Mummy Berry Fruit Rot and Shoot Blight Incidence In Blueberry: What Length of Evaluation Is Needed for Reliable Disease Assessment?

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 a variance decomposition, showed that a minimum of six years, and possibly eight or nine years of testing was 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 shared similar environmental responses in an effort to increase the predictability of disease response among cultivars.