First Report of Verticillium Wilt of Mango (Mangifera indica) Caused by Verticillium dahliae in Italy

Abstract

Mango (Mangifera indica L.) is an important fruit crop in many tropical and subtropical countries. This crop has been recently introduced in Italy, mainly in Sicily (southern Italy), where it proves to be a good commodity for the national market. However, the future of mango cultivation in Sicily is threatened by diverse biotic and abiotic factors, which may limit production and fruit quality. For this reason, an investigation into soilborne diseases of mango was carried out in summer 2009 and spring 2010 (1). During May 2009, typical symptoms of Verticillium wilt were observed in four young mango orchards, cv. Kensington Pride, in Catania Province. The symptoms observed included gradual leaf yellowing, marginal browning, slow growth, and dieback on one side of the shoots. The dead leaves remained attached to infected branches and no defoliation was observed. Cross sections of affected branches showed brown vascular discoloration. The incidence of infected trees was about 25% of 96 examined trees. Small pieces of brownish, vascular wood tissues were surface disinfested and placed onto potato dextrose agar (PDA). After 5 days of incubation at 25°C in the dark, the isolates were purified using the single-spore isolation method. Pathogen identification was initially based on morphological characteristics, and then confirmed by molecular methods. The colonies produced from all the tested isolates showed irregular shape, black microsclerotia, and hyaline, elliptical, single-celled conidia developed on verticillate conidiophores (2). For molecular identification, two specific primer pairs (Ver2-Ver3 and Vd7b-Vd10) of the intergenic spacer region (IGS) were used (3). A fragment of 339 bp was obtained by Ver2-Ver3 primer pair, which is a genus-specific primer, while a fragment of 139 bp was amplified by Vd7b-Vd10 primer pair specific for V. dahliae. To fulfil Koch's postulates, 10-month-old mango plants cv. Kensington Pride were inoculated by dipping the roots in Verticillium conidial suspension for 10 min. Conidial suspension was approximately 4 × 106 conidia/ml, prepared from Verticillium isolates Vd-1 and Vd-2 (10 plants for each isolate). Plants dipped in sterile water were used as controls. All plants were kept in a greenhouse at 25°C and 90 to 95% relative humidity. After 10 months, all inoculated plants showed symptoms identical to those observed in mango plants in the field; plants inoculated with water did not show symptoms. V. dahliae was consistently isolated from symptomatic plants but not from plants inoculated with water. To our knowledge, this is the first report of Verticillium wilt caused by V. dahliae on mango in Italy. Verticillium wilt is known to be a serious threat for the mango industry worldwide. The disease, still localized in Catania Province, may soon affects all Sicilian mango-growing provinces with serious economic consequences. References: (1) Y. M. Ahmed et al. J. Plant Pathol. 92:S4.71, 2010. (2) D. L. Hawksworth and P. W. Talboys. CMI Descriptions of Pathogenic Fungi and Bacteria, No. 256. CAB International, Wallingford, UK, 1970. (3) L. Schena et al. Phytopathol. Mediterr. 43:273, 2004.