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Summary: The root-lesion nematode, Pratylenchus penetrans , causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar ('Cosmopolia' and 'Brighton', respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage. [ABSTRACT FROM AUTHOR]

Root-lesion nematodes of the genus Pratylenchus are among the most important nematode pests that limit production of small-grain cereals. Four Pratylenchus species, viz. P. thornei, P. neglectus, P. penetrans, and P. crenatus, are considered of major economic significance in cereals of which P. thornei and P. neglectus are the most important and widely distributed species in cereal crops worldwide. However, P. thornei is more destructive causing estimated yield losses of up to 50% in the USA and 85% in Australia. This paper provides information regarding the global distribution of Pratylenchus species, yield loss due to their attack, their biology and pathogenic relation to plants, the research cutting edges in nematode identification of different Pratylenchus species, and their control through cultural practices and resistant varieties as correct identification of root-lesion nematodes can be difficult to achieve, particularly if a quick diagnosis is needed. In this context, in recent years, several molecular techniques for these Pratylenchus species have been developed such as quantitative PCR assays which are able to produce precise and rapid identification of several root-lesion nematodes species. So far, many global attempts have been made to control root-lesion nematodes in cereals, including cultural practices and development of resistant varieties. The use of resistant accessions is considered the most economically feasible and environmentally sustainable method. Resistance genes in several lines have been identified and are being used in numerous breeding programmes against root-lesion nematodes species. [ABSTRACT FROM AUTHOR]

A real-time quantitative PCR assay was developed for the accurate detection and quantification of the root-lesion nematode, Pratylenchus thornei. A qPCR primer set, including two primers and a probe, was designed based on the sequence of the ß-1,4- endoglucanase gene. The assay was optimised by using the primers with SYBR green I dye and setting the qPCR program to different annealing temperatures ranging from 62 to 69°C. Based on the Ct values, we retained the program with an annealing temperature of 69°C. The specificity of the qPCR assay including the probe was confirmed by the lack of amplification of DNA from 47 populations belonging to 15 other Pratylenchus species and nine isolates from P. thornei. The assay was very sensitive as it was able to detect a single individual of P. thornei, even when mixed with up to 80 individuals of P. penetrans. DNA was extracted from exactly 80 P. thornei individuals. A dilution series from this DNA resulted in a standard curve showing a highly significant linearity between the Ct values and the dilution rates (R² = 0.98; slope = -3.38; E = 97.6%). The qPCR assay developed in this study proved to be specific and sensitive, thus providing a fast and accurate tool for detection and quantification of this pathogen during research, as well as for diagnostic labs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]