In 2001, numerous Ya Li pear fruit from China with a disease apparently caused by an Alternaria sp. were intercepted at U.S. ports, raising concern because the disease was unknown in the United States. To identify the etiologic agent of the disease, single-spore cultures were established from intercepted fruit and were characterized by pathogenicity to wounded fruit, morphology, and sporulation pattern on three agar media, random amplified polymorphic DNA fragment pattern analysis, and species-specific polymerase chain reaction (PCR). These data indicated that the disease likely was caused by more than one species of Alternaria, and that none of the isolates from intercepted Ya Li fruit was A. alternata or A. gaisen. A species-specific PCR assay for A. gaisen demonstrated that no isolate from Ya Li was A. gaisen. A PCR assay for the AMT gene demonstrated that no isolate from Ya Li was A. 'mali'. Because of these data and the absence of a description to accommodate at least one of the taxa involved, A. yaliinficiens R. G. Roberts sp. nov. is described, and the disease caused by this and other species of Alternaria on Ya Li pear from China is referred to as "chocolate spot of Ya Li pear" to distinguish it from black spot of Japanese pear.
Keywords: citrus; host-specific; pathotype; toxin.