First Report of Ficus carica Bot Rot Caused by Botryosphaeria dothidea in China

Ficus carica L., belonging to the Moraceae family, is one of the earliest cultivated fruit trees. Fig is an important crop for dry and fresh consumption worldwide because it contains an abundant source of minerals and vitamins. Moreover, fig fruit has been a typical component in health-promoting diets for millennia. A previously uncharacterized disease was observed on fig fruit during 2016 and 2017 in Qingdao, Shandong Province, China (N 36°08′49″, E 120°25′5″). Approximately 5 to 8% of fruit on greater than 500 trees was lost due to the disease during the 2016 and 2017 seasons. The symptoms were first observed on green fruit, and infected fruit initially showed soaked symptoms on the surface, which subsequently became covered with fluffy mycelia that ultimately caused fruit decay. Infected fruit were collected, and small pieces of discolored or necrotic tissues were rinsed with 70% alcohol for 10 s followed by 1% NaOCl for 60 s, after which they were washed with sterile distilled water (Wang et al. 2015). Pieces were subsequently plated in Petri dishes containing potato dextrose agar (PDA) and incubated for 4 days at 28°C in the dark. The obtained isolates were purified through single-spore culture. Colonies of all isolates on the PDA plates were identical, producing mycelia that were initially white and fluffy but that subsequently turned gray and then black as they matured. Mycelia were hyaline, smooth, septate, 110.5 to 260 × 3 to 4 μm; stipe extension septate, erect to flexuous, 123.5 to 179 μm long, and 2 to 3.5 μm wide at the apical septum. Hyphae were hyaline and septate, consistent with the description of Botryosphaeria dothidea. The pycnidia contained hyaline, nonseptate, fusiform conidia measuring 13.5 to 26.5 × 4.8 to 8.0 μm. Perithecia contained clavate asci, which averaged 130.5 × 17 μm. The internal transcribed spacer region, partial translation elongation factor 1-alpha, and β-tubulin genes of the rDNA of the isolate were sequenced using primers ITS4/ITS5 (GenBank accession no. MN428793), EF1-728F/EF1-986R (MN478488), and Bt2a/Bt2b (MN508257), respectively (Sun et al. 2014). Based on morphological features and phylogenetic analysis, we concluded that the isolates belonged to B. dothidea. To test the pathogenicity, F. carica fruit were collected, surface sterilized with 1% NaOCl, and rinsed with sterilized distilled water. Plugs (5 × 5 mm) of B. dothidea from the PDA plate were placed on the surface of the fruit (n = 10) and incubated at 28°C and 60% humidity in the dark. Four days after inoculation, bot rot symptoms appeared, and the surfaces of the fruit were covered with fluffy mycelia. In contrast, fruit inoculated with PDA plugs that did not contain B. dothidea remained symptom-free. B. dothidea was reisolated from diseased fruit, fulfilling Koch’s postulates. To our knowledge, this is the first report of B. dothidea causing bot rot in F. carica in China.