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

Summary. Problems associated with identification of species attributed to the Xiphinema americanum group are reviewed to provide a 'benchmark' for a European Economie Union funded research collaboration. The principal objective of the research is to establi<;h a definitive morphological and molecular schcme for detection and diagnosis ofvirus-vector nematodes in the group. Forty-nine putative species are included in the group, together with two species considered species inquirendae. Infonnation and comments on the geographical occurrence and distribution of each species is provided. Thosc species for which there is unequivocal evidence of the nematodes' ability to transmit viruses arc listed, together with those species that IulVe been reported to have three or four juvenile stages. A series of polytomous identification keys is provided as a practical means for establishing a preliminary identification of X americanum group nematodcs occurring in the major geographical areas. The identification keys are provided in the expectation that researchers world-wide will provide constructive comment for improve­ ment with the objective of fmally establishing a practical, definitive morphological identification key.