Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 2010
Publication Date: March 14, 2011
Citation: Skantar, A.M., Handoo, Z.A., Carta, L.K., Zasada, I. A., Ingham, R.E., Chitwood, D.J. 2011. Morphological and molecular characterization of Globodera populations from Oregon and Idaho. Phytopathology. 101:(4)480-491. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plant roots and cause an estimated ten billion dollars of crop loss each year in the United States and 100 billion dollars globally. Cyst nematodes are an important group, damaging the roots of many kinds of plants worldwide. In the present study, ARS scientists describe the anatomical and molecular features of a new cyst nematode that was discovered in soil samples collected during surveys to detect potato cyst nematode (PCN). This research is significant because the new species shares key anatomical features with two PCN species of regulatory concern, the pale potato cyst nematode and the golden nematode. The newly described species can confound accurate diagnosis of PCN because current molecular tests are not set up to identify it. The morphological and molecular data describing this lookalike species will help scientists, regulators, and extension agencies to more accurately identify and prevent the spread of potato cyst nematodes.
Technical Abstract: A new species of Globodera, identified from three potato fields, is described herein as Globodera pseudopallida n. sp. Morphologically, G. pseudopallida n. sp. exhibits some unique features that are not consistent between populations; but molecularly, G. pseudopallida n. sp. is distinct from G. pallida, G. rostochiensis and G. tabacum. Compared to G. pallida, the cyst body length is slightly longer, and the second-stage juvenile stylet length is slightly shorter. In some individuals, the J2 stylet knob height is greater and the tail annules are more prominent than in G. pallida, and the tail abruptly narrows with a slight constriction near the posterior third of the hyaline terminus. Compared to G. rostochiensis, the hyaline tail terminus has a larger number of refractive bodies, and cysts of the new species have a smaller Granek’s ratio and fewer cuticular ridges between the anus and vulva. In some individuals, the tail termini of second-stage juveniles are more bluntly pointed, and the stylet knobs are more anteriorly directed with greater height than in G. rostochiensis. Unlike G. tabacum, the cyst wall often lacks a network-like pattern, and in some individuals, the juvenile tail terminus distinctly narrows after a constriction. In Globodera pseudopallida n. sp., multiplex PCR of the ITS rDNA region appeared similar to G. tabacum; however, hybrid ITS-RFLP patterns with individual bands in common with all three species were observed. Phylogenetic analysis of ITS rDNA sequences showed that Globodera pseudopallida n. sp. was most similar to populations from Argentina and Chile. Together these populations form a highly supported clade distinct from either European or Peruvian G. pallida, G. rostochiensis, or G. tabacum.