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Abstract
Georgia is one of the largest producers of blueberries in the United States, but the hot, humid climate provides ideal conditions for disease development. Among other disease issues
faced by growers, postharvest diseases caused by different group of fungi are of great concern.
The main aim of this research was to isolate, identify and characterize the pathogens associated
with postharvest diseases in blueberries. Characterization involved in vitro fungicide sensitivity
assessment of the Alternaria spp. and Botrytis cinerea populations and comparative virulence
assessment of the emerging pathogen Neopestalotiopsis spp. on blueberries and strawberries. A
mycelial growth inhibition assay was utilized to calculate EC50 values for Alternaria spp. and B.
cinerea against fungicides commonly utilized in the blueberry production system in Georgia.
Among the 46 Alternaria spp. isolates tested, all were sensitive to metconazole, fluazinam,
fludioxonil, and cyprodinil; however, 21 and 10 isolates, respectively, were identified with
resistance to boscalid and pyraclostrobin. In addition, 12 isolates with reduced sensitivity to
pydiflumetofen were detected. For B. cinerea, all 60 tested isolates were found to be sensitive to
fludioxonil, boscalid, and pyraclostrobin based on the determined EC50 values; however, 49 and
58 of the isolates, for boscalid and pyraclostrobin, respectively, exhibited minimum inhibitory
concentrations exceeding 100 ppm. Although, no highly resistant isolates were identified for
fenhexamid and cyprodinil, 12 isolates with moderate resistance to fenhexamid were identified,
and one weakly resistant, six low-resistant, and 3 moderately resistant isolates were identified for
cyprodinil. Moreover, a significant amount of Neopestalotiopsis spp. isolates were also
recovered from rotting blueberries, among which were a small number of isolates were found to
be phylogenetically identical to the emerging novel Neopestalotiopsis sp. causing disease
epidemics in strawberries in the Eastern U.S. Virulence assessments showed that these novel
Neopestalotiopsis sp. isolates from blueberry are as virulent as Neopestalotiopsis rosae isolates
in blueberries, relatively more virulent than N. rosae in strawberries, but not as virulent on
strawberry as a novel Neopestalotiopsis sp. isolate from strawberries. Taken together, all of
these findings provide valuable information regarding fungal fruit rots of blueberry in Georgia
and should aid in the management of these important pathogens.