ANALYSIS OF COCHLIOBOLUS-CARBONUM RACES BY PCR AMPLIFICATION WITH ARBITRARY AND GENE-SPECIFIC PRIMERS

The pathogenic races of Cochliobolus carbonum cause necrotic lesions of characteristic sizes and shapes on maize leaves. To distinguish the races at the molecular level, isolates of C. carbonum races as well as other related species were analyzed by PCR (polymerase chain reaction) amplification of genomic DNA using either arbitrary oligonucleotide primers or primers with homology to sequences within the Tox2 locus, which is essential for production of a host-specific toxin. Amplification products from isolates of the four pathogenic races of C. carbonum were very similar to each other and to those from species thought to be closely related but were substantially different from nonpathogenic race 0 and from most other species. One of the arbitrary primers tested distinguished isolates of C. carbonum race 3 by the absence of two amplification products present in the other pathogenic races. The patterns of amplification products from races 2 and 4 were indistinguishable with the primers tested, suggesting that the recently described race 4 is not substantially different from race 2. Primers from the Tox2 locus distinguished race 1 isolates from isolates of other races. Only isolates of race 1 contained a single amplification product of the expected length when these primers were used under stringent annealing conditions. The results indicate that PCR amplification with arbitrary primers or gene-specific primers is useful for differentiating the races of C carbonum and for examining their origins.