Arthrobotrys Dactyloides Research Articles

Fungi recovered from root-knot nematodes infecting vegetables under protected cultivation

A survey was conducted in root-knot nematode-infested plastic houses to determine the diversity and frequency of occurrence of fungi associated with the nematode. The relationships between percentage fungal parasitism and physicochemical properties of soil were also investigated. Fifty-nine plastic houses were sampled in southeastern Spain, 42 treated with nematicides and 17 left untreated. Eleven fungal genera and unidentified fungi were isolated from nematode eggs or juveniles. Fungal parasitism occurred more frequently in untreated (82.4%) than treated (50%) soils. The species richness in untreated soils ranged from 0 to 5, the Shannon–Wiener diversity index (a measurement of how many different fungi there are in site taking into account how evenly they are distributed among the site) from 0 to 2.01, and the evenness index from 0.46 to 0.99. In treated soils, species richness ranged from 0 to 4, the Shannon–Wiener diversity index from 0 to 1.61, and the evenness index from 0.81 to 1. Of the sites with nematophagous fungi, Arthrobotrys dactyloides (34%), Cylindrocarpon sp., Neosartoria hiratsukae (17%), and Fusarium solani (14%) were the fungi most frequently found. Physicochemical properties of soil were similar in nematicide treated and untreated soils. Percent fungal parasitism in untreated soils correlated positively with lime, silt and carbonate content of soil.

Variabilities of Two Drechslerella dactyloides Isolates in Korea and High Predacity Against Bursaphelenchus xylophilus

Drechslerella dactyloides generates elongate ellipsoid conidia and three-celled rings. Recently, Drechslerella dactyloides CNU 091025 and CNU 091026 were isolated in Korea, which generated elongate ellipsoid, Y-shaped and reaphook-shaped conidia, three-celled rings and fishhook-shaped traps. Therefore, molecular phylogenetic analysis, morphological variability, and nematode capturing ability were tested in this study. CNU 091025 generated two-celled or three-celled Y-shaped conidia, reaphook-shaped conidia, and elongate ellipsoid conidia, 17.2, 40.9, and 41.9%, respectively. Some fishhook-shaped rings connecting together formed two-dimensional web. Both fungi showed high trap-forming and nematode-capturing ability; especially CNU 091026 captured 100% Bursaphelenchus xylophilus within 24 h after inoculation.

Nematophagous Fungi Associated with Root Galls of Rice Caused by Meloidogyne graminicola and its Control by Arthrobotrys dactyloides and Dactylaria brochopaga

AbstractRoot galls of rice caused by Meloidogyne graminicola were examined for natural colonization by nematophagous fungi from four fields with different nematode infestations. Old galls from severely infested fields had a higher frequency of Monacrosporium eudermatum and Stylopaga hadra than young galls. The frequency of Arthrobotrys oligospora, Arthrobotrys dactyloides, Dactylaria brochopaga and Monacrosporium gephyropagum was lower. A greater proportion (%) of root galls were colonized by nematophagous fungi in those fields in which rice roots had a greater root gall index. This indicated that disease severity supported the colonization of galls by nematophagous fungi. In vitro predacity tests of four fungi showed that A. dactyloides was most effective in capturing and killing J2 of Mel. graminicola followed by D. brochopaga and Mon. eudermatum. Application of inocula of A. dactyloides and D. brochopaga in soil infested with Mel. graminicola, respectively, reduced the number of root galls by 86% and of females by 94%, and eggs and juveniles by 94%. The application of these fungi to soil increased plant growth: shoot length by 42.7% and 39.8%, root length by 45.5% and 48.9%, fresh weight of shoot by 59.9% and 56.7% and fresh weight of root by 20.3% and 25.1%, respectively, compared to these parameters for plants grown in nematode‐infested soil.

Conidial trap formation of nematode-trapping fungi in soil and soil extracts

Conidial traps (CT) in nematode-trapping fungi are trapping structures formed directly on germination of conidia, without an intermediate hyphal phase. Most of the nine fungi tested were able to form CT on water agar surfaces in the vicinity of soil, but the ability varied between species. Generally, the ability to form CT was greatest in Arthrobotrys dactyloides and Monacrosporium gephyropagum followed by Arthrobotrys superba and Arthrobotrys oligospora. The mechanism behind CT formation was further studied in soil extracts using a microwell plate assay. Preincubation of soil or soil extracts at room temperature before inoculation with conidia increased the incidence of CT. Reduction of the number of microorganisms in soil extracts by sterile filtration, dilution or heating decreased CT formation, as did the addition of nutrients. The results suggest that a certain level of competition for nutrients by microorganisms is necessary for CT formation. In contrast, we were unable to induce CT when conidia were allowed to germinate in pure culture on hyphal trap-inducing or non-inducing agar media with or without cell wall affecting compounds.

Effect of Fertilizers and Neem Cake Amendment in Soil on Spore Germination of Arthrobotrys dactyloides

Application of fertilizers such as urea, diammonium phosphate (DAP) and muriate of potash in soil adversely affected the spore germination of Arthrobotrys dactyloides. Amendment of soil with urea at the concentrations of 1.0%, 0.5% and 0.1% completely inhibited spore germination and direct trap formation on the conidium, whereas muriate of potash delayed and reduced the spore germination even at the lowest concentration. DAP also inhibited spore germination at 1.0% concentration, while at lower concentration the percentage of spore germination was reduced. Application of neem cake at the concentration of 0.5% also inhibited spore germination after 24 h of amendment. The inhibitory effect of neem cake was reduced after 15 days of amendment, while after 30 days after amendment the inhibitory effect was completely lost and the spore germinated by direct trap as in unamended soil. Nematodes were not attracted to ungerminated spores after 24 h of amendment. After 15 days of amendment nematodes were attracted to agar blocks containing fewer germinated spores after 24 h of incubation but after 48 h of incubation large number of nematodes were attracted and trapped by the germinated spores with direct traps. After 30 days of amendment, larger number of nematodes were attracted and trapped by direct traps.

Microbial parasites associated with Tylenchulus semipenetrans in citrus orchards of Catalonia, Spain

Citrus orchards in Catalonia, Spain were surveyed to identify microbial parasites of Tylenchulus semipenetrans, and their distribution and density. Of 62 orchards, 48 were positively infested with the citrus nematode. Fungal strains were isolated from single eggs, females or second-stage juveniles of the citrus nematode in 69% of the infested orchards. The fungi identified in order of occurrence were Paecilomyces lilacinus, Fusarium solani, Fusarium spp., Cylindrocarpon cylindroides, Verticillium fungicola, Cladosporium cladosporioides, F. oxysporum, Veronaea botryosa, Sepedonium chrysospermum, Volutella ciliata, Exophiala pisciphila and Acremonium sp. Fungal parasitism was related directly to the number of females g−1 of root and magnesium in the soil, and inversely, to the number of eggs g−1 of root and phosphorus in the soil (R 2=0.8654; P<0.0001). Nematode trapping fungi were isolated from soil samples in 29% of the orchards, and Monacrosporium elegans, Arthrobotrys dactyloides, A. javanica, A. superba and A. oligospora var. microspora, were the species present. Endospores of the hyperparasite Pasteuria adhering to vermiform stages of T. semipenetrans were found in 50% of the orchards infested with the citrus nematode.

Amendments of sugarcane trash induce suppressiveness to plant-parasitic nematodes in a sugarcane soil

In a field experiment at Bundaberg, Queensland, sugarcane trash was incorporated into soil with, or without, additional nitrogen supplied as either soybean residue or ammonium nitrate. The carbon inputs from plant material (lOtC/ha) were the same in all treatments, while both plus-nitrogen treatments received the same amount of nitrogen (210kgN/ha). Sugarcane was planted 23 weeks after amendments were incorporated, and 24 weeks later there were 95%fewer lesion nematodes (Pratylenchus zeae) in roots growing in amended soil than in roots from the unamended control. Populations of P. zeae and Tylenchorhynchus annulatus in amended soil were reduced by 85%and 71%, respectively. Bioassays in which forage sorghum was planted in soil collected during the experiment and inoculated with P. zeae indicated that amended soils were suppressive to the nematode at 20 weeks but not after 47 weeks. All amendments increased readily oxidisable carbon, microbial biomass, microbial activity and numbers of free-living nematodes, but had no effect on known predators of nematodes (i.e. dorylaimid and mononchid nematodes and three naturally occurring species of nematode-trapping fungi, Arthrobotrys conoides, A. thaumasium and Drechslerella dactyloides). However, an unidentified predatory fungus was found only in soil amended with sugarcane trash and was possibly involved in the suppression of plant-parasitic nematodes.

A New Technique for Single Spore Isolation of Two Predacious Fungi Forming Constricting Ring

A new technique for single spore isolation was developed for predacious fungi forming constricting rings directly on the spores using Dactylaria brochopaga and Arthrobotrys dactyloides. Constricting rings were induced directly on the spores by transferring the spores in 25 ppm solution of DL-Valine in sterile distilled water. Freshly hatched and thoroughly washed second stage juveniles of Meloidogyne incognita were transferred into cavity blocks containing induced rings for trapping and killing of nematodes. The killed nematodes were surface sterilized with streptomycin and inoculated into petri dishes containing maize meal agar media with 100 ppm streptomycin. The petri dishes were incubated at 29±1°C for few days which yielded axenic culture of these fungi.

Nonconstricting-ring formation in two species of nematode-capturing hyphomycetes

Dactylella leptospora and Dactylaria candida, and Arthrobotrys dactyloides (Hyphomycetes), capture nematodes by nonconstricting- and constricting-ring traps, respectively. In the formation of the constricting-ring trap of the latter fungus, the basal portion of a curved hyphal branch put forth a bud to fuse with its advancing tip to make a ring. However, in nonconstricting-ring formation in the former two fungi, the portion behind the tip of the curved branch did not develop such a bud before fusion with the tip.

Cloning of a Ca 2+/calmodulin-dependent protein kinase gene from the filamentous fungus Arthrobotrys dactyloides

A Ca 2+/calmodulin-dependent protein kinase (CaMK) gene was cloned and characterized from Arthrobotrys dactyloides, a nematode-trapping fungus. The resulting 373-amino-acid protein, FCaMK, has significant homology to mammalian CaMKs. FCaMK contains a serine/threonine kinase domain followed by a calmodulin-binding domain. The activation loop in FCaMK (amino acids 184–199) contains a phosphorylation site at threonine-188, which could be the target of a kinase activator. Truncated FCaMK mutants revealed that amino acids 296–324 are essential for calmodulin binding. An oligopeptide designed from residues 297–324 formed a stable peptide–calmodulin complex of 1:1 stoichiometry. Southern blot analysis detected a single copy of the fcamk gene, suggesting that FCaMK plays an important role in Ca 2+/calmodulin signaling in A. dactyloides.

Cloning of a Ca(2+)/calmodulin-dependent protein kinase gene from the filamentous fungus Arthrobotrys dactyloides.

A Ca(2+)/calmodulin-dependent protein kinase (CaMK) gene was cloned and characterized from Arthrobotrys dactyloides, a nematode-trapping fungus. The resulting 373-amino-acid protein, FCaMK, has significant homology to mammalian CaMKs. FCaMK contains a serine/threonine kinase domain followed by a calmodulin-binding domain. The activation loop in FCaMK (amino acids 184-199) contains a phosphorylation site at threonine-188, which could be the target of a kinase activator. Truncated FCaMK mutants revealed that amino acids 296-324 are essential for calmodulin binding. An oligopeptide designed from residues 297-324 formed a stable peptide-calmodulin complex of 1:1 stoichiometry. Southern blot analysis detected a single copy of the fcamk gene, suggesting that FCaMK plays an important role in Ca(2+)/calmodulin signaling in A. dactyloides.

Heterotrimeric G-protein and signal transduction in the nematode-trapping fungus Arthrobotrys dactyloides.

The fungus Arthrobotrys dactyloides produces specialized constricting rings to trap and then consume nematodes. The signal transduction pathway involved in the nematode-trapping process was examined. Mastoparan, an activator of G-protein, had a stimulatory effect on the inflation of ring cells, whereas a G-protein inhibitor, pertussis toxin, prevented ring-cell expansion. The 40-kDa G alpha of heterotrimeric G-proteins was specifically ADP-ribosylated by pertussis toxin. Using an antibody specific to the 35-kDa subunit G beta, we showed that immunogold-labeled G beta was more concentrated in ring cells than in the hyphae. In the absence of nematodes, the rings could be inflated by either pressurizing the culture in a syringe, raising intracellular Ca2+ concentrations, or adding warm water. We used these methods to reveal differences in responses to antagonists. The results support a model in which the pressure exerted by a nematode on the ring activates G-proteins in the ring cells. The activation leads to an increase in cytoplasmic Ca2+, activation of calmodulin, and finally the opening of water channels. The ring cells expand to constrict the ring and thus immobilize the nematode.

Nematode-Trapping Fungi in Organic and Conventional Cropping Systems

ABSTRACT Nematode-trapping fungi, nematodes, and microbial biomass were quantified in conventionally and organically managed field plots in the Sustainable Agriculture Farming Systems Project at the University of California at Davis. There were four replicate plots (0.135 ha per plot) for each management system, and plots were sampled three times each year for 2 years. The hypothesis that nematode-trapping fungi would be more abundant in organically managed plots was partially supported: the number of species of nematode-trapping fungi was slightly but significantly greater in organic than in conventional plots, two species (Arthrobotrys dactyloides and Nematoctonus leiosporus) were detected more frequently in organic plots, and the population densities of A. dactyloides and N. leiosporus were greater in organic than in conventional plots. Two other species (A. haptotyla and A. thaumasia), however, tended to be more numerous in conventional than in organic plots, and the total density of nematode-trapping fungi was similar in organic and conventional plots. Bacterivorous nematodes were more abundant and microbial biomass (substrate-induced respiration) was greater in organic than in conventional plots. Suppression of the root-knot nematode Meloidogyne javanica, as measured in a bioassay, was not related to management system or population density of nematode-trapping fungi but was positively related to microbial biomass.

Conidial trap formation of nematode-trapping fungi in soil and soil extracts

Conidial traps (CT) in nematode-trapping fungi are trapping structures formed directly on germination of conidia, without an intermediate hyphal phase. Most of the nine fungi tested were able to form CT on water agar surfaces in the vicinity of soil, but the ability varied between species. Generally, the ability to form CT was greatest in Arthrobotrys dactyloides and Monacrosporium gephyropagum followed by Arthrobotrys superba and Arthrobotrys oligospora. The mechanism behind CT formation was further studied in soil extracts using a microwell plate assay. Preincubation of soil or soil extracts at room temperature before inoculation with conidia increased the incidence of CT. Reduction of the number of microorganisms in soil extracts by sterile filtration, dilution or heating decreased CT formation, as did the addition of nutrients. The results suggest that a certain level of competition for nutrients by microorganisms is necessary for CT formation. In contrast, we were unable to induce CT when conidia were allowed to germinate in pure culture on hyphal trap-inducing or non-inducing agar media with or without cell wall affecting compounds.

Fungal Penetration of the Cyst Wall ofHeterodera glycines

Twelve fungal species were examined with the aid of light, scanning electron, and transmission electron microscopy to determine their capability to penetrate the cyst wall of Heterodera glycines. Arthrobotrys dactyloides, Dictyochaeta heteroderae, Exophiala pisciphila, Fusarium oxysporum, Neocosmospora vasinfecta, Paecilomyces lilacinus, Pyrenochaeta terrestris, Stagonospora heteroderae, Verticillium chlamydosporium, and a sterile fungus (black, yeastlike fungus) were observed to penetrate the cyst wall of Heterodera glycines. The light microscopy procedure reported herein was useful for determining the direction of fungal penetration of the cyst wall. Also, the procedure allowed for the examination of many specimens. Nine of these fungi penetrated the cyst wall from inside the cyst. At least three species, Exophiala pisciphila, Fusarium oxysporum, and Pyrenochaeta terrestris, also penetrated the cyst wall from the outside. Penetration by the black, yeastlike fungus was limited to the outer layers of the cyst wall. No fungal penetration was observed on cysts exposed to Gliocladium catenulatum or Hirsutella rhossiliensis for up to 1 month.

The Activity of Nematode-Trapping Fungi Following Their Encapsulation in Alginate

Granular formulations of Dactylella candida and Arthrobotrys dactyloides were prepared by encapsulating different quantities of fungal biomass in alginate, or by subjecting encapsulated biomass to further fermentation. Results of experiments with these formulations showed that the presence of nutrients and the quality and quantity of biomass in granules determined their level of activity against nematodes. The best formulations were those in which granules were fermented after the fungus had been encapsulated in alginate. These formulations produced a network of traps in soil which were maintained for at least 10 d and extended 5-10 mm from the granule. Experiments in microcosms showed that the number of second-stage juveniles of Meloidogyne javanica recovered from soil was reduced substantially when alginate preparations of both fungi were introduced.

Simple Screening Methods for Assessing the Predacious Activity of Nematode-Trapping Fungi

Australian isolates of nematode-trapping fungi were screened for activity against nematodes on agar and in soil. All isolates produced traps extensively on agar in response to Caenorhabditis elegans and, within 1-3 days, populations of this nematode were generally reduced by at least 90%. Juveniles of Meloidogyne javanica induced fewer traps on agar and most fungi took more than 3 days to reduce numbers of nematodes by more than 90%. Experiments in microcosms showed that predacious activity on agar gave little indication of the capacity of a fungus to trap nematodes when added to mineral soil. Species such as Dactylella candida and Arthrobotrys dactyloides, which formed detachable rings and knobs or constricting rings, consistently reduced the number of M. javanica juveniles recovered from soil whereas network-forming species sometimes did not. In studies using agar 'sandwich' and buried slide techniques to monitor trapping activity in soil, D. candida and A. dactyloides consistently produced traps within 5 days of being introduced, whereas network-forming species produced few traps in soil and their trapping activity varied from experiment to experiment.

Tests for Density-Dependent Parasitism of Nematodes by Nematode-Trapping and Endoparasitic Fungi

Abstract The relationship between parasitism by fungi and density of host nematodes (juveniles of Meloidogyne javanica ) was examined in soil microcosms. One of five fungi ( Hirsutella rhossiliensis , Arthrobotrys dactyloides , A. oligospora , Monacrosporium ellipsosporum , or M. cionopagum ) was added to untreated loamy sand at the start of each of five trials, host nematode density was controlled at four levels, and parasitism of assay nematodes (juveniles of Heterodera schachtii ) was assessed after 15 weeks at 20°C. Increases in percentage parasitism with host density were greatest for H. rhossiliensis , intermediate for M. ellipsosporum and A. dactylooides , and least for A. oligospora and M. cionopagum . Although background fungi (especially H. rhossiliensis ) in the loamy sand confounded the results, the relative strengths of the parasitic responses to host density were confirmed in an additional experiment in a loam soil that did not contain H. rhossiliensis . The failure of A. oligospora and M. cionopagum to respond to nematode density provides indirect evidence that substrates other than nematodes are important to these and probably other trapping fungi.

Trap Production by Nematophagous Fungi Growing from Parasitized Nematodes

Nematode-trapping fungi are generally considered facultative parasites that produce traps only under special conditions. However, Arthrobotrys dactyloides, A. oligospora, Monacrosporium ellipsosporum, and M. cionopagum produced many traps when growing from parasitized nematodes in saturation extracts of four soils. Thus, conditions that induce traps may normally prevail when these fungi grow from nematodes in soil, and parasitism may be more important to these fungi than has previously been recognized (...)

Multilaminate Bodies: Additional Candidates for Membrane Reserve in Trapping Rings ofDactylaria Brochopaga

Heintz and Pramer (1972) studying Arthrobotrys dactyloides Drechs., and Insell and Zachariah (1978) and Dowsett et al. (1977) studying Dactylaria brochopaga Drechs., have all suggested origins for a preformed reserve membrane material, or surface, necessary to accommodate the expansion of the protoplast of ring cells which occurs during the violent closure of the trapping rings produced by these fungi. While material identified by these authors may indeed fulfill the role attributed to them, we have recently identified multilaminate bodies in the cells of trapping rings which may serve as an additional source of membrane reserve material in both normal and giant ring (Tsai et al., 1975) traps of D. brochopaga; it is these we wish to bring to the reader's attention. Cultures of D. brochopaga in which the production of both normal-sized and giant ring traps are phenotypic traits were initiated on half-strength potato-carrot agar (PCA) (Anon., 1968) at 25 C. After 6 da, 7 mm diam agar plugs bearing mycelium were cut from the cultures using a sterile cork borer, and transferred to fresh PC A plates. These plates were taped shut, and incubated in the dark at 25 C for 7 da. At this time the plugs were displaced from their original r sition by rapping the plates sharply either against the palm of the hand or on the laboratory bench. It had been accidently determined that displacement induced formation of relatively large numbers of upright giant rings from that mycelium growing about what had been the circumference of the agar plugs' original position on the agar surface. For transmission electron microscopy, a modification of the procedure used by Dowsett et al. (1977) was employed. Seven-mm agar plugs bearing either normal or giant rings (or both) were cut using a sterile cork borer, trimmed to remove excess agar, and individual plugs were then placed in sterile Parr bottles. Just enough quarter-strength PC medium was added to each bottle to cover the agar plug, and the bottles were incubated at 25 C for up to 72 h. The fluid was then removed from the Parr bottles and the newly developed mycelium and the remains of the agar blocks were fixed following the procedure of Hess (1966), but modified to include Ruthenium Red stain (Luft, 1971). It had earlier been noted that new mycelium developed from plugs derived from the zone of induced giant ring formation described above, also produced giant and normal sized rings. It appears that the ring inducing factor(s) was (were) operative even in the absence of added nematodes, as were employed by Dowsett et al. (1977). The material was then dehydrated in an ethanol series, and embedded in resin (Spurr, 1969). Sections 1094