Studies on Radopholus similis and Radopholus citrophilus using electron microscopy
In the past, two races were recognized within the species Radopholus similis (EPPO A2 quarantine pest): one race attacking banana but not citrus (banana race), and the other attacking both citrus and banana (citrus race). In addition, other differences were observed between the two races, concerning karyotype (n=4 for banana race, n=5 for citrus race), isoenzymes, proteins and sexual behaviour. It was then proposed to consider the citrus race as a new species named R. citrophilus (EPPO A1 quarantine pest). R. citrophilus and R. similis could not be differentiated on the basis of morphological characters; and recently, it has been demonstrated (Hahn et al., 1996) that the chromosome number cannot be used as a diagnostic feature in R. similis. However, Huetel and Yaegashi (1988) have said that the observation of cuticular structure by scanning electron microscopy (SEM) could differentiate between R. citrophilus and R. similis. In the present study, two populations of R. similis from Guinea-Bissau and Côte d’Ivoire were studied by SEM. These two populations have similar cuticular structures, and showed a range of variation which overlap with the differences previously described by Huetel and Yaegashi (1988). Therefore, it is felt that R. similis and R. citrophilus cannot be distinguished by scanning electron microscopy. The authors suggested that it would appear more reasonable to consider R. citrophilus as a junior synonym of R. similis, the citrus and banana races representing two different pathotypes.
EPPO note: in these studies no populations of R. citrophilus were included.
Hahn, M.L.; Wright, D.J.; Burrows, P.R.; (1996) The chromosome number in Radopholus similis – a diagnostic feature?
Nematologica, 42, 382-386.
Huettel, R.N.; Yaegashi, T.Y.; (1988) Morphological differences between Radopholus citrophilus and R. similis.
Journal of Nematology, 20, 150-157.
Valette, C.; Mounport, D.; Nicole, M.; Sarah, J.-L.; Baujard, D. (1998) ;Scanning electron microscope study of two African populations of Radopholus similis (Nematoda: Pratylenchidae) and proposal of R. citrophilus as a junior synonym of R. similis.
Fundamental and Applied Nematology, 21(2), 139-146.