Genetic diversity of the pathogenic banana Fusarium wilt in northern Viet Nam

AbstractFusarium is one of the most important fungal genera of plant pathogens that affect the cultivation of a wide range of crops. Agricultural losses caused by Fusarium oxysporum f. sp. cubense (Foc) have a direct effect on the income, subsistence and nourishment of thousands of smallholder farmers worldwide. In addition, also commercial growers are strongly affected. For Viet Nam, predictions on the impact of Foc for the future are dramatic with an estimated loss in banana production area of 8% within the next 5 years and up to 71% within the next 25 years. In the current study we applied a combined morphological - molecular approach to assess the taxonomic identity and phylogenetic position of the different Foc isolates that were collected in northern Viet Nam. In addition, we aim to estimate the proportion of the different Fusarium races that are infecting bananas in northern Viet Nam. The morphology of the isolates was investigated by growing the collected Fusarium isolates on four distinct nutritious media (PDA, SNA, CLA, and OMA). Molecular phylogenetic relationships were inferred by sequencing partial rpb1, rpb2 and tef1a genes and adding the obtained sequences into a large phylogenetic framework. The present study showed that Foc Race 1 is the most common strain in northern Viet Nam, causing 74% of all the infections. A more in-depth molecular characterization shows that of the Foc Race 1 infections, 92% are caused by Fusarium tardichlamydosporum and 8% by F. duoseptatum. Compared to Foc Race 1, Foc TR4 (represented by F. odoratissimum) account for only 10.5% of the Fusarium wilting in northern Viet Nam demonstrating that Foc TR4 is not yet a dominant strain in the region. Foc Race 2 infections of Vietnamese bananas also account for 10.5% of the Fusarium wilting in northern Viet Nam. One of the isolates cultured from diseased bananas collected in northern Viet Nam was phylogenetically not positioned within the F. oxysporum species complex (FOSC), but in contrast fell within the Fusarium fujikuroi species complex (FFSC). As a result, it is possible that a new pathogen for bananas has been found. Besides being present on several ABB ‘Tay banana’, Foc Race 1 was also found as pathogen on wild Musa lutea, showing the importance of wild bananas as possible sink for Foc.