Determination of deoxynivalenol‐ and nivalenol‐producing chemotypes of Fusarium graminearum isolated from wheat crops in England and Wales

Abstract

Fusarium graminearum , one of the causal agents of fusarium head blight (FHB) of wheat in the UK, can be broadly divided into two chemotypes based on the production of the 8-ketotrichothecenes deoxynivalenol (DON) and nivalenol (NIV). DON-producing isolates can be further distinguished on the basis of the predominant acetyl DON derivative that they produce; 3-acetyl DON (3-AcDON) or 15-acetyl DON (15-AcDON). Functional Tri13 and Tri7 are required for the production of NIV and 4-acetyl NIV, respectively, whereas, in isolates that produce only DON and its acetylated derivatives, these genes are nonfunctional or absent. Infections caused by F. graminearum are becoming more frequent in the UK; however, it is unknown whether these represent more than one chemotype. In this study, polymerasae chain reaction (PCR) assays specific for functional and nonfunctional/deleted versions of Tri7 and Tri13 were used to characterize 101 single-spore isolates of Fusarium graminearum as DON or NIV chemotypes. Primer sets developed to Tri3 were used to classify DON chemotypes further by the acetyl derivative produced (3-AcDON or 15-AcDON). Isolates were collected from 65 fields located around England and Wales between 1997 and 2002. All three chemotypes were identified from the F. graminearum population of England and Wales, with 15-AcDON chemotypes predominating overall. All isolates characterized as 3-or 15-AcDON chemotypes had nonfunctional versions of both genes. Where multiple isolates were collected from a field, mixed-chemotype populations were identified. Variation in the number of 11-bp repeats in Tri7 was detected among 3-and 15-AcDON chemotypes. Seventy-two of the 76 DON chemotypes (95%) were classified as 15-AcDON producers and the remaining four isolates (5%) as 3-AcDON producers. In all four isolates with a 3-AcDON chemotype, Tri7 was deleted from the trichothecene gene cluster. There was no evidence of regional variation between 3-AcDON, 15-AcDON or NIV chemotypes within the F. graminearum population.

Genetic and phenotypic diversity within the Fusarium graminearum species complex in Norway

“…The 3- isolates belonging to population 2 were included in the analysis of aggressiveness, ten of these were included in the growth rate analysis c 17 3-ADON isolates were included in the analysis of aggressiveness, 16 of these were included in the growth rate analysis ADON chemotype also predominated among a small set of FGSC isolates from an earlier collection of Norwegian cereals (Langseth et al 1999(Langseth et al , 2001, and was found in oat and wheat samples collected between 2009 and 2011 in Sweden, whereas the 15-ADON chemotype was not observed (Fredlund et al 2013;Lindblad et al 2013 (Nielsen et al 2012). Our data add to a growing set of studies indicating a geographical partitioning of trichothecene types (chemotypes or genotypes) throughout Europe, with 3-ADON dominating in Northern Europe, whereas 15-ADON appears predominant in the Western and Southern Europe including the UK (Jennings et al 2004), Belgium (Audenaert et al 2009), Italy (Prodi et al 2009;Somma et al 2014), Luxembourg (Pasquali et al 2010), Poland (Stępień et al 2008), Hungary (Toth et al 2005), Germany (Talas et al 2011), and France (Boutigny et al 2014). …”

“…In addition, long distance dispersal of viable F. graminearum spores is possible (MaldonadoRamirez et al 2005;Schmale et al 2012). We speculate whether the increased prevalence of FGSC observed in several European countries (Chandelier et al 2011;Jennings et al 2004;Stępień et al 2008;Waalwijk et al 2003) including the Nordic countries (Bernhoft et al 2010;Fredlund et al 2008;Nielsen et al 2011;YliMattila 2010) may have facilitated the introduction of the 15-DON genotypes into new areas like Norway and Denmark. As such, the prevalence of 15-ADON genotypes and associated mycotoxin levels in Norwegian cereals should be monitored.…”

“…In addition, isolates with NIV genotypes were absent from our sample, but account for at least 10 % of the FGSC isolates in some other parts of Europe (Jennings et al 2004;Waalwijk et al 2003;Boutigny et al 2014;Stępień et al 2008;Somma et al 2014). The distribution of trichothecene types is likely influenced directly or indirectly by a variety of factors including climate, regional host composition, agricultural practices, and the recent and historical movement of pathogen populations into new areas.…”

“…infection levels in cereal seeds, as well as the increased levels of trichothecene contamination in cereal grains, observed in Norway in recent years (Bernhoft et al 2013). During the same period, members of the Fusarium graminearum species complex (FGSC) have become more prevalent in several European countries (Chandelier et al 2011;Jennings et al 2004;Stępień et al 2008;Waalwijk et al 2003) including the Nordic countries (Bernhoft et al 2010;Fredlund et al 2008;Nielsen et al 2011;Yli-Mattila 2010), partly replacing other Fusarium species.…”

“…In addition, chemotype differences have been maintained by selection and may have important consequences for pathogen fitness in different environments (Ward et al 2002). In Europe, 15-ADON is observed in South and Central European countries (Boutigny et al 2014;Jennings et al 2004;Talas et al 2011;Toth et al 2005), whereas in northwestern parts of Europe, 3-ADON has dominated (Fredlund et al 2013;Langseth et al 1999;Nielsen et al 2012;Yli-Mattila et al 2009). …”