Fusarium head blight of cereals: improving management of this difficult disease

Non-Peer Reviewe

Crop Sequence Influence on Fusarium Head Blight from Wheat and Barley

Non-Peer ReviewedOn the Canadian prairies, Fusarium head blight (FHB) mitigation requires an integrated pest management approach. The lack of highly resistant varieties and the limited effectiveness of fungicide make managing the disease difficult. A diverse crop rotation should be a sustainable strategy. We are investigating the effect of multiple crop sequences of host and non-host crops on FHB and other diseases of wheat and barley. The crop sequences include four of the most commonly grown field crops in western Canada and maize. The experiment is being conducted over three growing seasons (2018-2020) at six locations. The impact of the various crop sequences will be determined by the Fusarium spp. detected in the wheat crop in year three, the FHB index, yield, and quality (deoxynivalenol and protein content). Last year data showed a low FHB pressure across the prairies and high levels of deoxynivalenol (DON) were detected in harvested samples. Concerning the Fusarium spp., it was possible to isolate F. graminearum, F. poae and F. culmorum from the six locations in wheat, durum, barley and oats samples. Our aim is to increase sustainability of wheat and barley production in western Canada by providing information on which to develop best management practices for crop rotation

Sensitivity of Fusarium graminearum to tebuconazole, metconazole, and prothioconazole fungicides

Non-Peer ReviewedTriazole fungicides, along with cultural disease control strategies, has been a useful tool in managing Fusarium head blight (FHB) in the absence of satisfactory levels of FHB resistance in the commercial wheat varieties. Although the triazoles have been used across the world since 1990's for FHB management, there are still very few reports on resistance built-up in the pathogen population. In this study we determined the sensitivity of 254 Fusarium graminearum isolates collected from Western Canada to prothioconazole, metconazole and tebuconazole. Phenotyping for fungicide sensitivity of F. graminearum isolates revealed phenotypic variation in the population for sensitivity to the three fungicides. There was no evidence of cross-resistance between prothioconazole, metconazole and tebuconazole

Establishing a mycotoxin quantification platform to support FHB research and breeding programs

Non-Peer ReviewedFusarium head blight (FHB), caused by Fusarium spp., is a destructive disease of small grain cereals, such as wheat, barley, oat and canaryseed. Apart from grain yield losses and reduced baking and seed quality, a major concern with FHB is crop contamination with Fusarium-produced trichothecene mycotoxins, specifically deoxynivalenol (DON), also known as vomitoxin. These mycotoxins accumulate in the grain making it unfit for consumption by humans and animals. Significant DON contamination may render a crop unmarketable, or reduces the market value by 40-65%. Breeding productive cultivars with high disease resistance and low mycotoxin contamination is a priority for wheat breeders. However, measurement of DON content is not always included in breeding programs due to the lack of efficient quantification methods. Some methods are easy-to-use, but they lack the needed accuracy and sensitive, such as enzyme-linked immunosorbent assay (ELISA); while some chromatographic-based methods have relatively higher accuracy and sensitivity compared to ELISA, but require complex extraction and cleanup steps and longer running time, which are not cost-efficient and environmentally friendly. In this study, we established a tandem mass spectrometry (MS/MS) method, which employed a one-step acetonitrile extraction protocol and flow injection analysis (FIA)-MS/MS method (i.e. no analytical column) to reduce the complexity, cost and time. This method is designed for FHB breeding programs or DON quantification for other purposes that require a fast, high throughput DON phenotyping, but provides relatively high selectivity, accuracy and sensitivity compared to existing assays. This method has been fully validated according to the US Food and Drug Administration (FDA) Guidance for Bioanalytical Method Validation, including selectivity, linearity, accuracy, precision, recovery, matrix effects, stability and dilution integrity. With ease of use, high sensitivity and accuracy, this high throughput DON quantification method will increase breeding efficiency and accelerate the screening progress for FHB resistant germplasm

Deoxynivalenol (DON) Accumulation and Nutrient Recovery in Black Soldier Fly Larvae (Hermetia illucens) Fed Wheat Infected with Fusarium spp.

Fusarium head blight (FHB) is one of the most significant causes of economic loss in cereal crops, resulting in a loss of $50–300 million for Canadian agriculture. The infected grain (containing Fusarium-damaged kernels (FDKs)) is often both lower in quality and kernel weight, and it may be unsuitable for human and animal consumption due to mycotoxin presence. However, it still contains a considerable amount of nutrients. A method to recover the nutrients without the mycotoxins should be beneficial for the agricultural economy. In this study, our objective was to examine recovery methods of the nutrients in relation to mycotoxin accumulation in the insect. The FDKs were fermented with Aspergillus oryzae and/or Lactobacillus plantarum (solid-state fermentation (SSF)). The SSF kernels were then provided to 50 young, black soldier fly larvae (BSFL) for 12 days. Weight gain, chemical composition, and mycotoxin bioaccumulation of BSFL and spent feed were evaluated. After 12 days of insect culture, the BSFL grew 5–6 times their initial weight. While the overall weights did not significantly vary, the proteins and lipids accumulated more in SSF FDK-fed insects. During the active growth period, the larval biomass contained deoxynivalenol (DON), a mycotoxin, at detectable levels; however, by day 12, when the larvae were in the pre-pupal stage, the amount of DON in the insect biomass was nearly negligible, i.e., BSFL did not accumulate DON. Thus, we conclude that the combination of BSFL and SSF can be employed to recover DON-free nutrients from FHB-infected grain to recover value from unmarketable grain

Spike culture derived wheat (Triticum aestivum L.) variants exhibit improved resistance to multiple chemotypes of Fusarium graminearum.

Fusarium head blight (FHB) in wheat (Triticum aestivum L.), predominantly caused by Fusarium graminearum, has been categorized into three chemotypes depending on the major mycotoxin produced. The three mycotoxins, namely, 3-acetyldeoxynivalenol (3-ADON), 15-acetyldeoxynivalenol (15-ADON) and nivalenol (NIV) also determine their aggressiveness and response to fungicides. Furthermore, prevalence of these chemotypes changes over time and dynamic changes in chemotypes population in the field have been observed. The objective of this study was to identify spike culture derived variants (SCDV) exhibiting resistance to multiple chemotypes of F. graminearum. First, the optimal volume of inoculum for point inoculation of the spikelets was determined using the susceptible AC Nanda wheat genotype. Fifteen μL of 105 macroconidia/mL was deemed optimal based on FHB disease severity assessment with four chemotypes. Following optimal inoculum volume determination, five chemotypes (Carman-NIV, Carman-705-2-3-ADON, M9-07-1-3-ADON, M1-07-2-15-ADON and China-Fg809-15-ADON) were used to point inoculate AC Nanda spikelets to confirm the mycotoxin produced and FHB severity during infection. Upon confirmation of the mycotoxins produced by the chemotypes, 55 SCDV were utilized to evaluate FHB severity and mycotoxin concentrations. Of the 55 SCDV, five (213.4, 244.1, 245.6, 250.2 and 252.3) resistant lines were identified with resistance to multiple chemotypes and are currently being utilized in a breeding program to develop wheat varieties with improved FHB resistance

Breakdown of Rlm3 resistance in the Brassica napus-Leptosphaeria maculans pathosystem in western Canada

International audienceBlackleg disease, caused by the fungal pathogen Leptosphaeria maculans, is a serious disease of Brassica napus. The disease is mainly controlled by genetic resistance and crop rotation. However, L. maculans has displayed a high evolutionary potential to overcome major resistance genes in B. napus. This study aimed to analyze the major-gene and adult-plant resistance (APR) of Canadian B. napus varieties/lines (accessions) and the avirulence allele frequency in L. maculans populations in western Canada. For resistance identification, a set of L. maculans isolates with known avirulence genes were used to characterize major resistance (R) genes in 104 Canadian B. napus accessions and 102 seed samples collected from growers' fields; with 104 B. napus accessions further evaluated for APR under controlled conditions. In addition, avirulence genes of 300 L. maculans isolates collected from infected canola stubbles in growers' fields were determined by cotyledon inoculation and gene-specific PCR assays. The results indicated that R genes were present in the majority of these B. napus accessions, with the Rlm3 gene being predominant while other R genes were rarely detected. APR was identified in more than 50 % of the accessions. Predominance of Rlm3 in 102 seed samples from growers' fields suggested Rlm3-carrying B. napus varieties were currently widely used in western Canada. Avirulence allele frequency identification of field L. maculans isolates revealed the scarcity of the avirulence allele towards Rlm3, AvrLm3. This indicated the breakdown of Rlm3 resistance, which could be due to the over use of this single resistance gene in Canadian B. napus germplasm

Sensitivity of western Canadian <i>Pyrenophora teres</i> f. <i>teres</i> and <i>P. teres</i> f. <i>maculata</i> isolates to propiconazole and pyraclostrobin

<p><i>Pyrenophora teres</i> f. <i>teres</i> (<i>Ptt</i>) and <i>Pyrenophora teres</i> f. <i>maculata</i> (<i>Ptm</i>), the causal agents of the net and spot forms of net blotch of barley, respectively, can be managed in western Canada with fungicides containing propiconazole and pyraclostrobin. Given the potential for development of fungicide resistance, the sensitivity of a collection of <i>Ptt</i> and <i>Ptm</i> isolates to propiconazole and pyraclostrobin was evaluated using microtitre plate bioassays. The concentration of propiconazole needed to inhibit fungal growth by 50% (EC₅₀) was 1.5 mg L⁻¹ for <i>Ptt</i> and 2.3 mg L⁻¹ for <i>Ptm</i>, while the EC₅₀ of pyraclostrobin was 0.015 mg L⁻¹ for <i>Ptt</i> and 0.024 mg L⁻¹ for <i>Ptm</i>. Subsequently, 39 <i>Ptt</i> and 27 <i>Ptm</i> isolates were screened with discriminatory doses of 5 mg propiconazole L⁻¹ and 0.15 mg pyraclostrobin L⁻¹. Inhibition of growth as a result of propiconazole was 12–95% for <i>Ptt</i> and 48–92% for <i>Ptm</i>; growth inhibition as a result of pyraclostrobin was 40–100% and 24–100%, respectively. Two <i>Ptt</i> isolates were insensitive to propiconazole, while one <i>Ptm</i> isolate was insensitive to pyraclostrobin. The latter also showed decreased sensitivity to propiconazole. The identification of net blotch isolates insensitive to these fungicides emphasizes the need for farmers to employ integrated crop management strategies to avoid fungicide resistance build-up.</p

Virulence of <i>Pyrenophora teres</i> populations in western Canada

<p>Net blotch, caused by <i>Pyrenophora teres</i>, is an economically important disease of barley. The pathogen has two morphologically similar but genetically distinct forms: <i>P. teres</i> f. <i>teres</i> (<i>Ptt</i>) and <i>P. teres</i> f. <i>maculata</i> (<i>Ptm</i>), which cause net form net blotch (NFNB) and spot form net blotch (SFNB), respectively. The virulence of a collection of 39 <i>Ptt</i> and 27 <i>Ptm</i> isolates collected from western Canada was evaluated by inoculating these isolates onto sets of barley differential hosts. One week following inoculation, the second and third leaves of each plant were rated for disease severity on scales of 1–10 (for <i>Ptt</i>) or 1–9 (for <i>Ptm</i>). Plants rated <5 and ≥5 were scored as resistant and susceptible to <i>Ptt</i>, respectively, while plants rated 1–3 and >3 were scored as resistant and susceptible to <i>Ptm</i>. The experiment was repeated. Cluster analysis revealed 16 and 13 distinct pathotype groups, respectively, among the 39 and 27 representative <i>Ptt</i> and <i>Ptm</i> isolates. The barley differentials CI 5791 and CI 9820 were resistant to all isolates of <i>Ptt</i> except one, whilst the differential CI 9214 was resistant to all isolates of <i>Ptm</i> except two. Therefore, the differential lines CI 5791 and CI 9820, for <i>Ptt</i>, and CI 9214, for <i>Ptm</i>, can still be considered as potentially useful sources of resistance for Canadian barley breeding programmes.</p