Pratylenchus penetrans is a major nematode pest of vegetable crops in Japan. We investigated P. penetrans population dynamics and cabbage growth under the year-round application of sawdust cattle manure compost for continuous cabbage cropping (2002-2009) at Tsukuba, Japan. Cabbages were cultivated twice a year, during spring and autumn. Chemical fertilizer (CF), manure compost (MC) + 1/5CF, CF + 3/5MC + crop residue (CR), a triple amount of MC + 1/5CF, and 3MC + CR were applied to the field before transplanting the cabbages. Both the initial population (Pi) and final population (Pf) of P. penetrans were significantly high in CF, low in 3MC + 1/5CF and 3MC + CR, and average in MC + 1/5CF and CF + 3/5MC + CR in 2003-2005 and 2008-2009. Both Pf/Pi during cultivation and the decreased rate of Pi/Pf after cultivation showed no clear tendencies among compost treatments. In this study, host plant growth did not appear to be markedly restricted by the high densities of P. penetrans. By applying Seinhorst’s formula on the Pi and Pf of P. penetrans, we obtained 2 curves for CF and 3MC + CR, with 16.45 and 4.54 representing“ equilibrium density”, respectively. Pot experiment results supported the field experiment results, whereby the number of P. penetrans decreased as the quantity of MC increased (from 0 to 3%w/v). On the basis of these results, we concluded that manure compost application could have a suppressive effect on P. penetrans population dynamics.
We describe and illustrate the free-living marine nematode Deontostoma magnificum (Timm, 1951) Platonova, 1962 (Nematoda: Leptosomatidae) as a new record of this genus from Japanese waters. Specimens examined agree well with the original and redescriptions of D. magnificum in the characters of the cephalic capsule, the buccal cavity armed with mandibles and teeth-like structures, the ocelli, and the male genital organs. We also provide partial DNA sequences of the mitochondrial cytochrome c oxidase subunit I (COI) and the nuclear 18S ribosomal RNA genes for DNA based identification.
The nematophagous activities of mushrooms were evaluated on water agar plates. Five species of saprophytic mushroom including Cyptotrama asprata, Resupinatus applicatus, Panellus stipticus, Hohenbuehelia reniformes and Pleurotus salmoneostramineus showed the ability to immobilize and consume the pinewood nematode, Bursaphelenchus xylophilus. We further investigated the nematode-trapping ability of the most effective nematode scavenger, P. salmoneostramineus. Nematode-trapping structures with abundant toxin droplets were observed on the surface of the mycelia, and more than half of the inoculated nematodes were immobilized by this strain within 24 h. The nematophagous activity of this strain was greater than that of the well-known nematophagous species, P. ostreatus.
We evaluated fosthiazate, fenitrothion, and benomyl for the management of dagger nematodes (DNs, primarily Xiphinema brevicolle), in the root-ball soil of Japanese holly (Ilex crenata Thumb.). When root balls were drenched in diluted solutions of these agrochemicals, fenitrothion and benomyl were effective against DN populations but fosthiazate was not. Benomyl suppressed DN population recovery completely from 7 days to at least 60 days after treatment. Although fenitrothion suppressed DN populations completely for seven days after treatment, this duration of the suppressive effect was much shorter than that of benomyl, possibly because of the hatching of surviving eggs. The hatching of eggs that survived the fenitrothion treatment was hindered by post-treatment preservation at 5℃.
The lesion nematode (Pratylenchus zeae), the stunt nematode (Tylenchorhynchus leviterminalis), the spiral nematode (Helicotylenchus dihystera), and the lance nematode (Hoplolaimus columbus) were major plant-parasitic nematode (PPN) species identified in the sugarcane fields on Kitadaito Island, Okinawa, Japan, for which real-time PCR primer sets were developed. Since the four PPN species ubiquitously inhabited Kitadaito, P. penetrans, which was confirmed to be absent in Kitadaito, was used as a benchmark to establish a soil calibration curve. Kitadaito soil samples were inoculated with juveniles and adults of P. penetrans at densities of 8, 32, 128, and 256/10 g fresh soil, and a soil calibration curve was obtained: y =－0.95x + 34.83 (y = Ct values, x = log2 (the number of P. penetrans ). The soil calibration curve was consistent with a calibration curve derived from serially diluted DNA samples of handpicked single P. penetrans (y =－1.01x + 34.73), after adjusting the DNA dilution rates to the densities in soil. The results suggested that calibration curves developed using serially diluted DNA samples (y =－1.13x + 37.00, y =－0.99x + 30.76, y =－1.06x + 35.52, and y =－1.00x + 28.96 for P. zeae, T. leviterminalis, H. dihystera, and H. columbus, respectively) may be appropriate to quantify target PPN in Kitadaito soil.
Root-knot nematodes (Meloidogyne incognita) are one of the most economically damaging nematodes; thus it is important to know the molecular mechanisms involved in the phases of nematode infection. To use this nematode as a material for research, we must constantly prepare sufficient numbers of nematodes, preferably sterilized. Here we have developed alternative methods for culture, sterilization, and inoculation of root-knot nematodes that are especially suitable for the use of Arabidopsis thaliana Heynh as host plants.
The ability to distinguish inactivated nematodes from dead ones is sometimes difficult because of their immobile. We tested whether the NaOH method could be applied to distinguish second stage juveniles (J2s) of the root-knot nematode Meloidogyne incognita that were inactivated under different conditions. The J2s inactivated by abamectin, a GABA agonist, or under the hypoxic conditions caused by CO2, reacted to the addition of NaOH. On the other hand, the J2s inactivated by fosthiazate, an organophosphate that causes muscle contraction, and those by NaN3, which inhibits respiration, did not react well to the NaOH treatment. However, these J2s reacted to the NaOH treatment after subsequent removal of the chemicals. The J2s inactivated by low temperature showed no reaction to the NaOH treatment. The NaOH method was demonstrated to be applicable for naturally immobilized nematodes such as the entomopathogenic nematode Steinernema litorale and the plant parasite Aphelenchoides besseyi. These results suggest that the NaOH method is applicable to distinguish between inactivated and dead nematodes but caution is warranted with regard to treatment temperature and the modes of action of the chemicals that are used.
Species of root-knot nematode (RKN) from 50 green pepper fields in Miyazaki, Kagoshima, Kochi, and Ibaraki prefectures were surveyed. Ten to 25 second juveniles (J2s) and female adults were collected, respectively, from each field and the species were identified individually by PCR-RFLP method. As a result, all RKN specimens, except one, were Meloidogyne incognita. Then each infested soil sample from 31 of the fields was inoculated to 3 breeding lines of nematode-resistant chili peppers (CM334, LS2341 and PI322719). Many galls and egg masses were observed after the inoculation in 6 (ca. 19%) of the infested soils. This indicates that resistance-breaking nematodes dominated at a high frequency in these fields.