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Abstract

The effect of a sequence of host and non-host crops on the population dynamics of Pratylenchus penetrans was monitored for 2 years in a field. The sequence was pea (Pisum sativum, 25% cv. Colombia and 75% cv. Coca), French marigolds (Tagetes patula nana cv. Sparky); fallow; carrot (Daucus carota, cv. Amsterdamse bak); bean (Phaseolus vulgaris, cv. Avignon) and again fallow. Samples were taken every 21 days during the marigold crop and following fallow, and at planting and harvest for the other crops. From five 2 × 5 m2 plots, 15 cores were taken per plot to a depth of 70 cm and split into seven segments of 10 cm each. Within the plots, segments from corresponding depths were pooled and nematodes were estimated from a 200 g subsample. Densities of P. penetrans increased 2.2-fold under pea, but decreased by 90% after marigolds had been grown for 105 days. The P. penetrans population was reduced by about 90% in the soil layer above 40 cm while the reduction was about 80% below 50 cm after 105 days of marigold culture. Densities of P. penetrans declined exponentially in time under marigold and fallow. The effect of marigold was persistent as no increase in P. penetrans densities over the whole soil profile was noticed after two crop cycles of host plants.

In: Nematology

Abstract

Long-term efficacy of Pochonia chlamydosporia, a fungal parasite of root-knot nematodes, was tested in two cropping systems: one consisting of three consecutive lettuce crops and another consisting of one tomato crop followed by two lettuce crops. Plants were either grown in pots in soil inoculated with 5000 chlamydospores of P. chlamydosporia per cm3 soil or in soil without chlamydospores. Fifty or 25 second-stage juveniles (J2) of Meloidogyne javanica per 100 cm3 soil were applied in Tests 1 and 2, respectively. The high nematode inoculum density of Test 1 resulted in considerable plant death, showing that the fungus was unable to control high nematode levels. At the harvest of most crop cycles, fewer J2 were found in soil or roots or fewer egg masses per root system were counted in pots with P. chlamydosporia compared with pots without P. chlamydosporia. A one-time application of P. chlamydosporia was able to slow down the build-up of the M. javanica population for at least 5-7 months.

In: Nematology

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.

In: Nematology

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.

In: Nematology

Potato cyst nematodes (PCN) are the most economically important nematode pests of potato. Early harvesting is part of a preventive management approach for very early potato varieties. In Belgium, tubers are harvested before 20 June because it is assumed that no cyst formation occurs by that date. However, this assumption might not be valid any more because of climate change, the availability of new cultivars (with new traits), and the increasing prevalence of Globodera pallida. Therefore, pot, microplot and field trials were conducted to study the life cycle of PCN in early potato-growing conditions. The development of populations of G. pallida on three potato cultivars, Eersteling (susceptible to PCN), Première (resistant to G. rostochiensis) and Ambassador (partially resistant to G. pallida) and that of G. rostochiensis on cv. Eersteling was monitored in the growth chamber with simulation of field temperatures of the season. On cvs Eersteling and Première, second-stage juveniles (J2), males, females and cysts of G. pallida populations were found 28, 56, 63 and 77 days after infestation with cysts (DAI), respectively. The number of degree days (DD) for G. pallida to complete its life cycle using a base temperature of 4°C was calculated 450 DD4. On cv. Ambassador, females of G. pallida were never observed. J2, males, females and cysts of G. rostochiensis were detected 42, 70, 70 and 84 DAI, respectively. This species needed 398 DD6 at a base temperature of 6°C to complete its life cycle. Observations in two fields and in microplots under prevailing weather conditions in 2013 revealed that cysts of G. pallida and G. rostochiensis were formed on June 12, when the accumulated degree days were 463 DD4 and 401 DD6, respectively. Our observations show that both species of Globodera develop earlier than was assumed based on previous data. Therefore, harvesting based on the accumulated heat above the basal development temperature required by PCN species can replace the set harvest date.

In: Nematology

Abstract

The potato cyst nematode, Globodera rostochiensis, is a quarantine organism. Environmentally benign control measures for this economically important pest are needed. Green manures, in particular plants from the Brassicaceae, suppress some plant-parasitic nematodes and have potential as control agents. This study examined if growing and incorporating cover crops from the Brassicaceae family influenced hatching of G. rostochiensis. The effect of root diffusates and plant extracts, as well as soil incorporation of plant material from three commonly used species of green manures, was studied in in vitro bioassays and pot tests. The results showed that brassica diffusates and plant extracts were not nematicidal. In addition, although they did not cause hatch by themselves, pretreatment with these solutions enhanced subsequent hatch in host root diffusates. The results are discussed in the context of the hatching response of G. rostochiensis and the likely influence on field usage of these green manures.

In: Nematology

Abstract

The influence of temperature and root diffusates from different plants on the hatching behaviour of Pratylenchus penetrans was studied. Diffusates were obtained from maize (cv. Husar), carrot (cv. Masei), black salsify (cv. Omega), pea (cv. Alouette), bean (cv. Polder) and marigold (cv. Single Gold) at different plant ages. Soil leachate was used as a control treatment. Hatching was also examined in 10% dilutions of the root diffusates and the soil leachate. Hatching was monitored at 5-day intervals until 60 days at most. Test solutions were refreshed at the same intervals. Pratylenchus penetrans hatched more at 20°C than at 10, 15 or 25°C. Hatching was stimulated by all host diffusates, as well as marigold; it was highest in maize and bean diffusates (ca 50%). Except for carrot diffusate and soil leachate, hatching activity decreased with increasing plant age. It also decreased in 10% diluted root diffusates, except for pea, black salsify and soil leachate. There was no evidence for the presence of hatching inhibitors in the diffusate of any host.

In: Nematology

Root-lesion nematodes (Pratylenchus) have a worldwide distribution and cause severe production constraints on numerous important crops. During a survey of the wheat-growing area of Morocco, 17 populations of root-lesion nematode were collected. They were identified on the basis of their morphological and morphometric characters, and by molecular methods. Microscopic observations of females and males demonstrated the occurrence of P. penetrans in 13 of the 17 samples; P. thornei and P. pseudocoffeae were detected in four samples from Zaers and a single sample from Settat, respectively. A duplex PCR primer set was used to confirm the presence of P. penetrans while the species-specific forward primer PTHO and the common reverse primer D3B were used for P. thornei. For the remaining populations, the D2-D3 expansion segments of the 28S rRNA gene were amplified and the obtained sequences were compared with those of Pratylenchus species in the GenBank database. This comparison confirmed the morphological identifications and revealed a population of P. pinguicaudatus. The study of the phylogenetic relationship of the Moroccan Pratylenchus populations showed a high similarity (99-100%) between all P. penetrans populations. The population dynamics of six Pratylenchus populations from Morocco were evaluated on carrot disk cultures at 4, 8 and 12 weeks after inoculation, and at 10, 15, 20 and 25°C. The optimum temperature for reproduction of all populations was 20°C. After 8 weeks at this temperature, nematode numbers increased up to 458-fold, 310-fold and 252-fold for the four populations of P. penetrans, the P. thornei and the P. pseudocoffeae population, respectively.

In: Nematology

Abstract

Meloidogyne chitwoodi and M. fallax are quarantine organisms in Europe. One measure to restrict the spread of these nematodes is careful inspection of potato tubers. The distribution of M. chitwoodi in heavily infected tubers was studied and several methods for extraction of these nematodes from tubers were compared. The majority of the nematodes (96%) were found in the first 5.25 mm of the tuber, corresponding to the depth of the vascular ring. About half of them were found between 1.75 and 3.50 mm deep. Incubation of small pieces of tuber on Baermann funnels in the misting chamber during 36 days yielded about 12 times fewer juveniles than mixing potato tissues and extracting them using zonal centrifugation, a process that took about 1 h. Enzymatic maceration of potato tissues for 24 or 48 h did not liberate more nematodes than 2 min of blending the tissues at high speed. More nematodes, with 95% consisting of eggs, were extracted by zonal centrifuging than by pouring the macerated suspension over a set of 500 μm, 250 μm and 20 μm sieves.

In: Nematology

Abstract

The influence of both host and temperature on the vertical migration of Pratylenchus penetrans was examined in a series of experiments using maize, carrot, black salsify, pea, bean and potato. Plants were grown in a pot placed on top of a plastic pipe of variable length in a growth chamber. This pipe was planted into a second pot to maintain the humidity in the pipe. Nematodes were inoculated at the bottom of the pipe and were allowed to migrate upwards for 14 days after which the pipe was cut into 5 cm sectors from which the nematodes were extracted and counted. More nematodes migrated at 21°C than at 16 or 11°C. Migration of P. penetrans towards a host decreased with increasing distance between the nematodes and all hosts, with maize and bean eliciting the most attraction. They were the only hosts able to stimulate nematode migration up to the distal end of 31 cm pipes. Potato and carrot were the least influential hosts. Hosts differently influenced the migration only of second-stage juveniles (J2), with a greater percentage of J2 moving under maize and bean than under carrot. Under all hosts, adults migrated in greater proportions with increasing distance than did other stages. The attractiveness of hosts was age dependent. Generally, infectivity decreased with distance travelled by the nematode.

In: Nematology