The effect of introducing the aphid-pathogenic fungus Erynia neoaphidis into populations of cereal aphids

The aphid-pathogenic fungus Erynia neoaphidis, as dried fungus-infected aphids, was applied to caged plots of winter wheat infested with cereal aphids at two sites, one in Hertfordshire and the other in Hampshire, in 1983. In each trial, the fungus became established in the aphid populations in the treated plots even though conditions were drier than average and therefore sub-optimal for fungus spread. Treatment applied in the third week of June increased the proportion of infected aphids more than that applied two weeks later at one site, and the early application was the only treatment to have an obvious effect at the other. In spite of the observed effect of treatments on the proportion of infected aphids, the fungus failed to reduce the numbers of aphids relative to those in untreated plots, chiefly because in these plots many aphids were killed by fungi of the same species as that introduced and other related species from natural sources. Artificial introduction of E. neoaphidis acts too slowly and unpredictably to be likely to form a practical alternative to conventional insecticides for cereal aphid control.     

Methods of investigating populations of the take-all fungus (Ophiobolus graminis) in soil

Attempts to isolate Ophiobolus graminis directly from infested soils failed, so host-infection techniques were used to study soil-borne populations of the fungus. Extracting organic debris from soils and grading it by wet sieving through standard meshes concentrated the fungus. Fractions were tested for infectivity either as layers in pots of sand or by packing into short lengths of polyvinyl chloride tubing, through which wheat seedlings were grown. Coarse debris (retained by 420 μ aperture sieves) was most infectious and usually caused lesions within 3 weeks; whole soil and especially fine debris (< 420 μ) caused fewer and less severe infections, which often became apparent only after 3 weeks. Slight infectivity of the sediment fractions was attributed to imperfect separation of debris. Soil sampled in crop or stubble rows caused more infections than soil from between rows. Usually seedling infection was made manifest by root lesions and runner hyphae, but these symptoms were not always plain or conclusive. Many seedling roots that rotted when kept moist and in the light produced perithecia within 6 weeks. Although perithecia formed on some roots where neither lesions nor hyphae were found, they did not form on all diseased roots. More needs to be known about the factors influencing perithecial formation before it can be used as a reliable confirmatory test.     

Microbial populations and sludge characteristics in thermophilic aerobic sewage sludge digestion

Summary Estimates of bacterial numbers from raw sewage sludge and sludge treated by thermophilic aerobic digestion were compared with simple indicators of sludge quality and concentrations of potential substrates. Significant differences were found between sludge types for all but one of the variables examined (frequency of dividing cells). During a stable period of digestor operation, the average number of viable obligate thermophiles present in digested sludge (1.63 × 10⁶ ml^–1) was approximately 10²-fold greater than in feed sludge (1.10 × 10⁴ ml^–1). Total numbers of bacteria were slightly greater in digested sludge (3.24 × 10¹⁰ ml^–1) than in feed sludge (2.39 × 10 ml^–10), as were viable counts of bacteria at incubation temperatures of 37°C and 55°C. Significant correlation was found between viable counts of bacteria at 37°C and 55°C for digested sludge, and 65°C and 55°C for feed sludge. The numbers of obligate thermophiles present and the total of bacteria present were related to the temperature and pH of the digested sludge and inversely related to the numbers ofEscherichia coli and coliforms present, which were not detected at temperatures greater than 50°C.     

Kinetic behavior of mixed populations of activated sludge

The kinetic behavior of heterogeneous microbial populations of sewage origin was studied in a single-stage isothermal continuous flow completely mixed aeration tank. A series of experiments were carried out at various dilution rates using glucose as the growth limiting substrate. The steady-state behavior of the system was observed at each dilution rate and the results were found to fit fairly well with the steady-state equation bayed on the Monod model with an endogenous respiration term included, i.e., μ = μ_mS/(K_s + S) ? K_d. The growth kinetics of cells harvested at steady state for each dilution rate were studied using batch experiments. The multiple response data of the system as functions of time were used to estimate the parameter values in the above kinetic model. It was found that values of the growth parameters changed significantly and systematically with cell population. For example, values of μ_m were high at high dilution rates and low at low dilution rates. It was also found that only those batch growth parameters from cells obtained at fairly high dilution rates are comparable with those estimated by the results of steady-state operations. The results of this investigation suggest that (1) different cell populations pre dominated at different steady-state dilution rates, with high dilution rates resulting in predominantly fast-growing organisms and low dilution rates resulting in predominantly slow-growing cells, and (2) risk exists in any randomly picked batch experiment to predict the steady-state behavior of the system when heterogeneous microbial populations must be used.     

The effect of temperature on soil respiration

лсследедовались кривые респирации образцов разцов почвы и компоста при температурах от 8 до 48о С. В пределах 8-28х С повышение температуры проявляется только ускорением процессов, характеризуемых коз??ициентом Q₁₀ 1,6 2,0. Начиная с 38с С, проявляются аномалии: можно наблюдать частичное угнетение респирации, а кроме того максимумы, похожие не максимумы после прибавления субстрата. Зти максимумы обьясняют реактивной оксидацией в результате повышения температуры. Прибавление глюкозы к почве С еще ольше повышает зтот максимум. Вообще все аномалии у почвы С проявляются гораздо выразительнее.чем У компоста, который в течение созревания прошел стадией самосгревания.- Далее исследедовалась скорость респирации при переменах температуры во время опыта как в присутствии, так и в отсутсвии субстрата. На респирационной кривой можно после повышения ния температуры с 8 до 28о С наблюдать характерное переходное явление, которое в боих случаях, т. е. как для почры С, так и для компоста, отражается и на зндогенной респирации, и на респирационной кривй оксидации глюкозы (по отчислении зндогенной респирации).- В заключение высказыватмя нзгляд, что зто переходное явление предстанляет не аномалию, а общее явление, сопровождающее перемены температуры. Обсуждается его природа. лзучение влияния температуры на респирационные коивые, а в особенности изучение аномалтй и перходых явлений, может дать ценные ин?ормации об органическом вещестре почвы и о его минерализации.     

The effect of soil drying on millet

Summary Two tropical soils were collected when moist. Part of the soil was kept moist under aerobic conditions for one week (Treatment A) and the other part air dried over the same period and then remostened (Treatment B). The soils were then sown to millet. Both the yields and percentage nitrogen of the millet were very significantly increased by Treatment B and also the amount of mineral soil nitrogen produced. Additional treatments showed that yield increases were due to increased nitrogen mineralisation and that pathogenic conditions in the moist soil (Treatment A) were not responsible for the low yields.     

The polyphagous plant pathogenic fungus Botrytis cinerea encompasses host-specialized and generalist populations

The host plant is often the main variable explaining population structure in fungal plant pathogens, because specialization contributes to reduce gene flow between populations associated with different hosts. Previous population genetic analysis revealed that French populations of the grey mould pathogen Botrytis cinerea were structured by hosts tomato and grapevine, suggesting host specialization in this highly polyphagous pathogen. However, these findings raised questions about the magnitude of this specialization and the possibility of specialization to other hosts. Here we report specialization of B. cinerea populations to tomato and grapevine hosts but not to other tested plants. Population genetic analysis revealed two pathogen clusters associated with tomato and grapevine, while the other clusters co-occurred on hydrangea, strawberry and bramble. Measurements of quantitative pathogenicity were consistent with host specialization of populations found on tomato, and to a lesser extent, populations found on grapevine. Pathogen populations from hydrangea and strawberry appeared to be generalist, while populations from bramble may be weakly specialized. Our results suggest that the polyphagous B. cinerea is more accurately described as a collection of generalist and specialist individuals in populations. This work opens new perspectives for grey mould management, while suggesting spatial optimization of crop organization within agricultural landscapes.     

Impact of the nematophagous fungus Pochonia chlamydosporia on nematode and microbial populations

The microbial and nematode populations associated with two plants (tomato and cabbage) inoculated with the nematophagous fungus, Pochonia chlamydosporia var. chlamydosporia or root knot nematode (Meloidogyne incognita), or both, were compared with those in unplanted controls. The dominant factor affecting culturable microbial populations was found to be the presence or absence of tomato plants. Generally microbial colony counts were lowest in unplanted soil, small increases were associated with cabbage and significantly greater numbers with tomato plants. Differences in microbial diversity (estimated from community profiles of carbon substrate utlisation, using Biolog) were observed between planted and unplanted soils, however, there were few differences between soils with either of the two plants. The presence of P. chlamydosporia was associated with a reduction in the numbers of plant parasitic nematodes (51%-78%) including the migratory ectoparasites, whereas free-living nematodes, culturable bacteria and bacterial populations assessed by Biolog were unaffected by the application of fungus.     

Terrestrial Chironomidae on agricultural soil treated with sewage sludge

Adult Chironomidae were caught in emergence traps for three subsequent years (1988–1990) on agricultural soil. Larvae were extracted from soil samples taken since June 1989. The field was subdivided into 5 plots treated with different amounts of sewage sludge. On some plots the sludge was artificially enriched with heavy metalts. The phenology of Chrinonomidae in the three years and their distribution over the different plots are discussed. The results suggest that the abundance of Chironomidae is increased by sewage sludge and appears to be also increased by heavy metals.     

Biodegradation of oily sludge in Kuwait soil

Soil microorganisms were not inhibited by mixing oily sludge in soil up to 8.7% (w/w) oil (15% sludge). Adding NH ₄ ⁺ and phosphate increased microbial activity. Microbial activity was also affected by seasonal variation. Thermotolerant microorganisms were more predominant during the summer. After 29 months, 72%, 84%, and 83% of the soil was degraded in fertilized soils dosed with 2.9, 5.8 and 8.7% oil, respectively.     

The effect of aromatic compounds on the work of activated sludge.

The resistance of bacteria occurring in activated sludge purifying refining-petrochemical wastewaters to phenol, cresol and pirocatechin as well as the possibility of the purification of synthetic wastewaters carrying high concentrations of these compounds by sludge composed of resistant strains was studied. The most toxic of the studied compounds was phenol. Six out of 29 strains were resistant to high concentration of phenol (1000 mg/l). Activated sludge synthesized from strains resistant to phenol, cresol and pyrocatechin was tolerant to high concentrations of these compounds. Worsening of the work of the sludge, expressed by decrease of GOD, was observed at the concentrations of phenol, cresol and pyrocatechin of 2000, 400 and 300 mg/l, respectively.     

The effect of sewage sludge treatment processes on oocysts of Cryptosporidium parvum

T.N. WHITMORE AND L.J. ROBERTSON. 1995. The effect of common sewage sludge treatment processes on oocysts of the coccidian protozoan Cryptosporidium was evaluated in laboratory simulations. The ability of primary sewage sedimentation to remove Cryptosporidium oocysts was found to be poor. Thermophilic (55°C) aerobic digestion and sludge pasteurization at the same temperature were found to be effective treatments to inactivate Cryptosporidium oocysts. Approximately 10% of the oocyst population were found to be viable after 18 d exposure to mesophilic (35°C) anaerobically digesting sludge. The viability of Cryptosporidium oocysts decreased within the range 20–40% in sludge-treated soil mesocosms over 30 d. The survival results obtained, however, indicated that oocysts would survive well beyond this period.     

The effect of DD nematocide on soil micro-organisms

The application of DD, a 1∶1 mixture of 1,3-dichloropropene and 1,2-dichloropropane, at field rate, to soil had neither stimulatory nor suppressive effects on bacteria, actinomycetes, fungi and cellulose decomposing bacteria. The toxic effect of the nematocide onAzotobacter and nitrogen-fixing clostridia was slight, the organisms recovering in a very short time. In fumigated soils the counts ofNitrosomonas andNitrobacter were markedly reduced and remained lower than the counts in the untreated soils for the 30 days duration of the experiment. The inhibitory effects of DD were to some extent influenced by soil type, being most marked in sandy and loam and least in calcareous soils.     

The effect of fire on soil humic substances

Summary High temperature effects on soil humic substances were investigated both in natural and laboratory conditions. Differential Thermal Analysis and pyrolysis show that only temperatures above 250°C produce changes in the humic acid fraction. The mean change is a loss of weight due to decarboxylation. Isotachophoretic studies also show that temperatures higher than 250°C produce alteration in the separation pattern of the different subfractions due to changes in the ‘core’ or/and in the amount of carboxyl and hydroxyl groups. Isotachophoregrams done on soil samples extracted from an area before and after fire show no differences. This result is taken as an indication that there was no direct effect of the temperature on the soil humic substances.     

The effect of planting Pinus pinaster Ait. on populations of soil microarthropods and on litter decomposition at Gnangara,Western Australia

Litter decomposition rates and the population densities of soil microarthropods were measured in three Pinus pinaster stands thirty-one, twenty-three and eighteen years old, and on an area of native vegetation on sandy soil at Gnangara, W.A. Litter decomposition was faster in the soil than within the litter layer and was slowest at the litter surface. Decomposition was rapid in cool wet seasons and slow in hot, dry summers. Microarthropod population densities were similar on all sites (77–100 × 10³/m²) but species diversity was greatest under native vegetation and least under the youngest pine stand. The impoverished soil micro-fauna of the pine stands is unable to decompose pine or sclerophyll litter as fast as the full complement of soil microfauna in native vegetation.