A. Tekauz

Review: Recent developments in research on fusarium head blight of wheat in Canada

The recent increase in prevalence and severity of fusarium head blight (FHB), in cereals in Canada and elsewhere, has caused hardship and economic loss to producers and the grain industry. This review emphasizes Canadian contributions, but incorporates studies from North America to put that research into perspective. Since the reviews of Sutton in 1982 and Miller in 1994, significant advances in our understanding of the epidemiology of the disease have occurred that are fundamental to the development of appropriate management strategies. Also, we now better understand the genetics of resistance in wheat and there is a consensus that resistant cultivars will provide the most stable and durable solution to the problem of FHB. Our knowledge of the genetic basis of resistance in wheat, and the development of molecular markers to facilitate early generation selection for resistance to FHB, are essential tools to this end. Resistant cultivars will ensure stable yields and high-quality grain free of mycotoxins.

Review: Fusarium head blight of barley in western Canada

Fusarium head blight (FHB), caused primarily by Fusarium graminearum, has rapidly become the most notorious disease of cereals in parts of western Canada. The situation in barley is particularly striking, for until 1993 FHB was not observed in the crop at all, but by 1996 it affected every barley field examined in Manitoba. The disease is largely responsible for the decline in acreage and the loss of markets for both malting and feed barley in the region. Several aspects of FHB in barley are examined for this review, beginning with an overview and description of symptoms and disease epidemiology. Differences in the expression of FHB in barley as compared with wheat, including causal species, infection period, symptoms, and resulting damage (yield and quality losses) are described. These have implications for disease management, including breeding for resistance. The latter is ongoing at several institutions and should result in cultivars with improved resistance to FHB in future. Until then, an integrated protocol for disease management must be implemented to minimize the threat of FHB for producers and the industry.

RFLP mapping of a gene in barley conferring resistance to net blotch (Pyrenophora teres)

SummaryA progeny consisting of 283 anther-derived doubled haploid barley lines from a cross between the winter cultivars lgri (resistant) and Franka (susceptible) was tested for resistance to Pyrenophora teres. A single, dominant gene was detected and tagged by a series of closely linked RFLP markers located in the proximal portion of the long arm of chromosome 3, close to the centromere. Due to the unknown allelic relationship of this gene to another resistance gene previously assigned to chromosome 3, the preliminary designation Pt,,a is proposed. For marker assisted selection RFLP probe cMWG680, which maps 0.8 cM distal to the gene, was converted into a sequence tagged site marker.

Relative aggressiveness and production of 3- or 15-acetyl deoxynivalenol and deoxynivalenol by Fusarium graminearum in spring wheat

Abstract Fusarium graminearum is the principal cause of fusarium head blight in North America, a disease that has caused severe losses in yield and quality of cereals. In North America, the vast majority of F. graminearum isolates produce 3- or 15-acetyl deoxynivalenol (ADON) in addition to DON. Until recently, 15-ADON isolates predominated, but a rapid shift from 15-ADON to 3-ADON producers in Canada and north central USA has been documented. In order to better understand the effect of this population shift on relative aggressiveness of isolates and mycotoxin accumulation, we tested a total of 58 isolates for 3- and 15-ADON production on two Canadian spring wheat cultivars, ‘Roblin’ (susceptible) and ‘5602 HR’ (moderately resistant). In Experiment 1, three isolates from the Canadian provinces of Manitoba, Saskatchewan and Alberta, each of which produced either 15-ADON or 3-ADON, were tested using spray inoculation. In Experiment 2, 20 isolates which produced 15-ADON and 20 which produced 3-ADON from Manitoba, were tested using point inoculation. There were no significant differences in aggressiveness among isolates based either on geographic origin or mycotoxin type. Analysis of seeds from inoculated heads by gas chromatography/mass spectrometry indicated that the 3-ADON producing isolates had significantly higher DON levels than the 15-ADON isolates in ‘Roblin’ after both spray and point inoculation and in ‘5602HR’ after point inoculation. DON levels following point inoculation by 15-ADON isolates were similar in the two cultivars. The 15-ADON isolates from Alberta produced less DON than 15-ADON isolates from Manitoba and Saskatchewan. Consistently, more ADON was produced by 15-ADON isolates than by 3-ADON isolates. The results of the study suggest that if the percentage of 3-ADON isolates in Canada increases, DON levels in cereals are likely to increase in epidemic years.

Fusarium head blight of oat — current status in western Canada

The occurrence of fusarium head blight (FHB) in oat in Canada is reviewed, and preliminary results of recent studies in Manitoba are presented. Fusarium head blight was common in oat crops surveyed in southern Manitoba in 2002 and 2003, but visually, only low levels were evident. Fusarium graminearum and F. poae were the principal fungal species recovered from affected kernels. Levels of Fusarium spp. and deoxynivalenol (DON) varied among oat cultivars tested for their reactions to FHB in field trials. Putative Fusarium-damaged kernels were also assessed, but their identification was equivocal. As such, evaluation of DON and F. graminearum appear to be the best means of determining general FHB levels in oat and reaction differences among oat genotypes. Compared with wheat and barley, oat was less affected by FHB and may be more resistant to the disease. Dehulled oats (groats), when processed, had much lower levels of DON compared with whole oats. Effective management of FHB, including incorporation of improved levels of resistance and use of cultural options is needed to minimize the impact of the disease and ensure the sustainability of the crop in the region. Fusarium head blight is a major (new) disease of oat in western Canada.

RFLP mapping in barely of a dominant gene conferring resistance to scald (Rhynchosporium secalis).

A progeny consisting of 52 anther-derived doubled haploid barley lines from a F1 between the winter cultivars ‘Igri’ (susceptible) and ‘Triton’ (resistant) was tested for resistance to Rhynchosporium secalis. A dominant gene was detected and tagged by a series of cosegregating RFLP markers located in the proximal portion of the long arm of chromosome 3, close to the centromere. One of the cosegregating RFLP markers, cMWG680, was converted into a codominant sequence tagged site marker. Polymerase chain reaction analysis with this marker of a series of accessions carrying known resistance genes provided evidence that scald resistance in cv ‘Triton’ is due to the presence of the Rh gene.

Influence of inoculation method and growth stage on fusarium head blight in barley

The effect of inoculation method and growth stage on the development of fusarium head blight (FHB) in barley were evaluated under controlled conditions. Barley cvs. Argyle, AC Oxbow, Chevron, and AC Lacombe were inoculated with macroconidial suspensions of Fusarium graminearum Schwabe either by single floret injection at preanthesis, anthesis, or postanthesis or by spray application to the entire spike at heading, 7 days after heading, or 14 days after heading. Four weeks after inoculation, heads were evaluated visually for symptoms of FHB, then the spikes were hand threshed and the seed assayed for F. graminearum colonization. Visual determination of FHB generally overestimated the F. graminearum seed colonization in the injected spikes and underestimated it in sprayed spikes. Infection resulting from floret injection was limited to the inoculated spikelet and immediately adjacent spikelets, so variation in FHB resistance among cultivars could not be satisfactorily distinguished using this inoculation method. The growth stage at the time of floret injection had no effect on seed colonization by F. graminearum. Spray inoculations produced more seed colonized by F. graminearum than single floret injection and was better for distinguishing the levels of resistance in the cultivars. The most resistant cultivar, AC Oxbow, could be distinguished from the other cultivars, using this inoculation method. Although the plants were susceptible to FHB infection from heading to 14 days after heading, the cultivars were best differentiated by inoculating at 14 days after heading. Seed colonization by F. graminearum among the first, second, or third tillers was similar using either inoculation method.

The genetic basis of scald resistance in western Canadian barley cultivars

SummaryThe genetic basis of resistance to scald (Rhynchosporium secalis) within barley breeding populations is poorly understood. The design of effective genetically based resistance strategies is predicated on knowledge of the identity of the resistance genes carried by potential parents. The resistance exhibited by a broad selection of western Canadian barley lines was investigated by evaluating their reactions to five R. secalis isolates. Results were compared to the resistance exhibited by previously characterized lines. This comparison, combined with pedigree analysis indicated that there are two different resistance genes present inwwestern Canadian cultivars. These genes were shown to be independent through analysis of a segregating population derived from a cross between Falcon and CDC Silky. This evidence, along with observed linkage of the gene in CDC Silky with an allele specific amplicon developed for a Rhynchosporium secalis resistance locus on chromosome 3, provides evidence that the gene in Falcon is the Rh2 gene derived from Atlas, and the gene (s) in CDC Silky is located within the Rh/Rh3/Rh4 cluster and is similar to the Rh gene in Hudson.

Diversity of Fusarium head blight populations and trichothecene toxin types reveals regional differences in pathogen composition and temporal dynamics

Analyses of genetic diversity, trichothecene genotype composition, and population structure were conducted using 4086 Fusarium graminearum isolates collected from wheat in eight Canadian provinces over a three year period between 2005 and 2007. The results revealed substantial regional differences in Fusarium head blight pathogen composition and temporal population dynamics. The 3ADON trichothecene type consistently predominated in Maritime provinces (91%) over the sampled years, and increased significantly (P<0.05) between 2005 and 2007 in western Canada, accounting for 66% of the isolates in Manitoba by the end of the sampling period. In contrast, 3ADON frequency was lower (22%, P<0.001) in the eastern Canadian provinces of Ontario and Québec and did not change significantly between 2005 and 2007, resulting in two distinct longitudinal clines in 3ADON frequency across Canada. Overall, genetic structure was correlated with toxin type, as the endemic population (NA1) was dominated by 15ADON isolates (86%), whereas a second population (NA2) consisted largely of 3ADON isolates (88%). However, the percentage of isolates with trichothecene genotypes that were not predictive of their genetic population assignment (recombinant genotypes) increased from 10% in 2005 to 17% in 2007, indicating that trichothecene type became an increasingly unreliable marker of population identity over time. In addition, there were substantial regional differences in the composition of recombinant genotypes. In western and maritime provinces, NA2 isolates with 15ADON genotypes were significantly more common than NA1 isolates with 3ADON genotypes (P<0.001), and the reverse was true in the eastern provinces of Québec and Ontario. Temporal trends in recombinant genotype composition also varied regionally, as the percentage of 15ADON isolates with NA2 genetic backgrounds increased approximately three fold in western and Maritime provinces, while the opposite trends were observed in Québec and Ontario. The results indicate that F. graminearum population dynamics in Canada have been influenced by a complex adaptive landscape comprising different regional selective pressures, and do not reflect a simple model of dispersal and integration following the introduction of a novel pathogen population. In addition, we identified F. graminearum strains that produce the recently discovered A-trichothecene mycotoxin (NX-2) for the first time in Canada, representing a significant expansion of the known range of NX-2 producing strains in North America.

Progress in breeding for resistance to fusarium head blight in barley

In western Canada, from 2000 to the spring of 2003, much of the breeding effort to improve resistance of barley (Hordeum vulgare) to fusarium head blight (FHB) was conducted through a collaborative project supported by a number of funding agencies. The main results of this 3-year project were briefly discussed in the present study, with the conclusion that this project has laid the foundation for developing new barley cultivars with improved resistance to FHB. A new 3-year project with an increased national focus was initiated in the spring of 2003, with funding from the Western Grains Research Foundation and Agriculture and Agri-Food Canadas Matching Investment Initiative program. A brief description of the new project and an update on progress in 2003 is presented in this study. The new project will pursue most of the objectives of the former project, with one of the important additions being access to the FHB nursery at Charlottetown, Prince Edward Island. Although more deoxynivalenol analyses will be conducted using enzymed-linked immunosorbent assays for the new project, currently available capabilities for testing deoxynivalenol levels remain a major constraint in barley breeding. In conclusion, progress is being made in improving resistance to FHB in barley, but it will be a long-term effort.