Effect of soil moisture and sowing density on population growth ofEupatorium adenophorum andE. riparium

Summary Efect of sowing density on germination, establishment and growth of two perennial weeds,Eupatorium adenophorum spreng. andE. riparium Regel, was studied by sowing varying number of seeds of each species in pots. At high sowing density, seedling emergence did not proportionately increase with seed input. The yield and seed output per unit area was independent of sowing density. Survival of established plants was independent of soil moisture stress. The dry matter yield of both species declined at low moisture regime, the reduction being more inE. riparium. E. adenophorum produced more seeds at low moisture level, whileE. riparium at high moisture level. The resource allocation to roots was reduced due to moisture stress, especially inE. andenophorum.     

Effects ofMikania micrantha H.B.K. on germination and growth of weed species

Laboratory, greenhouse and field studies were conducted to determine the allelopathic potential ofMikania micrantha H.B.K. on the germination and growth of three weeds, namelyAsystasia intrusa Bl.,Chrysopogon aciculatus (Retz.) Trin. andPaspalum conjugatum Berg. The plant height of the test species decreased with increasing amounts of debris when either leaf or root debris of Mikania was present on the soil surface or incorporated into the soil. In general, incorporated debris caused greater reduction in height and seedling fresh weight than debris placed on the soil surface. Paspalum was more sensitive to either root or leaf of Mikania when incorporated into soil than on the soil surface. Leachate of Mikania leaf caused a significant reduction in radicle length and fresh weight of the seedlings of the test species. However, only Paspalum seeds showed significant decrease in germination when exposed to leaf leachate. Full-strength extract of either leaf or root caused a significant decrease in both germination and fresh weight of the test species. At the highest concentration, root extract of Mikania caused a marked reduction of radicle elongation of Paspalum.     

Microbial growth on polluted leaf and litter leachates: Effects on leachate pH and sulphate concentration

Summary Leaves and litter ofAcer pseudoplatanus L. (sycamore) were collected from woodland downwind of a coking works and from a site close to the industrial city of Sheffield and leached with water or simulated acid rain (pH 4.0). The effects of microbial growth on litter leachate, pH and sulphate concentration were determined by (a) allowing the indigenous litter flora to develop or (b) inoculating the fungusAureobasidium pullulans into sterilized leachates amended with synthetic aphid honeydew as carbon source. In both experiments microbial growth generally increased the pH and sulphate concentration of the leachates, independent of the origin of the litter or the leaching agent. The growth ofA. pullulans however, generally decreased the pH and sulphate content of sycamore leaf leachates. We conclude that the microbial mineralization of organic sulphur in deciduous litter leachate can act as a source of sulphate which could enhance cation leaching in atmospheric-pulluted soils.     

红薯叶片浸提液对5种主要农田杂草种子萌发及幼苗生长的化感作用

以发芽率、发芽势、根长、茎长和鲜重变化为种子萌发和幼苗生长参数,研究了作物红薯叶片水浸液对云南省农田5种恶性杂草牛膝菊、藿香蓟、鬼针草、马唐和稗草的化感作用。结果表明,红薯叶片水浸液对5种受体杂草种子发芽率的影响不明显,但对发芽势有显著抑制作用。牛膝菊、藿香蓟、鬼针草和马唐的根长和生物量随红薯叶片水浸液浓度增加而显著降低,其中对马唐的抑制最强,高浓度0.1 g/m L时对根长和生物量抑制率分别为92.04%和73.33%,而低浓度0.0125 g/m L时分别为40.99%和46.67%;其次为鬼针草、藿香蓟、牛膝菊;最差的是稗草,随浓度的变化趋势均不明显。随红薯叶片水浸液浓度增加牛膝菊、鬼针草和马唐的茎长显著地降低,其中对马唐的抑制最强,高浓度0.1 g/m L和低浓度0.0125 g/m L时分别为86.85%和70.64%;其次为鬼针草和牛膝菊;相反藿香蓟和稗草的茎长随浓度增加而显著增加,高浓度0.1 g/m L和低浓度0.0125 g/m L时对藿香蓟的促进率分别为86.97%和16.03%。红薯叶片水浸液低浓度0.0125 g/m L时对牛膝菊的茎长和生物量有促进作用(低促高抑)。从化感作用响应指数和综合效应指数的综合对比来看,红薯对牛膝菊、藿香蓟、鬼针草、马唐具有显著的化感抑制作用,随浓度增加其抑制能力显著增加;其中对马唐的为最强,其次为鬼针草、牛膝菊和藿香蓟,相反对稗草具有促进作用(除了浓度0.1 g/m L)。所有这些表明,红薯叶片水浸液对5种杂草化感作用的敏感性趋势总体为:马唐鬼针草牛膝菊藿香蓟,最不敏感或者具有促进作用的是稗草。     

3种作物(莴笋、茄子、小白菜)对香樟凋落叶化感作用的生理响应

为了解香樟(Cinnammum camphora)凋落叶对作物的生长和土壤微生物生物量碳、氮的影响,采用盆栽试验,施用不同添加量的香樟凋落叶,对3种作物莴笋(Lactuca sativa)、茄子(Solanum melongena)和小白菜(Brassica chinensis)的形态指标、生理指标和土壤微生物量C、N...     

The selective allelopathic interaction of a pasture-forest intercropping in Taiwan

An allelopathic interaction of a pasture-forest intercropping system was evaluated by field and greenhouse experiments and by laboratory assays. A study site was situated in the farm of Hoshe Forestry Experiment Station at Nantou County, Taiwan. After deforestation of Chinese fir (Cunninghamia lanceolata), a split plot design of 8 treatments was set up: open ground without planting as control, planted with kikuyu grass, planted with kikuyu grass andAlnus formosana, planted with kikuyu grass andZelkova formosana, planted with kikuyu grass andCinnamomum camphora, planted withA. formosana, planted withZ. formosana, and planted withC. camphora. Field measurements showed that weeds grew luxuriantly six months after treatment in plots which had not been planted with kikuyu grass. However, the growth of weeds was significantly retarded but that of woody plants was not affected when the plots were planted with kikuyu grass. As compared with the tap water control, the aqueous leachate of kikuyu grass stimulated the seedling growth ofC. camphora andA. formosana, but the extract stimulated the growth ofC. camphora and inhibited that ofA. formosana. In contrast, the aqueous extracts of three hardwood plants exhibited variable inhibition on the root initiation of kikuyu grass, and the extract ofZ. formosana revealed the highest phytotoxic effect. The aforementioned extracts and leachates were bioassayed against seed germination and radicle growth of four test plants, namely annual rye grass, perennial rye gras, tall fescue, and Chinese cabbage and against seedling growth ofMiscanthus floridulus. The extract ofZ. formosana revealed the highest phytotoxic effect on the test species while that of kikuyu grass showed the least effect. By means of paper chromatography and high performance liquid chromatography, phytotoxic phenolics were identified and the amount of phytotoxins present was highest in the extract ofZ. formosana but was lowest in that of kikuyu grass. The degree of phytotoxicity and amount of phytotoxins was in good correlation, indicating that a selective allelopathic effect was involved. The findings suggest that allelopathy may contribute benefits in the intercropping system to reduce the need for herbicides and to lessen the labour cost for weed control.Paper No. 346 of the Scientific Journal Series of the Institute of Botany, Academia Sinica, Taipei, Taiwan, Republic of China. This study was supported in part by grants of Academia Sinica, Taipei, and Council of Agriculture, Executive Yuan of the Republic of China.     

Fungal utilization of organophosphate pesticides and their degradation byAspergillus flavus andA. sydowii in soil

Fungal species were isolated which utilize organophosphate pesticides,viz. phosphorothioic (pirimiphos-methyl and pyrazophos), phosphorodithioic (dimethoate and malathion), phosphonic (lancer) and phosphoric (profenfos) acid derivatives. Pesticide degradation was studiedin vitro andin vivo (soil).Aspergillus flavus, A. fumigatus, A. niger, A. sydowii, A. terreus, Emericella nidulans, Fusarium oxysporum andPenicillium chrysogenum were isolated from pesticide-treated wheat straw. The number ofA. sydowii colonies was significantly promoted by 1 mmol/L pirimiphos-methyl, pyrazophos, lancer, dimethoate and malathion when used as phosphorus sources and by pirimiphos-methyl and pyrazophos when used as carbon sources. The number ofA. flavus colonies increased with 0.5 mmol/L lancer and malathion used as the only carbon sources.A. sydowii, A. niger, A. flavus, E. nidulans andF. oxysporum grew on, and utilized, 5 pesticides as phosphorus source and showed more than 50% mass growth.A. sydowii, A. flavus andF. oxysporum phosphatase hydrolyzed the pesticides suggesting that these species are important pesticide degraders.A. sydowii produced higher amounts of the phosphatase thanA. flavus andF. oxysporum. The enzyme was highly active against pyrazophos, lancer and malathion used as the only sources of organic phosphate.A. flavus andA. sydowii phosphatases efficiently hydrolyzed pesticides at 300 ppm in soil, the degradation at 1000 ppm was lower. Mineralization of 1000 ppm pesticides in soil amended with wheat straw was higher than in nonamended soil. All added pesticides except profenfos were degraded within 3 weeks. Lyophilized adapted biomass ofA. flavus andA. sydowii could thus be used for field biodegradation of these pesticides.     

A rapid identification method for aflatoxin-producing strains ofAspergillus flavus andA. parasiticus by ammonia vapor

The colony reverse of aflatoxin (AF)-producing strains ofAspergillus flavus andA. parasiticus turned pink when their cultures were exposed to ammonia vapor. The color change was visible for colonies grown on media suitable for AF production such as potato dextrose, coconut, and yeast extract sucrose agars after 2 d incubation at 25°C. Of the 120 strains ofA. flavus, A. parasiticus, and two related species inA. flavus group:A. oryzae andA. sojae tested in this study, only the AF-producing strains ofA. flavus andA. parasiticus showed the pink pigmentation. The color change occurred immediately after the colony was contacted with ammonia vapor. This method was useful for rapid screening the AF-producing strains ofA. flavus andA. parasiticus.     

Effects on plant production after addition of labile carbon to arctic/alpine soils

Biomass production was analysed in Festuca vivipara, grown for 3 months in pots with non-sterilized or sterilized soil after factorial addition of three levels of labile carbon combined with high and low levels of N and P. The soil was a nutrient-poor subarctic heath soil. In the non-sterilized soil plant biomass production increased strongly only in the treatment with high levels of both N and P, which suggests that both nutrients limited plant growth. In the sterilized soil addition of a high level of N without P addition gave almost the same growth response as in the combined NP treatment. This was because of a more than 30-fold increase of inorganic phosphorus in the soil as P was released from the killed microbial biomass after sterilization. Sugar addition reduced plant growth in all treatments. The reduction in plant growth was dose dependent within the range of 0–450 μg C g⁻¹ soil added to the non-sterilized soil, but the response levelled off at 233 μg C g⁻¹ soil in the soil that had been sterilized at the start of the experiment. The plant response, together with observed depletion of soil inorganic N and P, indicated that the microbial biomass immobilized nutrients efficiently and reduced plant growth when extra labile carbon was added. The inhibition of growth was lower, however, in the soil which had been sterilized, probably because of a slow recovery of the microbial populations in it. Two of the nutrient-carbon solutions closely matched the N, P and C concentrations in a solution containing leaf extracts of Cassiope tetragona and Betula tortuosa that had been used previously to test for possible allelopathic effects of compounds in the leaf extracts. These extracts also reduced plant growth. The growth reduction was equally large or larger after nutrient-sugar addition than after addition of leaf extracts in three out of the four possible combinations of species and sterilized or non-sterilized soil. In the fourth case (Betula extract added to sterilized soil), the effect was larger when leaf extract was added than after addition of the nutrient-carbon solution. This could be due to a low rate of microbial degradation of phytotoxic substances in this soil because of a slow recovery of the microbial populations after sterilization. The generally stronger or equal effect of the nutrient-sugar addition compared to the leaf extract addition leads to the conclusion that microbial nutrient immobilization and microbial competition for nutrients increased as a function of labile carbon addition with the extract. Hence, it appears that enhanced microbial activity and microbial nutrient immobilization rather than phytotoxic effects was the primary reasons for the reduced biomass production in F. vivipara even after addition of the leaf extracts. Received: 25 October 1996 / Accepted: 11 June 1997     

Aboveground and belowground responses to quality and heterogeneity of organic inputs to the boreal forest

Leaf litter and other organic resources returned to the soil are important regulators of ecological processes in forest ecosystems, and their ecological impacts may be strongly influenced both by their quality and by interactions between coexisting resource types. To date, most studies on effects of resource identity and mixing have only involved leaf litter, despite the fact that other resource types constitute a major input to the soil. We investigated how quality and heterogeneity of organic substrates found in boreal forests affects the activity and community structure of soil microbes, and plant growth. Six organic substrates (wood, charcoal, berries, sporocarps, vertebrate faeces and leaf litter) were added singly or in mixtures of two, three and six resource types to pots containing forest soil (with or without tree seedlings of Betula pendula Roth). The largest positive effects of single substrates on microbial basal respiration (BR), substrate-induced respiration (SIR) and microbial metabolic quotient (qCO₂) were found for nutrient-rich substrates (faeces and sporocarps) or substrates with high sugar-content (berries). Mixing of substrates had no effect on BR or SIR, but decreased qCO₂ or altered the microbial community structure for specific combinations of substrates. In contrast to the niche complementarity hypothesis, microbial catabolic diversity was not stimulated by greater diversity of resources. Seedling growth responses to single substrates were neutral or negative; the inhibition of growth probably resulted largely from microbial competition for nutrients. Substrate mixing enhanced seedling nutrient-uptake and growth for all mixtures containing sporocarps and leaf litter. Overall, plants responded more strongly to resource heterogeneity than microbes, and synergistic effects only occurred when nutrient-rich substrates were present within the substrate mixtures. In particular, our results demonstrate a role for complex and non-additive interactions among previously overlooked resource types returned to the soil in influencing ecosystem functions such as nutrient cycling and plant productivity.     

Nature of the Interference Mechanism of Sugarcane (Saccharum officinarum L.) Straw

Sugarcane (Saccharum officinarum L.) straw left in the field after harvest interferes with the growth of winter and summer weeds. In the last years, there was a progressive move away from burning sugarcane straw to retaining it on the soil surface after harvest to prevent soil degradation and environmental pollution. Water-soluble phenolics leachated from straw into soil may suppress weed growth. A study was carried out to investigate (1) the effect of biotic (unautoclaved) soil treated with burned and unburned sugarcane straw leachates on seedling growth and foliar proline content of beggarticks (Bidens subalternans L.) and wild mustard (Brassica campestris L.), (2) the modification of sugarcane straw phytotoxicity in abiotic (autoclaved) soil and biotic (unautoclaved) soil plus activated charcoal, and (3) changes of inorganic ions and phenolic contents in biotic soil after treatment with burned and unburned sugarcane straw leachate. Unburned straw leachate significantly inhibited root elongation of 7-d-old beggarticks and wild mustard seedlings. Burned straw leachate did not affect seedling growth of the assayed weeds suggesting that organic straw phytotoxins were involved. Experiments with activated charcoal, however, did not provide clear evidence supporting the involve of organic molecules in straw phytotoxicity. Unburned straw leachate incorporated in biotic soil was more inhibitory than in abiotic soil on root growth suggesting that microbial activity is involved in sugarcane straw interference. There was no evidence of nutrient microbial immobilization. Unburned sugarcane straw leachate increased total phenolic content in biotic soil more than in abiotic soil or biotic soil plus charcoal. Burned sugarcane straw leachate did not increase phenolic compounds levels in biotic soil. Linear regression analysis indicated a strong correlation between levels of soil phenolic contents and root growth inhibition. Soil characteristics evaluated in soil treated with burned and unburned sugarcane straw leachate suggest that straw phytotoxicity is related with organic molecules, such as phenolic compounds, rather than to variations in inorganic nutrients. Unburned straw leachate induced proline accumulation in seedling leaves of both beggarticks and wild mustard. Proline foliar content was higher in seedlings grown in biotic soil than in seedlings grown in biotic soil plus charcoal suggesting that straw organic constituents induced proline accumulation. Proline foliar content of seedlings grown in biotic soil treated with burned straw leachate was not significantly different from water control. The present study showed that sugarcane straw leachate interferes with seedling growth of beggarticks and wild mustard and that water-soluble phenolics can play a role in the seedling growth inhibition of the assayed weeds.     

Characterisation and reactivity continuum of dissolved organic matter in forested headwater catchments of Andean Patagonia

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Studies on some fungi isolated from the rhizosphere of tomato plants and the consequent prospect for the control of Verticillium wilt

Summary Biological control of Verticillium wilt disease with antagonistic micro-organisms was studied. Antagonism of some fungi, isolated from tomato rhizosphere, toVerticillium albo-atrum R & B. was observedin vitro. A clearly defined zone, in which the growth of the pathogen was inhibited, was observed withPenicillium spp. (includingPenicillium chrysogenum Thom) andFusarium culmorum (S.G. Sm) Sacc., whileTrichoderma viride pers. ex Fries,Gliocladium spp. andPenicillium vermiculatum Dangeard, suppressed the growth ofV. albo-atrum by penetrating, and overgrowing it. OnlyT. viride andP. vermiculatum culture filtrate added to the Dox's agar, reduced the radial growth ofV. alboatrum. Root-dip application of culture filtrates ofT. viride andP. chrysogenum was found to be most effective in controlling the disease, followed by other species ofPenicillium andGliocladium spp. WhileFusarium culmorum provided no control. Improvement of plant height and vigour with a better yield due to culture filtrate treatment occurred. Root-dip application of antagonistic fungal propagules (T. viride, P. chrysogenum) to tomato seedlings was also very effective in controlling wilt in tomato plants grown inV. albo-atrum infested soil. Dedicated to the memory of the late Prof. Ivor Isaac with whom I had the pleasure of working     

Effects of Single Chinese Fir and Mixed Leaf Litters on Soil Chemical, Microbial Properties and Soil Enzyme Activities

The quality of leaf litter can control decomposition processes and affect the nutrient availability for plant uptake. In this study, we investigated the effect of single leaf litter (Chinese fir – Cunninghamia lamcealata (Lamb.) Hook) and mixed leaf litters (C. lamcealata, Liquidamba formosana Hance and Alnus cremastogyne Burk) on soil chemical properties, soil microbial properties and soil enzyme activities during 2 years decomposition. The results showed that soil microbial biomass C, the ratio of soil microbial biomass C to total soil organic C (soil microbial quotient, Cmic/Corg) and soil enzymes (urease, invertase, dehydrogenase) activities increased significantly in mixed leaf litters treatments whereas soil chemical properties remained unchanged. However, soil microbial metabolic quotient (qCO₂) values and soil polyphenol oxidase activity were higher in the single Chinese fir leaf litter treatment that had a higher C:N (carbon:nitrogen) ratio (79.53) compared with the mixed leaf litter (C:N ratios of 76.32, 56.90, 61.20, respectively). Our results demonstrated that the mixed leaf litter can improve forest soil quality, and that soil microbial properties and soil enzyme activities are more sensitive in response to litter quality change than soil chemical properties.     

Inhibition of Aspergillus flavus growth and detoxification of aflatoxin B1 by the medicinal plant zimmu (Allium sativum L. × Allium cepa L.)

Aflatoxins are carcinogenic, teratogenic and immunosuppressive secondary metabolites produced by Aspergillus flavus and Aspergillus parasiticus. Aflatoxin contamination of peanut is one of the most important constraints to peanut production worldwide. In order to develop an eco-friendly method of prevention of A. flavus infection and aflatoxin contamination in peanut, aqueous extracts obtained from leaves of 30 medicinal plants belonging to different families were evaluated for their ability to inhibit the growth of A. flavus in vitro. Among them the leaf extract of zimmu (Allium sativum L. × Allium cepa L.) was the only one that showed antifungal activity against A. flavus and recorded 73% inhibition of A. flavus growth. The antifungal activity of the zimmu extract was significantly decreased upon dialysis with a dialysis membrane having molecular cut off 12 kDa or autoclaving at 121°C for 20 min or boiling at 100°C for 10 min and recorded inhibition of 52, 16 and 21%, respectively. When A. flavus was grown in medium containing zimmu extract the production of aflatoxin B₁ (AFB₁) was completely inhibited even at a concentration of 0.5%. When AFB₁ was incubated with zimmu extract a complete degradation of AFB₁ was observed 5 days after incubation. When the roots of zimmu were incubated in water containing 70 ng of AFB₁/ml, a reduction (by 58.5%) in AFB₁ concentration was observed 5 days after incubation. A significant reduction in the population of A. flavus in the soil, kernel infection by A. flavus and aflatoxin contamination in kernels was observed when peanut was intercropped with zimmu. The population of the fungal antagonist, Trichoderma viride in the zimmu-intercropped field increased approximately twofold.     

Do leaf surface characteristics affect<Emphasis Type="Italic">Agrobacterium</Emphasis> infection in tea [<Emphasis Type="Italic">Camellia sinensis</Emphasis> (L.) O Kuntze]?

The host range specificity ofAgrobacterium with five tea cultivars and an unrelated species (Artemisia parviflora) having extreme surface characteristics was evaluated in the present study. The degree ofAgrobacterium infection in the five cultivars of tea was affected by leaf wetness, micro-morphology and surface chemistry. Wettable leaf surfaces of TV1, Upasi-9 andKangra jat showed higher rate (75%) ofAgrobacterium infection compared to Upasi-10 and ST-449, whereas non-wettable leaves ofA. parviflora showed minimum (25%) infection. This indicated that the leaves with glabrous surface having lower 8 (larger surface area covered by water droplet), higher phenol and wax content were more suitable forAgrobacterium infection. Caffeine fraction of tea promotedAgrobacterium infection even in leaves poor in wax (Upasi-10), whereas caffeine-free wax inhibited bothAgrobacterium growth and infection. Thus, study suggests the importance of leaf surface features in influencing theAgrobacterium infection in tea leaf explants. Our study also provides a basis for the screening of a clone/cultivar of a particular species most suitable forAgrobacterium infection the first step inAgrobacterium-mediated genetic transformation.     

The effects of a single hot summer fire on soil fauna and on litter decomposition in jarrah (Eucalyptus marginata) forest in Western Australia

An area of jarrah (Eucalyptus marginata Sm) forest was burnt with a hot fire (ca 600 kw/ha) in March 1975. The meso- and microarthropod faunas were sampled in May, June and July 1976 and the decomposer activity of the soil and litter was estimated using buried cotton strips. The growth of jarrah seedlings in pots was measured under different litter and nutrient regimes. Feeding experiments with Eucalyptus, Banksia and Bossiaea litter were carried out on Podykipus sp., a litter millipede common at the site of the fire. Burning reduced the numbers of arthropods, the proportion of juveniles and the proportion of fungal feeders in the micro-arthropod population. The rate of decomposition was also reduced. The seedlings grew most under leaf Utter and millipede faeces and least under leaf ash. Podykipus sp. preferred Bossiaea litter (high nutrient content) to either Eucalyptus or Banksia litter (low nutrient content).     

Fungicide inhibition of aflatoxins,diacetoxyscirpenol and zearalenone production

The effect of fungicides on the production of aflatoxin byAspergillus flavus IMI 89717, diacetoxyscirpenol and zearalenone byFusarium graminearum was studied. In a yeast extract - sucrose medium, dicloran, iprodione and vinclozolin fungicides significantly inhibited mycelial growth ofA. flavus at 250 ppm and significantly decreased aflatoxin production at 100, 250 and 500 ppm, respectively. In potato — dextrose broth, these fungicides diminished the mycelial growth ofF. graminearum and production of diacetoxyscirpenol and zearalenone at 100 ppm. Sensitivity of toxigenic mycelia to fungicides increased approximately five-fold in a yeast extract-starch medium with an appreciable reduction in sugar uptake andα-amylase activity.     

Comparison of four media for the isolation ofAspergillus flavus group fungi

Four agar media used to isolate aflatoxin producing fungi were compared for utility in isolating fungi in theAspergillus flavus group from agricultural soils collected in 15 fields and four states in the southern United States. The four media wereAspergillus flavus andparasiticus Agar (AFPA, 14), the rose bengal agar described by Bell and Crawford (BCRB; 3), a modified rose bengal agar (M-RB), and Czapek's-Dox Agar supplemented with the antibiotics in BC-RB (CZ-RB). M-RB was the most useful for studying the population biology of this group because it permitted both identification of the greatest number ofA. flavus group strains and growth of the fewest competing fungi. M-RB supported an average of 12% moreA. flavus group colonies than the original rose bengal medium while reducing the number of mucorales colonies and the number of total fungi by 99% and 70%, respectively. M-RB was successfully employed to isolate all three aflatoxin producing species,A. flavus, A. parasiticus andA. nomius, and both the S and L strains ofA. flavus. M-RB is a defined medium without complex nitrogen and carbon sources (e.g. peptone and yeast extract) present in BC-RB. M-RB should be useful for studies on the population biology of theA. flavus group.Abbreviations M-RB Modified Rose Bengal Agar - CZ-RB Czapeks Rose Bengal Agar - BC-RB Bell and Crawford's Rose Bengal Agar - AFPA Aspergillus flavus andparasiticus agar     

Absence of a role for lytic microorganisms in the decline of bacteria andSaccharomyces introduced into soil

The populations ofKlebsieila pneumoniae, Escherichia coli, Enterobacter aerogenes, andPseudomonas sp. fell following their addition to soil, but species lysing these gram-negative bacteria were not detected. The numbers ofStaphylococcus aureus andMicrococcus flavus fell by more than four orders of magnitude and ofSaccharomyces cerevisiae by more than two orders after their addition to soil. Organisms lysing these gram-positive bacteria were present in soil, but their numbers did not increase as a result of the additions. Lytic activity againstS. aureus was detected in soil filtrates, but this activity was not enhanced by inoculation of soil with the bacterium. Addition of cycloheximide to soil suspensions delayed the fall in abundance ofM. flavus but did not suppress the lytic populations. We conclude that lysis is not responsible for the decline of bacteria orS. cerevisiae added to soil.