Cross-infection of subtropical and temperate fruits byColletotrichumspecies from various hosts

Forty-two isolates ofColletotrichum gloeosporioidesfrom almond, apple, avocado, mango, pecan, and eight isolates ofC. acutatumfrom apple, peach and pecan were compared by molecular analyses and a pathogenicity assay in order to determine genetic variability and host specificity. Polymerase chain reaction (PCR) amplification of genomic DNA using four different primers andHaeIII digestion patterns of genomic DNA (A+T-rich DNA) grouped theC. acutatumisolates separately from theC. gloeosporioidesisolates. Based on arbitrarily primed PCR (ap-PCR), intraspecies similarity among the isolates ofC. acutatumandC. gloeosporioidesranged from 78 to 93% and from 0 to 38%, respectively. Similarity between the isolates ofC. acutatumandC. gloeosporioidesranged from 0 to 26.5%. A+T-rich DNA grouped theC. acutatumisolates separately from those ofC. gloeosporioides, corresponding to ap-PCR analyses. Artificial inoculations with nine representative isolates on almond, apple, avocado, mango and nectarine fruit showed a variation in levels of infection. TheC. gloeosporioidesisolates from almond grew more slowly, causing significantly smaller lesions on all inoculated fruit than the other isolates. TheC. acutatumisolates from apple and peach caused similar levels of infection on all fruit, but differed significantly from theC. gloeosporioidesisolate from apple. Variation in lesion size was also observed with isolates ofC. gloeosporioidesfrom apple, avocado and mango for most fruit inoculations.