@ARTICLE{TreeBASE2Ref28629, author = {Chunhua Lin and Pengpeng Dong and Siqi Fang and Maofu Li and Wenbo Liu and Weiguo Miao}, title = {First Report of Avocado dieback disease Caused by Pestalotiopsis longiseta in China}, year = {2018}, keywords = {Avocado; Pestalotiopsis longiseta; China}, doi = {10.1094/PDIS-06-18-0939-PDN}, url = {http://}, pmid = {}, journal = {Plant Disease}, volume = {}, number = {}, pages = {}, abstract = {Avocado (Persea americana Mill.) is a commercially valuable fruit crop cultivated in tropical regions throughout the world and it is currently widely planted in south China. During Novermber 2017, serious dieback symptoms were found in avocado nursery plantation in Danzhou city, Hainan province. Approximately 30% of the plants showed the same symptoms on this nursery plantation (about 0.10 hectare), which were characterized by blight on green shoots at first, then formed necrotic lesions on the stem and leaves, and developed dieback of shoots and twigs. Four symptomatic twigs were sampled from different parts of the field for pathogen isolation. Lesion tissues were removed from the border between symptomatic and healthy tissue, surface sterilized in 75% ethanol solution (V/V) for 30 sec, soaked in 0.1% HgCl2 for 1 min, followed by rinsing four times in sterile distilled water, then air-dried and plated on potato dextrose agar medium plates (PDA), and incubated at 28℃ a 12-h photoperiod. Similar fungal colonies developed from all plated tissues (twelve stems) after 4 days. The fungal colonies on PDA were white and cottony, turning slightly yellow after 9 days at 28℃. Conidia were fusoid, ellipsoid, straight to slightly curved, 4-septa, 5.4-9.6 ?18.2-25.6 μm (n = 100) with a length/width ratio of 2.94 ? 0.42. Apical and basal cells were hyaline, while the three median cells were dark brown. All conidia had one basal appendage and two to four long tubular apical appendages (mostly 3). On the basis of colony and conidia morphology, they were initially identified as Pestalotiopsis genus. Genomic DNA of three isolates was extracted from mycelium from 7-day-old cultures growing on PDA and the internal transcribed spacer region ITS1-5.8 S-ITS2 gene (ITS), the partial beta-tubulin (TUB2) and translation elongation factor 1-alpha (TEF) gene regions were amplified with primer pairs ITS1/ITS4 (White et al. 1990), Bt2a/Bt2b(Glass and Donaldson 1995), EF1-526F/EF1567R (Carbone and Kohn 1999), respectively. All three gene sequences from the three isolates shared 100% identity. The three gene sequences of isolate A1809 were deposited in GenBank (Accession No.MH422008 for ITS, MH427372 for TUB, MH427373 for TEF1). A BLASTn search showed ITS and TUB2 sequences showed high identify (ITS, 100%; TUB2, 99%) with reference sequences of P.longiseta isolate MAFF 752008 (ITS, AB758106; TUB2, AB453900), Neopestalotiopsis clavispora CBS447.73 (ITS, KM199374; TUB2, KM199443), and some other species. The TEF sequence showed 99% identity with P.longiseta isolate MAFF 752008 (I AB453857), and 97% or less identity with other Pestalotiopsis species. For further confirmation, the combined ITS, TUB2 and TEF sequences of isolate A1809, P.longiseta, P.clavispora, and other Pestalotiopsis species were used for phylogenetic analysis via the Maximun Likelihood method with bootstrap 1000 replications. Evolutionary analyses were conducted in MEGA6. The resulting phylogenetic tree showed A1809 isolate and P. longiseta isolate MAFF 752008 formed a subclade with 99% bootstrap support (study ID ??? deposited in TreeBASE). For pathogenicity test, a conidial suspension (1?106 spores/mL) of A1809 isolate was prepared by harvesting conidia from 15-day-old cultures growing on PDA. The suspension was sprayed onto the tender tips of ten independent two-year-old potted young plants. Three additional trees sprayed with sterile distilled water were served as controls. All plants were covered with plastic bags for 48 h to maintain high humidity and kept at 28 ℃. At 7 days after inoculation, all ten tips of inoculated plants started to blight and formed necrotic lesions, and developed dieback symptom of green shoots similar to the original ones seen on the field trees after 15 days post inoculation. All control plants remained healthy. The fungi were re-isolated from the lesions of the three inoculated tips but not from the control twigs, and had the same morphological conidial characteristics (shape, size, septation, color and number of apcical and basal appendages) than isolate A1809. P.clavispora has been reported as the causal agent of stem end rot of avocado in Chile, and P. versicolor has been reported as postharvest diseases of avocado fruit in South Africa (Valencia et al. 2011). To our knowledge, this is the first report of P. longiseta causing avocado dieback disease in China.} }

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