First report of branch dieback of walnut caused by Neofusicoccum parvum in Korea.
In May 2012, lethal dieback disease of walnut tree was detected in two orchards in Andong, Kyoungbuk region, Korea, each with an incidence of 25-30%. Disease symptoms included blight and dieback of the stems, flowing resin, dark decay inside the bark of dead twigs, and defoliation. The bark of dead twigs was removed for observation of fungal structures. Pycnidia were embedded within the bark of dead twigs, and conidia were mostly fusoid, hyaline, smooth, thin-walled and unicellular. These characteristics are consistent with those reported previously for N. parvum [Botryosphaeria parva]. To confirm the identity of the isolates, the complete internal transcribed spacer (ITS) rDNA of the fungus was amplified and sequenced using PCR. The sequences were compared with other DNA sequences in the GenBank database using a BLAST search. BLAST analysis of the PCR product showed that the sequence had 99% identity with the nucleotide sequences for N. parvum (JQ411396.1 and GU997688.1). This is thought to be the first report of N. parvum as a pathogen of walnut in Korea.