Loquat (Eriobotrya japonica) is a subtropical tree with sour and sweet fruit and its leaf derivatives are often used to treat cough and asthma with phlegm. In 2011, a severe stem and leaf disease, with 30∼60% incidence, was observed in a local loquat cultivar “Ninghaibai” in Ninghai, Zhejiang Province, China. Infected plants exhibited brown spots on the stem and leaves, which became blackish brown to grayish white with some little sporadic black acervuli (137.9 to 189.3 μm in diameter). Leaf symptoms showed large necrotic lesions (more than 20 mm) that frequently, but not exclusively, appeared along the leaf margin or dorsal surface. Necrotic spots were water-soaked, irregularly shaped, and bordered by a tan halo. Fungal isolates were obtained by placing sterilized symptomatic tissue onto acidified potato sucrose agar (PSA) medium and consistently yielded white fungal colonies that produced acervuli (385.6 to 485.4 μm in diameter) containing black, slimy spore masses at 25°C for 7 days. Conidia (20.9 to 29.8 × 7.1 to 14.5 μm) were 5-celled and spindle shaped, and basal cells of the conidia were hyaline, while the other three middle cells were heterochrome. The upper two middle cells were darker than the lower one. The apical cell typically had 2 to 3 apical appendages, was 12.0 to 33.1 μm in length, and the basal appendage was 3.3 to 7.8 μm long. Based on these morphological features, the fungus was identified as Pestalotiopsis sydowiana (2). This characterization was further confirmed by PCR amplification and sequencing of internal transcribed spacer (ITS) of the ribosomal DNA of fungus with primers ITS1: 5′-TCCGTAGGTGAACCTGCGG-3′ and ITS4: 5′-TCCTCCGCTTATTGATATGC-3′ (3). A representative sequence was deposited in NCBI GenBank (Accession No. JX478272). This sequence showed 99% homology with previously deposited sequences of P. sydowiana (HQ248207.1 and FJ478105.1) from Colombia and China. Pathogenicity tests were conducted by inoculating 1-year-old seedlings and detached stems from healthy field trees of cv. Ninghaibai loquat with sclertium (20 × 5 mm) or conidial suspension (106 conidia ml−1). Control seedlings were only encircled the PSA blocks or sprayed with water. Both inoculated and control plants were covered with plastic bags at about 80% relative humidity and kept in a greenhouse at 20 to 30°C for 48 h. Detached stems were incubated to prevent desiccation in a humid chamber at 100% relative humidity and 25°C for 10 days. Four days after inoculation, lesions appeared on sclertium-inoculated seedlings or detached stems, approximately 10 days earlier than those on conidial suspension-inoculated seedlings or detached stems. Symptom observed on artificially inoculated seedlings or detached stems were similar to that observed in naturally infected plants. The control plants remained healthy. P. sydowiana was reisolated from the lesions of the infected stems and leaves but not from control leaves. It had been reported that other species of Pestalotiopsis, such as P. eriobotrifolia and P. eriobotryae-japonica, can only infect leaves of loquat (1); however, to our knowledge, this is the first report that P. sydowiana cause branch blight disease on loquat in China.
References: (1) G. G. Chen et al. Acta Agric. Univ. Zhejiangensis 16:153, 1990. (2) Q. X. Ge et al. Flora Fungorum Sinicorum: Pestalotiopsis, p. 185, Science Press, Beijing, 2009. (3) T. J. White, et al. PCR Protocols: A Guide to Methods and Applications, p. 315, Academic Press, San Diego, 1990.