F. Y. Chen,
L. M. Lu,
H. Z. Ni, and
Y. Wang, Citrus Research Institute of Zhejiang Province, Huangyan, 318020, China;
Y. G. Wang, Specialty Station of WenZhou Agricultural Bureau, Wenzhou, 325000, China; and
G. Q. Li, State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070, China
Chinese bayberry (Myrica rubra Siebold & Zucc.), an evergreen fruit tree, is widely grown in southern China. In 1999, severe twig dieback was observed on M. rubra in Taizhou and it spread to several major M. Rubra-producing areas of Zhejiang covering more than 6,000 ha by 2011. Symptoms were usually observed from June to November and first appeared as chlorosis of leaves and leaf drop, followed by the formation of dark brown lesions covered with white mycelia surrounding leaf scars. The lesions can extend to the whole twig and tree causing discoloration of the xylem. In most cases, infected trees die within 1 to 4 years. Two distinct fungi totaling 46 isolates were isolated from the surface-disinfested diseased twigs and cultured on potato dextrose agar (PDA) at 28°C. An isolate of each fungus, designated as C1 and B1, was characterized further following 10 days of growth on PDA at 28°C. C1 formed zonate, white colonies and black, acervular conidiomata with the conidia aggregated on acervuli as a creamy mass. Isolate B1 formed nonzonate, white colonies and black, acervular conidiomata with the conidia aggregated on acervuli as droplets. Conidia for each isolate were fusiform with five cells; one hyaline apical cell, one hyaline basal cell, and three, dark brown median cells. Conidia ranged from 17.8 to 25.2 × 6.7 to 9.2 μm for C1 and 21.2 to 27.8 × 4.3 to 7.5 μm for B1. There were two to three hyaline, filamentous appendages (9.8 to 23.5 μm long for C1 and 10.5 to 25.5 μm long for B1) attached to each apical cell, and one hyaline appendage (3.5 to 7.2 μm long for C1 and 3.0 to 6.8 μm long for B1) attached to each basal cell. The cultural and morphological characteristics of C1 (16 isolates) matched the description for Pestalotiopsis mangiferae while B1 (27 isolates) matched the description for P. vismiae (2). The PCR-amplified and sequenced internal transcribed spacer (ITS) region of the ribosomal DNA (ITS1-5.8S-ITS2) for isolate C1 (GenBank Accession No. JQ281542) and B1 (GenBank Accession No. JQ281543) were 99 and 100% homologous to that of the P. mangiferae isolate MM 102 (GenBank Accession No. GU722595) and P. vismiae isolate xsd08116 (GenBank Accession No. FJ481027), respectively. For pathogenicity tests, nine healthy detached leaves and 12 potted plants of M. rubra were wound inoculated with sterile water (control) or conidial suspensions (105 conidia per ml; 20 μl on each site) of C1 and B1, respectively, and maintained with relative humidity of more than 90% under fluorescent light at 28°C. Tests were performed twice. Necrotic lesions, resembling those that occurred in the field, were observed on all inoculated detached leaves and 33.3% of C1 and 25% of B1 inoculated potted plants 10 and 30 days following inoculation, respectively, while the controls remained healthy. Two fungi were reisolated from the lesions with identical morphology to the initial C1 and B1 inoculums. Therefore, P. mangiferae and P. vismiae were determined to be the causal agent for twig dieback of M. rubra in China. Pestalotiopsis spp. were previously reported as pathogens of loquat (4), mango (3), and blueberry (1) causing economic loss. To our knowledge, this is the first report of twig dieback disease of M. rubra caused by P. mangiferae and P. vismiae.
References: (1) J. G. Espinoza et al. Plant Dis. 92:1407, 2008. (2) Q. X. Ge et al. Flora Fungorum Sinicorum. Vol. 38, Pestalotiopsis. Science Press, Beijing, 2009. (3). Y. Ko et al. Plant Dis. 91:1684, 2007. (4). A. E. Perelló and S. Larran. Plant Dis. 83:695, 1999.