Morphometrics of Globodera tabacum tabacum, G. t. virginiae, and G. t. solanacearum (Nemata: Heteroderinae).

A morphometric evaluation of second-stage juveniles (J2), males, females, cysts, and eggs of several isolates of the tobacco cyst nematode (TCN) complex, Globodera tabacum tabacum (GTT), G. t. virginiae (GTV), and G. t. solanacearum (GTS) is presented. Morphometrics of eggs, J2, and males are considerably less variable than of females and cysts. No measurements of eggs and J2 are useful for identification of the three subspecies. Distance from the median bulb and excretory pore to the head end in J2 and males is quite stable. Stylet knob width of males is useful for identifying GTV isolates and tail length in separating males of GTT isolates from GTV and GTS. Body length/width (L/W) ratio of females and cysts discriminates GTT from GTV and GTS; stylet knob width is an auxiliary character for identifying GTV. This subspecies complex has a continuum of values for the other characters. Data suggest a close relationship between GTV and GTS, which also occur in close proximity in Virginia.