Screening and Marker Selection for Anthracnose Susceptibility in Florida Blueberry Cultivars

Blueberries are an important commercial crop in the US, with over 550 million pounds produced in 2014. Florida has become an important supplier of blueberries for the fresh market, particularly during the period from March to May. The success of Florida growers is due in large part to the development of southern highbush blueberry (SHB) cultivars (Vaccinium corymbosum) that need significantly less chilling hours for fruit production than typical temperate cultivars. These SHB cultivars and the mild subtropical winter climate allow growers to harvest when the price point is high. However, the humid summer conditions present with the subtropical climate often result in a high degree of disease incidence and severity. For example, anthracnose, caused by the Colletotrichum fungal pathogen, is a disease typically associated with postharvest fruit rots, but can also produce stem lesions and dieback in susceptible cultivars. This disease has recently been reported on two SHB cultivars (‘Flicker’ and ‘Scintilla’) grown primarily in central Florida, and the degree of susceptibility of other cultivars is currently unknown. Identification and confirmation of parents that are not susceptible to anthracnose stem dieback would facilitate crossing decisions for SHB breeding. The objectives of this research were to screen several SHB cultivars for susceptibility to anthracnose stem dieback. Screening for anthracnose susceptibility was performed using a spray inoculation of a virulent Colletotrichum isolate collected from field infections on ‘Flicker’. The isolate solution was prepared at a 10⁵ per ml concentration, and sprayed onto both whole plants under greenhouse conditions. Incidence was determined by the presence of stem lesions on any new shoot. Severity of disease over time was assessed by measuring lesion length with a digital caliper for a period of five days from first observation of disease symptoms. ‘Flicker’ plants were utilized as a positive control for disease incidence and severity.