Resistance to Fusarium oxysporum f. sp. cubense tropical race 4 in African bananas

Bananas (Musa spp.) constitute one of the most important staple food crops in Africa. Two major groups of bananas exist in Africa: the East African highland banana (EAHB, AAA) in East and Central Africa, and the plantains (AAB) in West Africa. Neither of these groups has been affected by Fusarium oxysporum f. sp. cubense (Foc) race 1, which is the primary fungal pathogen in the continent for banana. The susceptibility of EAHB and plantains to Foc tropical race 4 (TR4) is unknown, and was the focus of this study. A collection of 14 genetically diverse EAHB and plantain cultivars were evaluated in China and The Philippines to determine field resistance to Foc TR4. A field heavily infested with TR4 was used in Guangzhou, China, and another one in Davao City in The Philippines. Disease incidence was determined according to leaf yellowing, pseudostem splitting and confirmed rhizome discoloration. The fungus was also re-isolated from diseased materials and identified by polymerase chain reaction (PCR) using Foc TR4-specific primers. All EAHB and plantain cultivars, except EAHB Ibwi, proved to be resistant to the tropical strain of Foc race 4, with disease incidence ranging from 0-5% only. In The Philippines, Ibwi developed Fusarium wilt at an incidence of 32% compared to 46% for Williams and 79% for Grand Naines (both AAA genome, Cavendish subgroup). Similar results were observed in China where most cultivars were severely affected by the corm weevil. Our preliminary results indicate that African bananas are less vulnerable to Foc TR4 compared with some susceptible cultivars in Asia. A more extensive screening of African bananas is required considering the diversity of EAHB and plantains grown in that region.status: publishe