Mitochondrial DNA Variation in Host-specific Toxln-produclng Pathogens in the Genus Alternaria.

Abstract

A total of 27 strains from 13 Alternaria species, including 16 strains from seven pathogenic species which produce host-specific toxins (HSTs), were subjected to restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA). Southern blots of total DNA digested with BglII, HindIII or XbaI were probed with 32P-labeled mtDNA isolated from A. kikuchiana strain 15A. On the basis of polymorphisms in mtDNA digested with these enzymes, the HST-producing species could not be differentiated from one another or from A. alternata. On the basis of the RFLP profiles, 18 variant types of mtDNA were identified in 27 strains and named M1 to M18. The HST-producing species and A. alternata contained 11 types, M1 to M11, four of which were shared by different HST-producing species and A. alternata. In contrast, strains of seven other Alternaria species that are morphologically distinguishable from A. alternata carried different mtDNA types, M12 to M18. The dendrogram based on the RFLPs placed the HST-producing species within a single group together with A. alternata. Sub-clusters distinctively corresponding to species or host range were not detected in this group. These results strengthen the idea that HST-producing Alternaria pathogens are intraspecific variants of A. alternata and should be designated as pathotypes.