The Xiphinema americanum group. I. Putative species, their geographical occurrence and distribution, and regional polytomous identification keys for the group

Problems associated with identification of species attributed to the Xiphin ema americanum group are reviewed to provide a 'benchmark' for a European E conomic Union funded research collaboration. The principal objective of the research is to establish a definitive morphological and molecular scheme f or detection and diagnosis of virus-vector nematodes in the group. Forty-ni ne putative species are included in the group, together with two species co nsidered species inquirendae. Information and comments on the geographical occurrence and distribution of each species is provided. Those species for which there is unequivocal evidence of the nematodes' ability to transmit v iruses are listed, together with those species that have been reported to h ave three or four juvenile stages. A series of polytomous identification ke ys is provided as a practical means for establishing a preliminary identifi cation of X. americanum group nematodes occurring in the major geographical areas. The identification keys are provided in the expectation that resear chers world-wide will provide constructive comment for improvement with the objective of finally establishing a practical, definitive morphological id entification key.