Genetic relationships and isozyme variability in the Heterodera avenae complex determined by isoelectrofocusing

Isozyme variability was assessed among the principal species of the cereal cyst nematode complex to complete and enhance the information provided by classical nematode systematics, in order to clarify inter- and intraspecific relationships within this complex. Twenty populations of cereal cyst nematodes (Heterodera avenae, H. filipjevi, H. latipons and H. mani) were compared by means of five different isoenzymatic systems (esterase, malate dehydrogenase, phosphoglucoisomerase, phosphoglucomutase and superoxide dismutase) using isoelectrofocusing (IEF) on the electrophoretic separation. The results are in agreement with previous morphological and biochemical characterizations, which established genetic diversity between the Gotland strain and H. avenae and identified the Gotland strain with H. filipjevi. Populations from Israel, all included in the H. avenae group, exhibited well-defined intraspecific dissimilarity. The highest degree of polymorphism was found in the H. avenae group for all five enzymatic systems studied. The H. mani population was also included in the H. avenae group by these isozyme analyses. Malate dehydrogenase, phosphoglucoisomerase and phosphoglucomutase isozymes, fractionated for the first time by IEF in the cereal cyst nematode complex, displayed a higher level of polymorphism than using conventional electrophoresis. isoelectric focusing has proved to be a useful tool for detecting genetic diversity within and among species of the cereal cyst nematode complex and for taxonomic purposes.