Factors affecting the efficacy of Brassica species and ryegrass (Lolium perenne L.) on root-knot nematode infestation of tomato.

The effects of soil incorporation of metham-sodium and finely chopped plant residues of broccoli, cabbage, cauliflower, and grass against Meloidogyne incognito and M. javanica over increasing periods of time and a range of dose rates, with or without plastic covering were studied in growth chamber experiments. The scope of this study was to determine the direct effects of fresh organic amendments and the indirect effects of their volatiles on Meloidogyne spp. and tomato plant growth. Amendments were applied at the rate of 5 or 10 kg/m2. The most effective treatment in maintaining low numbers of nematodes was pre-treatment with volatiles of metham-sodium, which resulted in zero invasion of tomato roots. Application of fresh-chopped broccoli, grass and, in some instances, cauliflower also caused a significant reduction in the population of root-knot nematodes. Nematode reduction caused by broccoli was slightly better than by grass. On the other hand, cabbage incorporation did not suppress Meloidogyne spp. to the same extent, though a 19% reduction was observed, even at the lowest dose rate. Suppression of root-knot nematodes was greater in pots amended and covered with plastic tarp as compared to amended non-covered pots. Increased doses for all treatments were further effective in reducing the populations of root-knot nematodes. The direct effect of soil amendments was greater after 2 weeks, while the indirect effects of volatiles were lessened after 2 and 3 weeks.

First Report of the Stubby-Root Nematode Paratrichodorus teres Associated with Artichoke (Cynara scolymus) in Greece.

The polyphagous stubby-root nematode species, Paratrichodorus teres (Hooper) Siddiqi, was first described from soil under lettuce near Norwich, UK and subsequently reported from South Africa and the United States, but predominantly from temperate regions within Europe (4). P. teres is one of 13 economically important trichodorid species known to be vectors of Tobacco rattle virus (TRV) (4). Artichokes planted during 2000 in a field located in the Kandia area of the Argolis Region, Greece (37°32'N, 22°56'E) exhibited symptoms of a virus infection. Sampling was done to ascertain the presence of Longidorus fasciatus, a vector of artichoke Italian latent nepovirus known to occur in the area (1,4). In addition to L. fasciatus, an unknown trichodorid species and Tylenchorhyncus sp. were recovered from the root zone of artichoke at a number of sites within the field. Measurements and morphological examination of the female (n = 13, body length = 741.7 ± 25.5 µm, onchiostyle = 43.7 ± 0.8 µm, and position of vulva from anterior region relative to total body length V% = 53.8 ± 0.4 µm) and male (n =1, body length = 720.5 µm, onchiostyle = 43.5 µm, spicule length = 51.7 µm, and number of ventromedian precloacal supplements = 3) trichodorids isolated from soil samples conformed to the original description of P. teres and the generic polytomous key (2). Furthermore, morphological identification was supported by molecular data. DNA was extracted from seven individual trichodorids, each of which were placed into separate 0.5-ml micro-centrifuge tubes containing 20 µl of 0.25 M NaOH and incubated at 25°C overnight. Thereafter, samples were incubated at 99°C for 3 min and 10 µl of 0.25 M HCl, 5 µl of 0.5 M Tris-HCl, (pH 8.0) and 5 µl of 2% Triton X-100 were added to each tube. Samples were incubated at 99°C for a further 3 min and stored at -20°C. Template DNA was amplified using polymerase chain reaction with primers specific for 18S rDNA and sequenced (3). The resultant consensus sequence had 99.8% homology to P. teres populations isolated from Portugal and good homology (95 to 98%) with five other Paratrichodorus spp. listed on public sequence databases, e.g., NCBI GenBank. This constitutes a new geographic record and a possible association of P. teres on artichoke. References: (1) D. J. F. Brown et al. Eur. J. Plant Pathol. 103:501, 1997. (2) W. Decraemer. Fundam. Appl. Nematol. 21:37, 1998. (3) C. M. G. Oliveira et al. J. Nematol. 36:153, 2004. (4) C. E. Taylor and D. J. F. Brown. Nematode Vectors of Plant Viruses, CAB International Mycological Institute, Wallingford, UK, 1997.

Twin chorionicity and pre-eclampsia.

OBJECTIVE: To determine whether the incidence of pre-eclampsia is different in dichorionic compared to monochorionic twin pregnancies. METHODS: The study involved 666 twin pregnancies resulting in two live births after 24 weeks of gestation. Ultrasound examination at 10-14 weeks of gestation demonstrated that 171 (25.7%) were monochorionic and 495 (74.3%) were dichorionic twins. Pregnancy outcome information regarding the development of pre-eclampsia was obtained from the maternity units. The incidence of pre-eclampsia in the dichorionic and monochorionic twin pregnancies was compared. RESULTS: The incidence of pre-eclampsia in monochorionic twin pregnancies (9.4%) was not significantly different from that in dichorionic pregnancies (7.3%) ( P = 0.48). Multiple logistic regression revealed that chorionicity has no effect on the development of pre-eclampsia after adjusting for maternal age, ethnic group, maternal smoking, parity and gestational age at delivery ( P = 0.6; odds ratio for monochorionic compared with dichorionic twin pregnancies, 1.19; 95% confidence interval, 0.61-2.3). CONCLUSION: In twin pregnancies chorionicity does not affect the incidence of pre-eclampsia.

Observations on the feeding behaviour of Paratrichodorus anemones in relation to tobravirus transmission.

Feeding by P. anemones, an efficient vector of tobacco rattle virus (TRV), was investigated by video-enhanced interference light microscopy. Four stages were observed after transfer of individual nematodes, extracted from soil, to Nicotiana tabacum seedling roots in agar: i) acclimatisation; ii) approach and scrutiny; iii) preparation; and iv) feeding. Prior to commencement of stage 'iv' about 4 cells perforated by rapid onchiostyle thrusting remained alive, each having been almost immediately abandoned by the nematode. During the stage iv) approximately 5% of perforated cells remained alive. Feeding on individual cells was similar to that previously reported for Trichodorus similis: cells from which cytoplasm was ingested after a prolonged period of salivation were invariably killed, with adjacent cells being unaffected. During feeding a number of cells perforated but soon afterwards abandoned by P. anemones remained alive, providing an effective pathway for successful transmission of TRV to plants by the nematode.

Immunogold Localization of Tobacco Rattle Virus Particles within Paratrichodorus anemones.

Unequivocal evidence of the viral nature of virus-like particles observed at the specific site of retention of tobacco rattle virus (TRV) in Paratrichodorus and Trichodorus nematodes has not previously been available. A new staining technique using safranin-O, which does not affect viral antigenicity, was used with an antiserum raised against the coat protein of TRV and prepared for use with immunogold labelling. Application of this method enabled the occurrence and localization of particles of TRV to be confirmed in the pharynx of the natural vector of the virus, Paratrichodorus anemones, and provided unequivocal evidence that the particles observed were TRV particles. The TRV particles were observed attached only to the cuticle lining the posterior tract of the pharyngeal lumen of the vector. Therefore, the specific site of retention of TRV particles in P. anemones is apparently more localized than reported to occur in other vector trichodorid species.