Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2004
Publication Date: 2/1/2005
Citation: Roberts, R.G., Alternaria yaliinficiens sp. nov. on ya li pear fruit; from interception to identification. 2005. Plant Disease. 89(2):134-145.
Interpretive Summary: A new species of Alternaria, A. yaliinficiens R.G. Roberts, sp. nov. is described from infected fruit of Chinese Ya-Li pear intercepted at U.S. ports of entry in 2001. Strains of the new species were compared to other known Alternaria species reported to occur on Ya-Li pear fruit (A. alternata, A. gaisen) for the ability to cause disease on Ya-Li pear fruit, their microscopic appearance and for several genetic traits. Alternaria yaliinficiens was found to be unique in all of these comparisons, and was formally described as a new species. The disease was named "chocolate spot of Ya-Li pear". The presence of chocolate spot, caused by A. yaliinficiens and other exotic Alternaria species on intercepted Ya-Li pears has led to the suspension of the import program for Chinese Ya-Li pears each year since 2001.
Technical Abstract: In 2001 USDA officials at U.S. ports of entry intercepted a large number of diseased Chinese Ya-Li pears, the disease appearing to be caused by an Alternaria. These interceptions raised concern because the disease was unknown in the U.S. and the export workplan, which contained mitigative measures for A. gaisen and A. alternata, was ineffective in preventing the entry of diseased pears. To determine the identity of the etiologic agent of the disease, single sport cultures were established from intercepted fruit and were characterized by pathogenicity to wounded fruit, conidial morphology and pattern of sporulation on PCA, 1/2 PCA, hay and V8 juice agars, RAPD fragment pattern analysis and species-specific PCR. Comparison of morphological and pathological characters and RAPD fragment patterns indicated the disease likely was caused by more than one Alternaria, and that none of the isolates from intercepted Ya-Li fruit was A. alternata or A. gaisen. Species-specific PCR assays also demonstrated that no isolate from Ya-Li was A. gaisen or A. 'mali'. Based on these data and the absence of a description of at least one of the taxa involved, a new species, Alternaria yaliinficiens R.G. Roberts, sp. nov, is described, and the disease caused by this and other species of Alternaria on Chinese Ya-Li pears is referred to as "chocolate spot of Ya-Li pear" to distinguish it from black spot of Japanese pear.