Phylogenetic, Morphological, and Pathogenic Characterization of <i>Cladosporium</i> Species Associated with Fruit Rot of Blueberries and Table Grapes in the Central Valley of California

Cladosporium rot is an emerging postharvest disease of blueberries and table grapes in the Central Valley of California. To determine the causal agent(s), 308 isolates of Cladosporium spp. were collected from decayed blueberries and table grapes exhibiting Cladosporium rot symptoms. Phylogenetic analyses of the internal transcribed spacer, actin gene, and translation elongation factor 1-alpha gene, combined with morphological characterization, identified 12 Cladosporium species: C. anthropophilum, C. asperulatum, C. cladosporioides, C. delicatulum, C. floccosum, C. limoniforme, C. macrocarpum, C. ramotenellum, C. subtilissimum, C. tenellum, C. tenuissimum, and C. xylophilum. Ten species were identified with the three most prevalent species being C. asperulatum, C. cladosporioides and C. macrocarpum, accounting for 23.2, 18.9, and 34.1% of the isolates from blueberries, respectively. Seven species were identified with the three prevalent species being C. cladosporioides, C. limoniforme, and C. ramotenellum, accounting for 55.6, 22.9, and 18.1% of the isolates from table grapes, respectively. The optimal temperature for mycelial growth was 20°C for all isolates, except for C. tenuissimum that grew faster at 25°C. Although the species composition differed between the two fruit crops, pathogenicity tests on the fruit inoculated with representative isolates of each species showed that all 12 Cladosporium species were able to cause Cladosporium rot on both fruits. Delineation of species compositions responsible for Cladosporium rot will help develop control methods targeting specific pathogens.