Screening Southern Highbush Blueberry Genotypes for BotryosphaeriaStem Blight

Abstract

Stem blight and dieback are caused by a complex of fungi in the Botryosphaeriaceae (Bot) and are among the most damaging fungal pathogens affecting southern highbush blueberries (SHB; Vaccinium corymbosumL. hybrids) in the southeastern U.S. Currently, cultural practices do not effectively manage stem blight and dieback; therefore, resistance breeding offers the most promising method of control. A stem inoculation technique was used to screen SHB genotypes for resistance to stem blight. Two inoculum sources commonly found in southeastern production regions were tested on six cultivars to determine whether an individual isolate could be used for disease screening. There were significant differences between cultivar susceptibility and inoculum sources ( P< 0.05), but there was no significant interaction between cultivar and inoculum source (P= 0.14), indicating a single inoculum source could be used in further experiments. Un-rooted softwood cuttings collected from nine SHB cultivars and advanced selections to be used as parents in the University of Florida (UF) breeding program were tested in five successive inoculations. Genotype ( P< 0.0001) and experiment ( P< 0.0001) main effects, as well as the genotype by experiment interaction ( P= 0.0003) were significantly different, indicating a lack of repeatability for this screening method.