Plant pathologists at Cornell University in New York State have identified a new fungal pathogen that causes bitter rot disease in apples. For the first time, they also found a second related fungus, which is known to cause rot disease in other fruits, for the first time in apples.
If suitable crop protection is not used, apple losses from bitter rot in New York state can average up to 25 per cent per year, with reports of some organic farms losing up to 100% of their crop. Bitter rot also accounts for up to 5 per cent additional loss of marketable fruit in storage post-harvest.
Both of the identified pathogens belong to the genus Colletotrichum, which contains 189 species of fungi that cause devastating rot diseases in a wide variety of fruit crops, including banana, strawberry, citrus, avocado, papaya, mango and apple.
The dominant species found in the apples was C. fioriniae, followed by C. chrysophilum, which is found in other fruits but not apples until now, and the newly discovered C. noveboracense, named after New York state in Latin.
In the study, the researchers isolated Colletotrichum fungi in 400 separate cultures from samples collected in commercial and private apple orchards from eight New York counties with varieties including Idared, Gala, Fuji, Red Delicious, Golden Delicious, Empire and Granny Smith.
“We were shocked by what we found, just dumbfounded,” said paper co-author Srdjan Acimovic. “We found these two species, one that has never been described before and one that has been described before but never on this host.”
Photo Caption: Apple with bitter rot disease, caused by a Colletotrichum fungus.
Photo source: Cornell University / Srdjan Acimovic