Species-specific banding patterns of restriction endonuclease-digested mitochondrial DNA from the genus Pythium

Abstract

Restriction endonuclease-digested mitochondrial DNA from 29 Pythium spp. showed distinctly different species-specific electrophoretic banding patterns. Numerical comparisons among species were conducted by calculating the percentage of restriction fragments having the same apparent molecular size. The greatest interspecific similarity in banding patterns (67%) was observed between HindIII digests of Pythium heterothallicum and P. sylvaticum. However, comparisons among other species generally revealed similarities of less than 50%, and often less than 30%. The lack of similarity of restriction banding patterns was observed even with several species that share many common morphological features: P. arrhenomanes vs P. graminicola (20%), P. myriotylum vs P. aristosporum (28%), and P. torulosum vs P. vanterpoolii (32%). In contrast to the fragment size heterogeneity among different species, isolates of the same species have highly conserved restriction patterns. Ten isolates of P. oligandrum, collected from the United States, South Africa, and Czechoslovakia, had a minimum of 86% similarity in HindIII banding patterns. Similar results were observed with eight isolates of P. ultimum, five of P. acanthicum, six of P. spinosum, five of P. sylvaticum, and eight of P. irregulare. However, two isolates of P. irregulare exhibited a higher degree of heterogeneity and shared only 64 to 76% comigrating bands with the eight other isolates of this species.