Cross-infection of subtropical and temperate fruits by Colletotrichum species from various hosts

Forty-two isolates of Colletotrichum gloeosporioides for almond, apple, avocado, mango, pecan, and eight isolates of C. acutatum from 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 and HaeIII digestion pattens of genomic DNA (A + T-rich DNA) grouped the C. acutatum isolates separately form the C. gloeosporioides isolates. Based on arbitrarily primed PCR (ap-PCR), intraspecies similarity among the isolates of C. acutatum and C. gloeosporioides ranged from 78 to 93% and from 0 to 38%, respectively. Similarity between the isolates of C. acutatum and C. gloeosporioides ranged from 0 to 26.5%. A + T-rich DNA grouped the C. acutatum isolates separately from those of C. 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. The C. gloeosporioides isolates from almond grew more slowly, causing significantly smaller lesions on all inoculated fruit than the other isolates. The C. acutatum isolates from apple and peach and caused similar levels of infection on all fruit, but differed significantly from the C. gloeosporioides isolate from apple. Variation in lesion size was also observed with isolates of C. gloeosporioides from apple, avocado and mango for most fruit inoculations. (C) 1996 Academic Press Limited.