A polymerase chain reaction-based method to specifically detect Alternariaalternata apple pathotype (A. mali), the causal agent of Alternaria blotchof apple

Alternaria alternata apple pathotype (previously A. mali) causes Alternaria blotch on susceptible apple cultivars through the production of a host-spe cific toxin, AM-toxin. Identification of some Alternaria species, especiall y those that produce host-specific toxins, has been extremely difficult due to a high lever of variability which extends even to nonpathogenic isolate s. We have recently cloned and characterized a gene (AMT) that plays a cruc ial role in AM-toxin biosynthesis and demonstrated that it is only present in isolates of A. alternata apple pathotype. Using primers designed for the AMT gene, we developed a polymerase chain-reaction-based method to specifi cally detect AM-toxin producing isolates of A. alternata apple pathotype.