First Report of Brown Culm Streak of Phyllostachys praecox Caused by Arthrinium arundinis in Nanjing, China.

Early spring shoot bamboo (Phyllostachys praecox) is profitable for the production of bamboo shoots and is widely cultivated in Jiangsu and Zhejiang provinces in China. In recent years, a new disease named brown culm streak has commonly occurred in bamboo plantations. During initial stages, small yellow or sandy beige spots (1 to 2 mm diameter) develop on the culm. Spots expand and develop into fine brown streaks (10 to 15 × 1 to 2 mm), and the quantity of spots increases greatly at the mid-stage of the disease. The streaks continue to expand (10 to 30 × 2 to 3 mm) and may coalesce into brown patches that cover 70% of the culm surface in late stages of disease. Color of the internal bamboo cavity gradually changes from white to brown without an alcoholic odor, and plants eventually die. Diseased tissues (1 × 1.5 cm) were taken from the edges of brown streaks, surface disinfected in 0.1% HgCl₂ for 3 min, rinsed in distilled water three times, and incubated on potato dextrose agar (PDA) at 25°C. Based on colony and conidial morphology, six different fungi (ZBY01, ZBY02, ZBY03, ZBY04, ZBY05, and ZBY06) were isolated. A suspension of hyphal fragments (10⁶ pieces/ml) of each of the fungi was used to inoculate plants in the field. Healthy bamboo culms were stabbed with alcohol-sterilized needles after surface disinfection and wounds of each bamboo were inoculated with 3 ml hypha fragment suspensions by paintbrush, then covered with a piece of sterile plastic film. A control treatment was inoculated with sterile water. Each treatment had two replicates. Twenty days after inoculation, only fungus ZBY01 caused similar symptoms with the diseased bamboo in the field and was re-isolated from necrotic tissue of inoculated plants, thus fulfilling Koch's postulates. Mycelium of fungus ZBY01 covered entire PDA plates (90 mm diameter) after incubating for 6 days at 25°C and was white, flat, and floccose with moderate aerial mycelium. Mycelium consisted of smooth, hyaline, branched, septate hyphae, 2 to 3 μm diameter. Conidiophores were erect, septate, pale brown, smooth, and reduced to conidiogenous cells. Conidiogenous cells were pale brown, smooth, ampulliform, 6 to 9 μm long; the apical neck was 1 to 3 μm long, basal part 5 to 6 μm long. Conidia were 1-celled, dark brown to black, smooth, lenticular, 5 to 7 μm in diameter, 2 to 4 μm wide, lemon-shaped in side view, and spherical from top view with an equatorial ring. Based on morphological characteristics, it was identified as Arthrinium arundinis (Corda) Dyko & B. Sutton (1). The internal transcribed spacer (ITS) region from the isolate ZBY01 was amplified with PCR using ITS1-ITS4 primer pairs and the amplicon sequenced. Size of the sequenced region was 540 bp and had 99% identity with A. arundinis, which was in accord with morphological identification. The sequence was deposited in Gen Bank under accession number KF850624. To our knowledge, brown culm streak of P. praecox is a new disease of bamboo that has not been reported in other countries; however, A. arundinis has been reported as a pathogen on barley in Fairfield, Montana. Reference: (1) P. W. Crous and J. Z. Groenewald. A phylogenetic re-evaluation of Arthrinium. IMA Fungus. 4:133, 2013.