Fungivorous Nematodes Research Articles

Effect of Fusarium oxysporum f. sp. lycopersici and Meloidogyne incognita interaction on wilt disease incidence in tomato

Development of diseases in cultivated crops depends on the complex inter-relationship between host, pathogen and prevailing environmental conditions. The significant role of nematodes in the development of nematode–fungus interaction is demonstrated in many crops throughout the world. Therefore, the main objectives of this study were to evaluate the interaction between Fusarium oxysporum f. sp. lycopersici and Meloidogyne incognita. The experiment was laid out in a completely randomized design (CRD) with three replications in pot conditions. The results show that inoculation of nematode at 7th day prior to inoculation of fungus caused maximum reduction in plant growth parameters and increase per cent disease incidence followed by simultaneous inoculation of nematode and fungus as compared to control.

Impacts of saltwater intrusion on soil nematodes community in alluvial and acid sulfate soils in paddy rice fields in the Vietnamese Mekong Delta

Saltwater intrusion is a potential risk damaging crop diversity and productivity due to degraded soil physicochemical properties. However, little is known about how salinity affects the structure and function of soil nematodes community in intensive rice cultivated area. This study aimed (1) to assess the impacts of saltwater intrusion on the nematode community in alluvial and acid sulfate soils; and (2) to evaluate its relation with soil conditions. Saltwater intrusion reduced the abundance of both free-living nematodes (FLN) and plant-parasitic nematodes (dominated by Hirschmanniella) in soils. FLN community was different among sites with different physicochemical properties. The omnivorous genera Aporcelaimellus and Thornenema were only found in non-salt-affected alluvial soil, whilst Mesodorylaimus was dominant in salt-affected acid sulfate soil, suggesting that this genus might be tolerant to higher EC and soluble Na+, K+, Ca2+. The bacterivorous nematodes (dominant taxa Chronogaster, Rhabdolaimus) were dominant in both non-salt affected and salt-affected alluvial soils, which accounted for 48% and 40%, respectively, whilst it accounted for 21% in salt-affected acid sulfate soil. The abundance of fungivorous nematodes (Aphelenchoides, Ditylenchus, Filenchus) were greater in salt-affected alluvial soil in contrast to the other treatments, suggesting that these might be tolerant to salinity and low pH. Saltwater intrusion reduced biological diversity (Margalef, Shannon-Wiener, and Hill’s indices), maturity index (∑MI, MI25), and clearly affected functional guilds of nematode community, especially c-p 5 group was reduced in both salt-affected soils. This study suggests that saltwater intrusion showed a potential risk in the degradation of soil properties, as indicated by the altered nematode community, trophic structure, functional guilds and their ecological indices in paddy fields.

Soil fauna groups respond differentially to changes in crop rotation cycles in rice production systems

Permanently flooded rice cropping is increasingly converted to rotation systems including upland crops, managed with adaptive nitrogen fertilizer application schemes for the sake of both saving water and optimizing nutrient application. Such changes alter the diversity and composition of the edaphic fauna, with a critical impact on soil functioning. We conducted a survey at 12 plots in Central Luzon (Philippines) over four cropping seasons to quantify the response of soil nematodes, enchytraeids, and microarthropods (collembolans and mites) to different crop rotations. We additionally assessed the impact of three different N-fertilizer input levels. A marked shift from enchytraeids to microarthropods (i.e. from semi-aquatic to terrestrial taxa) occurred in crop rotations involving upland crops. Microarthropod abundance increased faster in permanently non-flooded rotation system than in rotation schemes including temporal flooding. Mites and most springtail taxa proved to be very vulnerable to crop-associated flooding. Enchytraeids, in contrast, responded positively. Bacterivorous and fungivorous nematodes were affected to a much greater degree by the level of nitrogen input than by crop rotation. N fertilizer application thus significantly altered the trophic composition only of the soil micro-food web. According to our results we propose that the establishment of a genuine terrestrial soil food web after cropping scheme conversion in the conditions of volcanic soils in Central Luzon island may potentially be driven by two processes: The first is associated with the seasonally disrupted increase of microarthropod abundance driven by individuals invading from associated habitats through the top of the bunds, accompanied by an extinction of the semi-aquatic mesofauna, and second, the recovery of microarthropods that are able to survive submerged conditions in low numbers. The marked effect of N fertilizer application on the microfauna indicates that fertilizer management may significantly impact the conversion process by altering the microbial base of the soil food web.

Functional organization of soil nematode communities of spruce in primary ecosystems

Based on the study of the structural and functional organization of nematode communities of primary ecosystems, it is possible to determine the degree of transformation of secondary ecosystems, because anthropogenic activity leads to changes in their formation. Nematode communities of indigenous ecosystems have preserved their evolutionary-formed structural and functional organization and the ratio of trophic groups. This ensures the integrity and stability of biogeocenoses. Therefore, such groups have a significant bioindication role. The research was conducted within the Skolivski Beskydy National Nature Park. A mixed beech forest was selected as the reference plot. For two years, we have been taking samples of litter and soil under the spruce canopy. Nematodes were separated from the soil using the Berman method on a Kempson device. De Man indices were used to determine species. Based on the division of nematodes into trophic groups according to G. Yeats, we calculated the part of each of them in the litter and soil. 
 The number of nematodes in the litter increases from the upper horizon to the humus. In freshly fallen leaves the variety of nematodes (horizon L) is the least. In 2014 and 2015 in the upper horizon of the litter at different times of the year, the number of phytonematodes varied from 22 to 28 %, in the enzymatic horizon from 30 to 35 %, and in the humus horizon from 38 to 47 % of the total number of phytonematodes. The three litter horizons have the largest number of omnivorous nematodes, which is about two-thirds of the total number of the community with the largest quantity in summer. The part of predatory nematodes in spring and autumn is about 10 %, and in summer increases to 15 %. Bacteriovorus nematodes make about 18 % in spring, 25 % in summer, and 22 % in autumn, with a predominance in the F-horizon of litter. The part of fungivorous nematodes in all horizons of litter is approximately 5 %, with a predominance of the total number of this trophic group in the enzyme horizon.
 Omnivorous nematodes are represented mainly by species of the genus Eudorylaimus and Aporcelaimellus, carnivorous nematodes belong to the genera Prionchulus, Iotonchus, Tripyla, and bacteriophages are dominated by nematodes of the genera Plectus and Acrobeloides, and the group of fungivorous is mainly represented by species of the genus Aphelenchoides. Our results were later used to compare changes in nematode communities in derived ecosystems.

Effects of microhabitats and soil conditions on structuring patterns of nematode communities in Japanese cedar (Cryptomeria japonica) plantation forests under temperate climate conditions

The effect of biotic factors impacted by abiotic conditions on nematode communities is not fully understood in forest ecosystems. Monoculture forests with low understory diversity would provide an ideal model system to investigate the relationship between nematode community structure and environmental factors in forest ecosystems. The aim of this study was to clarify the determinant environmental factors shaping community structures of soil nematodes in Japanese cedar (Cryptomeria japonica) forests. Nematodes collected from litter and soil samples were morphologically identified at the family or genus level and divided into trophic groups. Nematodes were discriminated into a total of 40 (including 2 unique taxa) and 52 (including 14 unique taxa) taxa in litter and soil samples, respectively. Variation in microhabitat substrates created contrasting nematode assemblages between litter and soil samples. Moreover, nematodes identified from litter habitats were a subset of those from soil samples. Bacterivorous and fungivorous nematodes were present in high proportions in both sample types. Herbivorous nematodes were the third most abundant trophic group in soil samples, but were rare in litter samples. The nematode community structure in soils was significantly ordinated by water, C, N, hyphae, and soil pH. The pH is most likely to affect ecological function of soil nematodes indirectly by altering microbial biomass. Our results showed that microhabitat substrates, that is, soil and litter, have a crucial effect on nematode assemblage patterns in temperate coniferous forests. Moreover, soil nematode assemblages were diversified due to the high spatial heterogeneity of proximate soil environments.

Trophic interactions as determinants of the arbuscular mycorrhizal fungal community with cascading plant-promoting consequences

BackgroundThe soil mycobiome is composed of a complex and diverse fungal community, which includes functionally diverse species ranging from plant pathogens to mutualists. Among the latter are arbuscular mycorrhizal fungi (AMF) that provide phosphorous (P) to plants. While plant hosts and abiotic parameters are known to structure AMF communities, it remains largely unknown how higher trophic level organisms, including protists and nematodes, affect AMF abundance and community composition.ResultsHere, we explored the connections between AMF, fungivorous protists and nematodes that could partly reflect trophic interactions, and linked those to rhizosphere P dynamics and plant performance in a long-term manure application setting. Our results revealed that manure addition increased AMF biomass and the density of fungivorous nematodes, and tailored the community structures of AMF, fungivorous protists, and nematodes. We detected a higher abundance of AMF digested by the dominant fungivorous nematodes Aphelenchoides and Aphelenchus in high manure treatments compared to no manure and low manure treatments. Structural equation modeling combined with network analysis suggested that predation by fungivorous protists and nematodes stimulated AMF biomass and modified the AMF community composition. The mycorrhizal-fungivore interactions catalyzed AMF colonization and expression levels of the P transporter gene ZMPht1;6 in maize roots, which resulted in enhanced plant productivity.ConclusionsOur study highlights the importance of predation as a key element in shaping the composition and enhancing the biomass of AMF, leading to increased plant performance. As such, we clarify novel biological mechanism of the complex interactions between AMF, fungivorous protists, and nematodes in driving P absorption and plant performance.3Rct2UgWKJzaMmE1q1nvDRVideo

Soil management induced shifts in nematode food webs within a Mediterranean vineyard in the Central Coast of California (USA)

The soil food web regulates several key processes that support soil health and agricultural production. Here we investigated how soil management within a commercial Pinot noir Mediterranean vineyard affects nematode abundance and community structure, as a proxy to evaluate the status of the soil food web. We compared the soil under the vine to the soil in the tractor row which receive different water and nutrient inputs and different strategies to manage herbaceous vegetation cover. Furthermore, we compared the effects of different fertilizers (organic, synthetic and no fertilizer) applied under the vine. Our results showed that the soil in the tractor row hosted a more complex food web, with a higher abundance of microbial feeding nematodes and processing of the soil C and organic matter through omnivore and bacterivore nematodes leading to higher amounts of plant available N, likely due to increased mineralization rates. Thus, the tractor row has a great value as a reservoir of biodiversity within vineyards and support soil ecosystem services such as C sequestration and N cycling. The soil under the vine was characterized by a higher abundance of herbivore nematodes and high plant parasitic index that were alleviated by the addition of organic fertilizers increasing the abundance of bacterivore and fungivore nematodes, contributing to a more balanced food web. Changes in nematode community composition and food web status were strongly associated to soil physicochemical properties such as the active C, nitrate and soil pH. Thus, a change in fertilizer management could significantly boost soil health in these intensively managed soils.

Responses of soil nematode community to monoculture or mixed culture of a grass and a legume forage species in China

Mixed cultivation of fast-growing grasses and nitrogen (N)-fixing legumes for forage production is widely considered effective for obtaining sustained high forage yields without depleting soil N levels. However, the effects of monoculture and mixed culture of these species on soil food webs are poorly understood. In this study, soil nematode communities were examined as indicators of the soil food web structure of monoculture and mixed culture of grass and legume at three N levels, i.e., 338 (low), 450 (moderate), and 675 (high) kg N ha−1 year−1 across 2 years in wet and dry seasons, using the grass Paspalum wetsfeteini and the legume Medicago sativa (alfalfa), both commonly cultivated worldwide. Repeated-measures analysis of covariance showed that compared with grass monoculture, legume monoculture and grass-legume mixture increased abundances of herbivorous, bacterivorous, and fungivorous nematodes in the soil food web under the low and moderate N fertilization levels. Principal response curve results showed that the abundance of Helicotylenchus, a plant parasite, was significantly higher under legume monoculture than other planting systems at the low N fertilization level. Structural equation model analysis indicated that the legume increased bacterivore abundance, while increasing N fertilization decreased omnivore abundance. The legume might increase the quantity and quality of food resources for soil biota, resulting in the bottom-up control of soil nematode communities. Our results indicate that targeted control of a soilborne pathogen, Helicotylenchus, is required in alfalfa-based planting systems. In addition, high inorganic N application, which is detrimental to legume-rhizobia symbiosis, nullified the otherwise positive effects of legumes on soil nematodes.

Contrasting effects of nitrogen deposition and increased precipitation on soil nematode communities in a temperate forest

Elevated nitrogen (N) deposition and increased precipitation often occur simultaneously, and have an interactive effect on terrestrial ecosystems, particularly in N-limited temperate forests. However, the effects of interactions between elevated N deposition and increased precipitation on soil communities are unclear. In the present study, we employed a novel approach to simulate N deposition and precipitation by applying N solution and water to the forest canopy, and explored how throughfall chemical properties and soil nematode communities responded to elevated N deposition and increased precipitation. We found that N deposition positively affected nematode communities by increasing the abundance of nematodes in some bacterivorous and fungivorous nematode groups. In contrast, increased precipitation suppressed bacterivorous and fungivorous nematodes, particularly of those guilds related to nutrient enrichment. Our results suggest that the positive effects of N deposition on nematode communities may be cancelled out by increased precipitation in temperate forest ecosystems, when elevated N deposition and increased precipitation occur simultaneously. This was not observed in previous studies simulating N deposition and precipitation, which was probably due to that they have been mostly based on understory manipulation without considering canopy processes.

Potential of the fungal feeding nematode Aphelenchus avenae to control fungi and the plant parasitic nematode Ditylenchus destructor associated with garlic

Together with several fungi, the plant parasitic nematode Ditylenchus destructor is among the pathogens that cause serious damage to garlic production areas in Japan. Because D. destructor is a plant and fungal feeder, its infestation may be influenced by the garlic plant-associated fungi and suppressed through control of those fungi. However, no information is currently available regarding the interaction between the nematode and the fungi. Aphelenchus avenae is a non-parasitic fungivorous nematode, which can potentially control plant-pathogenic fungi. Assuming an interaction between the garlic-associated fungi and D. destructor, A. avenae may contribute to suppress D. destructor through fungal control. The present study investigated the interaction between the fungi isolated from garlic and D. destructor as well as the preference of D. destructor and A. avenae for those fungi, aiming to control the fungi and D. destructor using A. avenae. Most fungi isolated from garlic attracted both D. destructor and A. avenae, allowing their propagation. In vitro experiments involving the simultaneous inoculation of D. destructor and A. avenae on a fungus mat showed a better propagation of A. avenae than D. destructor on several fungi as well as the suppression of the D. destructor propagation rate. Similarly, pot experiments involving the simultaneous inoculation of A. avenae showed suppression of D. destructor propagation. The fact that D. destructor is attracted to, feeds on, and propagates on garlic-associated fungi suggests that those fungi can be a host for D. destructor, playing an important role for the nematode's infestation of garlic fields. Further, A. avenae propagation on the fungi and its ability to suppress the propagation of D. destructor suggest that A. avenae is a potential biological agent to control both the garlic-associated fungi and D. destructor.

Temperature changes affect multi-trophic interactions among pines, mycorrhizal fungi, and soil nematodes in a microcosm experiment

Nematodes serve a key role in soil nutrient cycling by eating bacterial cells and fungal hyphae. However, little is known about how temperature changes affect multi-trophic interactions among host trees, root-associating fungi, and nematodes. The aim of this study was to identify abiotic and/or biotic factors that affect soil nematode communities. We constructed a pot microcosm with sandy soils from a coastal Pinus thunbergii forest. The soil-filled pots were incubated for 8 months at 20, 25, or 30 °C with or without pine seedlings. In the pots with seedlings, we measured the percentages of black, white, and brown ectomycorrhizal (ECM) formations on roots. Nematodes retrieved from the soils were morphologically identified to genus and differentiated by both trophic and community structures. The occurrence of ECM formation ranged from 85.7%–91.9%. Black ECM roots were significantly dominant at 30 °C (47.0 %), whereas white ones were significantly dominant at 20 °C (43.0 %) and 25 °C (53.0 %). The number of nematodes at 25 and 30 °C was significantly greater than that at 20 °C irrespective of the presence or absence of seedlings. In terms of trophic compositions, the relative abundance of fungivorous nematodes significantly increased from 10.4 % at 20 °C to 27.5 % at 25 °C to 44.6 % at 30 °C in the presence of pine seedlings. A non-metric multidimensional scaling scatter plot showed that the nematode communities clustered significantly among temperature treatments. Structural equation modeling indicated that nematode trophic compositions were directly regulated by temperature and the presence of pine seedlings. Our findings suggest that temperature has some cascading effects on the formation of nematode communities, and pine seedlings and associating ECM fungi contributed synergistically to the formation of their communities.

Research on Fusarium wilt disease of guava

Wilting of guava trees has been regarded as national problem in India. Since, it is highly remunerative crop; disease is extremely important. The guava wilt was first reported in Taiwan during 1926 and in India during 1935. Several pathogenic fungi, nematodes and bacteria were found associated with the wilted trees of guava around the world; however, Fusarium spp. has been considered as major pathogen. Research on guava wilt carried out under network projects at ICAR-CISH revealed the cultural, morphological, molecular and pathogenic variability of Fusarium spp. across the India and its bio-management. Early age wilting of trees has mostly been observed due to complex of Fusarium oxysporum f. sp. Psidii, F. solani and Meloidogyne enterolobii. Enough research work on pathogenicity, cultural/morphological characters, molecular characterization, epidemiology and management of Fusarium spp. has been carried out but effect of interaction between Fusarium-Meloidogyne complex on expression of guava decline is yet to be thoroughly worked out. Complete guava crop management package should be developed, including healthy planting material production, proper care for nutrition, regular pruning and management of nematode fungus complex.

Long-term effects of charcoal on nematodes and other soil meso- and microfaunal groups at historical kiln-sites – a pilot study

Charcoal additions considerably alter the chemical and physical properties of soil. However, direct and indirect charcoal-induced effects on soil biota, particularly on meso- and micro-invertebrates are scarcely assessed. This pilot study aimed to investigate abundances of meso- and micro-invertebrates, particularly free-living nematodes, in soil and decaying leaf litter on ancient charcoal kiln sites in comparison to adjacent control sites. For nematodes we additionally investigated feeding type distribution. The abundance of nematodes tended to be lower in kiln-soils and reduced in litter on kiln sites, while the abundance of most groups remained unaffected by charcoal. Additionally, the proportion of fungivorous nematodes was higher in litter, but remained unaffected in soil. In conclusion our pilot study indicates that charcoal additions affected nematode communities whereas other mesofaunal groups seem to remain unaffected.

Combining microfluidics and RNA-sequencing to assess the inducible defensome of a mushroom against nematodes

BackgroundFungi are an attractive source of nutrients for predators. As part of their defense, some fungi are able to induce the production of anti-predator protein toxins in response to predation. A previous study on the interaction of the model mushroom Coprinopsis cinerea by the fungivorous nematode Aphelenchus avenae on agar plates has shown that the this fungal defense response is most pronounced in the part of the mycelium that is in direct contact with the nematode. Hence, we hypothesized that, for a comprehensive characterization of this defense response, an experimental setup that maximizes the zone of direct interaction between the fungal mycelium and the nematode, was needed.ResultsIn this study, we conducted a transcriptome analysis of C. cinerea vegetative mycelium upon challenge with A. avenae using a tailor-made microfluidic device. The device was designed such that the interaction between the fungus and the nematode was confined to a specific area and that the mycelium could be retrieved from this area for analysis. We took samples from the confrontation area after different time periods and extracted and sequenced the poly(A)+ RNA thereof. The identification of 1229 differentially expressed genes (DEGs) shows that this setup profoundly improved sensitivity over co-cultivation on agar plates where only 37 DEGs had been identified. The product of one of the most highly upregulated genes shows structural homology to bacterial pore-forming toxins, and revealed strong toxicity to various bacterivorous nematodes. In addition, bacteria associated with the fungivorous nematode A. avenae were profiled with 16S rRNA deep sequencing. Similar to the bacterivorous and plant-feeding nematodes, Proteobacteria and Bacteroidetes were the most dominant phyla in A. avenae.ConclusionsThe use of a novel experimental setup for the investigation of the defense response of a fungal mycelium to predation by fungivorous nematodes resulted in the identification of a comprehensive set of DEGs and the discovery of a novel type of fungal defense protein against nematodes. The bacteria found to be associated with the fungivorous nematode are a possible explanation for the induction of some antibacterial defense proteins upon nematode challenge.

Trichoderma atroviride from Predator to Prey: Role of the Mitogen-Activated Protein Kinase Tmk3 in Fungal Chemical Defense against Fungivory by Drosophila melanogaster Larvae.

The response to injury represents an important strategy for animals and plants to survive mechanical damage and predation. Plants respond to injury by activating a defense response that includes the production of an important variety of compounds that help them withstand predator attack and recover from mechanical injury (MI). Similarly, the filamentous fungus Trichoderma atroviride responds to MI by strongly modifying its transcriptional profile and producing asexual reproduction structures (conidia). Here, we analyzed whether the response to MI in T. atroviride is related to a possible predator defense mechanism from a metabolic perspective. We found that the production of specific groups of secondary metabolites increases in response to MI but is reduced after fungivory by Drosophila melanogaster larvae. We further show that fungivory results in repression of the expression of genes putatively involved in the regulation of secondary metabolite production in T. atroviride Activation of secondary metabolite production appears to depend on the mitogen-activated protein kinase (MAPK) Tmk3. Interestingly, D. melanogaster larvae preferred to feed on a tmk3 gene replacement mutant rather than on the wild-type strain. Consumption of the mutant strain, however, resulted in increased larval mortality.IMPORTANCE Fungi, like other organisms, have natural predators, including fungivorous nematodes and arthropods that use them as an important food source. Thus, they require mechanisms to detect and respond to injury. Trichoderma atroviride responds to mycelial injury by rapidly regenerating its hyphae and developing asexual reproduction structures. Whether this injury response is associated with attack by fungivorous insects is unknown. Therefore, determining the possible conservation of a defense mechanism to predation in T. atroviride and plants and elucidating the mechanisms involved in the establishment of this response is of major interest. Here, we describe the chemical response of T. atroviride to mechanical injury and fungivory and the role of a MAPK pathway in the regulation of this response.

REDUCING PLANT PARASITIC NEMATODES BY THE MONONCHIDA NEMATODE ORDER

Ponte Academic JournalJul 2019, Volume 75, Issue 7 REDUCING PLANT PARASITIC NEMATODES BY THE MONONCHIDA NEMATODE ORDERAuthor(s): DJAMAL EDINE BERRABAH ,HOCEINI F., KHAOUANI B., BOUARFA S., DOUMANDJI S., DOUMANDJI-MITICHE B.J. Ponte - Jul 2019 - Volume 75 - Issue 7 doi: 10.21506/j.ponte.2019.7.5 Abstract:The inventory of nematodes associated with Alfa in the natural reserve of Mergueb located in Ain Elhadjel- Wilaya of M\'Sila (35 � 35\' N 03 � 56\' E), characterized by a semi arid bioclimate, revealed the diversity of thirteen genus. In a second area, the experimental station ITAFV M�d�a (36 � 11 \' N; 02 � 50\' E) located in the semi-arid bioclimatic stage, seventeen genus of nematodes found in the differents vineyard soils. These nematode genus divided according to their diets in four trophic groups: phytophagous (Paratylenchus sp. Tylenchorhynchus sp., Pratylenchus sp., Nothotylenchus sp. and Xiphinema sp., the fungivorous (Aphelenchus sp., Tylenchus sp., and Ditylenchus sp.), the bacteriovorous (Rhabditis sp., Cephalobus sp. and Chiloplachus sp.) and omnivorous predator (Dorylaimus sp. and Discolaimus sp.) while the nematode�s densities vary depending to the study sites. This study of nematode populations associated with Vine and Alfa in the northerrn of Algeria, allowed us to enhance the effect of the predatory nematodes Mononchida order. Our investigations have focused on a set of eight stations. The results express the degree of predation of nematodes by the Mononchida order on different trophic groups of nematodes while Mononchus is positively correlated to the bacterivorous and fungivorous nematodes but negatively to plant parasitic nematodes.\r\nKey � words: Trophic Group, Predation, Alfa, Vine. Mononchida Download full text:Check if you have access through your login credentials or your institution Username Password

Bidirectional Propagation of Signals and Nutrients in Fungal Networks via Specialized Hyphae

Intercellular distribution of nutrients and coordination of responses to internal and external cues via endogenous signaling molecules are hallmarks of multicellular organisms. Vegetative mycelia of multicellular fungi are syncytial networks of interconnected hyphae resulting from hyphal tip growth, branching, and fusion. Such mycelia can reach considerable dimensions and, thus, different parts can be exposed to quite different environmental conditions. Our knowledge about the mechanisms by which fungal mycelia can adjust nutrient gradients or coordinate their defense response to fungivores is scarce, in part due to limitations in technologies currently available for examining different parts of a mycelium over longer time periods at the microscopic level. Here, we combined a tailor-made microfluidic platform with time-lapse fluorescence microscopy to visualize the dynamic response of the vegetative mycelium of a basidiomycete to two different stimuli. The microfluidic platform allows simultaneous monitoring at both the colony and single-hypha level. We followed the dynamics of the distribution of a locally administered nutrient analog and the defense response to spatially confined predation by a fungivorous nematode. Although both responses of the mycelium were constrained locally, we observed long-distance propagation for both the nutrient analog and defense response in a subset of hyphae. This propagation along hyphae occurred in both acropetal and basipetal directions and, intriguingly, the direction was found to alternate every 3hr in an individual hypha. These results suggest that multicellular fungi have, as of yet, undescribed mechanisms to coordinate the distribution of nutrients and their behavioral response upon attack by fungivores.

Natural 13C abundance reveals age of dietary carbon sources in nematode trophic groups

We determined the 13C/12C ratio (expressed as δ13C ‰) of microbial biomass and nematode trophic groups in a small-plot field experiment with soil converted from C3- to C4-crop (silage maize) 20 years ago. During this period, the plots were subjected to three different organic input treatments: 1) maize stubbles and roots left after harvest (MS), 2) MS plus annual addition of aboveground maize biomass (MS + B), and 3) MS plus annual addition of faeces from sheep fed exclusively with maize (MS + F). The different δ13C value of C3- and C4-crops allowed us to distinguish between old (>20 years old) C3-derived C and recent (<20 years old) C4-derived C incorporated into microbial biomass and nematodes.The δ13C value of phytophagous nematodes closely matched that of the maize. Bacterivorous nematodes had higher δ13C values than fungivorous nematodes and microbial biomass indicating that the C sources of bacterivorous nematodes are more recent than those of fungivorous nematodes and microbial biomass. At low abundance of fungivorous nematodes (MS and MS + F), the microbial biomass had higher δ13C values than the fungivorous nematodes, whereas their δ13C values were comparable at higher densities of fungivorous nematodes (MS + B). The higher C4-derived input in MS + F and MS + B treatments increased the δ13C values of bacterivorous nematodes and microbial biomass.In MS and MS + B treatments, recent C4-derived C accounted for 50 and 70% of microbial biomass-C, respectively. Corresponding values for fungivorous and bacterivorous nematodes were 30 and 75%, and 65 and 85%, respectively.We conclude that fungal-based decomposition pathways contribute more to the turnover of old soil C than bacterial-based decomposition. A substantial fraction of the microbial biomass and fungivorous nematode C in the MS treatment (50 and 70%, respectively) was C deposited in the soil more than 20 years ago, confirming that decade-old SOC remains biologically active.

Differential Selection by Nematodes of an Introduced Biocontrol Fungus vs. Indigenous Fungi in Nonsterile Soil.

Trophic interactions of introduced biocontrol fungi with soil animals can be a key determinant in the fungal proliferation and activity. This study investigated the trophic interaction of an introduced biocontrol fungus with soil nematodes. The biocontrol fungus Trichoderma harzianum ThzID1-M3 and the fungivorous nematode Aphelenchoides sp. (10 per gram of soil) were added to nonsterile soil, and microbial populations were monitored for 40 days. Similar results were obtained when the experiment was duplicated. ThzID1-M3 stimulated the population growth of indigenous nematodes (p < 0.05), regardless of whether Aphelenchoides sp. was added. Without ThzID1-M3, indigenous nematodes did not increase in number and the added Aphelenchoides sp. nematodes almost disappeared by day 10. With ThzID1-M3, population growth of nematodes was rapid between 5 and 10 days after treatment. ThzID1-M3 biomass peaked on day 5, dropped at day 10, and then almost disappeared at day 20, which was not influenced by the addition of nematodes. In contrast, a large quantity of ThzID1-M3 hyphae were present in a heat-treated soil in which nematodes were eliminated. Total fungal biomass in all treatments peaked on day 5 and subsequently decreased. Addition of nematodes increased the total fungal biomass (p < 0.05), but ThzID1-M3 addition did not affect the fungal biomass. Hyphae of total fungi when homogenously distributed did not support the nematode population growth; however, hyphae of the introduced fungus did when densely localized. The results suggest that soil fungivorous nematodes are an important constraint on the hyphal proliferation of fungal agents introduced into natural soils.

Soil indicators respond to changes in banana plantation management

The north Queensland region of Australia produces over 90% of Australia's bananas. However, to maintain its importance as a banana-growing region, producers are seeking innovative methods to manage their plantations in order to protect environmentally sensitive areas, reduce impacts from climatic events and suppress soil borne diseases. The development of a healthy soil is an aspiration sought to address these constraints, using indicators based on soil physical, chemical and biological parameters. From 2012 to 2015, 86 soil samples were received for analysis from different banana management scenarios; conventional (53), newly planted fields (15), and Ecoganic production (18). Ecoganics is a farmer certification program that combines environmental management systems with sustainable production practices. A stepwise-discriminate analysis was used to determine a minimum set of soil parameters required to discriminate between management systems. Ten soil parameters: fluorescein diacetate hydrolysis rate (FDA), nematode enrichment and channel indices, B/(B+F) ratio (bacterivorous nematodes relative to bacterivorous and fungivorous nematodes), nematode diversity, and abundance of Fu2 fungivorous nematodes, Om4 omnivorous nematodes, Ba1 and Ba3 bacterivorous nematodes and abundance of the plant-parasitic nematode Helicotylenchus multicinctus were required to separate the different banana management systems. However, the separation of banana management groups had a 19% error, with the leave-one-out validation model confusing Ecoganic bananas with conventional bananas 22% of the time. The results confirmed that crop management has considerable effects on soil biology. The use of soil indicators can guide farm management decisions to implement practices most likely to overcome banana production constraints.