Soil Inoculum Potential Research Articles

Inhibitory Effect of Tall Hedge Mustard (Sisymbrium loeselii) Allelochemicals on Rangeland Plants and Arbuscular Mycorrhizal Fungi

Exotic weeds can interfere with neighboring species by releasing allelochemicals that either directly inhibit growth and distribution of associated species or affect them indirectly by disrupting their interaction with soil organisms, such as arbuscular mycorrhizal fungi (AMF). The allelopathic potential of tall hedge mustard was assessed using aqueous root and shoot extracts in seed germination and radicle growth bioassays. Aqueous tall hedge mustard root and shoot extracts strongly inhibited seed germination and growth of bluebunch wheatgrass, Idaho fescue, and spotted knapweed, but had minimal autotoxicity. Chemical analysis of tall hedge mustard tissues revealed the presence of two major glucosinolates—isopropyl andsec-butyl glucosinolate. The degradation products of these glucosinolates (isopropyl isothiocyanate andsec-butyl isothiocyanate) were identified in dichloromethane extracts of tall hedge mustard aqueous root and shoot extracts. Commercially available isopropyl isothiocyanate andsec-butyl isothiocyanate inhibited seed germination and radicle growth, suggesting their role in the allelopathic potential of tall hedge mustard. Tall hedge mustard aqueous extracts and isothiocyanates incorporated into an agar medium inhibited the spore germination of the AMF,Glomus intraradices. Tall hedge mustard infestations were also found to reduce the AMF inoculum potential of soil under field conditions. The results from this study show that tall hedge mustard produces chemicals that can inhibit the growth of neighboring plant species and their AMF associates.

Cause and duration of mustard incorporation effects on soil-borne plant pathogenic fungi

Two fungal plant pathogens, Rhizoctonia solani AG 2-2 and Fusarium oxysporum f.sp. lini, were studied in relation to general responses of soil fungi and bacteria following incorporation of Brassica juncea. Our aim was to understand to what extent the changes in the biological and physicochemical characteristics of the soil could explain the effects on the studied pathogens and diseases, and to determine the temporal nature of the responses. Short-term effects of mustard incorporation (up to 4 months) were investigated in a microcosm experiment, and compared with a treatment where composted plant material was incorporated. In a field experiment, the responses were followed up to 11 months after removal or incorporation of a mustard crop. In general, responses in the variables measured changed more after incorporation of fresh mustard material than after addition of similar amounts of composted plant material (microcosms) or after removal of the mustard crop (field). The soil inoculum potential of R. solani AG 2-2 decreased directly after incorporation of mustard, but increased later to disease levels above those in the untreated soil. Neither of these effects could be explained by changes in the population density of R. solani AG 2-2. Fusarium spp. were less influenced, although an increase in the suppressiveness to Fusarium wilt was observed after mustard incorporation as compared with the treatment where mustard was removed. The microbial responses to mustard incorporation were more pronounced for bacteria than for fungi. After an initial substantial increase, the bacterial density decreased but remained above the levels in the control treatment throughout the experimental periods. The bacterial community structure was modified up to 8 months after mustard incorporation. We conclude that incorporation of fresh mustard influences soil microbial communities, especially the bacteria, and has a potential to control the pathogenic activity of R. solani 2-2 on a short-term perspective. The time dependency in microbial responses is important and should be taken into consideration for the evaluation of the potential of Brassicas to control plant disease on a field scale.

Broad-spectrum detection and quantitation methods of Soil-borne cereal mosaic virus isolates

A broad-spectrum reverse transcription-polymerase chain reaction (RT-PCR) protocol was developed for detecting Soil-borne cereal mosaic virus (SBCMV) isolates, responsible for mosaic diseases in Europe, using primers targeting the highly conserved 3′-untranslated region of RNA-1 and RNA-2 of SBCMV. The 3′-end region is a privileged target for the detection of a wide range of isolates, because of sequence conservation, of the tRNA-like structure, the major role in viral replication and the signal amplification due to the presence of numerous genomic and subgenomic RNAs. The primers were also designed for virus quantitation using real-time RT-PCR with SYBR-Green chemistry. No cross-reaction with Wheat spindle streak mosaic virus, frequently associated with SBCMV, was observed. The use of RT-PCR and real-time quantitative RT-PCR allowed a more sensitive detection and quantitation of SBCMV to be made than was the case with ELISA. The methods enabled European isolates of SBCMV from Belgium, France, Germany, Italy and the UK to be detected and quantified. Real-time RT-PCR represents a new tool for comparing soil inoculum potential as well as cultivar resistance to SBCMV.

Population dynamics and biocontrol efficacy of the nematophagous fungus Hirsutella rhossiliensis as affected by stage of the soybean cyst nematode

Monitoring the population dynamics of a biocontrol agent in soil is important for understanding, predicting and increasing its efficacy. In this study, the population dynamics and the efficacy of a promising biocontrol agent against nematode, the fungus Hirsutella rhossiliensis, were investigated in greenhouse experiments with quantitative real-time polymerase chain reaction (PCR) and bioassay. To explore the effects of the fungus on nematode inoculum, soil infested with eggs or second-stage juveniles (J2) of Heterodera glycines was used. The results showed that the quantity of H. rhossiliensis DNA based on real-time PCR decreased over time, regardless of eggs or J2 as inoculum. The quantity of H. rhossiliensis DNA [femtogram (fg)/g soil] was highest (3.83 ± 1.96 × 10 8 fg/g soil) when the fungus was first added to soil and then decreased rapidly to 3.24 ± 1.22 × 10 7 fg/g in egg-infested soil and 7.34 ± 2.94 × 10 7 fg/g in J2-infested soil 17 days after planting, and then declined gradually between 17 and 59 days after planting. The data based on the bioassay showed that the percentage of J2 parasitized by H. rhossiliensis decreased throughout the experiment in both egg- and J2-infested soils. H. rhossiliensis controlled H. glycines more effectively in J2-infested soil than in egg-infested soil. At the end of the experiments (59 days after planting), nematode suppression and plant growth promotion in J2-infested soil were 79% and 55%, respectively, which were higher than the 34% and 2% in egg-infested soil. In soil that was not inoculated with the fungus, the number of H. glycines was 10 times higher in J2-infested soil than in egg-infested soil, indicating the greater nematode inoculum potential in soil infested with J2. DNA yield of H. rhossiliensis was statistically higher in J2-infested soil than in egg-infested soil in earlier period (prior to day 31) ( p < 0.05), which is consistent with the hypothesis that the numbers of J2 present during and soon after fungal inoculation are critical for maintaining the population density and biocontrol efficiency of the fungus.

Spatial distribution of Aphanomyces euteiches inoculum in a naturally infested pea field

The main objective of the study was to describe the horizontal and vertical distribution of Aphanomyces root rot in a naturally infested pea field. Measurements of inoculum potential clearly indicated a horizontal distribution of inoculum among several foci in the field, these foci differing in size and disease intensity. A highly significant relationship was observed between disease severity on plants during the cropping season and soil inoculum potential. In terms of the vertical distribution of inoculum in the soil, detection was maximal at a depth of 10 to 40 cm, but inoculum was detected down to a depth of 60 cm. Generally, inoculum potential was lowest for the layers at depths of 0 to 10 and 50 to 60 cm. Inoculum distribution and the value of the methodologies used are discussed in terms of possible use for epidemiology and disease forecasting.

Reaction of genotypes from several species of grain and forage legumes to infection with a French pea isolate of the oomycete Aphanomyces euteiches

The susceptibility/resistance to Aphanomyces euteiches of various genotypes (cultivars and breeding lines) of several grain legume species was assessed in controlled conditions. A total of 279 genotypes from the major grain legumes grown in temperate climates (faba bean, chickpea, lentil, lupin and common vetch) and three other legumes frequently cultivated in France (French bean, clover and alfalfa) were screened with one pea-infecting isolate from France. Four different categories of susceptibility/resistance were identified among the legume species/cultivars tested with the pea A. euteiches isolate: (1) susceptible legume species (lentil, alfalfa, French bean) among which low levels of partial resistance was observed; (2) legume species including susceptible genotypes and genotypes with high levels of resistance (common vetch, faba bean and clover), (3) species with a very high level of resistance (chickpea) and (4) species displaying no symptoms (lupin). It is therefore important to consider pathogen-species and pathogen-genotype interactions when defining the host specificity of A. euteiches and considering the possible role of different legume species in increasing or decreasing the soil inoculum potential.

Modélisation de cinétiques de la maladie de la tache de la carotte provoquée par un complexe d'agents pathogènes du genre Pythium dominé par le Pythium violae

Carrot cavity spot is caused by a complex of pathogens belonging to the genus Pythium, including Pythium violae. The disease is characterized by the appearance of sunken elliptical lesions on the taproot. The objective of the present study is to identify, understand, and prioritize the processes that induce the spatio-temporal kinetics of epidemics of cavity spot. We favoured the hypothesis that considers primary infection (from soilborne inoculum) and secondary infection (root-to-root contaminations from existing lesions, i.e., auto- and allo-infections). Epidemics were obtained during a 3-year field experiment after artificial soil infestation of plots with P. violae at increasing inoculum doses. Different kinetics of cavity spot were described using standardized disease measurements. The analysis of the incidence curves showed the early appearance of a plateau, with differences in the disease level that are positively correlated with the inoculum doses. These differences disappeared at the end of the cropping season. Three simulation models, integrating or not the concomitance of the primary and secondary infections, were fitted to the disease incidence to test if progress curves were compatible with the hypothesis of the occurrence of both infection processes: the logistic model, the bilogistic model of Hau and Amorim, and the model of Brassett and Gilligan without temporal decline of the soil inoculum potential. The quality of the fitting was correct in the three cases, and the hypothesis of the occurrence of secondary infections was not refuted. This result is an important argument to demonstrate the polycyclic nature of the disease.

In vitro selection of an effective fungicide against Armillaria mellea and control of white root rot of grapevine in the field

Armillaria mellea (Vahl ex Fr) Kummer is an aggressive pathogen which causes white root rot in a wide range of hosts. Most chemicals tested so far against Armillaria, both in vitro and in the field, have not been effective in reducing fungal growth and/or preventing plant decline and mortality. In the present work the effects of four DMI (sterol demethylation inhibitor) fungicides, cyproconazole, hexaconazole, propiconazole and tetraconazole, and another six downwardly mobile systemic chemicals, azoxystrobin, cubiet (copper bis(ethoxy-dihydroxy-diethylamino)sulfate), fosetyl-Al, potassium phosphite, sodium tetrathiocarbonate (STTC) and 2-(thiocyanomethylthio)benzothiazole (TCMTB), on the mycelial growth of A. mellea were compared and evaluated; the product yielding the best results in in vitro experiments was selected to determine its efficacy in preventing decline and mortality of grapevines in the field. Best results on in vitro fungal growth reduction were obtained with the four azoles tested, in particular with cyproconazole and hexaconazole, achieving 67-72% mycelial growth inhibition at the lowest dose. Results obtained in the field showed that a dose of 50 mg AI litre(-1) of cyproconazole once or twice a year was efficient in controlling the disease even in vines seriously affected by the pathogen. However, further research is required to study minimum effective doses, residual effects and the convenience of the application of annual dressings in damaged vineyards, so as to gradually reduce the pathogen inoculum potential in soil and control the disease while reducing chemical residues in the plant and preventing development of fungal resistance.

Soil Inoculum Potential And Arbuscular Ycorrhizal Colonization Of Acer Rubrum In Forested And Developed Landscapes

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test two independent hypotheses: (1) landscape trees show lower levels of AMF colonization than forest trees, and (2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% versus 22%). However, soil­sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% versus 4%). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between field and landscape maples appeared to reflect differences in soil chemical properties rather than in inoculum potential. The results of this study suggest that not all disturbed landscape soils are deficient in AMF propagules.

(115) Soil Inoculum Potential and Mycorrhizal Colonization of Acer rubrum in Forested and Developed Landscapes

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test the hypotheses that: 1) landscape trees show lower levels of AMF colonization than forest trees; and 2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% vs. 22%; P= 0.0002). However, soil-sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% vs. 4%; P= 0.0081). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between forest and landscape maples appeared to reflect differences in soil chemical properties rather than in soil inoculum potential.

Mycorrhiza formation and nutrient concentration in leeks (Allium porrum) in relation to previous crop and cover crop management on high P soils

An improved integration of mycorrhizas may increase the sustainability in plant production. Two strategies for increasing the soil inoculum potential of mycorrhizal fungi were investigated in field experiments with leeks: Pre-cropping with mycorrhizal main crops and pre-establishment of mycorrhizal cover crops. Experiments on soils with moderate to high P content (26–50 mg kg−1 bicarbonate-extractable P) showed that the previous crop influenced mycorrhiza formation, uptake of P, Zn, and Cu, and early growth of leek seedlings. A cover crop of black medic, established the previous autumn, increased the colonization of leek roots by mycorrhizal fungi. During early growth stages, this increase was 45–95% relative to no cover crop. However, cover cropping did not significantly increase nutrient concentration or growth. These variables were not influenced by the time of cover crop incorporation or tillage treatments. Differences in colonization, nutrient uptake and plant growth diminished during the growing period and at the final harvest date, the effects on plant production disappeared. High soil P level or high soil inoculum level was most likely responsible for the limited response of increased mycorrhiza formation on plant growth and nutrient concentrations.

Evidence for mutualist limitation: the impacts of conspecific density on the mycorrhizal inoculum potential of woodland soils

The ability of seedlings to establish can depend on the availability of appropriate mycorrhizal fungal inoculum. The possibility that mycorrhizal mutualists limit the distribution of seedlings may depend on the prevalence of the plant hosts that form the same type of mycorrhizal association as the target seedling species and thus provide inoculum. We tested this hypothesis by measuring ectomycorrhizal (EM) fine root distribution and conducting an EM inoculum potential bioassay along a gradient of EM host density in a pinyon-juniper woodland where pinyon is the only EM fungal host while juniper and other plant species are hosts for arbuscular mycorrhizal (AM) fungi. We found that pinyon fine roots were significantly less abundant than juniper roots both in areas dominated aboveground by juniper and in areas where pinyon and juniper were co-dominant. Pinyon seedlings establishing in pinyon-juniper zones are thus more likely to encounter AM than EM fungi. Our bioassay confirmed this result. Pinyon seedlings were six times less likely to be colonized by EM fungi when grown in soil from juniper-dominated zones than in soil from either pinyon-juniper or pinyon zones. Levels of EM colonization were also reduced in seedlings grown in juniper-zone soil. Preliminary analyses indicate that EM community composition varied among sites. These results are important because recent droughts have caused massive mortality of mature pinyons resulting in a shift towards juniper-dominated stands. Lack of EM inoculum in these stands could reduce the ability of pinyon seedlings to re-colonize sites of high pinyon mortality, leading to long-term vegetation shifts.

Thuja plicata exclusion in ectomycorrhiza-dominated forests: testing the role of inoculum potential of arbuscular mycorrhizal fungi

The ability of trees dependent on arbuscular mycorrhizal (AM) fungi to establish in ectomycorrhizal forests is unknown. On northern Vancouver Island, Canada, there are sharp boundaries between mixed red cedar (Thuja plicata)-hemlock (Tsuga heterophylla) (CH) stands, and stands of hemlock and amabilis fir (Abies amabilis) (HA). We tested differences in AM colonization of red cedar between ectomycorrhiza-dominated (HA) stands and stands containing red cedar (CH), across a range of light levels. We used a soil bioassay approach to determine whether there was sufficient AM fungal inoculum in the HA tree stands to colonize red cedar seedlings. Seeds of hemlock and red cedar were sown in forest floor samples collected from the two types of forests, and shade treatments ranging from < 1 to 53% of full sunlight were imposed. After 6 months, seedling survival and root and shoot biomass were quantified, and red cedar seedlings were sampled for AM fungal colonization. Hemlock survival and growth did not differ between soil types, suggesting there was no substrate-associated limitation to its establishment in either forest type. Red cedar colonization by AM fungi was significantly correlated with light levels in CH soils but arbuscular mycorrhizas were absent in roots of red cedar seedlings grown in HA soil. Red cedar survival and relative growth rate were significantly greater in the CH than in HA soil; higher growth was due primarily to greater shoot growth in CH soils at high light levels. The low soil inoculum potential for red cedar in ectomycorrhiza-dominated stands may account for the virtual exclusion of red cedar seedlings from these forests.

Assessing the resistance of winter wheat to wheat spindle streak mosaic bymovirus

Management of Wheat spindle streak mosaic virus (WSSMV), a bymovirus, relies on resistant cultivars. We compared the results from mechanical inoculation with virus-infected plant sap with those of a previous study from natural infection in field trials. The six cultivars tested (Century, Wichita, TAM 200, Geneva, Harus, and Augusta) became infected via mechanical inoculation of leaves, ruling out resistance to virus replication in leaves as the basis for resistance in the cultivars considered resistant in field trials. 'Augusta' (susceptible), 'Geneva' (resistant), and germplasm KS92WGRC22 (highly resistant) were compared in field plots for numbers of symptomatic versus asymptomatic tillers. Individual plants having both infected and uninfected tillers were found only in the two resistant wheats. Resistance in 'Geneva' and KS92WGRC22 could be due to uneven movement of virus from roots into tillers or to reduced virus replication in roots. If reduced virus replication in roots is the source of resistance in a cultivar, then cropping with such a cultivar would contribute less to the inoculum potential of soil than cropping with susceptible cultivars. Soil transmission of virus occurred in field soil gathered from the root zone of symptomatic 'Augusta', but not in field soil from the root zone of asymptomatic KS92WGRC22. These results suggest that infected plants can, in a single crop cycle, contribute significantly to the soil reservoir of WSSMV.Key words: winter wheat, Wheat spindle streak mosaic virus, WSSMV, Wheat yellow mosaic virus, WYMV, bymoviruses, soilborne viruses, resistance evaluation.

Terrestrial vertebrates promote arbuscular mycorrhizal fungal diversity and inoculum potential in a rain forest soil

We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore communities and mycorrhizal inoculum potential (MIP) of a tropical rain forest soil by comparing plots where terrestrial vertebrates had been excluded for 3 years to adjacent control plots. We extracted spores from soil using sucrose density gradient centrifugation and assayed MIP by growing seedlings of maize (Zea mays) and a rain forest tree (Flindersia brayleana) in intact soil cores from exclosure and control plots. Control plots had significantly higher spore abundance, species richness and diversity than exclosures. Spore community composition also differed significantly between exclosure and control plots. Seedlings of both plant species grown in control cores had significantly higher arbuscular‐mycorrhizal colonization than those grown in exclosure cores. This study suggests that loss of vertebrates could alter rates of mycorrhizal colonization with consequences for community and ecosystem properties.

Mycorrhizal inoculum potential of soils from alley cropping plots in Sénégal

Intact soil cores were sampled from around three leguminous tree species ( Acacia nilotica, Acacia tortilis and Prosopis juliflora) in 10-year-old alley-cropping plots at Thiénaba, Sénégal. Cores were removed from two depths (0–25 and 25–50 cm) and at two distances from the trunk (1 and 5 m). Duplicate soil cores were taken for assessment of root concentration (cm/100 cm 3 soil), mycorrhizal infection (% of infected root length) and spore concentration in the soils. In order to determine the mycorrhizal inoculum potential (MIP) of the soils, a mycorrhizal bioassay of the soil cores was conducted in the greenhouse using millet seedlings. For all plots, seedlings grown in soils from the surface layer (0–25 cm) were larger and formed higher levels of infection than those grown in soils from 25 to 50 cm depth. Mycorrhizal infection of the seedlings was greatest in soil from the A. tortilis plots and, unlike the other tree species, also the greatest in soil collected near the tree. Positive relationships were found between the growth and infection of the bioassay seedlings and the root and spore concentrations in the field soils. Seedling growth and infection may also have been related to higher levels of carbon in the field soils. The results indicated that root and spore concentrations in the field soils were good indicators of MIP, but that levels of root infection were not. The results also indicated the potential benefit to crop yield of maintaining high levels of mycorrhizal propagules in alley-cropping soils and a possible role of the trees in maintaining these sources of inoculum.

Low ectomycorrhizal inoculum potential and diversity from soils in and near ancient forests of bristlecone pine (Pinus longaeva)

Intersite variation in ectomycorrhizal (ECM) inoculum potential in soils from 16 sites located in arid subalpine areas of the White Mountains of California was quantified. The study sites included valleys dominated by big sagebrush (Artemisia tridentata Nutt.) and mountainsides dominated by ancient Great Basin bristlecone pine (Pinus longaeva Bailey). ECM inoculum potential was not detected at three of four valley sites nor in 42% of forest soil samples. Only 10 mycorrhizal species were detected in bioassays, and four of those accounted for 94.5% of all colonized seedlings, in order of decreasing abundance these were Pyronemataceae sp., Rhizopogon sp., Wilcoxina rehmii Yang &amp; Korf, and Cenococcum sp. These species were identified also from in situ mycorrhizal roots. The abundance of the dominant Pyronemataceae sp. was significantly positively correlated with pH, which at all forest sites was high compared with typical conifer forest soils. Our results show that the ECM inoculum potential of soils is low, homogeneous, and spatially restricted in these ancient high-elevation forests.Key words: fungal community, molecular ecology, spore dispersal.

Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize

Low-input agricultural systems that do not rely on fertilizers may be more dependent on vesicular-arbuscular mycorrhizal [VAM] fungi than conventionally managed systems. We studied populations of spores of VAM fungi, mycorrhiza formation and nutrient utilization of maize (Zea mays L.) grown in moldboard plowed, chisel-disked or no-tilled soil under conventional and low-input agricultural systems. Maize shoots and roots were collected at four growth stages. Soils under low-input management had higher VAM fungus spore populations than soils under conventional management. Spore populations and colonization of maize roots by VAM fungi were higher in no-tilled than in moldboard plowed or chisel-disked soil. The inoculum potential of soil collected in the autumn was greater for no-till and chisel-disked soils than for moldboard plowed soils and greater for low-input than conventionally farmed soil. The effects of tillage and farming system on N uptake and utilization varied with growth stage of the maize plants. The effect of farming system on P use efficiency was significant at the vegetative stages only, with higher efficiencies in plants under low-input management. The effect of tillage was consistent through all growth stages, with higher P use efficiencies in plants under moldboard plow and chisel-disk than under no-till. Plants grown in no-tilled soils had the highest shoot P concentrations throughout the experiment. This benefit of enhanced VAM fungus colonization, particularly in the low-input system in the absence of effective weed control and with likely lower soil temperatures, did not translate into enhanced growth and yield.

SOLARIZATION FOR THE CONTROL OF SOIL-BORNE PATHOGENS IN FOREST NURSERIES IN TEMPERATE CLIMATE

Soil solarization was carried out at three eucalyptus forest nurseries in Argentina in order to evaluate an alternative method for controlling damping-off of seedlings. The experiments were performed at forest nurseries, located in a temperate climate (province of Buenos Aires), infected with Fusarium (mainly F. oxysporum) and Pythium species, using single and double layers of transparent polyethylene film during summer months (January and February). Effectiveness of the treatments was evaluated using a biological assay enabling assessment of soil inoculum potential. Soil temperatures reached during solarization at the three nurseries were 44, 45 and 49°C, respectively. The soilborne pathogens were controlled within 4 weeks using a single layer in one of the nurseries and using a double layer in the two others. Although the temperatures generated in the soil were not very high, the results suggest that the antagonistic microflora present in the native virgin soils in Argentina and or biological processes may have contributed to the control of these pathogens.

Interactions among Arbuscular mycorrhizal (AM) Inoculum Potential of Soil, Landscape Position and Erosion

Interactions among Arbuscular mycorrhizal (AM) Inoculum Potential of Soil, Landscape Position and Erosion