Soil Dilution Method Research Articles

Effects of different parameters on cellulase production by Trichoderma harzianum TF2 using solid‐state fermentation (SSF)

Solid‐state fermentation is one of the easiest and cheapest methods for producing microbial bioactive com‐ pounds. Trichoderma harzianum has long been recognised as one of the potential fungi for this purpose. Trichoderma sp. were isolated from banana rhizosphere using the soil dilution method and later screened for their ability to produce cellulases using filter paper activity (FPase) and the carboxylmethyl cellulase (CMCase) test. Trichoderma sp. were also subjected to one factor change at a time to determine the effects of different parameters on cellulase production. It was observed that T. harzianum TF2 showed the ability to produce higher cellulase activity when wheat bran was used as the substrate. The results showed that 38.5 U/g of cellulase was produced with the use of wheat bran coupled with an incubation temperature of 28 °C and moisture content of 60%. T. harzianum TF2 showed good potential for use as a culture for cellulase production in this study due to its higher cellulase production under solid‐state fermentation, with the possibility of its application to industry.

Harnessing the Phytase Production Potential of Soil-Borne Fungi from Wastewater Irrigated Fields Based on Eco-Cultural Optimization under Shake Flask Method

Indigenous fungi present in agricultural soils could have synchronized their inherent potentials to the local climatic conditions. Therefore, the fungi resident in the untreated wastewater irrigated agricultural field might develop their potential for producing various enzymes to handle the induced full organic load from domestic wastewater and toxic chemicals from the textile industry. Around 53 various fungal isolates were grown and separated from the soil samples from these sites through soil dilution, soil-culture plate, and soil-culture plate methods. All the purified fungi were subjected to a phosphatase production test, and only 13 fungal strains were selected as phosphatase producers. Among them, only five fungi identified as Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Penicillium purourogenum, and Mucor rouxii based on morphological similarities, showing higher phosphate solubilizing indices, were utilized for eco-cultural fine-tuning to harness their full production potential under shake flask (SF) method. Among various media, orchestral tuning, 200 µM sodium phytate as substrate with 1.5 mL of inoculum size of the fungi, pH 7, temperature 30 °C, glucose, and ammonium nitrate as carbon and nitrogen additive with seven days of incubation were found to be the most appropriate cultural conditions to harness the phytase production potential of the selected fungi. Aspergillus niger and Aspergillus flavus showed initial phytase activity (5.2 Units/mL, 4.8 Units/mL) and phytase specific activity (2.85, 2.65 Units/mL per mg protein) during screening to be enhanced up to 17 ± 0.033 (Units/mL), 16 ± 0.033 (Units/mL) and (13 ± 0.012), 10 ± 0.066 (Units/mL per mg protein), respectively, with the above-mentioned conditions. The phytase enzyme produced from these fungi were found to be almost stable for a wide range of pH (4–8); temperature (20–60 °C); insensitive to Ca2+ and Mg2+ ions, and EDTA, Ni2+, and Ba2+ inhibitors but highly sensitive to Mn2+, Cu2+, and Zn2+ ions, and Co2+, Cr3+, Al3+, Fe2+ and Ag1+ inhibitors. It was suggested that both phytase-producing strains of A. niger and A. flavus or their crude phytase enzymes might be good candidates for application in soils to release phosphates from phytate and a possible valuable substitute of phosphate fertilizers.

Outbreak of Leaf Miner and Root Knot Nematode-wilt Disease Complex on Cucumber- A New Threat under Protected Cultivation in District Gurugram Haryana

Background: Crops are constantly exposed to various organisms feeding on above and belowground parts under both natural and protected conditions. As compare to open field, the warm and humid conditions besides abundant food under protected conditions provide a stable environment for pest and disease development either alone or together. However, the natural enemies i.e. predators, parasites and parasitoids that keep pests and pathogens under control naturally are not present under protected environment. For these possible reasons, pest and pathogens often develop in polyhouses more rapidly and with greater severity than open fields.Methods: A polyhouses study was carried out during last two months June and July in Patudi block of district Gurugram, Haryana where growers are facing failure of cucumber crop due to outbreak of insect pests- disease complexes on common host cucumber. On closer observation, symptoms of leaf miner as mining lines on leaves and galls or knots on roots the symptoms of root knot nematode were encountered. Further detailed lab based investigation were carried out on affected cucumber plant and root samples with the objective for isolation and identification of both pests and pathogens. For leaf miner morphological identification, the pattern of the feeding tunnel and the layer of the leaf being mined by leaf miner is one of the diagnostic key are useful to determine the species and instar of the leaf miner. However, Sieving and decantation method for nematode isolation and soil dilution method for fungal isolation were carried out and followed by morphological identification. Result: Two types of herbivore i.e. leaf miner Liriomyza trifolii (Burgess) on aerial parts while root knot nematode, Meloidogyne javanica and wilt causing fungus Fusarium oxysporum f. sp. cucumerinum were identified on the basis of their specific morphological characters. Galled roots of cucumber were affected by combined attack of vascular bundle feeders, root knot nematode, Meloidogyne javanica and wilt causing fungus Fusarium oxysporum f. sp. cucumerinum identified in both soil and root samples. This kind of field report on cucumber crop under protected cultivation has not been reported so far in which three types of pest and pathogens are feeding on the same host. Poly houses or ‘hot spots’ are selected for detailed investigation especially for growers’ friendly management in addition to interaction studies of upper and lower ground herbivores on cucumber crops.

Occurrence and Diversity of Soil Microflora in Potato Fields of Bangladesh

Microflora from potato rhizosphere soil was isolated from different potato fields of Bangladesh. Seventeen soil samples were analyzed for the presence of microflora in selected potato field soils. Seven fungal species and one bacterium species were morphologically characterized using soil dilution and streak plate methods. The predominant fungi isolated including Alternaria sp., Aspergillus sp., Penicillium sp., Rhizopus sp., Bipolaris sp., Phytophthora sp., Fusarium sp. and one bacterium was identified as Ralstonia solanacearum. Individual colonies of fungi and bacteria were counted on Potato Dextrose Agar (PDA), V8 juice Agar and their presence in soil was compared in respect of different locations of potato fields. The occurrence of Phytophthora sp. was medium in Tongibari and lower in Singair Union, Sonargaon, Matlab Dakshin, Gobindaganj, Palashbari, Gopinathpur and Bagmara. The highest counts of R. solanacearum were found in Singair Union, Tongibari and Daudkandi and the lowest counts were made in Palashbari and Bagmara. This was the first reported examination of the microbial diversity of soil microflora in some selected potato fields of Bangladesh.

Patterns of Occurrence and Activity of Entomopathogenic Fungi in the Algarve (Portugal) Using Different Isolation Methods.

Entomopathogenic fungi (EPF) are distributed in natural and agricultural soils worldwide. To investigate EPF occurrence in different botanical habitats and soil-ecoregions, we surveyed 50 georeferenced localities in the spring of 2016 across the Algarve region (South Portugal). Additionally, we compared three EPF isolation methods: insect baiting in untreated or pre-dried-soil and soil dilution plating on a selective medium. We hypothesized that forest habitats (oak and pine semi-natural areas) and the acidic soil ecoregion may favor EPF occurrence. Overall, EPF species were present in 68% of sites, widely distributed throughout the Algarve. The use of selective media resulted in higher recovery of EPF than did either soil-baiting method. Contrary to our hypothesis, neither vegetation type nor ecoregion appeared to influence EPF occurrence. Traditional and molecular methods confirmed the presence of five EPF species. Beauveria bassiana (34% of sites), was the most frequently detected EPF, using pre-dried soil baiting and soil dilution methods. However, baiting untreated soil recovered Fusarium solani more frequently (26% of sites), demonstrating the utility of using multiple isolation methods. We also found Fusarium oxysporum, Purpureocillium lilacinum and Metarhizium anisopliae in 14%, 8% and 2% of the sites, respectively. Three abiotic variables (pH, soil organic matter and Mg) explained 96% of the variability of the entomopathogen community (EPF and entomopathogenic nematodes) in a canonical correspondence analysis, confirming the congruence of the soil properties that drive the assemblage of both entomopathogens. This study expands the knowledge of EPF distribution in natural and cultivated Mediterranean habitats.

Screening, identification and antagonistic effect evaluation of biocontrol strains to Asarum leaf blight

Leaf blight is the main disease of Asarum. At present, chemical treatment is main measure for disease control, and there is no report on biological control. In order to achieve the biological control of Asarum leaf blight, the biocontrol strains with antagonistic effect on Asarum leaf blight were screened. The rhizosphere bacteria of healthy Asarum plants were isolated by soil dilution method, and the isolated strains were screened by the methods of antagonistic antifungal and fermentation liquid antifungal, then the strains were identified and the control effect in vivo was determined. Abiocontrol bacterial strains S2-31 which with high antagonism to leaf blight was obtained from more than 100 isolated strains. The inhibitory rates of antagonistic antifungal and fermentation liquid antifungal reached 92.47% and 60.56%, respectively. It was identified by morphology and 16 S rDNA sequence analysis, and the strain was identified as Brevibacillus laterosporus. The results of indoor potted experiment showed that the control effect was 79.87%, 71.44% and 66.82% on the 3 rd, 5 th and 7 th day after inoculation, respectively, which indicated that S2-31 could reduce the disease index and control the development of Asarum leaf blight.

Occurrence and diversity of entomopathogenic fungi (Beauveria spp. and Metarhizium spp.) in Australian vineyard soils

Entomopathogenic Ascomycetes: Hypocreales fungi occur worldwide in the soil; however, the abundance and distribution of these fungi in a vineyard environment is unknown. A survey of Australian vineyards was carried out in order to isolate and identify entomopathogenic fungi. A total of 240 soil samples were taken from eight vineyards in two states (New South Wales and Victoria). Insect baiting (using Tenebrio molitor) and soil dilution methods were used to isolate Beauveria spp. and Metarhizium spp. from all soil samples. Of the 240 soil samples, 60% contained either Beauveria spp. (26%) or Metarhizium spp. (33%). Species of Beauveria and Metarhizium were identified by sequencing the B locus nuclear intergenic region (Bloc) and elongation factor-1 alpha (EFT1) regions, respectively. Three Beauveria species (B. bassiana, B. australis and B. pseudobassiana) and six Metarhizium species (M. guizhouense, M. robertsii, M. brunneum, M. flavoviride var. pemphigi, M. pingshaense and M. majus) were identified. A new sister clade made up of six isolates was identified within B. australis. Two potentially new phylogenetic species (six isolates each) were found within the B. bassiana clade. This study revealed a diverse community of entomopathogenic fungi in sampled Australian vineyard soils.

Isolation of potential fluorescent pseudomonads from Kuini (Mangifera odorata) planted soil and their potential as biofertilizer

Pseudomonas sp. are known to be good Plant Growth Promoting Rhizobacteria (PGPR). In this study, Pseudomonas sp. were isolated from soil planted with kuini (Mangifera odorata) using soil dilution method and spread onto King’s B media. Five isolates of Pseudomonas sp. were observed to give promising results in the phytohormone and antimicrobial test conducted. These isolates are Pseudomonas sp. isolate K24pf, K29pf, K32pf, K33pf and K37pf. From the 5 potential isolates, Pseudomonas sp. isolate K29pf was chosen because it showed potential activity in producing marked amounts of Indole-3-Acetic Acid and gibberellic acid. Pseudomonas sp. isolate K29pf also produced antimicrobial activities towards Ralstonia solanacearum, Erwinia caratovora, Erwinia mallotivora and Colletotrichum gloeosporioides. Seed germination test showed that Pseudomonas sp. isolate K29pf was able to promote approximately 90% growth of Brassica chinensis seeds. Pot trial conducted showed that Treatment 3 (+OF+PGPR) was able to increase Brassica chinensis root by 36.5% and 28.4% of its biomass compared to treatment using Treatment 1 (+OF).

Isolation and identification of fungi from extreme environments in Nassiriyah city soils

The present study aimed to isolation and identification some mycoflora from 40 soil sample in 6 sites ( Remnants of fat-born, parks, edges of the river, animal wastes, sewage and rubbish) during October 2015 to January 2016 in Nassiriyah city, Iraq. According to different environmental factors. The present study showed the isolated genera from different sits and that were include Aspergillus, Penicillium, Mucor, Rhizopus, Cladosporium, Sepedonium, Alternaria, Bipolaris, Chrysosporium, Candida, Rhododendron, Humicola, Geotrichum, Fusarium and Acremonium. They were isolated by dilution method, direct plate method, alcohol and heat treatment technique using the cultural media viz. PDA, SDA and PCA. Aspergillus represented the highest fungal isolate which represent 62 (37.12%) isolation followed by Penicillium with 47 (28.14%), Mucor 22 (13.16%), Rhizopus 15 (8.98%), Cladosporium 6 (3.59%), Sepedonium and Alternaria 3 (1.80%), Bipolaris, Chrysosporium and Candida 2 (1.20%), and finally Rhododendron, Humicola and Geotrichum recorded the lowest fungal isolation with one isolate (0.60%). The study results showed that soil dilution method gave a best fungal growth in comparison with direct plate method and alcohol and heat treatment technique in 25 ºC and pH= 6. Potato Dextrose Agar appeared as an optimum in comparison with other media such as SDA and PCA.

Development of Metarhizium anisopliae as a Mycoinsecticide: From Isolation to Field Performance.

A major concern when developing commercial mycoinsecticides is the kill speed compared to that of chemical insecticides. Therefore, isolation and screening for the selection of a fast-acting, highly virulent entomopathogenic fungus are important steps. Entomopathogenic fungi, such as Metarhizium, Beauveria, and Nomurea, which act by contact, are better suited than Bacillus thuringiensis or nucleopolyhedrosis virus (NPV), which must be ingested by the insect pest. In the present work, we isolated 68 Metarhizium strains from infected insects using a soil dilution and bait method. The isolates were identified by the amplification and sequencing of the ITS1-5.8S-ITS2 and 26S rDNA region. The most virulent strain of Metarhizium anisopliae was selected based on the median lethal concentration (LC50) and time (LT50) obtained in insect bioassays against III-instar larvae of Helicoverpa armigera. The mass production of spores by the selected strain was carried out with solid-state fermentation (SSF) using rice as a substrate for 14 days. Spores were extracted from the sporulated biomass using 0.1% tween-80, and different formulations of the spores were prepared. Field trials of the formulations for the control of an H. armigera infestation in pigeon peas were carried out by randomized block design. The infestation control levels obtained with oil and aqueous formulations (78.0% and 70.9%, respectively) were better than the 63.4% obtained with chemical pesticide.

A Study on Soil Thermophilic and Thermotolerant Fungi in Thamar-Yemen

جمعت 38 عينة تربه من مواقع مختلفه في محافظة ذمار/ اليمن وذلك للفترة من 4/2012 -2/2013. اتبعت طريقتي الزرع المباشر والتخافيف لعزل الفطريات وحساب الوحدات المكونة للفطريات وذلك باستعمال وسطي آكر البطاطا والجزر وأميرسون. عُزل 23 فطارً تعود لـ 14 جنساً تشمل 11 فطرا ناقصاً و 10 فطريات كيسيه وفطرين لاقحيين فضلاً عن الخيوط الفطرية العقيمة السوداء والبيضاء. اربعة عشرة عزلة فطريه منه عُدت تسجيلا جديدا للمجتمع الفطري اليمني هي: Acremoniummurorum, Acrophialophorafusispora, Chaetomiumatrobrunneum, C.gracile,C.strumarium ,C.therophilevar.coprophpile ,Corynascussepedonium ,Emericellarugulosa, Melanocarpusalbomyces , paecelomycesinflatus Papulosporathermophila, Rhizomucormiehi, . Scytalidiumthermophilum, and Talromycesthermophilus. و ظهرت الوحدات المكونة للفطريات عددا اعلى اثناء الاشهر المعتدلة الحرارة والرطبه (36667) مما في الاشهر الجافه (20400)وكانت الفروق معنويه عند مستوى اقل من 0,05 بينما كانت النسبة المؤية للتماثل الكلي بين الاجناس الفطريه عاليا بين الفترتين (78,57%) . اظهرت نتائج اختبار النشاط الانزيمي للفطريات المعزولة قابلية متفاوته في لانتاج السليوليز, الاميليز, اللايبيز, البروتيز, الزايلينيز, والفينوال اوكسيديز فيما اعطت عزلات .Corynascus sepedonium, Eemericellane dulansand Malbranchea cinnamomea . نتيجة موجبه لجميع الانزيمات .

Fungal communities in barren forest soil after amendment with different wood substrates and their possible effects on trees’, pathogens, insects and nematodes

AbstractScots pine sawdust, composted bark or coarse, post-harvest woody debris from conifers had been spread over the surface of barren forest soil before planting with Scots pine. The effects of the Scots pine sawdust, composted bark or coarse, post-harvest woody debris from conifers on the abundance and diversity of culturable fungi were investigated. The amendments were aimed at increasing the soil suppressiveness toArmillariaandHeterobasidion.The classical soil-dilution method was chosen for qualitative and quantitative analyses of fungal communities in soils because of its proven reliability and consistency. The soil was inhabited by saprotrophic fungi from Ascomycota and Zygomycota, including species known to be potential antagonists ofArmillariaorH. annosum(i.e.Clonostachys + Trichodermaspp.,Penicillium commune, P. daleae,P. janczewskii) or stimulants ofArmillaria(i.e.Pseudogymnoascus roseus,Trichocladium opacum). Eleven years after treatment, the abundance and diversity of fungi, the abundance ofP. commune, and locally the abundance ofP. janczewskiiincreased, whileClonostachys + Trichodermaspp., and locally,P. daleaeandT. opacumdecreased. Amending the barren soil with organic matter does not guarantee effective, long-term suppressiveness of the sandy loam soil toArmillariaandHeterobasidion.Increased abundance of entomopathogenic and nematophagous species, 11 years after treatment, does suggest the long-term possibility of insect or nematode control in soil.

Natural Occurrence of Potential Fungal Biopesticide Nomuraea Rileyi (Farlow) Samson Associated with Agriculture Fields of Tamil Nadu, India and it s Compatibility with Metallic Nanoparticles

In the present study, natural occurrence of major fungal biopesticide Nomuraea rileyi (Farlow) Samson associated with agricultural field soil in an area around TamilNadu, India was studied adapting culture dependentmethod. Agricultural field soil samples were collected from ten different sites. Soil dilution method was used toisolate N. rileyi. A total of 123 isolates of N.rileyi were obtained. Among the 10 sampling sites, Nomurea rileyi was isolated from 4 sites belonging to Hasthampatty (Salem) Rajakoil (Vellore) Vadavali (Coimbatore), Pullarakottai(Viruthunagar), High frequency of fungal occurrence was recorded in vadavali (60%) followed by Pullarakottai(17%), Hasthampatty (13%,) Rajakoil (10%). Non Nomurae rileyi strains belong to Beauveria sp and Metarhiziumsp were also isolated. Fungal occurrance was highly influenced by soil physico-chemical parameters. Effect ofmetallic nanoparticles such as silver, copper and the respective nanoparticles coated with chitosan on the posttreatment persistance of N. rileyi was also studied.Distinct effcet on the growth of N. rileyi was recorded in copper nanoparticles with high concentration.

Mutualisms are not constraining cross‐continental invasion success of Acacia species within Australia

AbstractAimStudying plant–soil interactions of introduced species in different parts of their global range could assist in managing biological invasions by elucidating the level of host specificity of key mutualists. We assessed the role of the soil microbial community (with an emphasis on symbiotic nitrogen‐fixing bacteria, collectively termed rhizobia) in determining cross‐continental invasion success of five woody legume species.LocationAustralia.MethodsFor each species, we compared growth of plants in soils from their native and non‐native ranges using a glasshouse study, a soil dilution method (most probable number) and T‐RFLP to assess rhizobial abundance and community composition, respectively.ResultsAcacia longifolia was the only species that had significantly larger above‐ground biomass when grown in soils from its non‐native range. Rhizobial abundance was equally high across species and ranges, indicating plants are unlikely to be limited by soil rhizobial abundance in non‐native ranges. Acacia cyclops, A. saligna and Paraserianthes lophantha formed associations with different rhizobial communities in non‐native vs. native range soils. Acacia longifolia and A. melanoxylon associated with similar rhizobial communities in their native and non‐native ranges, suggesting that rhizobia may have been accidentally introduced into their novel range with seeds or seedlings.Main conclusionsInvasive success of these five legume species is not constrained by the abundance of rhizobia in novel ranges for established legume populations, at least within Australia. Although differences in rhizobial community composition were evident between the native and non‐native ranges for three of the five species, these were not associated with differences in plant growth. Increased above‐ground biomass of A. longifolia when grown in soil from its non‐native range suggests that invasive success of this species may be associated with differences in the non‐rhizobial components of soil microbial communities in the novel range. This information could assist in management practises by facilitating a more instructive and effective screening for invasiveness.

Effects of a Carbendazim-Mancozeb Fungicidal Mixture on Soil Microbial Populations and Some Enzyme Activities in Soil

The effects of a Carbendazim-Mancozeb fungicidal mixture on microbial populations and some enzyme activities of three selected soils of Kwara State, Nigeria were studied. The soil dilution method was used to isolate bacteria, fungi, actinomycetes and some functional microbial groups from treated soils. Cultivation and enumeration of the soil microorganisms were made on different selective media. Assays for cellulases and pectinases in the treated soils were carried out. The populations of actinomycetes,bacteria and fungi were reduced significantly by the application of the fungicide. The fungicide applied at a concentration of 2.34mg/kg soil had a greater (p < 0.05) inhibitory effect than the recommended concentration of 1.67mg/kg soil. The populations of nitrogen fixers nitrifying bacteria and cellulolytic organisms were also significantly (p < 0.05.) reduced at the two concentrations. The fungicidal mixture equally lowered the cellulose and pectinase enzyme activities in soil significantly, with a return to normalcy by 60 days after treatment. A re-establishment of the soil microbial populations was observed by 21 days after treatment. It was concluded that the use of the Carbendazim-Mancozeb mixture should be with caution since it reduced the populations of ecologically important non-target organisms and that the recommended concentration should be adhered to.

IN-SITU SELECTION OF SUITABLE PLANTS FOR THE PHYTOREMEDIATION OF MULTI-METALS–CONTAMINATED SITES IN CENTRAL TAIWAN

Soils contaminated with metals are a serious problem in central Taiwan; 70% of the metals-contaminated soils in Taiwan are distributed there. We used soil turnover and dilution methods to reduce the total concentration of metals in soil, but this technique may be not suitable for other sites because of their shallow soil depths, which were less than 60 cm. Central Taiwan has the largest flower market in Taiwan and we propose that using local flower species to clean up the metals-contaminated soils is a feasible solution. A 1.3-ha area contaminated by multiple metals (As, Cr, Ni, Cu, and Zn) located in central Taiwan was selected for this large-area phytoremediation experiment. According to the Taiwan Environmental Protection Administration project contract, in-situ selection experiments were conducted to select 12 potential species from 33 tested species for further large area experiment. After in-situ planting of 33 species of plants in the contaminated soil for 33 d, bougainvillea and cockscomb showed yellow-colored leaves and withered as the result of the toxicity of metals. Herbaceous plants can accumulate higher concentration of metals and have higher bioconcentration factor in relative to woody plants. Three weighting models of growth condition and the metal-accumulated concentration of plants growing in the site were evaluated and compared. Six woody plants and six herbaceous plants were selected as high potential metal accumulators for a further large-area experiment.

Почвенные микроскопические грибы прибрежного района Баренцева моря (окрестности поселка Варандей)

The paper is a report of soil microfungi of the Barents Sea coast. 49 species of saprotrophic filamentous microfungi belonging to 22 genera were isolated by soil dilution methods from three tundra locations. 82-89% of strains were psychrophiles and psychrotrophs. 76-92% of isolates had tolerance to high concentration of NaCl in the media. Geomyces pannorum (Pseudogymnoascus roseus), Penicillium chrysogenum, P. expansum and Trichoderma viride were most often in these soil samples in all habitats studied. The microfungi Acremonium strictum and Phoma sp. were very frequent in different peat-bog habitats.

Fusarium solani f.sp.cucurbitae andF. oxysporum f.sp.niveum inoculum densities in tunisian soils and their effect on watermelon seedlings

Populations ofFusarium solani f.sp.cucurbitae (Fsc) andFusarium oxysporum f.sp.niveum (Fon) in naturally infested soil of watermelon fields were counted by the soil dilution method with subsequent pathogenicity tests. Inoculum density varied within the same region from one field to another, ranging between 9 and 1600 CFU g−1 soil forFsc and from 0 to 200 CFU g−1 soil forFon. Fusarium crown- and root-rot-diseased seedlings were observed in most soils (93%); however, Fusarium wilt was observed in only 34% of soil samples. The disease incidence on cv. ‘Giza’ (Y) increased significantly with inoculum density in the soil (X) (P<0.001). ForFsc, the relationship between inoculum density and disease incidence was characterized by the equation Y=0.0005X+0.165 (R2=0.67). ForFon, the equation was Y=0.003X−0.0014 (R2=0.88). Based on these equations, the estimated inoculum densities required to cause 50% disease incidence (DI50) on cv. Giza plants was 670 and 171 CFU g−1 soil forFsc andFon, respectively.

Influence of soil lead (Pb) levels on fungal occurrence, growth and sporulation

The emission of exhaust fumes into the environment, which are eventually deposited in to soils, contributes to the increasing hazardous levels of lead in the soil ecosystem. Kenya has a high number of automotives that emit high levels of exhaust fumes that make lead a major environmental pollutant. At high levels, lead has adverse effect on the soil microbiota. This study was designed to investigate the effect of lead on mucoraceous fungi in a roadside habitat. Mucoraceous fungi are mostly saprophytes and play an important role in nutrient cycling, elemental storage and transport in the soil. Soil plate and dilution methods were used to isolate fungi from the topsoil collected from the Kiambu roadside habitat and forest stand. The soil lead content was determined by atomic absorption spectrometry. The effect of lead on the occurrence, growth and sporulation of the fungi was studied. Lead concentration of up to 160 &mu;g g-1 was recorded from the roadside, habitat soils. This decreased with increase in distance away from the road. The mucoraceous fungi showed a decline in frequency of occurrence and species diversity with increasing lead pollution load in the soil. However, Cunninghamella spp. were predominantly present in the heavily contaminated soils and showed good in vitro growth in lead agar medium. Cunninghamella. elegans, which was the most common species showed tolerance for lead. Theses results showed that lead negatively affected the occurrence and diversity of mucoraceous fungi. The presumed tolerance of lead by species of Cunninghamella presents them as candidates for use in remediation of contaminated soils. Key Words: Mucorales, soil fungi, soil contamination, lead, pollution, exhaust fumes. J. Trop. Microbiol Vol.2 2003: 27-34

Accuracy and precision of population estimates of Verticillium dahliae on growth media in quantitative soil assays

Verticillium dahliae Kleb. is a serious pathogen of many plant species. Growth media used to measure population density of V. dahliae in soil were evaluated for high recovery of the pathogen, as well as accuracy and precision of population estimates from naturally and artificially infested sandy loam soil using the soil dilution method. Recovery of V. dahliae from naturally infested field soil was highest on soil pectate Tergitol agar (SPT), soil extract agar + sodium polypectate (SEAP), modified pectate agar (MPA), potato dextrose agar + streptomycin sulphate (PDAS), and Talboys' prune lactose agar (TPA); however, PDAS and TPA were overgrown with contaminating fungi, making enumeration difficult. Use of SPT medium resulted in the most precise population estimate with a standard error (SE) of 12.6% of the mean followed by use of pectate agar (PA) (SE = 14.8%) and SEAP (SE = 19.1%). Ethanol, biotin, and Dox salts enhanced recovery of V. dahliae from naturally infested soil, but combining Dox salts with ethanol and biotin significantly reduced population density. Soil extract had no significant effects on population density. Accuracy of V. dahliae population estimates from sterile artificially inoculated soil was highest on modified soil extract agar (MSEA) (64%) followed by SPT (58%). However, accuracy of V. dahliae population estimates from nonsterile artificially inoculated soil was highest on SPT (36%). Soil extract is not an essential ingredient and biotin may increase recovery of V. dahliae from soil.Key words: Verticillium dahliae, verticillium wilt, population density, recovery, accuracy, precision.