91ϵÁÐ

Abstract

In 2004 a newly identified species of Fusarium was described and named as F. langsethiae, since then the fungus has been shown to be a weak pathogen in cereals producing mostly symptomless infections when present. However F. langsethiae has a preference for oats where it can result in a combined concentration of the mycotoxins HT2 + T2 in unprocessed grains as high as 9990 µg kg-1, the tolerable combined daily intake for which is 0.1µg kg-1 body weight day-1. Genetic resistance exists within the current UK oat breeding lines and has been examined through the measurement of HT2+T2 concentrations found in oat cultivars grown in AHDB Recommended List trials. However, to date, a reliable method of artificially infecting oats with F. langsethiae to create equivalent concentrations of the HT2 + T2 mycotoxins as seen in previous surveys and that would also adequately test the cultivars ability to resist becoming infected as well as their ability to prevent the spread of any infection has not been demonstrated. Such a method would allow more detailed examinations of individual cultivar resistances to the fungus, and will be further developed within this project. The genetic basis for resistance will be examined through the identification and comparison of quantitative trait loci through the use of genetically mapped populations of oat breeding lines in screening trials using the developed inoculation method.

Description

Fusarium is the causal agent of Fusarium Head/Panicle Blight and mycotoxin contamination in cereals.  Several species have been identified and undergone extensive study such as Fusarium graminearium and F. culmorum, producers of deoxynivalenol (DON) and zearalenone (ZON) mycotoxins in wheat, both of which carry legislative limits.  This has resulted in the development management strategies including the use of fungicides and resistant cultivars. 

From 2002 to 2005 a survey was carried out (Edwards, 2009) on the effects of agronomic practices on the mycotoxin content and profile of UK oat and barley crops.  The survey revealed that although barley had low incidence and severity of HT2 and T2 mycotoxins, on a par with wheat, quantifiable concentrations (greater than 10 µg kg^-1) of these trichothecenes were found in 92% of oat samples.  Across all years the combined mean concentration was 570 µg kg^-1 for oats as compared to the highest concentration in barley of 138 µg kg^-1. 

In 2004 a newly identified species of Fusarium was described and named as Fusarium langsethiae (Torp and Nirenberg, 2004), the fungus was found to produce neosolaniol, iso-neosolaniol, HT2, T2 toxin, 4- and 15-acetyl T2 tetraol, T-2 triol and T-2 tetraol and 4,15-diacetoxyscirpenol.  Given the close morphological similarity to F. poae, and its similar mycotoxin profile to F. sporotrichioides it is possible that F. langsethiae has in fact been encountered in previous studies but not identified as a distinct species. 

Fusarium Langsethiae is now known to be the chief producer of HT2 and T2 mycotoxins in UK oats. In a study conducted at 91ϵÁÐ (Edwards et al., 2012) flour samples of known mycotoxin concentration from the aforementioned study (Edwards, 2009) were assayed using real time PCR to quantify the concentration of F. langsethiae, F. poae, and F. sporotrichioides DNA in the flour.  F. langsethiae was found in almost all the samples, and F. poae in 90%, whereas F. sporotrichioides was absent from all samples.  A regression analysis showed no correlation between F. poae DNA concentrations and HT2 and T2 mycotoxins, however a strong correlation was found with F. langsethiae DNA (P< 0.001, r²= 0.60).  Although there are other species of Fusarium that can synthesise HT2 and T2 mycotoxins; F. sibiricum, F. sporotrichioides and F. armeniacum (T2 only) Edwards et al., 2012 presents strong evidence from the correlation that the previously seen high levels of HT2 and T2 mycotoxins found in oats were a result of F. langsethiae infection.

Opoku et al., 2013 surveyed wheat, barley, oat and triticale crops over three years (2009 – 2011) in Shropshire and Staffordshire under commercial conditions and using real time PCR the concentration of F. langsethiae DNA was measured in plant organs at various growth stages.  Concentrations of F. langsethiae DNA were lower and less consistent in terms of the plant organs infected in wheat, barley (spring and winter), and triticale than in oats. 

The picture begins to clarify to show that F. langsethiae is the major producer of potentially harmful concentrations of HT2 and T2 trichothecenes in UK oats, but also that the problem is restricted to oats due the preference of F. langsethiae for oats and its weak pathogenicity for other cereals (Imathiu et al, 2009).

The difficulty thus far in the study of F. langsethiae has been two fold; firstly the fungus elicits few if no symptoms in the host oat crop (Opoku et al., 2013) and secondly the inability to artificially inoculate field crops with the pathogen (Imathiu, 2008).

So far the epidemiology of F. langsethiae is unknown, Opoku et al., 2013 suggested a lifecycle for the fungus the crucial aspect of which was the increased growth of the fungus on the emerged heads of the plants with the pathogen almost undetectable prior to anthesis.  In two of the three years surveyed Opoku had data showing the low level presence of the pathogen at panicle emergence and from this he postulated the infection occurred at panicle emergence with the subsequent fungal growth happening in the spikelets of the crop. 

Artificial inoculation methods have been attempted at the seedling stage (Imathiu, 2010), (Divon et al, 2012) as well as later stages such as booting, anthesis and early dough (Divon et al, 2012), these included spray inoculations as well as injection methods.  The fungus has been found not to be pathogenic to seedlings, but there has been increasing success with inoculations applied to the later stages of plant growth i.e. booting onwards (Divon et al, 2012).

It has been seen that there are significant differences in the accumulation of HT2 and T2 mycotoxins between current oat cultivars, this is especially prevalent within winter oat cultivars (Edwards, 2015).  Within winter cultivars there is on average a far higher concentration of HT2+T2 than in spring varieties (Edwards, 2015).  The highest mycotoxin concentration average in winter oats from 2012-2014 was Balado at 848 µg kg^-1 and the lowest was Maestro at 218 µg kg^-1 (Edwards, 2015).  Therefore there is scope for selecting for resistance within the current collective oat genome.

This project therefore aims to:

Establish a method of infecting oats with F. langsethiae to create equivalent concentrations of the HT2 + T2 mycotoxins as seen in previous surveys and that would also adequately test  a plant's ability to resist infection and mycotoxin accumulation.

Identify Quantitative Triat Loci within winter oat breeding lines that infer resistance or susceptability to F. langsethiae infection and susequent mycotoxin accumulation.