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Appl Environ Microbiol. 1994 September; 60(9): 3055-3062
Copyright © 1994, American Society for Microbiology. All Rights Reserved.

Nuclear Ribosomal DNA Variation and Pathogenic Specialization in Alternaria Fungi Known To Produce Host-Specific Toxins

¹ School of Agricultural Sciences, Nagoya University, Chikusa, Nagoya 464-01, Japan

ABSTRACT

A total of 99 strains of 11 Alternaria species, including 68 strains of seven fungi known to produce host-specific toxins, were subjected to analysis of restriction fragment length polymorphism (RFLP) in nuclear ribosomal DNA (rDNA). Total DNA was digested with XbaI, and the Southern blots were probed with a nuclear rDNA clone of Alternaria kikuchiana. The hybridization gave 17 different RFLPs from the 99 strains. On the basis of these RFLPs, populations of host-specific toxin-producing fungi could not be differentiated from one another nor from nonpathogenic A. alternata. Each population of the toxin-producing fungi carried rDNA variants. Nine different types, named A1 to A6 and B1 to B3, were detected among the toxin-producing fungi and nonpathogenic A. alternata. All of the populations contained the type A4 variant, and the other rDNA types were also shared by different toxin-producing fungi and A. alternata. In contrast, Alternaria species that are morphologically distinguishable from A. alternata could be differentiated from A. alternata on the basis of the rDNA RFLPs. Polymorphisms in rDNA digested with HaeIII and MspI were also evaluated in 61 Alternaria strains. These restriction enzymes produced 31 variations among all of the samples. The seven toxin-producing fungi and nonpathogenic A. alternata could not be resolved by phylogenetic analysis based on the RFLPs, although they could be differentiated from the other Alternaria species studied. These results provide support for the hypothesis that Alternaria fungi known to produce host-specific toxins are intraspecific variants of A. alternata specialized in pathogenicity.

^* Corresponding author. Mailing address: School of Agricultural Sciences, Nagoya University, Chikusa, Nagoya 464-01, Japan. Phone: 81-52-789-4030. Fax: 81-52-789-4012.

This paper is dedicated to the late Syoyo Nishimura, who provided us the opportunity to carry out this study and to learn his eminent way of thinking about host-specific toxins.

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