Responses of Blueberry Genotypes to Infection by Botryosphaeria dothidea. T. C. Creswell, Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. R. D. Milholland, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 71:710-713. Accepted for publication 10 March 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0710.

Host tissue maturity, wound age, inoculum concentration and type, and pathogenic variability were evaluated for their effects on development of blueberry stem blight. Inoculation of succulent, partially hardened stems produced lesions that developed more rapidly and reflected differences in cultivar susceptibility more accurately than inoculation of woody stems. Fewer infections occurred with increasing age of wounds, but some wounds remained susceptible even after 4 wk. Mycelial inoculations produced disease responses similar to those produced by conidial inoculations on three blueberry cultivars. A highly significant isolate × cultivar interaction occurred in an 11-isolate × 12-cultivar matrix, indicating the presence of pathogenic variability, i.e., isolate specificity for cultivars. A weaker isolate × cultivar interaction in an 11-isolate × 6-cultivar matrix indicated, however, that the degree of adaptation of pathogen genotypes to specific blueberry cultivars is not great. Isolates of B. dothidea were placed in two virulence groups according to their disease reactions on three cultivars. Evaluation of blueberry breeding material for resistance to B. dothidea should include inoculations with representative isolates from each of the two virulence groups. Accurate assessment of cultivar susceptibility should include inoculation of succulent, partially hardened stems within 24 hr of wounding and the use of either mycelial or conidial inoculum applied at a rate of 5 × 10³ conidia per wound or higher.