Symptomology and epidemiology of Exobasidium leaf and fruit spot of blueberry (Russell J. Ingram)
Over the past two decades, Georgia has become one of the largest producers of cultivated blueberries in the United States. As production expanded, several new blueberry yield/quality reducing diseases emerged. The most recent notable disease was Exobasidium leaf and fruit spot, caused by the newly described fungal pathogen Exobasidium maculosum. Although leaf spotting and quality-reducing green spots on fruit had been noted in producer fields for many years prior, it was considered more of a curiosity and not determined to be a production issue. Almost a decade ago, this attitude changed as producers in Mississippi and elsewhere in the Southeast began reporting refusal of fruit lots at the packing house as a result of fruit being heavily affected by Exobasidium. Since these initial refusal reports, the disease has become increasingly problematic and in some cases has caused producers to abandon production in certain fields. The pathogen is known to produce both basidiospores and yeast cells, but the life cycle/disease cycle, including the overwintering biology and primary and secondary inocula, was largely unknown. To address these deficits, field studies were initiated in 2014, including epiphytic population enumeration, trap plants, a leaf spot symptom demography study and spore trapping, in order to better understand the epidemiology and biology of the pathogen. Results from monitoring dormant blueberry surface populations in 2014 and 2015 showed that E. maculosum is capable of overwintering epiphytically, as observed on all blueberry tissues tested. The demography and trap plant data collected in 2015 suggested that dispersal of primary inoculum occurs shortly after leaf/flower emergence, in late March through to late April, and that infection of primarily young and tender tissue is favored by prolonged rainy periods (>3 days week-1). Disease (leaf spot symptom) progress in 2015 indicated that the disease is active in the field from March through to late May, and that initial fruit and leaf infections occur simultaneously. Additional observations revealed a novel symptom of lesions on emerging shoots causing girdling and blighting. Although initial results suggest that the disease is monocyclic, further confirmatory studies will be conducted in the coming years and the results will guide future management practices.
Russell J. Ingram won an ISHS student award for the best poster at the XI International Vaccinium Symposium in USA in April 2016.
Russell J. Ingram, University of Georgia, 2105 Miller Plant Sciences Bldg, 30601 Athens, GA, USA, e-mail: firstname.lastname@example.org