Potato cyst nematodes (PCNs) are a major pest of solanaceous crops such as potatoes, tomatoes, and eggplants and have been widely studied over the last 30 years, with the majority of earlier studies focusing on the identification of natural hatching factors. As a novel approach, we focused instead on chemicals involved in nematode orientation towards its host plant. A new dual choice sand bioassay was designed to study nematode responses to potato root exudates (PRE). This bioassay, conducted together with a traditional hatching bioassay, showed that biologically active compounds that induce both hatching and attraction of PCNs can be collected by water extraction of incised potato roots. Furthermore, our results demonstrated that PCN also were attracted by potato root volatiles. Further work is needed to fully understand how PCNs use host plant chemical cues to orientate towards hosts. Nevertheless, the simple attraction assay used in this study provides an important tool for the identification of host-emitted attractants.
Sixteen Swedish PCN populations (nine Globodera rostochiensis and seven G. pallida populations) were compared with 20 other European populations (nine G. rostochiensis and 11 G. pallida populations) from Germany, the Netherlands, Norway and the United Kingdom in an AFLP study. Seven AFLP primer combinations were used to amplify genomic DNAs extracted from cysts. A dendrogram, based on UPGMA and evaluated by bootstrap analysis, contained two main clusters, one for each species. The Swedish Ro1 populations were very similar to corresponding populations from other parts of Europe. Remaining G. rostochiensis populations appeared as a genetically heterogeneous group with two Swedish populations being most dissimilar. Within G. pallida there was strong support for differentiating Pa1 populations from Pa2/3 populations. All Swedish G. pallida populations were grouped in the Pa2/3 cluster, and there were indications that they might have two main European origins. On the whole, the study indicates that there is considerable heterogeneity in Swedish PCN populations, justifying the maintenance of effective phytosanitary regulations.
Two Globodera rostochiensis and two G. pallida populations (pure and mixed) were analysed by identification methods based on morphology/morphometrics. To assess the accuracy of the identification, PCR analysis was performed on the same specimens. The investigation comprised juveniles, cysts and males. Seven of the most commonly used morphological/morphometric characters were examined: stylet length, length of stylet shaft plus knobs and stylet knob shape of second-stage juveniles; number of cuticular ridges between anus and vulval basin, distance between anus and vulval basin and Granek's ratio of cysts; and spicule shape of males. Altogether, 480 specimens were analysed and assessed. There were statistically significant differences between means of the G. rostochiensis and G. pallida populations in most characters and, in part, between populations of the same species. However, no individual morphological-morphometric character proved to be discriminant for species determination as in all cases there was a large overlap. A statistical discriminant analysis showed that with our populations, the values of a commonly used table of characters for separation of the two species had to be adjusted in order to produce the break points. By judging more than one character, the identification process could be considerably improved, suggesting the possibility of designing a computerised expert system.
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