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Occurrence of Phoma Blight Caused by Phoma destructiva on Tomato (Solanum lycopersicum) in Malaysia

    Affiliations
    Authors and Affiliations
    • T. S. Rashid
    • K. Sijam
    • A. Nasehi
    • J. Kadir , Department of Plant Protection
    • H. M. Saud , Department of Agriculture Technology
    • H. K. Awla , Department of Plant Protection, Faculty of agriculture, University Putra Malaysia, 43400 UPM, Serdang, Selangor Darul Ehsan, Malaysia.

      In May 2013, tomato (Solanum lycopersicum) plants cultivated in the Cameron Highlands, Pahang State, Malaysia, had extensive fruit, stem, and leaf spots. In severe cases, disease incidence reached 70% in glasshouses. Leaf lesions were initially small (1 to 2 mm), black on either surface enlarging to 1 to 2 cm in diameter, irregular to round in shape, and slightly sunken and zonate; stem lesions were longer but similar in appearance. Fruit lesions were sunken black spots of variable size at sites of wounds, insect punctures, or stem scar cracks. Samples of the disease were collected from infected fruits, stems, and leaves in different infected glasshouses. Tissue cut from the edges of lesions were surface sterilized in 1% sodium hypochlorite for 2 min, rinsed twice with distilled water, dried on sterilized tissue paper, plated on oatmeal-agar (OA) plates, and incubated at 25°C. Nine isolates were obtained and identified as Phoma destructiva Plowr. on the basis of morphological characteristics (Laundon 1971; Boerema et al. 2004). Colonies were as greenish gray to dark bluish green of the mycelial mat on OA. Conidia were produced in pycnidia with common pseudoparenchymatous wall structure, and were ellipsoidalyes or oblong, and 2.5 to 7.5 µm long and 1.5 to 2.5 µm wide. To confirm the morphological identification, DNA of the representative isolate TS24 was extracted from mycelium and the internal transcribed spacer region (ITS) and the beta-tubulin (tub2) were amplified with the universal primers ITS1/ITS4 (White et al. 1990) and Bt2a‎/ Bt2b‎ (Glass and Donaldson 1995‎), respectively. PCR products were purified using the commercial PCR purification kit (GF-1 PCR Clean-Up Kit) and sequenced both directions. A GenBank BLAST search revealed that the ITS and tub2 sequences were 99% identical to those of P. destructiva sequences deposited in GenBank (ITS Accession Nos. AF268191 and KT309796; tub2 Accession Nos. GU237602 and GU237601). The consensus sequences of the ITS and tub2 were deposited in GenBank (KR559677 and KU507405, respectively). The representative isolate TS24 was used to perform pathogenicity tests. Four fruits, stems, and leaves (cultivar 152177-A) were wound inoculated with a sterile scalpel, and pipetting a 5-µl droplet of a conidial suspension (5 × 106 conidia/ml) on each wound. Four controls were wound inoculated similarly with sterilized, distilled water. Inoculated fruits, stems, and leaves were incubated in humid chambers at 25°C with 95% RH and a 12-h photoperiod. After 5 days, symptoms of the disease similar to those observed in the infected greenhouse began to develop on the plant parts inoculated with the fungus, but not on the controls. P. destructiva was consistently reisolated from fruits, stems and leaves inoculated with the pathogen, but not from the controls. Pathogenicity test was repeated with the same results. To our knowledge, this is the first report of Phoma blight caused by P. destructiva on tomato in Malaysia.

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