Comparative study of morphological, cultural and molecular markers for the characterization of Pseudocercosporella herpotrichoides isolates

Nirenberg's classification system and the polymerase chain reaction (PCR) combined with restriction enzyme digestion of an amplified ribosomal DNA fragment, were compared for the characterization of sixty isolates of Pseudocercosporella herpotrichoides, from various geographical areas and with differing fungicide sensitivity. With Nirenberg's system, it was possible to identify most isolates as P. herpotrichoides var. herpotrichoides or P. herpotrichoides var. acuformis. However, identification was slow and sometimes inconclusive as overlap occurred between the two varieties for all criteria examined. Molecular markers identified two distinct types among the isolates tested and generally good correlation was found between the PCR-based assay and Nirenberg's system, but the molecular assay was more accurate and faster.