulation of A. alternata f. sp. sphenocleae using the sporulation medium (S-medium) technique was rapid. Conidia were produced within 24 h and continuous sporulation was still observed until 120 h. The best primary agar media for conidia production were PDA, ½ PDA and VJA, while water agar was the poorest. Conidia production was optimized with the addition of 20 g l -1 of calcium carbonate (CaCO 3 ) and the addition of 2 ml of sterile distilled water on the medium. The most virulent conidia were produced when the primary agar was ½ PDA, the CaCO 3 concentration was 20 g l -1 , and the cultures were incubated at 18 o C in the dark. Conidiophore induction occurred on nutrient rich media and was stimulated by NUV, while formation of conidia proceeded in darkness after nutrients were depleted under warm dry or cool moist conditions. Culture media, growth conditions, and CaCO 3 affected the inoculum potential of A. alternata f. sp. sphenocleae conidia.     

Medium- and Light-dependence of Growth and Conidiomata Production in Phaeocytosporella zeae Pathogenic to Maize

Culture appearance, mycelium growth and pycnidial conidiomata formation in Phaeocytosporella zeae cultivated on potato dextrose agar (PDA), Leonian agar and carnation leaf agar (CLA) during permanent dark (25 C) or a 12-h photoperiod (24/18°C) are described. Different media and light conditions significantly affected fungus growth and the occurrence of conidiomata.
Dark conditions favoured more mycelium growth of the fungus than alternating light and dark. Moreover, fungus growth was more rapid on PDA and CLA media than on Leonian agar. Carnation leaf agar and a 12-h photoperiod provided excellent conditions for the promotion of rapid conidiomata formation in a number of P. zeae isolates.     

Effects of culture media, temperature, pH, and light on growth, sporulation, germination, and bioherbicidal efficacy of Phoma exigua, a potential biological control agent for salal (Gaultheria shallon)

In order to evaluate the potential use of Phoma exigua isolate PFC 2705 (PFC2705) as a biological control agent for salal (Gaultheria shallon), effect of cultural and environmental parameters on growth, conidia production, and pathogenicity of P. exigua were characterized in studies conducted under laboratory and greenhouse conditions. Within a range of 5-30°C, the optimum growth and germination temperature range was 20-25°C. The effect of pH on mycelial growth and conidial germination was not significant from pH 5 to 10. Fluorescent light significantly enhanced sporulation of the fungus on most agar media tested, yet was not necessary for growth. The type of culture media significantly affected mycelium growth, sporulation, and conidia germination. Age of mycelia used as inoculum affected the disease severity on salal. PFC2705 suppressed the growth of mature salal plant by inciting lesions on leaves, branch tips, and axillary buds and caused 56% death of the total biomass above ground. Characteristics such as easy inoculum production, wide range of growth environments, and high infectivity on salal increased the potential of P. exigua as a biocontrol agent for management of salal.     

In vitro growth of some species of Ascochyta Lib.

Fungi from the genus Ascochyta are generally facultative saprotrophs, which cause diseases in both monocots and dicots. Over 1 000 species belonging to this genus have been identified, 18 of which infect monocot plants from the family Poaceae. This study analyses the effects of temperature and light on the growth of selected fungi which infect monocots (A. agrostidis, A. avenae, A. brachypodii, A. desmazieri, A. digraphidis, A. ducis-aprutii, A. festucae, A. graminea, A. hordei, A. hordei var. americana, A. hordei var. europea, A. hordei var. hordei, A. melicae, A. phleina, A. skagwayensis, A. sorghi, A. stipae, A. zeicola), grown on three types of media; Potato Dextrose Agar (PDA), Coon??s agar (CN) and oatmeal agar (OMA). The fastest growth among the analyzed fungi at low temperatures was found in Ascochyta melicae, while at high temperatures it was A. zeicola. The fastest in vitro growth (average of all fungi) was observed on CN medium at 20°C (3.4 mm/day), while the lowest on OM medium at 5°C (1.0 mm/day). Radial mycelial growth in dark and the light conditions varied. On average, all isolates grew faster in the dark (3.1 mm/day) than in the light (1.9 mm/day). The greatest effect on the production of pycnidia was found for the isolates. Variation in growth and production of pycnidia depended on temperature, medium and lighting for fungi from the genus Ascochyta infecting monocots. Such variation indicates a potential occurrence of these fungi in different environments.     

Optimising sporulation and virulence in Drechslera avenacea

Studies were conducted on agar media to optimise sporulation of Drechslera avenacea, a fungal pathogen being evaluated as a biological control agent for Avena species (wild oats). Conidium production was affected by nutrition, pH, temperature and light conditions. Of the agar media tested, Czapek Dox agar (CZA) and half-strength oatmeal agar (½OMA) were the only media where sporulation occurred at all temperatures tested under a 12-h light:12-h dark photoperiod (L/D). The optimum temperature for conidium production was 20°C on ½OMA, whereas there was no optimum temperature on CZA. Under a 12-h near-ultraviolet (NUV):12-h dark photoperiod (NUV/D), similar numbers of conidia were produced on CZA at 6.66, 14.56, and 22.78 W m^?2, whereas on ½OMA conidium production was the highest at 14.56 W m^?2. When NUV/D and L/D conditions were compared, similar numbers of conidia where produced on CZA, whereas ½OMA conidium production was superior under the NUV/D photoperiod. Considerable variation in sporulation and degree of virulence of D. avenacea was detected among isolates from different geographic areas. The most virulent conidia were obtained on ½OMA at 20°C incubated under continuous illumination NUV light. Therefore, the most suitable conditions for conidium production of D. avenacea were growth for 1 week on ½OMA at 20°C under continuous NUV at an intensity of 14.56 W m^?2. Under these conditions, 1.1×10⁵ conidia mL^?1 were produced which is the highest sporulation yet reported for any Drechslera spp., which are traditionally poor sporulators.     

The Biology of the Acaropathogenic Fungus Hirsutella kirchneri

The acaropathogenic fungus Hirsutella kirchneri (Rostrup) Minter , Brady and Hall grew best and produced most mycelia on a medium containing yeast extract , dextrose and agar; conidial production , however , was maximal or potato dextrose agar (PDA) . The best growth on both media was at 25 C and conidial germination was high within a wide range of temperatures (10 - 35 C) . Colony growth , mycelial mass production and conidial yield were best under alternating dark and light regimes . Maximal germination occurred under dark conditions . When grown in continuous light the fungus produced synnemata (compacted conidiophores) which remained viable for 22 weeks . Of six species of phytophagous mites assayed , three spider mites and a rust mite became infected by the fungus , as did , to a limited degree , a parasitic mite . Another four mites , including two pests , a scavenger and a predator , were unaffected . The fungus grew on and sporulated from heat - killed cadavers of a dead mealybug (Homoptera) . Conidial germination and penetration into live mites , under saturation condi tions , were affected little by temperatures . Intra - host growth was temperature dependent , with mite death beginning on the second or third day post - infection . Maximal sporulation from infected mites took place at 25 C . Mortality was quickest at 25 C when mites were held under saturation conditions , but some death also occurred at lower relative humidities . These data are discussed with a view to using H. kirchneri in the biological control of plant mites .     

中华羊茅内生真菌Neotyphodium sp.生物学与生理学特性的研究

本文对中华羊茅Festuca sinensis内生真菌Neotyphodium sp.的生物学与生理学特性进行了报道。研究发现:中华羊茅内生真菌能在10-30℃生长,5℃和35℃几乎不能生长,最适生长温度是25℃;适宜的pH是7-9;不同的碳、氮源利用能力不同,利用能力最好的分别是甘露醇和酵母浸液;在不同培养基上的生长速度与产孢特性存在差异,马铃薯葡萄糖琼脂(PDA)培养基上生长最快,水琼脂(WA)和海水营养琼脂(SNA)培养基上生长最慢,但WA和SNA产孢最多。     

Effects of temperature,light, carbon and nitrogen nutrition on reproduction in Phoma medicaginis

Reproduction by three isolates ofPhoma medicaginis growing on potato dextrose agar was studied. The formation of pycnidia was optimum at 30°C whereas the optimum for the formation of conidia was 20°C. Light consistently increased the numbers of pycnidia and conidia over those formed in darkness and more conidia were produced in light at 23°C than at 30°C. The effects of carbon and nitrogen sources on reproduction were studied using modified Richard's medium as the basal medium. Fourteen carbohydrates, 11 amino acids, 9 inorganic nitrogen sources and urea were evaluated by replacing the carbohydrate or nitrogen in Richard's medium with the test substance. Generally, the monosaccharides and disaccharides were about alike and superior to polysaccharides for the production of pycnidia. The carbon sources were about equally useful for production of conidia, but the polysaccharides were superior to the other two classes of carbon sources when the number of conidia/pycnidium was calculated. Generally, the formation of pycnidia and conidia was favored by nitrate more than by ammonium nitrogen sources. The average number of conidia/pycnidium was greatest, however, when the nitrogen source was NH₄NO₃. All amino acids tested appeared to be useful nitrogen sources for production of pycnidia but none were especially good for conidia production. L-isoleucine was superior to the other amino acids tested. Of three isolates used, Illinois 23 consistently produced more pycnidia and conidia that did isolates Minnesota 2 and Missouri 5. Usually the significant interactions between isolates and other treatments were due to a greater response by isolate Ill. 23. It was concluded that the reproduction ofP. medicaginis varies significantly with the isolates of the fungus, the environment, and nutrients as well as with interactions among these factors, and conclusions about the influence of a particular factor will depend on whether the formation of pycnidia, conidia or conidia/pycnidium is being studied.Paper No. 7425, Scientific Journal Series, Minnesota Agricultural Experiment Station.     

Biological and physiological characteristics of Neotyphodium gansuense symbiotic with Achnatherum inebrians

Biological and physiological characteristics of Neotyphodium gansuense were compared with Neotyphodium coenophialum and Epichlo? festucae at a range of temperatures and pH values, and on carbon and nitrogen amended media. N. gansuense was able to grow at 10-30 degrees C, but not at 5 degrees C, and slowly at 35 degrees C. The optimal temperature for both N. gansuense and N. coenophialum was 25 degrees C, but that of E. festucae was 20-25 degrees C. The optimal pH ranges for mycelial growth of N. gansuense, N. coenophialum and E. festucae were 5-9, 5-9 and 5-7, respectively. The Neotyphodium and Epichlo? endophytes varied in their ability to grow on media containing different carbon and nitrogen nutrients. The preference of N. gansuense for carbon source was sucrose>glucose, lactose, sorbitol, inulin, maltose, mannitol, starch, fructose>xylose. Growth of all three endophytes tested was significantly improved by peptone, tryptone, casein, yeast extract and l-proline. Yeast extract, peptone, casein, tryptone, l-proline, potassium nitrate, ammonium oxalic acid and l-leucine significantly improved growth of N. gansuense. However, ammonium nitrite was not utilized at all by any tested endophyte. N. gansuense grew significantly better on potato dextrose agar (PDA) and oat meal agar (OMA) than on corn meal agar (CMA) and drunken-horse-grass agar (DA), and most slowly on water agar (WA) and saltwater nutrient agar (SNA).     

Cocoa-based media for culturing Phytophthora palmivora (Butl.) Butl., causal agent of black pod disease of cocoa

Green cocoa pod husk agar (GCPA), ripe cocoa pod husk agar (RCPA), green cocoabean agar (GCBA), ripe cocoa bean agar (RCBA), green cocoa mucilage agar (GCMA)and ripe cocoa mucilage agar (RCMA) were prepared and assessd for their clarity andfor potential to support mycelial growth and sporulation of P. palmivora. Oatmeal agar (OMA), potato-dextrose agar (PDA), vegetable 8 juice agar (V8JA) and pineapple crown agar (PCA) were included for comparison. The highest radial growth rates of 8.3 and 7.2 mm/day were recorded, respectively, on OMA and GCPA but these were not significantly different (P ≤ 0 05) from each other. The two media also supported good aerial mycelial growth but were not clear. Radial mycelial growth rates of 6.5, 7.0 and 6.6 mm/day were obtained on GCMA, RCPA and V8JA, respectively, and these rates were also not significantly different from each other. Of the three media, only the GCMA was clear and supported the best aerial mycelial growth. In comparison, the RCMA supported a significantly lower radial growth (4.6 mm/day) of P. palmivora than the three media. Growth rates were least on RCBA, PCA and PDA but sporulation was poorest on PDA, PCA and V8JA. GCMA was found to be the best medium based on all the growth parameters and media characteristics. GCMA has been used effectively to isolate/detect P. palmivora from infected cocoa pod tissues. Apart from differences in radial growth rate, both the GCMA and RCMA were similar in all other respects and are recommended for culturing P. palmivora. This revised version was published online in June 2006 with corrections to the Cover Date.     

Metarhizium robertsii illuminated during mycelial growth produces conidia with increased germination speed and virulence

Light conditions during fungal growth are well known to cause several physiological adaptations in the conidia produced. In this study, conidia of the entomopathogenic fungi Metarhizium robertsii were produced on: 1) potato dextrose agar (PDA) medium in the dark; 2) PDA medium under white light (4.98 W m^?2); 3) PDA medium under blue light (4.8 W m^?2); 4) PDA medium under red light (2.8 W m^?2); and 5) minimum medium (Czapek medium without sucrose) supplemented with 3 % lactose (MML) in the dark. The conidial production, the speed of conidial germination, and the virulence to the insect Tenebrio molitor (Coleoptera: Tenebrionidae) were evaluated. Conidia produced on MML or PDA medium under white or blue light germinated faster than conidia produced on PDA medium in the dark. Conidia produced under red light germinated slower than conidia produced on PDA medium in the dark. Conidia produced on MML were the most virulent, followed by conidia produced on PDA medium under white light. The fungus grown under blue light produced more conidia than the fungus grown in the dark. The quantity of conidia produced for the fungus grown in the dark, under white, and red light was similar. The MML afforded the least conidial production. In conclusion, white light produced conidia that germinated faster and killed the insects faster; in addition, blue light afforded the highest conidial production.     

Survival, growth and pathogenicity of Gaeumannomyces graminis var. graminis with different methods of long-term storage

The fungal plant pathogen Gaeumannomyces graminis var. graminis was preserved with 12 different storage methods. Five strains, each with unique morphological and pathological characteristics, were used for comparison of the methods. The storage treatments included potato-dextrose agar slants, with or without mineral oil, stored at either 4 C, 28 C or ambient temperature; colonized agar plugs placed in glycerol solution at either -75 C or -20 C; colonized agar plugs placed in sterile deionized water at either 4 C or ambient temperature; and mycelial growth on intact or precut pieces of filter paper, desiccated and stored at ambient temperature. Survival was evaluated at 6, 12, 24, 36, 48 and 120 mo. The three best treatments for survival were PDA slants, with or without mineral oil, and colonized agar plugs stored in water, all at ambient temperature. All five fungal strains were recovered from all four replicates at each sampling date for agar plugs stored in water at ambient temperature. The worst treatments were agar slants and agar plugs in water stored at 4 C and agar plugs stored in glycerol at -20 C. Morphological characteristics were not affected by storage treatments. In general, there were minimal or no effects on growth and pathogenicity for all strains for all storage treatments with survival. Colonized agar plugs stored in water at ambient temperature provides an economical storage method (materials and labor) that does not need an electrical power for long-term maintenance.     

Clostridium botulinum growth and toxin production in tomato juice containing Aspergillus gracilis.

The ability of spores of one type A and one type B strain of Clostridium botulinum to grow and produce toxin in tomato juice was investigated. The type A strain grew at pH 4.9, but not at pH 4.8; the type B strain grew at pH 5.1, but not at pH 5.0. Aspergillus gracilis was inoculated along with C. botulinum spores into pH 4.2 tomato juice; in a nonhermetic unit, a pH gradient developed under the mycelial mat, resulting in C. botulinum growth and toxin production. In a hermetic unit, mold growth was reduced, and no pH gradient was detected; however, C. botulinum growth and low levels of toxin production (less than 10 50% lethal doses per ml) still occurred and were associated with the mycelial mat. The results of tests to find filterable or dialyzable growth factors were negative. It was demonstrated that for toxin production C. botulinum and the mold had to occupy the same environment.     

A novel computerised image analysis method for the measurement of production of conidia from the aphid pathogenic fungus Erynia neoaphidis

A semi-automated method has been developed for the quantification and measurement of conidia discharged by the aphid pathogen Erynia neoaphidis. This was used to compare conidiation by E. neoaphidis-mycosed pea aphid cadavers, mycelial plugs cut from agar plates, mycelial pellets from shake flasks and by mycelial pellets from different phases of liquid batch fermenter culture. Aphid cadavers discharged significantly more and significantly smaller conidia than plugs or pellets. The volume of conidia discharged was stable over the period of discharge (80 h), but more detailed analysis of the size frequency distribution showed that more very small and very large conidia were discharged after 5 h incubation than after 75 h incubation. Biomass harvested at the end of the exponential growth phase in batch fermenter culture produced significantly more conidia than biomass from any other growth phase. The implications of these findings for the development of production and formulation processes for E. neoaphidis as a biological control agent are discussed.     

Molasses supplementation promotes conidiation but suppresses aflatoxin production by small sclerotial Aspergillus flavus

AIMS: To find a supplemental ingredient that can be added to routinely used growth media to increase conidial production and decrease aflatoxin biosynthesis in small sclerotial (S strain) isolates of Aspergillus flavus. METHODS AND RESULTS: Molasses was added to three commonly used culture media: coconut agar (CAM), potato dextrose agar (PDA), and vegetable juice agar (V8) and production of conidia, sclerotia, and aflatoxins by A. flavus isolate CA43 was determined. The effect of nitrogen sources in molasses medium (MM) on production of conidia, sclerotia and aflatoxins was examined. Water activity and medium pH were also measured. Conidia harvested from agar plates were counted using a haemocytometer. Sclerotia were weighed after drying at 45 degrees C for 5 days. Aflatoxins B(1) and B(2) were quantified by high-performance liquid chromatography. Addition of molasses to the media did not change water activity or the pH significantly. Supplementing CAM and PDA with molasses increased conidial production and decreased aflatoxins. Two-fold increased yield of conidia was found on MM, which, like V8, did not support aflatoxin production. Adding ammonium to MM significantly increased the production of sclerotia and aflatoxins, but slightly decreased conidial production. Adding urea to MM significantly increased the production of conidia, sclerotia and aflatoxins. CONCLUSIONS: Molasses stimulated conidial production and inhibited aflatoxin production. Its effect on sclerotial production was medium-dependent. Water activity and medium pH were not related to changes in conidial, sclerotial or aflatoxin production. Medium containing molasses alone or molasses plus V8 juice were ideal for conidial production by S strain A. flavus. SIGNIFICANCE AND IMPACT OF THE STUDY: Insight into molecular events associated with the utilization of molasses may help to elucidate the mechanism(s) that decreases aflatoxin biosynthesis. Targeting genetic parameters in S strain A. flavus isolates may reduce aflatoxin contamination of crops by reducing the survival and toxigenicity of these strains.     

Visible light during mycelial growth and conidiation of Metarhizium robertsii produces conidia with increased stress tolerance

Light conditions during mycelial growth are known to influence fungi in many ways. The effect of visible-light exposure during mycelial growth was investigated on conidial tolerance to UVB irradiation and wet heat of Metarhizium robertsii, an insect-pathogenic fungus. Two nutrient media and two light regimens were compared. Conidia were produced on (A) potato dextrose agar plus yeast extract medium (PDAY) (A1) under dark conditions or (A2) under continuous visible light (provided by two fluorescent lamps with intensity 5.4 W m(-2)). For comparison, the fungus was also produced on (B) minimal medium (MM) under continuous-dark incubation, which is known to produce conidia with increased tolerance to heat and UVB radiation. The UVB tolerances of conidia produced on PDAY under continuous visible light were twofold higher than conidia produced on PDAY medium under dark conditions, and this elevated UVB tolerance was similar to that of conidia produced on MM in the dark. The heat tolerance of conidia produced under continuous light was, however, similar to that of conidia produced on MM or PDAY in the dark. Conidial yield on PDAY medium was equivalent when the fungus was grown either under continuous-dark or under continuous-light conditions.     

Clostridium botulinum growth and toxin production in tomato juice containing Aspergillus gracilis.

The ability of spores of one type A and one type B strain of Clostridium botulinum to grow and produce toxin in tomato juice was investigated. The type A strain grew at pH 4.9, but not at pH 4.8; the type B strain grew at pH 5.1, but not at pH 5.0. Aspergillus gracilis was inoculated along with C. botulinum spores into pH 4.2 tomato juice; in a nonhermetic unit, a pH gradient developed under the mycelial mat, resulting in C. botulinum growth and toxin production. In a hermetic unit, mold growth was reduced, and no pH gradient was detected; however, C. botulinum growth and low levels of toxin production (less than 10 50% lethal doses per ml) still occurred and were associated with the mycelial mat. The results of tests to find filterable or dialyzable growth factors were negative. It was demonstrated that for toxin production C. botulinum and the mold had to occupy the same environment.     

Effect of Nutrition and Physical Factors on Mycelial Growth and Production of Pigments and Nonchromatic UV-absorbing Compounds of Alternaria eichhorniae

Alternaria eichhorniae is a host-specific biocontrol agent for managing waterhyacinth ( Eichhornia crassipes ) in Egypt. An important diagnostic characteristic of this fungus is the production of crimson-red phytotoxic pigments in the medium under certain conditions. A virulent isolate, A. eichhorniae 5 (Ae5), was studied to determine the optimum conditions for its growth and production of pigments and nonchromatic UV-absorbing metabolites (UVACs). The maximum production of pigments was obtained when cultures were grown on potato dextrose agar (PDA) with 20% dextrose, an initial pH of 4.5 at 25–30°C under continuous darkness or diurnal light, and without wrapping the culture plates. The maximum yields of the nonchromatic, 229- and 286-nm-absorbing compounds were obtained on PDA with 20–50% of dextrose at 20–30°C under continuous darkness. Culture plates, unwrapped or wrapped with only one layer of Parafilm at pH from 3.8 to 6.2 were favourable in this respect. There was a strong inverse relationship between linear mycelial growth and pigmentation as a function of light. Furthermore, the reduction in aeration, presumably proportional to the number of layers of Parafilm wrappings, led to lower levels of the red pigment(s) and the nonpigmented UVACs, to reduced mycelial growth, and a suppression of sporulation. Different culture-filtrate fractions of Ae5 were tested for phytotoxicity. At the concentrations of 0.5 and 1% w/v of the partially purified culture filtrate fractions, all except the butanol 1 fraction, had no toxic effect on waterhyacinth leaf-segments. Butanol fractions at 10% (w/v) concentration were significantly more damaging than aqueous fractions (10% w/v) and the area of necrosis increased with time.