Botryosphaeriaceae species are important causal agents of blueberry stem blight worldwide. Blueberry stem blight has become an important disease, potentially affecting the quality and production of blueberries in China. It is difficult and time-consuming to identify at the species level using morphological methods. The aim of this study was to develop polymerase chain reaction (PCR) assays for the diagnosis and early detection of latent infections of blueberry stems by Botryosphaeria spp. Species-specific primers, based on the ribosomal DNA internal transcribed spacer region and β-tubulin gene, were designed and selected for use in PCR assays. Three primer pairs, Lt347-F/R for Lasiodiplodia theobromae, Np304-F/R for Neofusicoccum parvum and FaF/Bt2b for Botryosphaeria dothidea, successfully amplified specific PCR fragments of different sizes on pure cultures or from blueberry stems inoculated and naturally infected blueberry plants with three pathogens, respectively. These primers did not amplify any PCR fragments from other blueberry stem disease-associated pathogens, such as Phomopsis spp. and Pestalotiopsis spp. This PCR protocol could detect as low as 100 pg to 1 ng of purified fungal DNA. This PCR-based protocol could be used for the diagnosis and detection of these pathogens from pure cultures or from infected blueberry plants.

Chrysophanol (1,8-dihydroxy-3-methylanthraquinone) is a free anthraquinone compound and a secondary metabolite of medicinal plant rhubarb. Chrysophanol has been reported to have both protective and curative activity against Sphaerotheca fuliginea (Schlechtend.:Fr.) Pollacci, the causal agent of cucumber powdery mildew. In this paper the ultrastructure of powdery mildew on cucumber leaves was studied using electron microscopy after the leaves were treated with chrysophanol. Results showed that preventive treatments with chrysophanol affected fungal development, including spore germination, appressorial formation, and penetration. In the curative treatment, chrysophanol affected fungal survival, resulting in broken cell wall of germ tubes, swelling and collapse of hyphal tips, hyphal malformation, delayed and reduced sporulation. The morphological changes induced by chrysophanol at the ultrastructural level were reflected by haustorium deformation, vacuolization, abortion, and necrosis. Host cell walls infected or adjacent to haustoria were thickened. All these morphological changes of S. fuliginea further confirmed the fungicidal activity of chrysophanol on powdery mildew of cucumber.