Abstract
Fusarium 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 Fusariumoxysporumf.sp.cubense (Foc) directly affect the income, subsistence, and nourishment of thousands of farmers worldwide. For Viet Nam, predictions on the impact of Foc for the future are dramatic, with an estimated loss in the banana production area of 8% within the next five 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 collected in northern Viet Nam. In addition, we aimed to estimate the proportion of the different Fusarium races 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 phylogenetic framework. Molecular characterization shows that c. 74% of the Fusarium isolates obtained from infected banana pseudostem tissue belong to F.tardichlamydosporum. Compared to F.tardichlamydosporum, F.odoratissimum accounts for c.10% of the Fusarium wilt in northern Viet Nam, demonstrating that Foc TR4 is not yet a dominant strain in the region. Fusariumcugenangense – considered to cause Race 2 infections among bananas – is only found in c. 10% of the tissue material that was obtained from infected Vietnamese bananas. Additionally, one of the isolates cultured from diseased bananas was phylogenetically not positioned within the F.oxysporum species complex (FOSC), but in contrast, fell within the Fusariumfujikuroi species complex (FFSC). As a result, a possible new pathogen for bananas may have been found. Besides being present on several ABB ‘Tay banana’, F.tardichlamydosporum was also derived from infected tissue of a wild Musalutea, showing the importance of wild bananas as a possible sink for Foc.
Highlights
For millions of people, bananas are an important food crop
Fusarium wilt infections are prevalent in most of northern Viet Nam as they have been observed in all provinces of northern Viet Nam that were sampled in this study
The 19 Fusarium wilt infections collected based on the typical plant Fusariosis symptoms (Fig. 2) were cultured and further morphologically and molecularly analysed
Summary
One of the most important fungal plant pathogens impacting the cultivation of numerous agricultural crops is the ascomycete Fusarium (e.g., rice, coffee, tomato, melon, wheat; Dean et al 2012). Fusarium has a considerable economic, social and biological impact on the daily livelihood of millions of people worldwide. F. oxysporum is one of the two most devastating pathogens, besides F. gramineum. The F. oxysporum species complex (FOSC) is responsible for wilt diseases of various crops (e.g., cotton and tomato wilt) but is mainly known from its massive impact on the banana industry (Panama disease). For more than 100 years, the fungus has affected banana production worldwide (Ploetz and Pegg 1997; Ploetz 2015a)
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