X. R. Chen and
Y. P. Xing, College of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China;
T. X. Zhang and
J. T. Zheng, Ningbo Technology Extension Center for Forestry and Specialty Forest Products, Ningbo 315010, China; and
J. Y. Xu,
Z. R. Wang, and
Y. H. Tong, College of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China. This study is supported by Jiangsu Province Basic Research Program (Natural Science Foundation) (BK2011443) and Major Project of Ningbo City, Zhejiang Province for Science and Technology Development (2009C10004)
Red bayberry (Myrica rubra Seib. & Zucc.) has great economic importance in eastern and southern China. However, increasing cultivation of red bayberry has resulted in an increase in diseases such as leaf necrosis. In April 2011, a survey was conducted to identify the causal agents of leaf necrosis of red bayberry (cv. Biqi) in Cixi City, Zhejiang Province. Symptoms began with oval and pale brown lesions (2 mm in diameter) that developed into a round to irregular shape (4 to 12 mm in diameter) with pale brown centers and dark brown borders. After approximately 4 months, necrotic lesions expanded to the leaf tips or margins. Black acervuli developed on lesions at later stages. Leaf tissues were surface sterilized with 0.5% sodium hypochlorite for 3 min and rinsed in sterile water before plating onto potato dextrose agar (PDA). Seven isolates were obtained from four samples from four fields on PDA at 25°C. The colonies were cottony white with filiform edges and produced a honey yellow color into the agar at 7 days. Conidia were produced in ink-like fruiting bodies at 4 days at 25°C on PDA. Conidia were straight or slightly curved, fusiform, and five celled with constrictions at the septa. Conidia ranged from 18.7 to 25.8 × 6.2 to 7.7 μm with hyaline apical and basal cells. Thirteen percent of the apical cells had two and the rest had three hyaline appendages ranging from 11.2 to 26.0 μm long. Basal appendages were hyaline, straight, and varied from 3.6 to 5.8 μm long. The color of three median cells was light to dark brown and demonstrated versicolorous. These morphological characteristics matched those of Pestalotiopsis sydowiana (Bresadola) Sutton (1). The morphological identification of the fungus was confirmed by nucleotide blast analysis of the 5.8S subunit and flanking internal transcribed spacers (ITS1 and ITS2) of rDNA regions (GenBank Accession No. JQ322999), which revealed 100% with those of other P. sydowiana isolates (e.g., GenBank Accession No. FJ478105). Koch's postulates were confirmed with 20 healthy leaves of the same size on three branches of three plants in the field. Leaves were wounded by pressing slightly with sterile needles. Mycelial plugs (5 mm in diameter) obtained from the periphery of 7-day-old cultures were placed onto the wounds and covered with sterile-water-saturated cotton. Wounded leaves treated with sterile agar plugs served as controls. The inoculated leaves were sealed in moist plastic bags for 24 h to establish high humid conditions at 21 to 30°C. After 23 days, symptoms on all inoculated leaves were identical to those described above, whereas noninoculated control leaves did not show any symptoms. The fungus was consistently reisolated from the lesions. To our knowledge, this is the first report of P. sydowiana causing leaf necrosis of M. rubra in China. Results can help to better understand the diseases threatening red bayberry trees and develop effective control strategies for better fruit production.
Reference: (1) E. F. Guba. Monograph of Monochaetia and Pestalotia. Harvard University Press, Cambridge, MA, 1961.