Submitted to: Nematology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/3/2004
Publication Date: 6/6/2005
Citation: Molinari, S., Lamberti, F., Duncan, L.W., Halbrendt, J., Mckenry, M., Abawi, G.S., Magunacelaya, J.C., Crozzoli, R., Lemos, R.M., Nyczepir, A.P., Nagy, P., Robbins, R.T., Kotcon, J., Moens, M., Brown, D.J. 2004. Sod polymorphism in xiphinema americanum-group (nematoda: longidoridae). Nematology. 6:867-876. Interpretive Summary: The distribution of longidorids (i.e., dagger nematodes) on Prunus in the southeastern United States is largely unknown. In 2000, Dr. Franco Lamberti, Nematologist from the Instituto di Nematologia Agraria, Bari, Italy, visited my laboratory in Byron, Georgia. The purpose of that visit was to obtain as many Longidorid species from fruit and native tree species in Georgia. Following a comparative microscope study, a species identified as Xiphinema pacificum was detected on peach; the first report of this nematode species within the United States. This species belongs to the much debated X. americanum-group. Determining the general polymorphism of the SOD loci within the X. americanum-group, without any relationship with morphological identification of the populations was investigated. Isoelectrofocusing of superoxide dismutase (SOD) isoforms was carried out on the extracts of 117 nematode populations belonging to the so-called Xiphinema americanum-group. These populations came from USA, Chile, Argentina, Venezuela, Portugal, Italy, Crete, Montenegro, Slovakia, Hungary, Egypt, and India. The high degree of SOD polymorphism of this nematode collection allowed arranging the populations into 7 different homogeneous groups, characterized by specific combinations of SOD markers. Xiphinema pacificum (i.e., acronym = GG15) was classified into Group 1, Subgroup B. These data provide useful insights into factors associated with the genetic diversity for the X. americanum-group and may explain why some groups (i.e., USA populations) have the ability to transmit plant viruses as compared with other groups.
Technical Abstract: Isoelectrofocusing of superoxide dismutase (SOD) isoforms was carried out on the extracts of 117 nematode populations belonging to the so-called Xiphinema americanum-group. These populations came from USA (77), Chile (5), Argentina (1), Venezuela (5), Portugal (15), Italy (2), Crete (1), Montenegro (1), Slovakia (4), Hungary (3), Egypt (1), and India (2). A total of 17 bands of enzyme activity were observed in the screening, while single enzyme phenotypes showed from 2 to 8 bands. The high degree of SOD polymorphism of this nematode collection allowed arranging, by a cluster analysis, the populations into 7 different homogeneous groups, characterized by specific combinations of SOD markers. Sub-groups could be discriminated for larger groups. The small groups 3 and 5 were constituted mostly by populations from USA east coast states (i.e., NY and PA, respectively). The larger Group 1 resulted from the association of populations coming from various and distant North American States. In other large groups North American populations are present together with South American and European populations. Generally, data presented here suggest that geographic separation and different hosts do not seem to be the source of genetic diversity for the X. americanum-group. When an adequate number of populations were collected from the same country, the variability expressed by such sub-sample was comparable with that of the whole nematode collection. For the first time homogeneous populations of a large collection of X. americanum were associated by molecular means in order to explore further approaches to establish the taxonomy and phylogeny of this debated group.