Effect of temperature and moisture content on Egyptian peanut seed-borne fungi

In peanut seeds adjusted to various levels of moisture content (8.5 %, 13,5 %, 17.5 % and 21 % on a dry-weight basis) and stored for six months at 5°, 15°, 28° and 45 °C, seed-borne fungi were monthly identified and counted using the dilution plate method, and the germinability of seeds was tested. The total count of seed-borne fungi (recovered at 28 °C) increased regularly and the germinability declined with the rise moisture content and with the lengthening of the storage period. At 5°, 15° and 28 °C,A. fumigatus was almost the most dominant fungal species followed by several fungi such asAspergillus flavus, A. niger, A. terreus, Penicillium funiculosum, P. notatum, Pyrenochaeta decipians andScopulariopsis brevicaulis. The degree of dominance of each fungal species depended upon the conditions of storage and the length of storage period.A. flavus gained its highest count in seeds adjusted to 13.5 % stored at 15 °C for 1 month.Penicillium predominated at 17.5 % and 21 %, and at 13.5 % and 17.5 % when the seeds were stored for long periods at 5° and 15 °C respectively.The total count of thermophilic fungi (recovered at 45 °C) significantly increased with the rise of moisture content and with the lengthening of the storage period between 1 and 2 months and regularly declined after 4 months.A. fumigatus was so extremely dominant that it was the main component of the total fungal flora. Several fungi truly thermophilic were isolated also. They were,Mucor pusillus, Humicola grisea var.thermoidae, H. insolens, H. lanuginosa (Thermomyces lanuginosus) andSporotrichum thermophile.     

Effect of constant temperatures on germination, radial growth and virulence of Metarhizium anisopliae to three species of African tephritid fruit flies

The effect of temperatureon conidial germination, mycelial growth, andsusceptibility of adults of three tephritidfruit flies, Ceratitis capitata(Wiedemann), C. fasciventris (Bezzi) andC. cosyra (Walker) to six isolatesof Metarhizium anisopliae were studied inthe laboratory. There were significantdifferences among the isolates in the effect oftemperature on both germination and growth.Over 80% of conidia germinated at 20, 25 and30°C, while between 26 and 67% conidiagerminated at 35°C and less than 10% at15°C within 24 hours. Radial growth was slowat 15°C and 35°C with all of theisolates. The optimum temperature forgermination and mycelial growth was 25°C. Mortality caused by the six fungal isolatesagainst the three fruit fly species varied withtemperature, isolate, and fruit fly species.Fungal isolates were more effective at 25, 30and 35°C than at 20°C. The LT₉₀values decreased with increasing temperature upto the optimum temperature of 30°C. Therewere significant differences in susceptibilitybetween fly species to fungal infection at allthe temperatures tested.     

Studies on soil fungistasis: Effect of certain physical and biological factors

Summary The effect of different physical and biological factors like soil sterilization, incubation period of soil, spore age, amendment of certain fungal species and their metabolites on soil fungistasis has been investigated.Different degree of sterilization affected the fugistasis differently. Soil heating above 80°C completely annulled the fungistasis. No fungistasis was recorded in soil samples steamed for 15 mts in an autoclave.Incubation of soil samples to longer duration resulted in increased fungistasis. Maximum fungistatic value was noted in samples incubated for 15 days at 25±1°C.Spore age also played important role in fungistasis. A positive relation was noted in the spore age and fungistasis upto 30 days of age and thereafter the increase in fungistasis was not well marked.Varying inhibitory effect was noted on the spore germination of the test fungi in relation to amendment of certain fungi individually and in different combinations to the soil.Aspergillus flavus alone and in combination ofAspergillus niger proved most inhibitory. The filtrate of the different fungi also induced fungistasis in soil. In this case alsoA. flavus was most effective.     

The effect of different temperatures on fatty-acid synthesis and polyunsaturation in cell suspension cultures

Cell suspension cultures of Catharanthus roseus G. Don, Glycine max (L.) Merr. and Nicotiana tabacum L. were incubated with [¹⁴C]acetate, [¹⁴C]oleic acid and [¹⁴C]linoleic acid at five different temperatures ranging from 15 to 35° C. When the incubation temperature was increased, [¹⁴C]acetate was incorporated preferentially into [¹⁴C]palmitate, with a concomitant drop in [¹⁴C]oleate formation. Between 15 and 20° C, [¹⁴C]oleic acid accumulated in C. roseus cells. In all cultures, optimum desaturation of [¹⁴C]oleic acid to [¹⁴C]linoleic acid occurred between 20 and 25° C, and in G. max this was also the optimal range for desaturation of [¹⁴C]linoleic acid to [¹⁴C]linolenic acid. Elongation of [¹⁴C]palmitic acid was inhibited when cultures grown at 15° C for 25 h were subsequently incubated with [¹⁴C]acetate at 25° C. [¹⁴C]oleic acid accumulated in G. max and C. roseus cultures grown at 35° C for 25 h and subsequently incubated at 25° C. Desaturation of [¹⁴C]oleic acid increased up to 25° C, but then decreased or leveled off depending on the cell line and on the temperature prior to incubation.     

A method to obtain rapid zoosporogenesis of Pythium insidiosum

Nine strains of Pythium insidiosum the etiologic agent of pythiosis, were inoculated on 2% water agar plus grass blades and then incubated one day at 25°C, 35°C and 37°C. Sporangium and secondary biflagellate-type zoosporas from the parasitized grass blades were noticed in induction medium after one hour of incubation at 35 °C and 37 °C. The number of sporangia and zoospores were lower at 25 °C, than 35 °C and 37 °C. Increasing the days of incubation of the parasitized grass blades resulted in the increase in the time of incubation in the induction medium. Corn meal agar, Schmitthenner medium and Sabouraud dextrose agar were also tested but the sporangium and zoosporas were always observed after five hours of incubation in induction medium.     

Decomposition of organic matter by fungi in saline soils

The object of the present investigation was to study the fungal decomposition of organic matter from different sources, added to the saline soils. The organic matter added was in the form of fresh cuttings of two salt tolerant harbaceous plants namelyDiplachne fusca (Kallar grass) andSesbania aculeata (Dhancha). In addition to these treatments, farm yard manure and press mud (waste of sugar industry) were also used as a source of organic matter. Twelve combinations of these treatments were studied. A number of fungi were isolated from differently treated saline soils incubated at 30 °C. Among the fungi isolatedAspergillus spp. andFusarium solani had the highest frequency of occurrence. The relative cellulolytic ability of 10 fungal species was also estimated.Alternaria humicola andNigrospora sp. were found to be the most cellulolytic among the fungi isolated. The decrease in organic matter due to microbial decomposition was found to be most rapid during first two weeks of incubation. Among the treatments with one organic matter source, press mud produced maximum humus equal to 0.28 %. The pH and electrical conductivity increased slightly due to the closed system where no leaching took place.     

Effects of temperature on growth rates of fungi from subantarctic Macquarie Island and Casey,Antarctica

Summary The linear growth rates of fungal isolates were measured on agar plates at temperatures ranging from 4° to 35°C. Fungi tested included the major fungal colonizers of leaves and litter of the three dominant plant species on subantarctic Macquarie Island, and major fungal species associated with plant and soil communities near Australia's Casey Station on the Antarctic Continent. All fungi grew at 4°C and were classified as psychrotrophs. Maximum growth rates were recorded at temperatures of 10° to 20°C for 13 of the 15 isolates from Macquarie Island and for all six isolates from Casey. Most of the leaf colonizing fungi from Macquarie Island had optimum growth temperatures of 15°C whereas all litter fungi from Macquarie Island and Casey fungi except Thelebolus microsporus had optimum growth temperatures of 20°C or above. Maximum growth of all species was at temperatures above those normally prevailing in their natural environments, with most species growing at 4°C at between 10% and 30% of their maximum rates. However, microclimatic effects may have resulted at times in temperatures near their growth optima. The highest growth rates at 4°C were recorded for Phoma spp. 1 and 2, Phoma exigua and Mortierella gamsii from Macquarie Island and Mortierella sp. 1 from Casey. Thelebolus microsporus and sterile sp. G from Casey also grew relatively fast at 4°C, and these species, and Phoma sp. 3 and Phoma exigua from Macquarie Island had the lowest Q-₁₀ values for the temperature range 4° to 15°C.     

Effects of paraquat on selected microbial activities in soil

Paraquat, applied as Gramoxone, to a nonamended sandy loam soil at five times the suggested field application rate (10 lb/A 115g/cm²) increased the numbers of bacteria, actinomycetes, and fungi during a 14-day incubation at 25°C. This increase was attributed to the use of compounds in the Gramoxone formulation rather than the use of paraquat. Treatment at one and five times the normal rate reduced CO₂ evolution by 44% and 67%, respectively, in soil amended with 2% glucose during a 12-day incubation. Similar treatments reduced CO₂ evolution in 1% straw-amended soil by 39% and 58%, respectively, during a 28-day incubation. Cellulose decomposition of cotton duck containing 13 and 176g of paraquat per milligram of material was inhibited for 15 and 28 days, respectively, in soil containing a large population of cellulolytic microorganisms. A concentration of 5000g/gm of paraquat was necessary to inhibit nitrification in soil by 44% druing a 28-day incubation at 20°C. Paraquat inhibited C₂H₂ reduction in artificial aggregates of soil amended with 2% glucose and incubated anaerobically at 25°C. Nitrogenase activity in aggregates was inhibited by 43% and 52% at concentrations of 580 and 720g/gm of paraquat respectively. The inhibitory effects of the herbicide were reduced when soil was amended with organic matter in the form of peat or straw. The availability of paraquat controlled the toxicity of the herbicide to soil microorganisms.     

Hydrolysis of vegetable oils and triglycerides by thermotolerant and zoopathogenic species ofAspergillus from Nigerian palm produce

The ability ofAspergillus fumigatus Fres. andAspergillus nidulans (Eidam) Wint obtained from Nigerian palm produce to degrade vegetable oils and triglycerides and the production and activity of their extracellular lipases were studied. Both species readily hydrolysed palm oil and palm kernel oil among others liberating free fatty acids in the process. Good growth with mycelia production of both fungi were also recorded on the triglycerides used as sources of carbon at 37 °C with the best results obtained on palmitic and oleic acids, the predominant fatty acids in palm oil. Extracellular lipases were detected in the culture filtrates of both fungi within 48 h of incubation on an oat-meal chaff medium at 37 °C. Peak enzyme production occurred within the 10-day incubation period. The upases of both fungal species were most active at a pH of 5.6 and a temperature of 45 °C. The best glyceride for assaying the lipase activities of these fungi was trihexanoin while palm oil was a better vegetable oil than the conventional groundnut oil used for the same purpose. Because of the zoopathogenic nature of these fungi, attention is drawn to the potential health risks which their presence on the palm products where they were obtained pose to the consumers.     

Mycoflora,and mycotoxins production in Nigerian corn and corn-based snacks

Thirty-one fungal species, mostly toxigenic and belonging to 11 genera were isolated from corn, corn cake and corn roll snack samples.Aspergillus, Penicillum andFusarium accounted for 10, 6 and 3 of the species and altogether, they constituted 90, 94 and 88 percent of the total fungi in corn, corn cake and corn roll snack respectively. Mycotoxins (aflatoxins and ochratoxin A) were detected in 45, 80 and 12 percent while the means and ranges of the total aflatoxins recorded were: 200(25–770 ppb); 233(15–1070 ppb) and 55(10–160 ppb) for corn, corn cake and corn roll snack samples respectively. Ochratoxin A was detected at toxicologically significant levels in only 15 percent of the corn cake samples analyzed. All the strains ofAspergillus flavus andA. ochraceus tested produced aflatoxin B and ochratoxin A, respectively, when they were cultured on each of the three substrates. In each case, substantial quantities of the toxins were produced from 25 to 35°C with the peak level recorded at 30°C. Toxin production was detected only in substrates with 15 percent moisture content and above; reaching the maximum at 25 or 30 percent moisture level. No substantial differences in the amount of toxins were elaborated with further increase in substrates' moisture content. Of the three substrates, corn cake was the most suitable for aflatoxin B production while they were all equally suitable for the elaboration of ochratoxin A.     

The influence of cultivar and temperature on carbohydrate and amino acid exudation from gram seeds and on pre-emergence damping-off byRhizoctonia bataticola

Summary Three gram varieties varying in susceptibility to pre-emergence damping-off caused byRhizoctonia bataticola were compared for amounts of seed exudation. The results showed that the greatest seed exudation occurred with the variety G-130 which is the most susceptible to pre-emergence damping-off compared with the resistant varieties BG-203 and C-214. Germinating gram seeds exuded greater quantities of soluble carbohydrate and amino acids when incubated at 35°C than at 15 or 25°C. Exudates from seeds germinated at 35°C stimulated more mycelial growth ofR. bataticola than did exudates from seeds incubated at 15 or 25°C. Evidence is presented suggesting that increased seed exudation is a major factor contributing to increased pre-emergence damping-off of gram seedlings byR. bataticola at high temperatures.     

Immunochemical analysis of trichothecenes produced by various fusaria

The production of type A trichothecene mycotoxins by 19 Fusaria, including 12Fusarium sporotrichioides, 4F. chlamydosporum and 3F. graminearum at 15°C and 25°C over a 35-day period was analyzed by ELISA using antibodies cross-reactive with most type A trichothecenes after conversion to T-2 tetraol tetraacetate. The toxin production peaked at 20–25 days of incubation with maximum yield between 4–6 mg type A trichothecene/ml of culture medium for 5F. sporotrichioides cultures and between 1 to 2 mg/ml for 6F. sporotrichioides cultures. OneF. sporotrichioides produced 700 µg type A trichothecenes/ml of culture medium. Detectable type A trichothecene was also found in the culture extracts ofF. chlamydosporum andF. graminearum, but the yield was very low (less than 100 µg/ml). Quantitative determination of individual trichothecenes was achieved by separation of different toxin in HPLC and followed by ELISA analysis. Eight to 10 immunoreactive peaks, corresponding to various type A trichothecenes, were detected in all the fungal extracts. T-2 tetraol (T-2-4ol), 4-acetyl-T-2 tetraol (4-Ac-T-2-4ol), neosolaniol (NEOS), diacetoxyscirpenol (DAS), HT-2 and T-2 toxin accounted for more than 85% of the total toxins. In general, low temperature was preferred for total type A trichothecene production. More T-2-4ol, 4-Ac-T-2-4ol, HT-2 and DAS were produced at 25°C. In contrast, more T-2 toxin and NEOS were produced at 15°C. Transformation of T-2 toxin and NEOS to polar metabolites such as T-2-4ol, 4-acetyl-T-2-4ol and HT-2 by various strains were observed at both temperatures after 25 days incubation.     

Studies on the fungus flora of three grains in Egypt

In wheat, corn and sorghum grains twenty-six genera and seventy-seven species including sixteen ofAspergillus and twenty-one ofPenicillium were identified.In grain samples adjusted to various moisture levels (up to 18.8 % on a dry-weight basis) and stored for 4 months at 8, 20 and 30 C seed-borne fungi were monthly identified and counted, and the germinability of the grains was tested. In the control samples (moisture content 7.1–8.2 %) temperature had no effect on the fungal counts and on the precentage germination. With the rise of temperature and moisture content the fungal counts markedly increased and the germinability declined.The list of fungi dominant in one or more of the experiments, included eight species ofAspergillus, six ofPenicillium, two ofFusarium and one each ofAlternaria andCurvularia. The order of dominance of these fungi varied according to the type of grain, the length of storage and the treatment.A. niger was the dominant organism in the control samples of the three grains. It could grow successfully at high moisture contents but above 15 %, it was usually overgrown by other fungi. In wheatP. citrinum andA. sydowii, in cornP. citrinum andA. terreus, and in sorghumA. terreus andA. niger were the dominant fungi at moisture contents above 15 % after four months storage at 30 C. When stored at 8 CPenicillium species tended to predominate over other fungi in grains with high moisture contents.In surface-sterilized grains adjusted to 15 % moisture content, inoculated with six dominant fungi separately and incubated at 30 C,A. niger, P. citrinum andP. variabile caused severe deterioration in the three grains;A. ochraceus in wheat only andF. moniliforme in wheat and corn;C. spicifer was slightly injurious to the three grains.     

Effect of temperature on growth and nitrogen mineralization of fungi and fungal-feeding nematodes

Dish and column microcosms containing alfalfa-sand medium were established to determine effect of temperature on growth and N mineralization ability of two fungi (Rhizoctonia solaniand Botrytis cinerea) and two nematodes (Aphelenchus avenaeand Aphelenchoides composticola). The microcosms were incubated at 15, 20, 25 and 29 °C for 21 days. In the dish microcosms, hyphal growth rates of both fungal species increased with temperature in the range of 15–25 °C. Above that temperature range, the growth rate of R. solani remained almost constant while that of B. cinereadecrease considerably. The population growth rate of A. avenae increased with temperature between 15 and 29 °C on colonies of R. solani and B. cinerea in dish microcosms. The growth rate of A. composticola also increased in the range of 15–25 °C but decreased greatly beyond that temperature range independent of the fungal species as food source. Inorganic N (NH₄ ⁺ + NO₃ ^–) was collected from each column microcosm by leaching every 3 days. In the columns containing R. solani, there was a significant effect of temperature on the amount of N detected in the fungus+A avenaeor A. composticolabut not in the fungus alone columns. The total amount of N was greatest at 29 °C for A. avenaeand at 20 °C for A. composticola columns, concurrent with the population growth rates of the nematodes. In the columns containing B. cinerea, the effect of temperature on the amount of inorganic N was not significant in either the fungus alone or fungus+nematode columns, although the population growth rates of the both nematode species were highest at 20 °C. For B. cinerea, the N amount across temperatures was the same or larger for the fungus alone as for the fungus+nematode columns. In general, the contribution of fungal-feeding nematodes to N mineralization was small in any combinations of fungus and nematode species at any temperature. Similarity in C/N ratio of the fungal and nematode biomass, organic substrate C/N ratios too low for measurable increase in net mineralization by the nematodes and small reproduction of the nematodes in the column microcosms were probable contributory factors.     

Studies on the aquatic hyphomycetes of a sulfur spring in the Western Ghats, India

Studies on the occurrence of aquatic hyphomycetes were carried out in Panekal sulfur spring in the Western Ghats, India by incubation of leaf litter and analysis of natural foam and of induced foam. Sampling was done once every three months over a period of two years from September 1989 to June 1991. The temperature, pH, dissolved oxygen, and sulfide content of water were also measured. No fungi were observed within the spring, whereas 16 species belonging to 13 genera were isolated from two outflow sites of the stream. The percent frequency of Triscelophorus monosporus was high (24.0%). The temperature of water in the spring ranged between 30.0 and 38.5°C and the sulfide content between 3.2 and 4.3 mg 1^–1. Studies showed that sulfide water (4.0 mg 1^–1). from the spring inhibited the growth of the colonies of Dactylella aquatica, Phalangispora constricta, Tetracladium setigerum, Vermispora cauveriana, and Wiesneriomyces laurinus. When the leaves colonized by aquatic hyphomycetes were incubated at different temperatures in sulfur-spring water and stream water separately, sporulation was not observed in any of the fungi at and above 35°C except Phalangispora constricta, which could sporulate at 35°C. At lower temperatures (15–30°C) relatively fewer species were found to sporulate in sulfur-spring water than in stream water. Correspondence to: K.M. Kaveriappa     

Evaluation of a fluorescent method (fluorescein diacetate and ethidium bromide solution) in the study of the viability Cryptococcus neoformans strains

The effectiveness of the fluorescent viability test (fluorescein diacetate-FDA and ethidium bromide-EB-solution) compared to the plaque counting test (Miles & Misra M & M) was performed on 10 samples of Cryptococcus neoformans cultivated in Sabouraud dextrose agar at 25 °C. The optimum incubation period of 50 minutes was determined. Growth curves of the fungal strains studied based on the mean cell number were drawn for both the FDA & EB and M & M methods. The statistical evaluation (Student's T test) of the average sum of the viable cell counts showed that the FDA-EB method is more sensitive than the M & M test for the studied species. The growth curves of the samples usually followed a homogeneous pattern comparable to other non-dimorphic fungi.     

Temperature and seedling age affect susceptibility of perennial ryegrass seedlings to pathogenic fungi

Summary Effects of temperature and seedling age on survival of perennial ryegrass (Lolium perenne L.) seedlings grown on sand-wheat wholemeal cultures of different isolates ofFusarium spp. (9 isolates),Pythium spp. (9 isolates), andChaetomium spp. (1 isolate) are reported. Some isolates were virulent over the whole range of temperatures tested (7.5–27.5°C). The virulence of others depended on temperature. Most isolates were less virulent at intermediate temperatures (12.5–22.5°C) than at higher or lower temperatures. At 25°C ryegrass seedlings were susceptible to fungal attack for only a limited period after germination commenced. This period differed for different fungi, but for most isolates tested, seedlings were resistant after 2–3 days.     

Generic composition of fungi in soil aggregates

A structure of fungal flora was studied in aggregates of various diameter in a chernozemic rendzina and a lessivè soil. Aggregate diameter influenced strongly the distribution of fungi such asCephalosporium, Fusarium, Penicillium and sterile mycelia. The percentage of the above fungi changed with changing aggregate diameter as follows:Cephalosporium: 1–3>5–7 >0.5 in lessivè soil and ≤0.5>5–7>1–3 in chernozemic rendzina,Fusarium: ≤0.5>1–3>5–7 in lessivè soil and 5–7>1–3>0.5 in chernozemic rendzina,Penicillium: 5–7>0.5>1–3 in lessivè soil and 1–3>0.5>5–7 in chernozemic rendzina. The effect of aggregate size on the generic composition of fungal flora in the outer and inner parts of the aggregates was weaker than on that in the whole aggregates. This held especially forCephalosporium, Fusarium and sterile mycelia in the outer part of aggregates andPenicillum in the inner one. Moreover, the percentage of some fungi in whole aggregates of both soils was affected byV _a/V _w in the aggregates. Additional effect in lessivè soil aggregates was that of the percentage of pores measuring 0.1–0.05 μm. Some pores affected the contents of some fungi in the outer part of the aggregates of both soils and in the inner one of chernozemic rendzina aggregates.     

Microbial cell responses to a non-ionic surfactant

Summary The effects of a non-ionic surfactant, Pluronic F-68, on growth of microbial cell cultures have been studied. Growth ofSaccharomyces cerevisiae at 30°C or 37°C as measured by viable cell counts was unaffected by culture with pluronic. However, corresponding absorbance measurements forS. cerevisiae incubated with 5–10% pluronic were lower than controls at both temperatures. Absorbance ofE. coli cultures was also significantly reduced by incubation with 5.0–10.0% pluronic at both temperatures although viable counts again revealed no significant inhibition of growth.