Search

We tested a formulation composed of a mixture of Bidens pilosa var. radiata extract (BPE) and nematode-trapping fungi for its effects on Meloidogyne incognita. In earlier evaluations of the effects of plant extracts on the hyphal growth of 5 species of nematode-trapping fungi with different capture organs (traps), the growth of all species was slightly inhibited. However, an investigation on the number of capture organs and nematode-trapping rates revealed that Arthrobotrys dactyloides formed significantly more rings and nematode traps than those of the control. An evaluation of simple mixed formulations prepared using sodium alginate showed that nematodes were captured with all formulations tested. The simple mixed formulation showed a particularly high capture rate. Furthermore, in a pot test, although the effects of a single formulation made from the fungus or plant extract were acceptable, the efficacy of the simple mixed formulation against M. incognita root-knot formation was particularly high., 論文

We tested a formulation composed of a mixture of Bidens pilosa var. radiata extract (BPE) and nematode-trapping fungi for its effects on Meloidogyne incognita. In earlier evaluations of the effects of plant extracts on the hyphal growth of 5 species of nematode-trapping fungi with different capture organs (traps), the growth of all species was slightly inhibited. However, an investigation on the number of capture organs and nematode-trapping rates revealed that Arthrobotrys dactyloides formed significantly more rings and nematode traps than those of the control. An evaluation of simple mixed formulations prepared using sodium alginate showed that nematodes were captured with all formulations tested. The simple mixed formulation showed a particularly high capture rate. Furthermore, in a pot test, although the effects of a single formulation made from the fungus or plant extract were acceptable, the efficacy of the simple mixed formulation against M. incognita root-knot formation was particularly high.

Growth and capture activities of nematophagous fungi in soil were observed using the low temperature scanning electron microscopy technique. The advantages of this sample preparation technique, compared with conventional scanning electron microscopy, are that it does not involve chemical fixation and dehydration of the sample and, therefore, gives a more accurate view of organ isms in soil. Growth, sporulation, trap formation, capture and digestion of nematodes were observed in soil using the nematode-trapping fungi Arthrobotrys superba, A. dactyloides and A. oligospora CT, and the endoparasite Drechmeria coniospora.

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.

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.

Five isolates of Arthrobotrys dactyloides (A, B, C, D, and E) were isolated from different locations of India. Their variability in relation to morphology, radial growth, and nematode capturing or trap-forming ability was observed. All of the five isolates produced two-celled slender conidia, whereas wider two- and three-celled conidia were produced by isolates A, C, D, and E only. The wider two- and three-celled conidia were not observed in cultures of isolate B. The isolate B produced macroconidia as well as microconidia. The microconidia were produced on separate conidiophores of smaller size. Macroconidia and microconidia were never produced on the same conidiophore, but the two types of conidiophores were produced on same or different hyphae. Similar to macroconidia, the microconidia also produced constricting rings of smaller size in presence of Meloidogyne graminicola. The constricting rings formed on microconidia did not capture second-stage juveniles of M. graminicola because of their smaller size. Among all the isolates, isolate B showed slow growth and higher nematode-capturing ability or trap-forming ability.

Variability in growth and sporulation of five isolates of Arthrobotrys dactyloides was studied on five agar, 6 bran and 5 grain media. Potato dextrose agar (PDA) supported maximum growth of isolate A, C and E, while growth of isolate B and D was significantly lower on this medium. On Czapek's agar and yeast glucose agar media the differentiation in the isolates in relation to growth was poor than PDA. The other two media showed much poorer differentiation. On Czapek's agar medium, sporulation was recorded in isolate B only, whereas other isolates showed rare sporulation. Among the bran media, pea bran agar medium supported maximum growth of all the isolates except isolate B. Gram and rice bran agar media were next best. However, the growth of isolate B on the gram bran agar medium was more or less equal as other isolates. On pigeon pea bran agar medium, isolate E failed to grow while other isolates recorded poor growth. On lentil bran agar medium, only isolate B and D recorded little growth, whereas other isolates failed to grow. All the isolates recorded good sporulation on bran agar media except pigeon pea and lentil bran agar media. The grain agar media supported moderate to very good growth of all the isolates. In general isolate B remained slow growing on these media except gram grain and sorghum grain agar media on which growth of this isolate was comparable to other isolates. Sporulation in general, was good on all the grain agar media. Among different substrates screened, barley grain and pea bran were found superior to others for mass culture of isolate A of A. dactyloides.

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. Constrictin...

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 (...)

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

Constricting rings are normally formed in the presence of nematodes. The fungi can be induced to form rings if treated with certain organic substances such as animal extracts and sera. One of the fungi discussed, Arthrobotrys dactyloides Drechsler, will produce rings without the addition of stimulants. Ring formation is not due to starvation of the fungus. An experiment describing the growth of the fungi on to cover-glasses indicates that the rings may be initiated as a result of the contact with the glass surface.

The predaceous fungus Arthrobotrys dactyloides forms ring-like traps which constrict and mechanically catch nematodes that have entered them. We have found that the fast death of the captured prey is caused by ammonia produced by the fungus. We have also devised a semiquantitative method for the detection of nematode-attracting substances and have shown that A. dactyloides produces compounds of this type, one of which is carbon dioxide.

The growth responses of a prototroph and an auxotroph of Arthrobotrys dactyloides were compared, on several nutrient media. The prototroph can utilize a variety of nitrogenous compounds almost equally, but the auxotroph has an exacting requirement for several amino acids together. Both strains utilize sucrose best among the three sugars tested as a C-source but the prototroph responds strongly to phospholipid, in addition. They differ in their needs for purines, pyrimidines and B vitamins.

The formation and the closure of constricting rings by a nematode-trapping fungus were recorded by means of time-lapse cinephotomicrography. Analysis of the film revealed that hyphal rings resulted from a sequence of morphological events not previouisly described. Cell inflation and ring constriction were induced by touch, increased temperature, and electrical stimutlation. The inflation process was not particularly sensitive to metabolic inhibitors and appears to operate without an expenditutre of energy on the part of the cell.