Garcia-Lopez E.,Institute Fitosanidad Fitopatologia |
Mora-Aguilera J.A.,Institute Fitosanidad Fitopatologia |
Villegas-Monter A.,Institute Fitosanidad Fitopatologia |
Villegas-Monter A.,Institute Recursos Geneticos y Productividad |
And 3 more authors.
Plant Disease | Year: 2016
Malformation disease is an important disease of mango (Mangifera indica L.) worldwide. This disease was first observed in 2008 in mango orchards in the Azua and Peravia provinces of Dominican Republic. Vegetative symptoms included loss of apical dominance, and swollen apical and lateral buds; fasciculated, thickened, and misshapen stems with shortened internodes and dwarfed leaves. From July to September 2013, malformed vegetative shoots were collected in mango ‘Keitt’ orchards located in Azua de Compostela County with a disease incidence from 1 to 40%. Pieces of symptomatic tissue were surface sterilized in 1% sodium hypochlorite for 2 min, rinsed three times in sterile distilled water, dried for 10 min, and transferred to potato dextrose agar medium (PDA). The petri plates were incubated at 28°C for 5 days in a 12-h photoperiod. The most frequent fungal colonies were purified, and monosporic cultures obtained in PDA. Fungal colonies developed aerial mycelium, producing orange to red pigments in the medium after 3 days of incubation. Macroconidia were slender, slightly falcate, with a beaked apical cell and a footlike basal cell, and were 3 to 7 septate and 24.2 to 58.8 × 2.5 to 3.5 μm. Microconidia were ovoid or oval, with 0-septate conidia abundant and 1-septate conidia less common, 6.5 to 9.3 × 2.2 to 3.3 μm, and usually aggregated in false heads. Coiled sterile hyphae were observed; chlamydospores were absent. The fungus was identified as Fusarium pseudocircinatum according to descriptions by Leslie and Summerell (2006). To confirm the identification, DNA was extracted from a pure culture (Azua-1) and the translation elongation factor 1-alpha (TEF-1α) and beta-tubulin (BT) gene regions were amplified by PCR using primers EF1/EF2 and BT1/BT2 (Kvas et al. 2008). Sequences were deposited at GenBank (Accession Nos. KT253884 and KT253885). BLAST analysis of these regions showed 99% identity with sequences of F. pseudocircinatum (GU737398, AF160271, GU737390, and GU737391). To verify the pathogenicity, the isolate Azua-1 was used to inoculate 10 healthy 6-month-old mango ‘Puntica’ seedlings by infiltration of 30 μl of a conidial suspension (2 × 106 spores/ml) with a hypodermic needle into an apical bud. Ten control plants were infiltrated with 30 μl of sterile distilled water. Plants were maintained in a nursery at 27 ± 2°C. All inoculated plants developed typical vegetative malformation symptoms after 11 months, whereas no symptoms were observed on the control plants. The fungus was reisolated only from malformed plants by incubating diseased shoot pieces in PDA, fulfilling Koch’s postulates. This fungus only has been reported causing mango malformation disease in Mexico (Freeman et al. 2014). Urgent actions are necessary to protect 4,370 ha of high-quality mango production in Dominican Republic and the promising mango export trade from this disease. Special attention is needed in production areas intensively managed with practices such as pruning, water stress and grafting. © 2016 The American Phytopathological Society. Source