Mummy Berry Fruit Rot and Shoot Blight Incidence in Blueberry: Prediction, Ranking, and Stability in a Long-term Study

Authors: Ehlenfeldt, Mark; Polashock, James; STRETCH, ALLAN - USDA ARS (RETIRED); Kramer, Matthew

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2009
Publication Date: 5/30/2010
Citation: Ehlenfeldt, M.K., Polashock, J.J., Stretch, A.W., Kramer, M.H. 2010. Mummy Berry Fruit Rot and Shoot Blight Incidence in Blueberry: Prediction, Ranking, and Stability in a Long-term Study. HortScience. 45:92-97.

Interpretive Summary: Problem Mummy berry is an important disease of cultivated blueberry and the USDA has done considerable work screening germplasm to identify sources of resistance. An important factor in such screening work is knowing what environmental factors affect the results and how many years of evaluation are needed to produce reliable estimates of disease incidence. In this study we investigated highbush blueberry cultivar resistance to both phases of this disease and, utilizing ‘standards’ of known susceptibility over many years, and we examined the factors affecting disease incidence in controlled inoculations. Our results show that, due to a significant environment effects, a minimum of six years of testing should be considered to obtain reliable rankings of cultivar susceptibility to either mummy berry shoot blight or mummy berry fruit infection. We identified temperature and the amount and frequency of precipitation in January-March to be partially predictive of disease incidence. We were able to group cultivars that shared similar environmental responses and believe that this will allow growers, extension agents, and researchers to more effectively predict cultivar responses to this disease.

Technical Abstract: Mummy berry is an important disease of cultivated blueberry. The disease has two distinct phases; a blighting phase initiated by ascospores and a fruit infection stage initiated by conidia. In this study we investigated blueberry cultivar resistance to both phases of the disease and, utilizing ‘standards’ of known susceptibility over many years, and examined factors affecting disease incidence in controlled inoculations. The analysis of our data, including variance decomposition, shows that a minimum of six years of testing is necessary to obtain reliable rankings of cultivar susceptibility for either phase of the disease. This is largely due to uncertainty arising from the large environment x genotype interaction. For individual cultivars, temperature and the amount and frequency of precipitation in January-March were predictive of later disease incidence, though specific predictive factors and their coefficients differed among cultivars. We grouped cultivars that appeared to share similar environmental responses in an effort to increase predictability of response to this disease.