Population Genetic Analyses of Fusarium asiaticum Populations from Barley Suggest a Recent Shift Favoring 3ADON Producers in Southern China

Abstract

Fusarium asiaticum is the predominant causal agent of Fusarium head blight (FHB) in southern China. The genetic diversity was assessed by analyzing 448 single-spore F. asiaticum isolates from 18 sampling sites that were 10 to 2,000 km apart, using seven highly informative variable number of tandem repeat (VNTR) markers. This analysis showed a significant degree of population subdivision (P < 0.001) among populations from upper, middle, and lower valleys of the Yangtze River, with little gene flow (Nm = 1.210). We observed a strong association between this genetic population subdivision and the mycotoxin produced. Our results show that the dramatic cline in trichothecene chemotypes may be explained by a recent and significant invasion of 3-acetyldeoxynivalenol (3ADON) producers in FHB pathogen composition in the middle valley. Using Bayesian statistics, we found a biased gene flow from 3ADON to nivalenol (NIV) populations. In addition, we observed significant genetic differentiation and linkage disequilibrium between NIV- and 3ADON-producing isolates at the same sampling sites. The impact of the changed agronomy and trade of cereal commodities on the spread of the new Fusarium population and the consequent increase of FHB observed in southern China are discussed.

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

“…A significant longitudinal cline in trichothecene chemotype frequencies in Canada was attributed to the recent introduction and spread of a novel, and potentially more vigorous, F. graminearum population with a 3-ADON chemotype . A very similar situation was described for F. asiaticum populations differing in trichothecene type in China (Zhang et al 2010(Zhang et al , 2012. Recent introductions may also account for regional differences in trichothecene chemotype composition reported in Louisiana and Uruguay, although regional differences in host composition were suggested as a major factor Umpiérrez-Failache et al 2013).…”

“…The origin of this population structure is unclear, but may have resulted from the introduction and spread of a novel population prior to our sampling. Similar conclusions were drawn from the observation o f w i d es p r e a d c o -o cc u r r e n c e o f d i v e rge n t F. graminearum populations in North America Ward et al 2008) and from the observed population structure within F. asiaticum in China (Zhang et al 2010(Zhang et al , 2012.…”

“…In Canada, Ward et al (2008) observed that the emerging 3-ADON populations had higher fecundity (conidia production), larger conidia spores, higher growth rates, as well as higher production of DON compared to the 15-ADON population. In China, F. asiaticum of the 3-ADON type were rapidly replacing populations characterized by the NIV type and were more aggressive on wheat, more toxigenic, produced more and larger conidia, had higher growth rates, and were resistant to higher concentrations of benzimidazole (Zhang et al 2010(Zhang et al , 2012. These authors speculated that the observed phenotypic differences could provide fitness advantages to a population resulting in a range expansion and significant changes in population frequencies.…”

Novel Fusarium head blight pathogens from Nepal and Louisiana revealed by multilocus genealogical concordance

“…The biogeographic structure exhibited by the four species within this subclade suggests that they may have evolved allopatrically within Asia. While F. asiaticum has been reported to be more prevalent in southern regions of China and Japan (Gale et al, 2002;Qu et al, 2007;Suga et al, 2008;Yang et al, 2008;Zhang et al, 2010), F. ussurianum is currently only known for the Far East of Russia, and F. vorosii appears to be largely restricted to the Far East of Russia and Hokkaido, Japan (Starkey et al, 2007;Yli-Mattila et al, 2009), although the first isolate of the latter species was initially discovered in Hungary (Tóth et al, 2005). Assessing whether F. nepalense is endemic to Nepal will require additional sampling to identify its phylogeographic distribution.…”

Evidence for natural resistance towards trifloxystrobin in Fusarium graminearum

“…It was the purpose of this study to characterize a F. graminearum strain collection isolated between 1969 and 2009 for its (in)sensitivity towards trifloxystrobin and to provide evidence for either acquired or natural resistance. Moreover, given the recent observations of a shift of the F. graminearum chemotype composition in different agricultural conditions (Ward et al 2008;Gale et al 2007;Zhang et al 2010) it could be hypothesized that a selective pressure caused by the increased use of fungicides might have favoured a certain chemotype. Because it has been noted that oxidative stress is triggered by fungicides and that chemotypes respond differently to oxidative stress (Ponts et al 2009), we also tested if the level of sensitivity to strobilurins differed among chemotypes.…”