Controlling Fusarium Head Blight in oat

Abstract

Oats (Avena sativa) is a versatile crop grown worldwide for animal feed and human consumption. Humanoat consumption has recently risen due to its various health benefits. However, oats are susceptible toFusarium head blight (FHB) caused by various Fusarium fungi. FHB reduces yield and leads to mycotoxinaccumulation. The most commonly reported mycotoxins in oat are trichothecenes deoxynivalenol (DON)and T-2/HT-2 toxins. Trichothecenes inhibit eukaryotic protein biosynthesis and cause acute and chronictoxicoses in human and animals. Effective control of FHB is important for ensuring safety and quality ofoats. This thesis examines various aspects of FHB in oats, relevant to the development of better FHBcontrol strategies.Accurate FHB symptom identification is crucial for breeding resistant oats, but the symptoms of FHB arecryptic, causing errors in scoring the disease during trials. This work presents an affordable method forassessing FHB symptoms in oats by de-hulling mature seeds. Symptoms of blackening and discolorationof the oat kernels significantly correlate with Fusarium DNA and mycotoxin accumulation and thus canbe used as quantitative disease indicators.To enhance pathogen resistance, identifying and characterizing plant resistance genes is key. In thiswork two oat genes coding for DON-detoxifying UDP-glucosyltransferases (UGTs) were identified andcharacterised. Transcripts of two oat UGTs were highly upregulated in response to DON treatment andF.graminearum infection. The genes conferred resistance to several trichothecenes when expressed inyeast. Both UGTs, recombinantly expressed in E.coli were confirmed for their ability to detoxify DON.These genes could potentially be used for developing genetic markers for FHB resistance in oat.Further in this thesis, biocontrol possibilities for FHB in oats are investigated. The fungal BCAClonostachys rosea's potential against FHB is examined. Treating oat spikelets with C. rosea reducedFusarium DNA and DON content in mature kernels. C.rosea enhanced both rate of DON detoxificationand expression of DON-detoxifying UGTs. Furthermore, there was significant upregulation of markers ofinduced resistance, including PR proteins and the WRKY23 transcription factor, indicating that thebiocontrol effect of C. rosea is attributed to the induction of plant defences.Additionally, oats' own endophytes were explored for FHB biocontrol. Fungal endophytes from oatspikelets were isolated and tested for reducing FHB in greenhouse trials. The most successful isolatePseudozyma flocculosa significantly reduced FHB symptoms, F. graminearum biomass, and DONaccumulation in oat. Treatment of oat with P. flocculosa induced expression of genes encoding for PRproteins, known to be involved in FHB resistance.

Abstract (Swedish)

Oats (Avena sativa) are a versatile cereal crop cultivated worldwide. Accounting for 2% of global grain production, they rank as the seventh most important cereal. Approximately 23 million tonnes of oat grain is produced annually, with the majority stemming from spring-sown cultivars in Canada, Russia, and Northern Europe. Although used mostly for animal feed, oats have increased in their popularity for human consumption over the past 25 years due to their numerous health benefits. High in protein, unsaturated lipids and soluble fibre beta-glucan, oats promote cholesterol reduction, improved glycaemic control, and gastrointestinal health. They are also safer than, e.g., wheat for individuals with celiac disease. In addition, oats have high nitrogen use efficiency, making them suitable for organic crop systems.

However, oats are vulnerable to Fusarium head blight (FHB), a disease caused by various fungal species in the genus Fusarium. FHB not only reduces crop yields but also results in accumulation of harmful mycotoxins in grains. The most common toxins produced by Fusarium fungi belong to a class of compounds called trichothecenes, including deoxynivalenol (DON) and T-2/HT-2 toxins. These mycotoxins can cause vomiting, diarrhoea, and other gastrointestinal symptoms in humans and animals upon ingestion. Trichothecenes exert their harmful effects by interfering with protein biosynthesis in eukaryotic cells. Mycotoxin levels in food and feed commodities are regulated by governing bodies, including European Food Safety Authority and the US Food and Drug Administration. As mycotoxin contamination due to FHB poses a significant public health concern, effective FHB disease control is crucial for farmers and food producers.

Managing FHB in cereals is challenging, with integrated pest management (IPM) strategies offering the best approach for controlling FHB. IPM combines multiple control methods, such as use of disease-resistant cultivars, agronomic practices, and chemical or biological control strategies, tailored to the specific needs and environmental conditions of each growing region. However, no oat varieties are completely resistant to FHB. Genetic resistance to FHB disease is a complex trait, influenced by multiple genes and environmental factors, making breeding for FHB resistance challenging. The absence of a complete oat genome sequence had further impeded progress in this area. Fortunately, in 2022, two high-resolution genome sequences were made public, offering invaluable tools for researchers and breeders to understand the genetic basis of important oat traits and develop new technologies, such as gene editing, to enhance resistance of oat against diseases.

When it comes to breeding disease-resistant oats, correctly identifying FHB symptoms is essential. However, unlike wheat and barley, in oat FHB symptoms are hidden beneath thick hulls, and to complicate matters further, these symptoms are easily confused with signs of natural ripening of oats. This often leads to guesswork and errors in disease scoring, resorting to costly chemical and molecular biological analyses. Consequently, the quest continues for a quicker, affordable, and dependable method to reveal these elusive FHB symptoms in oat. To improve genetic resistance against pathogens, it is crucial to identify plant resistance genes and study their functions. One example is the genes encoding UDP- dependent glucosyltransferases (UGTs), which detoxify mycotoxins and other harmful compounds. UGTs bind DON and other trichothecenes with a glucose molecule, transforming the resulting compound into a much less toxic substance. Enhanced activity of such enzymes was directly linked to FHB resistance. In cereal crops like barley, wheat, and rice, researchers have identified several genes, including UGTs, that contribute to FHB resistance. However, the genetic foundation of oats' resistance to FHB has yet to be explored thoroughly.

Together with utilizing moderately resistant cultivars, agronomic practices such as crop rotation and soil tillage can effectively control FHB. In addition, fungicides can reduce FHB severity and prevent mycotoxin production in wheat and barley, but they are largely ineffective against FHB in oats. Even if effective fungicides against FHB in oat could be developed, there is a considerable risk of pathogens developing resistance against fungicides as well as growing societal concerns of negative environmental impacts of excessive fungicide use.

Sustainable and eco-friendly alternatives to fungicides include microbial biological control agents (BCAs), which have been found to reduce FHB symptoms and mycotoxin accumulation in wheat and barley. BCAs encompass bacteria, fungi, and other microorganisms that protect plants through various modes of action, including direct pathogen destruction, competition for nutrients and space, production of antifungal compounds, and induction of plant resistance mechanisms. Recently, endophytic microorganisms, have been gaining interest as potential BCAs. Endophytes, a mix of fungi, bacteria, and other microorganisms, reside within living plant tissues without causing harm. Instead, these quiet inhabitants often boost plant growth and help their hosts fend off pathogen attacks and abiotic stress, while using the plant as a shelter and food source. Although research on BCAs and endophytes against FHB in oats is scarce, studies have shown promising results in wheat.

This work examines different aspects of controlling FHB in oats, such as more accurate disease symptom assessment, identification and functional characterization-detoxifying UGT genes in oats, and the use of BCAs and endophytes forFHB control.

• author: Khairullina, Alfia
• supervisor: Leif Bülow; David B. Collinge
• opponent: Prof. Doohan, Fiona, University College Dublin, Ireland.
• organization: Pure and Applied Biochemistry
• publishing date: 2023-09-04
• type: Thesis
• publication status: published
• subject: Agricultural Science
• keywords: FHB, oat, UDP-glucosyltransferase, deoxynivalenol, mycotoxins, biocontrol, Clonostachys rosea, Fusarium head blight, Fusarium graminearum, endophytes
• pages: 108 pages
• defense location: Lecture Hall KC:C, Kemicentrum, Naturvetarvägen 14, Faculty of Engineering LTH, Lund University, Lund.
• defense date: 2023-09-29 13:00:00
• ISBN: 978-91-7422-981-3
• ISBN: 978-91-7422-980-6
• language: English
• LU publication?: yes
• id: 8f113833-5196-419f-919b-f6215211129e
• date added to LUP: 2023-09-04 11:24:29
• date last changed: 2023-09-06 08:29:37