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 c lassical nematode systematics, in order to clarify inter- and intraspecific relationships within this complex. Twenty populations of cereal cyst nemat odes (Heterodera avenae, H. filipjevi, H. latipons and H. mani) were compar ed by means of five different isoenzymatic systems (esterase, malate dehydr ogenase, phosphoglucoisomerase, phosphoglucomutase and superoxide dismutase ) using isoelectrofocusing (IEF) on the electrophoretic separation. The res ults are in agreement with previous morphological and biochemical character izations, which established genetic diversity between the Gotland strain an d H. avenae and identified the Gotland strain with H. filipjevi. Population s from Israel, all included in the H. avenae group, exhibited well-defined intraspecific dissimilarity. The highest degree of polymorphism was found i n the H. avenae group for all five enzymatic systems studied. The H. mani p opulation was also included in the H. avenae group by these isozyme analyse s. Malate dehydrogenase, phosphoglucoisomerase and phosphoglucomutase isozy mes, fractionated for the first time by IEF in the cereal cyst nematode com plex, displayed a higher level of polymorphism than using conventional elec trophoresis. isoelectric focusing has proved to be a useful tool for detect ing genetic diversity within and among species of the cereal cyst nematode complex and for taxonomic purposes.