Occurrence of Stem-end Rot on Mango Fruits Caused by Lasiodiplodia theobromae in Korea

Abstract

Mango ( Mangifera indica L.), an economically important fruit cropin the subtropics and tropics, was recently introduced into Korea. Itis being cultivated over an area of 20 ha with an annual productionof approximately 300 tons in Jeju Island. In July 2010, stem-end rotswere found on fruits of mango (cv. Irwin) grown in a greenhouse inJeju. In the early stage, the affected fruits appeared as small brownspots. As they enlarged, the lesions became circular, dark brown toblack and water-soaked patches and progressed from the surface toinner part of the fruit (Fig. 1A). Two fungal isolates were obtained from lesions on mango fruits.Cultures were initially white to smoke grey, with fluffy aerialmycelium on potato dextrose agar and became gray or black with afew medium grays in laterstage (F ig.1B) . The pycnidia produced onthe 14-day-old cultures (Fig. 1C) were simple, often aggregated,stromatic, ostiolate and hairy. Paraphyses within the pycnidia werehyaline,cy lindrica septate, occasionallyl, branched. Conidiogenouscells were hyaline, thin-walled, smooth, cylindrical, holoblastic(Fig. 1D). Young conidia were hyaline, unicellular and subovoid toellipsoid, with a granular content (Fig. 1E). Mature conidia wereone-septate, dark brown, thick walled, ellipsoidal, with longitudinalstriations (Fig. 1F) and measured 17.5 −26.8 × 12.3 −17.1 μm (mean22.7 × 14.7 μm). No teleomorph was observed in culture. The twofungal isolates were identified as Lasiodiplodia theobromae (Pat.)Griffon & Maubl. [Synonym: Botryodipodl ia theobromae Pat].bas edon their morphological and cultural characteristics, and correspondedto previous description for the species (Alves et al., 2008).To confirm the identification, the complete internal transcribedspacer (ITS) rDNA regions and translation elongation factor 1-alpha (EF1-α) of the two fungal isolates, ML1001 and ML1005were amplified using the primers ITS1/ITS4 and EF1-688F/EF1-1251R asd escribed by Alvese at . (20l 08) and sequencedTh . ere sultingsequences were deposited in GenBank (Accession numbersJN542561 and JN542562 for ITS rDNA, JN542563 and JN542564for EF1-α). Sequences of reference isolates were retrieved fromGenBank. A phylogenetic tree derived from combined sequences ofITS rDNA and EF1-α was constructed by the neighbor-joiningmethod with Kimura’s two-parameter distance model using MEGAversion 5.0. In the phylogenetic tree, the present isolates placed inthe same clade with L. theobromae in GenBank and clearlydistinguished from the closely related Lasiodiplodia species, L.parva and L. pseudotheobromae (Fig. 2).Pathogenicity tests were made on mango fruits. The fruits wereperforated with 3 mm cork borer, followed by drop-inoculated with100 μl of conidial suspensions (5×10