Species specific identification of the Neofabraea pathogen complex associated with pome fruits using PCR and multiplex DNA amplification.

Five species of pathogenic fungi belong to Neofabraea. One of these, N. krawtzewii (syn. N. populi), is responsible for bark lesions on poplar (Populus) trees. The other four species cause post-harvest bull's eye rot of pome fruits, and at least two of these also cause bark cankers on pome fruit trees. Morphological variation among these species is slight, and overlap in geographic range sometimes occurs. As a consequence, identification based on conventional criteria can be tenuous. PCR primers with putative species specificity were developed following genetic analysis of the beta-tubulin gene for isolates of each of the five species of Neofabraea. PCR conditions required to achieve specificity of the primer sets were determined, and a multiplex PCR protocol was developed to optimize their diagnostic utility on apple fruits. A protocol with higher annealing temperatures in the initial PCR cycles followed by lower temperatures in later cycles gave complete species-specificity when the primer sets were used individually and in multiplex, resulting in successful detection of the pathogens from axenic culture and infected apple fruits.