Apple bitter rot fungi of New York and Virginia – which Colletotrichum species are there?
Žaklina Pavlović: Cornell University, Plant Pathology and Plant-Microbe Biology Section
<div>Bitter rot disease of pome fruits is an emerging problem in southern New York (NY) orchards and intermittently on apple fruit in storages. Factors contributing to disease outbreaks might include increasing frequency of warm wetting events during the summer, planting of susceptible and late-maturing cultivars, reduced number of cover sprays, and 77 days preharvest interval limit in use of an effective fungicide, mancozeb. Fruit losses in 2016 at some NY locations reached 20% on high income cultivars like Honeycrisp. Previous research based on gene sequencing identified at least 18 <em>Colletotrichum</em> species that infect apples or pears worldwide. Preliminary data indicated a prevalence of <em>C. fioriniae</em> from <em>C. acutatum</em> species complex in NY. We isolated nearly 600 fungal isolates from apple and pear fruits collected at 12 locations in NY and three in Virginia (VA), and 60 of them were selected for further characterization. Based on multiplex two-step PCR assays with previously reported primers, at least two species from both <em>C. acutatum</em> and <em>C. gloeosporioides</em> species complexes were present in NY and VA. Moreover, RAPD-PCR analysis indicated species variability among both species complexes. This is the first report of PCR-validated species in <em>C. gloeosporioides</em> complex in NY. Different biology and variable susceptibility of <em>Colletotrichum spp.</em> to fungicides may impact best management practices for minimizing selection for fungicide resistance in bitter rot species.</div>
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