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Maurice Moens and Yunliang Peng

Abstract

A method for screening Rosa accessions for their host suitability to Pratylenchus penetrans was developed. The best conditions were obtained in growth chambers with plants grown in sand, inoculated with 250 P.penetrans per 50 cm3 pot and fertilised weekly with 0.75 g/dm3 soluble fertiliser (containing 20% N, 20% P2O5, 20% K2O and balanced trace elements). Fifty days after nematode inoculation, these conditions permitted greater nematode multiplication than any other combination tested and also allowed good host development. When used for the screening of 21 Rosa accessions, these conditions revealed a large variation in host suitability. Least multiplication (Pf/Pi) was observed on R. virginiana (1.36) but this did not differ significantly from that on R. multiflora (2.87). The greatest Pf/Pi was on R. canina cv. Superba but this did not differ significantly from that on R. canina cv. Pollmeriana. The correlation of Pf/Pi with the nematode population and the number of eggs within the roots was significant; the percentage of nematodes outside roots was negatively correlated with Pf/Pi. The intermediate host status of R. corymbifera cv. Laxa, one of the most common rootstocks, was confirmed. Differences in host status became statistically significant when intra-accession variation was observed with a larger number of plants.

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Yunliang Peng and Maurice Moens

Abstract

A method for screening the tolerance of Rosa rootstocks and species to Pratylenchus penetrans was developed after observing the effects of nutrition and initial nematode population density on damage to Rosa corymbifera cv. Laxa. The correlation between initial P.penetrans densities and the weight of host plants fitted (R2 > 0.90) the Seinhorst model, Y = ym for Pi ≤ T, and Y = ym · m + ym(1 – m)z(Pi–T). All inoculated plants of R. virginiana and R. eglanteria survived while there were differences in the mortality after inoculation of 12 other Rosa rootstocks or species. Pratylenchus penetrans caused significant reductions in the numbers of the leaves and roots, and in fresh weights of shoots, roots and whole plants of all 14 accessions. Among these species and cultivars, reductions in root number were least for R. virginiana whereas fresh weights of roots, shoots and whole plants were least affected for R. eglanteria, and the greatest reductions were of R. corymbifera cv. Laxa and R. glauca. Plant mortality and the reduction of shoot and plant weights of surviving plants were positively correlated with the reduction in numbers of secondary roots. The numbers of secondary roots at inoculation were negatively correlated with the degree by which plant weight was reduced and with plant mortality observed 50 days later. Differences in tolerance among species as observed by differences in reduction of plant growth parameters were confirmed by differences of the parameters derived from applying the Seinhorst model to the species.

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Maurice Moens and Yunliang Peng

Abstract

Plant-parasitic nematodes are divided according to their feeding strategy into three major groups: sedentary endoparasites, migratory endoparasites and ectoparasites. Compared to what is known about sedentary endoparasitic nematode species, resistant and tolerant relationships between the nematodes from the latter two groups and their hosts are much less documented. However, methods for screening and evaluation of the resistance and tolerance of plants to migratory plant-parasitic nematodes have been well developed and sources of resistance and tolerance to these nematodes have been found. Advances have been made in breeding resistance to migratory plant-parasitic nematodes in rice, alfalfa, banana, pine trees, grape, woody fruits and other crops. Although accessions immune to stem, leaf and bud nematodes are found quite frequently, host resistance to migratory root-parasitic nematodes has been detected less frequently and generally only partly reduces nematode multiplication. Host tolerance to migratory nematodes is important even for resistant varieties and therefore is gaining attention. An insufficient degree of resistance and tolerance, their variability with the environment, and their linkage to undesired agricultural or horticultural characters are commonly observed. Polygenic bases for plant resistance and tolerance to migratory nematodes have been demonstrated by genetic and biochemical observations and make breeding even more complicated than that for resistance to sedentary plant-parasitic nematodes. These factors, with the presence of different nematode species in the field and community and population differences in pathogenicity, hinder the availability of host resistance and tolerance and offer a big challenge.

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Yunliang Peng and Maurice Moens

Abstract

0.1% malachite green alone (15 min) or with 0.5% streptomycin sulphate were efficient to surface sterilise Pratylenchus penetrans. These treatments did not significantly reduce nematode movement, nor attraction to and penetration into Rosa dumetorum cv. Laxa seedlings. Streptomycin sulphate (0.2%, 24 h) and a split treatment of streptomycin sulphate (0.2%, 24 h) and malachite green (0.1%, 10 min) did not reduce surface contamination. Combinations based on mercuric chloride (0.05-0.1%, 1-1.5 min) affected the behaviour of juvenile and adult stages of P. penetrans. Storage (30 days) at 4 degrees C reduced the survival of P. penetrans and its attraction to and penetration into rose seedlings. Effets de la sterilisation superficielle et du stockage au froid sur le comportement in vitro de Pratylenchus penetrans - Un traitement de 15 min a l'aide de vert de malachite a 0,1%, seul ou additionne de sulfate de streptomycine a 0,5%, sterilise superficiellement Pratylenchus penetrans de facon efficace. De tels traitements ne diminuent pas les mouvements du nematode non plus que son attraction par et sa penetration dans les racines de plants de Rosa dumetorum cv. Laxa. L'utilisation de sulfate de streptomycine a 0,2% pendant 24 h ou un traitement en deux temps par le sulfate de streptomycine (0,2%; 24 h) puis par le vert de malachite (0,1%; 10 min) ne diminuent pas la contamination superficielle. Les traitements combines comprenant du chlorure de mercure (0,05-0,1%; 1-5 min) affectent le comportement des juveniles et des adultes de P. penetrans. Un stockage de 30 jours a 4 degrees C diminue la survie de P. penetrans ainsi que ses potentialites d'attraction et de penetration vis-a-vis des plants de rosier.

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Maurice Moens and Wim Wesemael

Abstract

In the Belgian provinces Antwerp and Limburg, the root-knot nematode, Meloidogyne chitwoodi, is widespread. These regions are important production areas of carrot, Daucus carota, for the processing industry. Nineteen carrot cultivars were screened for potential resistance for M. chitwoodi. Egg masses of M. chitwoodi were found on all cultivars. However, there were no egg masses on more than 80% of plants of cvs Berlanda, Bolero, Chantenay, Nantucket and Parmex. By contrast, on cvs ABK, Douceur, Maxi and Merida egg masses were formed on all of the tested plants. To gain information about the damage caused by M. chitwoodi, carrots were grown in soil infected with different densities of nematodes. There was no effect of M. chitwoodi on the length, width and weight of the carrot taproot. Damage caused by M. chitwoodi was manifested by severe galling near the lenticels. Inoculation of nematodes 6 weeks after the carrots emerged resulted in a higher percentage of infected carrots and damaged taproots compared with earlier inoculation times. The effect of the time of harvest on nematode infection and damage was examined. When harvested 100 days after sowing in soil with low nematode densities (two second-stage juveniles (J2)/100 g soil), no damage was reported. Harvesting 120 and 140 days after sowing resulted in 10 and 20% damaged carrots, respectively. With initial M. chitwoodi densities of 25 J2/100 g soil, the percentage of damaged taproots increased from 10% when harvested 100 days after sowing to 70% when harvested 140 days after sowing. In a field trial, 11.5% of the carrots were damaged after a field period of 139 days and the initial M. chitwoodi population increased from 3 to 111 J2/100 g soil. It is recommended that growing carrots in M. chitwoodi-infested fields should be avoided. However, damage can be limited in fields with low initial nematode populations when the growing period is reduced.

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Sergei Subbotin, Maurice Moens and Lieven Waeyenberge

Abstract

Amplified ITS region products of rDNA from 25 valid species and one unidentified species from the genus Heterodera and from Meloidodera alni were digested by 26 restriction enzymes. A combination of seven enzymes clearly separated the agriculturally most important species from each other and from their sibling species. Species specific digestion profiles of ITS regions and a table with approximate sizes of digested fragments for several identification enzymes are given. Heterogeneity of ITS regions was revealed for some cyst forming nematode species. Des fragments amplifiés de la région de l’ITS du rDNA de 25 espèces valides et d’une espèce non identifiée du genre Heterodera et de Meloidodera alni ont été soumis à une digestion par 26 enzymes de restriction. La combinaison de sept enzymes a permis une séparation nette des espèces les plus importantes en agriculture, tant les unes par rapport aux autres que par rapport aux espèces jumelles. Sont donnés les profils spécifiques de digestion des régions de l’ITS et un tableau regroupant les tailles approximatives des fragments digérés pour plusieurs enzymes d’identification. L’hétérogénéité des régions de l’ITS a été révélée chez quelques espèces de nématodes à kyste.

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Lieven Waeyenberge, Maurice Moens and Nicole Viaene

Abstract

ITS1, the 5.8S rRNA gene and ITS2 of the rDNA region were sequenced from 20 different Pratylenchus species. Additionally, the same region was sequenced from seven populations of P. penetrans. After purifying, cloning and sequencing the PCR products, all sequences were aligned in order to find unique sites suitable for the design of species-specific primers for P. penetrans. Since ITS regions showed variability between and even within populations of P. penetrans, only three small DNA sequences were suitable for the construction of three potentially useful species-specific primers. New species-specific primers were paired with existing universal ITS primers and tested in all possible primer combinations. The best performing primer set, supplemented with a universal 28S rDNA primer set that served as an internal control, was tested in duplex PCR. The ideal annealing temperature, Mg2+ concentration and primer ratios were then determined for the most promising primer set. The optimised duplex PCR was subsequently tested on a wide range of different Pratylenchus spp. and 25 P. penetrans populations originating from all over the world. To test the sensitivity, the duplex PCR was conducted on DNA extracted from a single P. penetrans nematode mixed with varying amounts of nematodes belonging to another Pratylenchus species. Results showed that a reliable and sensitive P. penetrans species-specific duplex PCR was constructed.

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Wim Wesemael, Nicole Viaene and Maurice Moens

Abstract

In Europe, root-knot nematodes are increasingly important. Out of more than 90 Meloidogyne species currently described, 23 have been found on the continent. In the cooler climates, Meloidogyne hapla, M. naasi, M. chitwoodi and M. fallax are prevalent. Meloidogyne arenaria, M. javanica and M. incognita are the most common species in warmer conditions of southern Europe, but also in glasshouses in northern Europe. Morphological identification of root-knot nematodes is difficult and time consuming; therefore, many research groups have been developing molecular techniques for identification of Meloidogyne species. Meloidogyne chitwoodi and M. fallax are quarantine organisms and subject to regulations, and the highly aggressive M. enterolobii has been added to the EPPO alert list. Differences between temperate and tropical Meloidogyne species and their prevalence in Europe imply the need for different management strategies in south and north Europe. Possible crop rotations for the control of root-knot nematodes are limited due to the wide host range of several important species. The banning of methyl bromide and restrictions on other fumigant pesticides in the EU have increased the application of biofumigation significantly in south Europe. The egg-parasitising fungus Paecilomyces lilacinus is commercialised in Germany and applied as dispersible granules for application in water. Intensive research is conducted on the egg-parasitising fungus Pochonia chlamydosporia, and the obligate parasitic bacterium Pasteuria penetrans. European research has paid much attention to resistance breeding and selection. The Mi gene of tomato is widely used but resistance-breaking populations of M. incognita and M. javanica have been reported in different countries.

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Sergei Subbotin, Maurice Moens and Deliang Peng

Abstract

A method for rapid identification of juveniles and cysts of the soybean cyst nematode based on PCR with species specific primers is described. The PCR assay was tested on 53 populations originating from China, Russia, USA and Brazil. A single cyst or second stage juvenile of Heterodera glycines alone or in a mixture with other soil inhabiting nematodes was detectable.

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Dirk De Waele, Maurice Moens and Gamal Elbadri

Abstract

Summary - The reproduction of Radopholus similis isolates from different origins and hosts was compared in carrot disk cultures at different temperatures. At 15°C, only the isolates collected from ornamental plants in Europe reproduced. The greatest fecundity was observed at 25°C. The reproduction factor (final population/initial population: Pf/Pi) ranked the isolates in similar order for four of the temperatures studied (15, 20, 25 and 30°C). When carrot discs at 28°C were inoculated with single females of isolates selected from those with different reproductive factors, this ranking was confirmed. This suggests that reproduction is controlled by intrinsic isolate characteristics which are not influenced by temperature. Isolates with most reproduction had a greater percentage of reproductive females than isolates with less reproduction, associated with a high ratio of females : males and a high proportion of females in the total production. The mean offspring per productive female was similar for high and low reproducing isolates.