THE GENOME SIZE AND CHROMOSOME COMPLEMENT OF THE POTATO CYST-NEMATODE GLOBODERA-PALLIDA

The genome size of Globodera pallida was estimated by direct microdensitometry of stained somatic nuclei in comparison to those of Caenorhabditis elegans. There was no significant difference between the genome sizes of these nematodes and thus the genome of G. pallida is estimated to be composed of 1 x 10(8) base pairs. This value is of the same order as genome sizes calculated previously for a variety of other nematode species. Chromosomes in the dissected gonads of G. pallida females were visualized using five staining methods: propionic acid/orcein, Feulgen, Giemsa and two fluorescent stains, DAPI (4'6-diamidino-2-phenylindole) and Hoechst 33258 (Bisbenzimide). Propionic acid/orcein proved to be the best staining method and despite the small size of the chromosomes it was used to demonstrate that G. pallida has a diploid chromosome complement of 18 (n = 9).