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

Abstract

Mummy berry (Monilinia vaccinii-corymbosi) is an important disease of cultivated blueberry (Vaccinium spp.). The disease has two distinct phases: a blighting phase initiated by ascospores and a fruit infection stage initiated by conidia during bloom. In this study, we investigated, in a nursery setting, blueberry cultivar resistance to both phases of the disease and, using multiple “standards” with a range of susceptibilities, examined, over 9 to 12 years, factors affecting disease incidence in controlled inoculations. The analyses of our data show that a minimum of 8 years of testing is necessary to obtain stable rankings of cultivar susceptibility for the fruit infection phase of the disease. Insufficient years of data were available to estimate this for the blight phase. Eight years are necessary largely as a result of uncertainty arising from the large environment × genotype interaction, estimated to be more than double any other source of observed variation, other than that resulting from sampling/individual plants. For individual cultivars, temperature and the amount and frequency of precipitation in January to March (when neither plant nor pathogen were presumed active and when both were in cold frames somewhat protected from environmental conditions) were predictive of later disease incidence. For most cultivars, the same weather variables at the same time period were found to be predictive for independently modeled cultivars. Additional cultivars, with only a few years' data, were grouped with the standard with which they shared similar environmental (year) responses and possibly similar disease predictive models.