TY - JOUR
T1 - Characterizations of an Emerging Disease
T2 - Apple Blotch Caused by Diplocarpon coronariae (syn. Marssonina coronaria) in the Mid-Atlantic United States
AU - Khodadadi, Fatemeh
AU - Martin, Phillip L.
AU - Donahue, Daniel J.
AU - Peter, Kari A.
AU - Acimovic, Srd An G.
N1 - Funding Information:
Funding: This material is based upon work supported by the Cornell Cooperative Extension’s Eastern New York Commercial Horticulture Program through a Challenge Fund Grant project number 10139 titled “Confirm the Presence and Distribution of a New Apple Disease in Eastern New York” to S. G. Aćimovićand D. J. Dohahue, complimented by unrestricted research program funds of S. G. Aćimović. This work was also supported by the United States Department of Agriculture–National Institute of Food and Agriculture and Federal Appropriations under Project PENO004694 (accession 1018736) and the State Horticultural Association of Pennsylvania for K. A. Peter.
Publisher Copyright:
© 2022 The American Phytopathological Society.
PY - 2022/7
Y1 - 2022/7
N2 - Apple orchards with minimal or reduced fungicide inputs in the MidAtlantic region of the United States have experienced outbreaks of severe premature defoliation with symptoms that matched those of apple blotch disease (ABD) caused by Diplocarpon coronariae. Fungal isolates obtained from symptomatic apple leaves and fruit produced uniform slow-growing, dark-gray colonies on peptone potato dextrose agar and had conidia. Internal transcribed spacer DNA sequences matched with D. coronariae and Koch's postulates were fulfilled when typical ABD symptoms occurred when reinoculated onto apple leaves and fruit. Spore dispersal in nonfungicide-treated orchards detected with quantitative PCR was low in early spring and dropped to undetectable levels in late May and early June before rising exponentially to highs in July and August, which coincided with symptom development. Only low spore numbers were detected in fungicide-treated orchards and nearby forests. In preliminary fungicide tests, fluxapyroxad, thiophanate methyl, and difenoconazole effectively inhibited mycelial growth of isolates in vitro. When apple cultivars Fuji and Honeycrisp were inoculated with D. coronariae, Honeycrisp showed delayed onset of symptoms and lower disease severity, and the transcription profile of seven host defense-related genes showed that PR-2, PR-8, LYK4, and CERK1 were highly induced in Honeycrisp at 2 and 5 days postinoculation. This is the first report of ABD in the MidAtlantic United States, which includes studies of seasonal D. coronariae spore dispersal patterns, preliminary fungicide efficacy, and host defense-related gene expression to assist development of best ABD management practices.
AB - Apple orchards with minimal or reduced fungicide inputs in the MidAtlantic region of the United States have experienced outbreaks of severe premature defoliation with symptoms that matched those of apple blotch disease (ABD) caused by Diplocarpon coronariae. Fungal isolates obtained from symptomatic apple leaves and fruit produced uniform slow-growing, dark-gray colonies on peptone potato dextrose agar and had conidia. Internal transcribed spacer DNA sequences matched with D. coronariae and Koch's postulates were fulfilled when typical ABD symptoms occurred when reinoculated onto apple leaves and fruit. Spore dispersal in nonfungicide-treated orchards detected with quantitative PCR was low in early spring and dropped to undetectable levels in late May and early June before rising exponentially to highs in July and August, which coincided with symptom development. Only low spore numbers were detected in fungicide-treated orchards and nearby forests. In preliminary fungicide tests, fluxapyroxad, thiophanate methyl, and difenoconazole effectively inhibited mycelial growth of isolates in vitro. When apple cultivars Fuji and Honeycrisp were inoculated with D. coronariae, Honeycrisp showed delayed onset of symptoms and lower disease severity, and the transcription profile of seven host defense-related genes showed that PR-2, PR-8, LYK4, and CERK1 were highly induced in Honeycrisp at 2 and 5 days postinoculation. This is the first report of ABD in the MidAtlantic United States, which includes studies of seasonal D. coronariae spore dispersal patterns, preliminary fungicide efficacy, and host defense-related gene expression to assist development of best ABD management practices.
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U2 - 10.1094/PDIS-11-21-2557-RE
DO - 10.1094/PDIS-11-21-2557-RE
M3 - Article
C2 - 35156848
AN - SCOPUS:85129906304
SN - 0191-2917
VL - 106
SP - 1803
EP - 1817
JO - Plant disease
JF - Plant disease
IS - 7
ER -