Comparison of in vitro and in planta sporogenesis in Neofusicoccum species from blueberry

Stem diseases are an economically important problem in the production of blueberry (Vaccinium spp.). The diseases cause significant crop loss, including the death of entire bushes. Resistance phenotyping assays require large numbers of conidia. A fast and reliable in vitro method to mass produce viable and pathogenic Neofusicoccum spores would be more suitable than the current in planta methods. Two strains each of N. parvum and N. ribis were used to develop a new in vitro method, which involved interrupting mycelial mats produced on agar plates, with wet and dry cycles. Spores were generated at room temperature after 7—12 days’ incubation. Spore production varied among replicate tests and the four isolates used. Neofusicoccum ribis isolate Nr175 (LUPP1348) generated the most spores in the shortest time. Pathogenicity assays using spores generated in vitro suggest that these spores are more virulent and pathogenic than those produced in planta.