First Report of Fusarium oxysporum f. sp. cubense Tropical Race 4 Causing Panama Disease in Cavendish Bananas in Pakistan and Lebanon

Abstract

Panama disease of banana, caused byFusarium oxysporumf. sp.cubense(Foc), poses a great risk to global banana production. Tropical race 4 (TR4) of Foc, which affects Cavendish bananas as well as many other banana cultivars (Ploetz 2006), was confirmed for the first time outside Southeast Asia in Jordan in 2013 (Garcia-Bastidas et al. 2014). In Pakistan, bananas are produced in the Sindh and Balochistan provinces (91% [31,000 ha] and 9% of the country’s production, respectively). Symptoms ofFusariumwilt, including wilting of leaves and vascular discoloration in rhizomes and pseudostems, were first observed in 2012 in a 2-ha Cavendish plantation in Baoo Pooran (ca. 24°N, 68°E), Sindh Province. By January 2014, approximately 121 ha were affected. In Lebanon, bananas are produced for local consumption and regional export, especially to Syria. Yellowing of leaves and internal vascular discoloration in the pseudostems was first observed in Cavendish plants in October 2013 in the Mansouri and Berghliyeh regions. Thus far, 1 ha has been affected. Infected pseudostem tissue samples from Pakistan and Lebanon were processed for Foc isolation and characterization as described byGarcia-Bastidas et al. (2014). White colonies developed from the surface sterilized (70% ethanol) tissue on Komada’s medium (Leslie and Summerell 2006) and nine single microconidia isolates were generated, four from the Pakistan sample and five from the Lebanon samples and transferred to quarter-strength PDA. All isolates phenotypically resembledF. oxysporum(Leslie and Summerell 2006) and were diagnosed as vegetative compatibility group (VCG) 01213, which was confirmed by PCR, thereby corroborating that VCG01213 only represents TR4 strains (Ploetz 2006). Subsequently, one of the isolates from Pakistan (Pak1.1A) and one isolate each from Mansouri (Leb1.1A) and Berghliyeh (Leb1.2C) in Lebanon were analyzed for pathogenicity. Inoculum production and inoculation were according toDita et al. (2010)by dipping (30 min, 106spores/ml) root-wounded 10-week-old Cavendish cv. Grand Naine plants, which were then placed in sand in 3-liter pots under 28°C, 70% relative humidity, and a 16-h diurnal light periods for 6 weeks. Sets of three plants were each treated with either Pak1.1A, Leb1.1A, Leb1.2C, or TR4 (reference isolate II-5, which was diagnosed as TR4 by PCR and pathogenicity analyses, seeDita et al. 2010). Control sets were each treated with either Foc Race1 (Cruz das Almas, Brazil, seeDita et al. 2010) or water. After 4 weeks, all plants inoculated with the isolates from Pakistan, Lebanon, and TR4 (II-5) produced typical symptoms of Fusarium wilt. After 6 weeks, internal symptoms were recorded and tissue was collected from all plants and plated on Komada’s medium. TR4 was confirmed by PCR from isolates that were recovered from all symptomatic plants. No isolates were recovered from plants infected with Race 1 or the water controls, all of which remained asymptomatic. Thus, we confirm the presence of TR4 in Pakistan and Lebanon and its continued expansion and distribution in Western Asia. Although comparatively limited production areas have been affected to date, increasing damage will undoubtedly occur in these countries in the near future.