Diagnosis and Management of Lesion Nematodes (Pratylenchus spp.)

Lesion nematodes (Pratylenchus spp.) remain key nematode parasites in a variety of crops in California, and continue to be viewed as an important topic among the Nematology Workgroup members. Within the genus there are many different species, that can be distinguished – sometimes by only very subtle – morphological differences. Correct species identification is crucial to reliable management because of differences in host range and virulence between the species. A three-way approach was followed to address the issues concerning lesion nematode identification. 1) Improve the microscopic diagnostic capabilities of current UC, CDFA, and private laboratories throughout California. The UCR group (J. Baldwin, M. Mundo, and P. De Ley) organized a training class on morphological identification of lesion nematodes. This class was attended by representatives of diagnostic and research labs throughout the state. Novel illustrated Lucid® computer-based keys including video microscope images are being developed as an identification aid to Pratylenchus species. Approaches to date were demonstrated at the recent Nematology Workshops. At these events, participants were given a CD-ROM with detailed videos on the morphology of lesion nematode and other nematodes. On the basis of feedback from these workshops, identification tools are being refined, further developed and distributed. 2) At the field level, provide training for growers and PCA’s in nematode biology and management. Westerdahl, Ploeg, and Becker presented numerous presentations during the past two years for growers and PCA’s throughout the state, in which they addressed biology, damage and importance of lesion nematodes. Further half-day hands-on demonstration sessions will be conducted if requested. 3) Develop molecular methods for identification of lesion nematode species. Lesion nematodes populations that were cultured on root explants or carrot disks at UCR were used to fine-tune a molecular diagnostics protocol at UC Davis. The method that was developed allows identification of individual lesion nematode species that are of economic importance in California. Al-Banna, L., A. T. Ploeg, V. M. Williamson, and I. Kaloshian 2004. Discrimination of Six Pratylenchus Species Using PCR and Species-Specific Primers. Journal of Nematology 36:142-146. A PCR-based assay for identification of six species of Pratylenchus common in California is described. In this assay, five forward species-specific primers were designed from the internal variable portion of the D3 expansion region of the 26S rDNA and were each used with a single, common reverse primer. The optimized species-specific primers produced unique amplicons from their respective target, and did not amplify DNA from other Pratylenchus species. With this assay we were able to identify single females to species level. This method obviates the need for subsequent RFLP or sequence analysis of the PCR product and can be used as a rapid diagnostic tool in epidemiological and management studies.