Abstract: A new branch disease on Rhododendron was observed in a planting base in Jinning District，Kunming，Yunnan. The disease incidence was more than 20%. Disease symptoms included twig dieback and stem canker. Pathogens were isolated from the disease samples. The pathogenicity test，morphological and molecular identification were studied and cultivar resistance of Rhododendron were evaluated. The results showed that the mycelium was white initially and turned gray-black later. Conidia were one-celled，ellipsoidal to fusiform，with the length of 17.2 to 32.8 μm and the width of 4.7 to 7.8 μm. The internal transcribed spacer（ITS）region was amplified using the ITS1/ITS4 primer pair. BLAST analysis of the sequence showed 99% homology with the sequence of Neofusicoccum parvum. Based on the morphology and ITS sequence analysis，the pathogen was identified as N. parvum. The optimum temperature for mycelium growth was 25 ℃. The mycelial growth rate increased rapidly at pH 5–7，and the optimum pH value was 7. The utilization rates of sucrose and ammonium sulfate were the highest among all carbon and nitrogen sources，respectively. Different cultivars exhibited different disease resistances，including two immune cultivars，two highly resistant cultivars，three resistant cultivars，three moderately susceptible cultivars，four susceptible cultivars and four highly susceptible cultivars.

Key words: Rhododendron, dieback, Neofusicoccum parvum, biological characteristic, disease index