Feeding trials ofAphelenchus avenae on soil bacteria and actinomycetes

Summary Aphelenchus avenae and various unidentified bacteria and actinomycetes were cultured from soil samples taken from a pine-forest and a wheat-field. The nematode failed to reproduce in significant numbers on cultures of these micro-organisms and was apparently unable to utilize them as food sources.     

Mycoflora of Argentinian corn harvested in the main production area in 1990

Corn (Zea mays) is the main cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the corn kernels. This paper reports on the identification of internal and external mycoflora of corn kernels harvested in the main production area in Argentina in 1990. A mycological survey was carried out on 178 corn samples, from five locations in that area and the isolation frequency and relative density of the prevalent fungal genera compared. GenusFusarium was the most prevalent component of the internal seedborne mycoflora in the five locations.Penicillium was prevalent in all locations, taking into account the frequency. However, this genus was predominant only in two locations, when the relative density was considered. The predominantFusarium wasF. moniliforme and the most frequently isolated species ofAlternaria, Aspergillus andPenicillium wereA. alternata, A. flavus andP. decumbens, respectively.Diplodia species were not isolated from any of the samples.     

Populations ofSitobion avenae andAphidius ervi on spring wheat in the northwestern United States Spatial distribution and sequential sampling plans based on numerical and binomial counts

During a three-year field survey of the English grain aphid,Sitobion avenae (F.) (Homoptera: Aphididae) and the parasitoid,Aphidius ervi Haliday (Hymenoptera: Aphidiidae; represented by aphid mummies) on spring wheat, data sets were generated which consisted of 47 estimates of mean density (m aphids per tiller), variance (s ²), and the proportion of empty tillers (P ₀ forS. avenae and 22 estimates of the same statistics forA. ervi, respectively. Each estimate of the aphid and parasitoid populations was based on counts per individual tiller on each sampling occasion. Taylor's power law was found to fit the data sets better than Iwao'sm ^*−m regression model. Taylor's slope forS. avenae (1.3076) was significantly higher than that forA. ervi (1.1519), indicating thatS. avenae was more aggregated thanA. ervi. Based on temporal changes in spatial aggregation represented by an index, 1/k [wherek was estimated asm ²/(s²−m)],S. avenae was most aggregated at low densities during the early infestation period and tended to be less aggregated as density increased, whereasA. ervi was more likely to be randomly distributed. A commonk was detected for neitherS. avenae norA. ervi because the slopes from the linear regression ofk onm significantly exceeded 0. Sequential sampling plans, based on numerical (complete) and binomial (presence or absence) counts, for the aphid and parasitoid species were developed using Taylor's parameters and those estimated from the linear regression of ln(m) on ln[−ln[P ₀], respectively. Suggestions are made concerning the use of the sampling plans and the levels of precision that may be attained.     

New records of the carabidicolous laboulbeniales (Ascomycetes) of Japan

Six carabidicolous species of Laboulbeniales are reported as new for the Japanese mycoflora. They areDixomyces stomonaxi, Laboulbenia picardii, L. tenera, L. slackensis, L. aristata andL. kwangjuensis. Two forms ofD. stomonaxi are distinguished, one form of which resemblesD. nigromarginatus. A remarkable ornamentation consisting of a coillike pattern occurs on the receptacle ofL. picardii. InL. tenera andL. slackensis, the outer appendage has somewhat constricted, blackened septa near the base.Laboulbenia aristata andL. kwangjuensis have spirally arranged outer wall cells. Antheridia were observed inL. tenera, L. slackensis, L. aristata andL. kwangjuensis.     

Glasshouse evaluation of the growth ofAlnus rubra andAlnus glutinosa on peat and acid brown earth soils when inoculated with four sources ofFrankia

The effects of soil type (an acid peat and 2 acid brown earths) andFrankia source (3 spore-positive crushed nodule inocula and spore-negative crushed nodules containing the singleFrankia ArI5) on nodulation, N content and growth ofAlnus glutinosa andA. rubra were determined in a glasshouse pot experiment of two years duration. Plants on all soils required additional P for growth. Growth of both species was very poor on peat withA. glutinosa superior toA. rubra. The former species was also superior toA. rubra on an acid brown earth with low pH and low P content. Some plant-inoculum combinations were of notable effectivity on particular soils but soil type was the major source of variation in plant weight. Inoculation with crushed nodules containingFrankia ArI5 only gave poor infection of the host plant, suggesting that inoculation with locally-collected crushed nodules can be a preferred alternative to inoculation withFrankia isolates of untested effectivity. Evidence of adaptation ofFrankia to particular soils was obtained. Thus, while the growth of all strains was stimulated by mineral soil extracts, inhibitory effects of peat extracts were more apparent with isolates from nodules from mineral soils than from peat, suggesting that survival ofFrankia on peat may be improved by strain selection.     

Impact of intercropping aphid-resistant wheat cultivars withoilseed rape on wheat aphid (Sitobion avenae) and its natural enemies

The effects of intercropping of wheat cultivars and oilseed rape on the densities of wheat aphid, Sitobion avenae, and their arthropod natural enemies were evaluated. Three winter wheat cultivars with different resistant levels to S. avenae were used: ‘KOK’ (high resistance), ‘Xiaobaidongmai’ (low resistance) and ‘Hongmanghong’ (susceptible). The results showed that the densities of S. avenae were significantly higher on the monoculture pattern than on either the 8-2 intercropping pattern (eight rows of wheat with two rows of oilseed rape) or the 8-4 intercropping pattern (eight rows of wheat with four rows of oilseed rape). The mean number of predators and the mummy rates of S. avenae were significantly higher in two intercropping patterns than those in the monoculture pattern. The densities of S. avenae, ladybeetles, and mummy rate of S. avenae were significantly different among different wheat cultivars. The highest densities of S. avenae and ladybeetles were found on wheat cultivar Hongmanghong. The lowest densities of S. avenae associated with high mummy rate of S. avenae were found on wheat cultivar Xiaobaidongmai. The results showed that wheat-oilseed rape intercropping conserved more predators and parasitoids than in wheat monoculture fields, and partial resistance of wheat cultivar Xiaobaidongmai had complementary or even synergistic effects on parasitoid of S. avenae.     

Geophagy by the bonnet macaques (Macaca radiata) of southern India: A preliminary analysis

Bonnet macaques (Macaca radiata) in the Marakkanam Reserved Forest of southern India consume termitaria soils. Samples from the ingested termite mounds are compared with samples taken from the surrounding uneaten soils in an attempt to determine why the termitaria soils are eaten. Particle size, clay and primary mineral composition, geochemistry, and scanning electron microscopic analyses are used to search for a possible explanation for geophagy among the bonnet macaques. Kaolin minerals abound throughout the Marakkanam soil sample suite. But the termitaria soils are distinguished by the presence of small amounts of smectite. An abundance of kaolin minerals in combination with small amounts of smectite strongly resembles the mineralogy ofeko, a traditional African remedy for stomach ailments, and Kaopectate™, a western anti-diarrhoeal preparation. The percentage of mature leaves and fruits ofAzadirachta indica consumed by the bonnet macaques is relatively high. Plant feeding deterrents, such as, acid detergent fibre (ADF) and the inherent nature of the fruits ofAzadirachta indica, when consumed in large quantities to act as a purgative, could cause gastrointestinal upsets and diarrhoea. At Marakkanam, bonnet macaques ingest termitaria earth that would act as a pharmaceutical agent to alleviate gastrointestinal upsets and control diarrhoea.     

Analysis of wheat resistance to the cereal aphidSitobion avenae using electrical penetration graphs and flow charts combined with correspondence analysis

The behaviour ofSitobion avenae (F.), was compared on resistant wheat lines ofTriticum monococcum (L.) and a susceptible variety ofTriticum aestivum (L.). Firstly, stylet penetration activities were monitored with the Electrical Penetration Graph (EPG) technique and subsequently analysed using flow charts combined with correspondence analysis. Plant resistance was shown to be associated with repeated penetrations without access to either the xylem or the phloem, and with numerous failures in starting a sustained sap ingestion (as represented by pattern E2). Access to sieve elements of the phloem did not seem to be much affected on resistant plants but it took the aphid three times as long to produce a sap ingestion pattern when maintained on the resistant lineT. monococcum n^o 44 (Tm44) as compared with aphids maintained on susceptible plants. As a result the total time spent in ingesting from sieve elements was reduced by 72% on Tm44. Secondly, direct observations of freely-moving apterous adults were performed. Aphids did not discriminate between resistant and susceptible wheat during the first 30 min of access to test leaves, but only 4 out of 25 aphids were still probing after eight hours on resistant Tm44. The relevance of these results to possible location of the resistance factor(s) are discussed. Although detection of plant resistance before sieve elements are reached can not be rigorously excluded, the factors involved inT. monococcum resistance toS. avenae undoubtedly occur within the phloem vessels.     

Tolerance ofRhizobium leguminosarum bv.phaseoli to acidity and drought

Ten strains ofRhizobium leguminosarum bv.phaseoli isolated from soils of Morocco were more tolerant than three culture collection strains to acid conditions in culture media or in sterile soil. The survival rate of a tolerant strain in a sandy acid soil was greater than a sensitive strain at different humidity levels. These properties should give locally selected strains an advantage in nodulatingPhaseolus vulgaris roots in soils similar to those used here.     

Behavioural differences between Aphidius ervi populations from two tritrophic systems are due to phenotypic plasticity

The Palaeoarctic parasitoid Aphidius ervi Haliday (Hymenoptera, Aphidiidae) parasitises legume aphids in its region of origin. In Chile, it parasitises both legume and cereal aphids. This special situation was studied at two levels: (i) the host searching behaviour of A. ervi from two different tritrophic systems (Acyrthosiphon pisum on alfalfa and Sitobion avenae on wheat) was investigated in dual choice tests in a wind tunnel between odours from both A. pisum-alfalfa host plant complex (HPC) and S. avenae-wheat HPC, and (ii) the genetic structure of A. ervi populations from both sources using molecular markers. Responses of A. ervi females to volatile olfactory cues emanating from A. pisum-alfalfa HPC and S. avenae-wheat HPC were significantly higher towards the HPC on which they were reared during the last generation before experimentation, regardless of the origin of the parasitoid. As previously described for this parasitoid species, oviposition experience was also of major relevance in the preferences of female parasitoids. On the other hand, variation in mitochondrial DNA segments and RAPD-PCR polymorphism using total DNA showed the absence of host-based population structure and a high genetic homogeneity between these A. ervi populations. These results reject the possible existence of different host-strains of this parasitoid in Chile.     

15N-marked aphids for predation studies under field conditions

Individuals ofSitobion avenae (F.) (Homoptera: Aphididae) were marked with the stable isotope ¹⁵N through feeding on cereal seedlings which were immersed in a¹⁵N-enriched nutrient solution. Increased ¹⁵N-contents were obtained in all aphids with no detrimental effect on survival and fertility. When ¹⁵N-marked aphids were transferred to non ¹⁵N-enriched seedlings, after a short initial decreasing phase, ¹⁵N-contents remained nearly constant in time. A content of 10% ¹⁵N in the nutrient solution of the seedlings was sufficient for marking the aphids.     

Effect of Manipulations on the Host Selection Behavior of Sitobion avenae (Homoptera: Aphididae)

The study of aphid host selection and feeding behavior is difficult because aphids have to penetrate the plant to reach their feeding site, phloem tissue. The activity of the stylets, salivation or food intake, can not be observed externally and requires an indirect visualization technique such as the Electric Penetration Graph (EPG). The plant selection behavior of Sitobion avenae on potato varied depending on whether an ethological or EPG method was used to study it. A similar variation did not occur with Myzus persicae or Rhopalosiphum padi. The application of water-based silver conductive paint onto the thorax, as normally used for EPG, or onto the abdomen of Sitobion avenae alates resulted in increased duration and frequency of probing compared to results from ethological observations. Our results indicated that EPG manipulations might have different effects on different species of aphids and that a comparison of EPG and ethological data is required to confirm that the EPG method does not bias aphid feeding behavior.     

Interference betweenSalsola kali L. seedlings: Implications for plant succession

Studies were conducted to determine the cause of the decline of the early successional species,Salsola kali L., in the years following its colonization of disturbed soils in arid regions of the western United States. DriedS. kali plant material significantly stimulated the growth ofS. kali but had no effect on the growth or levels of mycorrhizal infection ofAgropyron smithii, a later successional grass. In contrast, root leachates fromS. kali caused a depression in the growth ofS. kali, but had no effect on the growth or mycorrhizal infection ofA. smithii. In the reciprical experiment, root leachates fromA. smithii had no effect on mycorrhizal fungi,S. kali, orA. smithii. This study contradicts earlier studies of the allelopathic potential ofS. kali litter and supports the importance of direct interference betweenS. kali seedling as the cause of the die-off ofS. kali during secondary succession.     

Distribution of soil fractions and location of soil bacteria in a vertisol under cultivation and perennial grass

Effects of soil management on soil characteristics were investigated on the rhizosphere (RPP) and the nonrhizosphere (NRPP) soil of a re-grass vertisol underDigitaria decumbens and in the soil under continuous cultivation (CC). A low energy technique allowed to separate eight size and density fractions, including macro- and micro-aggregates while preserving soil bacteria. Organic C and N, microbial biomass C and the number of total bacteria (AODC) and ofAzospirillum brasilense and their distribution were determined in soil fractions isolated from the CC, NRPP and RPP soils. Soil macroaggregates (>2000 m) were similarly predominant in the NRPP and RPP soils when the dispersible clay size fraction (<2 m) respresented more than 25% of the CC soil mass. The main increase of C content in RPP originated from the macroaggregates (> 2000 m) and from the root fraction, not from the finer separates. The proportion of organic C as microbial biomass C revealed the low turnover of microbial C in the PP situations, especially in the clay size fraction of the NRPP soil. A common shift of AODC toward the finer separates from planted soils (CC and RPP) revealed the influence of living plants on the distribution of soil bacteria. The relative abundance ofA. brasilense showed the presence of the active roots ofDigitaria in the macroaggregates and their contact with the dispersible clay size fraction of the rhizosphere soil.     

Two interesting cleistothecial Ascomycetes from soils

A new variety ofThermoascus, Thermoascus crustaceus var.verrucosus, is described and illustrated. It is characterized by producing prominently verrucose ascospores. The other characters are almost identical with those of the type variety.Leucothecium coprophilum, a rare ascomycete that has only previously been reported from Spain, is recorded from soils in Taiwan and Korea.     

Preharvest seed infection byAspergillus flavus group fungi and subsequent aflatoxin contamination in groundnuts in relation to soil types

Preharvest seed infection byAspergillus flavus and aflatoxin contamination in selected groundnut genotypes (fourA. flavus-resistant and fourA. flavus-susceptible) were examined in different soil types at several locations in India in 1985–1990. Undamaged mature pods were sampled at harvest and seed examined forA. flavus infection and aflatoxin content in two or more trials at ICRISAT Center on light sandy soils and red sandy loam soils (Alfisols), and on Vertisols, at Anantapur on light sandy soils, and at Dharwad and Parbhani on Vertisols. Rainy season trials (1985–1989) were all rainfed. Post-rainy season trials were irrigated; late-season drought stress (90 days after sowing (DAS) until harvest at 125 DAS) was imposed in the 1987/88 and 1989/90 seasons.A. flavus infection and aflatoxin contamination levels were much lower in seed of all genotypes from Vertisols than in seed from Alfisols across locations and seasons. Vertisols also had significantly lower populations ofA. flavus than Alfisols. There were no marked differences between light sandy soils and red sandy loam soils (Alfisols) in respect of seed infection byA. flavus and aflatoxin contamination. Significant interactions between genotypes and soil types were evident, especially in theA. flavus-susceptible genotypes. Irrespective of soil types,A. flavus-resistant genotypes showed lower levels of seed infection byA. flavus and other fungi than didA. flavus-susceptible genotypes. The significance of the low preharvest aflatoxin risk in groundnuts grown on Vertisols is highlighted.ICRISAT Journal Article No. JA 1122     

Differing amounts of genetic polymorphism in testes and male accessory glands ofDrosophila melanogaster andDrosophila simulans

We surveyed genetic polymorphism by two-dimensional gel electrophoresis of male reproductive tract proteins in 20 isofemale lines each ofDrosophila melanogaster andDrosophila simulans. After classifying 244 such proteins ofDrosophila melanogaster and 271 ofDrosophila simulans by their distribution between testes and accessory glands within the reproductive tract, significant correlations were found between genetic polymorphism and tissue distribution. In both species, gland-specific proteins were significantly more polymorphic than testis-specific proteins, as well as those found in both testes and glands. Simultaneously, inDrosophila simulans, proteins found in roughly equivalent relative abundance in both testes and glands were significantly less variable than gland-specific and testis-specific proteins, as well as those with a quantitative difference in relative abundance between testes and glands. These correlations may reflect general differences in variability between extracellular and intracellular proteins and between proteins with broad as opposed to tissue-specific distributions.We thank the Natural Sciences and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).     

Measurements of genetic variability for symbiotic dinitrogen fixation in fieldgrwon fababean (Vicia faba L.) using a low level15N-tracer technique

Before starting a breeding program aimed at improving the nitrogen nutrition ofVicia faba, the authors tried an alternative technique to the acetylene reduction assay, to measure some genetic variability in the plant material. The quantity of dinitrogen fixed by several cultivars ofVicia faba was estimated using a low enrichment¹⁵N tracer method and high precision¹⁵N mass spectrometry. The fababeans were cultivated for two years in two different soils. The percentage of fixed dinitrogen in the seed varied between genotypes from 40 to 83% of the total nitrogen and was positively correlated with the total seed nitrogen (r=0.64 to 0.86). A highly significant positive correlation was also found between the total seed nitrogen and the quantity of fixed dinitrogen in the seed (r=0.95 to 0.99). The technique used to measure dinitrogen fixation proved to be useful and reliable enough to discriminate between various genotypes, grown over a period of two years in two different soils. However, several non-fixing control plants showed significant differences in their¹⁵N enrichment and the problem of choosing a good reference plant was raised and discussed.     

Filipin-sterol complexes in bean rust- and oat crown rust-fungal/plant interactions: Freeze-etch electron microscopy

Summary Treatment with the polyene antibiotic filipin resulted in the formation of granular protuberances of the plasmamembranes of the mesophyll cells of bean (Phaseolus vulgaris) and oat (Avena sativa) plants, and of intercellular hyphal cells of the rust fungiUromyces appendiculatus var.appendiculatus andPuccinia coronata var.avenae, as seen by freeze-etch electron microscopy. The granules were also occasionally seen in intracellular vesicles ofU. appendiculatus. None were found in any intracellular organelles of plant or fungal tissue. The granules ranged in size from about 20–25 nm in the plant tissue and 21–27 nm in the fungal tissue. They were concluded to be filipin-sterol (FS) complexes. The extrahaustorial membranes of either bean or oat rustinfected tissue were generally devoid of FS complexes. The extrahaustorial membrane is continuous with the host plasmamembrane but appeared to have a lower sterol content as compared to the non-invaginated plasmamembrane. The results are discussed in relation to membrane associations at the host-parasite interface.Contribution No. 1011. Winnipeg Research Stn.     

Species richness and seasonal abundance of ectomycorrhizal fungi in plantations of<Emphasis Type="Italic"> Eucalyptus dunnii</Emphasis> and<Emphasis Type="Italic"> Pinus taeda</Emphasis> in southern Brazil

The abundance and diversity of ectomycorrhizal fungi (EMF) was assessed based on the collection of basidiocarps during 12 months comprising the spring of 1995, and the summer, autumn, and winter of 1996, in three stands of young, middle-aged, and rotation age plantations of Pinus taeda and Eucalyptus dunnii, in the state of Santa Catarina, southern Brazil. A total of 3,085 collections yielded 34 presumed EMF taxa in ten genera, including mushroom-like and sequestrate species. Fruiting patterns of EMF differed with host and season, and host specificity was apparent in some. The overall relative importance (RI) and the Shannon diversity index (H) suggested that stands of E. dunnii had a more diverse aboveground EMF community than those of P. taeda. Overall, species of Scleroderma and Laccaria were not only the most abundant but also had the highest biomass values. The results show that a small number of species of abundant biomass and a larger number of species of less-abundant biomass characterize each forest class.