Cytology of the Heterodera Trifolii Parthenogenetic Species Complex

Abstract

Twenty-four populations belonging to the Heterodera trifolii species complex from various geographical areas were found to reproduce by mitotic parthenogenesis (apomixis). The chromosome number as determined in metaphase I figures of maturing oocytes, varied from 24 to 35. With a basic chromosome number of n = 9 accepted for the genus Heterodera, two chromosomal forms were recognized within H. trifolii, one triploid and another tetraploid, each one comprising also several aneuploid forms. Cytogenetic information does not support the present taxonomic treatment of the group which needs to be revised. A cytological mechanism assumed to be responsible for the presence of giant eggs and giant 2nd-stage juveniles in these forms is discussed.