Role of ascospore production by Claviceps purpurea in aetiology of ergot disease in male sterile wheat

Four phylogenetic species of ergot from Canada and their characteristics in morphology, alkaloid production, and pathogenicity

Four ergot species (Claviceps ripicola, C. quebecensis, C. perihumidiphila, and C. occidentalis) were recognized based on analyses of DNA sequences from multiple loci, including two housekeeping genes, RNA polymerase II second largest subunit (RPB2), and translation elongation factor 1-α (TEF1-α), and a single-copy ergot alkaloid synthesis gene (easE) encoding chanoclavine I synthase oxidoreductase. Morphological features, ergot alkaloid production, and pathogenicity on five common cereal crops of each species were evaluated and presented in taxonomic descriptions. A synoptic key was also provided for identification.

Spatial Patterns of Ergot and Quantification of Sclerotia in Perennial Ryegrass Seed Fields in Eastern Oregon

Ergot, caused by Claviceps purpurea, is a major disease of perennial ryegrass grown for seed in eastern Oregon. The objective of this research was to quantify and describe the spatial patterns of ergot severity in each of three 50-ha commercial fields of perennial ryegrass grown for seed in 2012 and 2013. In total, 1,433 and 1,405 quadrats were sampled among the three fields in 2012 and 2013, respectively, and the percentage of quadrats with ergot ranged from 59 to 90%. The mean incidence of infected seed heads in each quadrat ranged between 13 and 29%, while mean severity in each quadrat ranged from 0.2 to 0.5 sclerotia per seed head. Significant autocorrelation and clustering were observed in all three fields in both years, as indicated by Moran's I and spatial analysis by distance indices of aggregation. The mean number of ergot sclerotia collected from each field after harvest ranged between 4 and 15 sclerotia m^-2 in 2012 and 18 and 119 sclerotia m^-2 in 2013. Sclerotia left in perennial fields after harvest are a significant source of inoculum that should be targeted for control. This is the first study to quantify spatial patterns of ergot in perennial ryegrass and provides insights into possible mechanisms that contribute to ergot etiology and epidemiology.

The identification of QTL controlling ergot sclerotia size in hexaploid wheat implicates a role for the Rht dwarfing alleles

Four QTL conferring resistance to ergot were identified in the UK winter wheat varieties 'Robigus' and 'Solstice'. Two QTL co-located with semi-dwarfing alleles at the Rht loci Rht - 1B and Rht - 1D implicating a role of these DELLA proteins in infection success of Claviceps purpurea. The fungal pathogen Claviceps purpurea infects ovaries of a broad range of temperate grasses and cereals, including hexaploid wheat, causing a disease commonly known as ergot. Sclerotia produced in place of seed carry a cocktail of harmful alkaloid compounds that result in a range of symptoms in humans and animals, causing ergotism. Following a field assessment of C. purpurea infection in winter wheat, two varieties 'Robigus' and 'Solstice' were selected which consistently produced the largest differential effect on ergot sclerotia weights. They were crossed to produce a doubled haploid mapping population, and a marker map, consisting of 714 genetic loci and a total length of 2895 cM was produced. Four ergot reducing QTL were identified using both sclerotia weight and size as phenotypic parameters; QCp.niab.2A and QCp.niab.4B being detected in the wheat variety 'Robigus', and QCp.niab.6A and QCp.niab.4D in the variety 'Solstice'. The ergot resistance QTL QCp.niab.4B and QCp.niab.4D peaks mapped to the same markers as the known reduced height (Rht) loci on chromosomes 4B and 4D, Rht-B1 and Rht-D1, respectively. In both cases, the reduction in sclerotia weight and size was associated with the semi-dwarfing alleles, Rht-B1b from 'Robigus' and Rht-D1b from 'Solstice'. Two-dimensional, two-QTL scans identified significant additive interactions between QTL QCp.niab.4B and QCp.niab.4D, and between QCp.niab.2A and QCp.niab.4B when looking at sclerotia size, but not between QCp.niab.2A and QCp.niab.4D. The two plant height QTL, QPh.niab.4B and QPh.niab.4D, which mapped to the same locations as QCp.niab.4B and QCp.niab.4D, also displayed significant genetic interactions.

Evaluation of Resistance to Ergot, Caused by Claviceps purpurea, in Kentucky Bluegrass, Based on Incidence and Severity Estimates

Ergot, caused by Claviceps purpurea, is an important disease of Kentucky bluegrass grown for seed. Resistance is a preferred means of disease control, although approaches to evaluating ergot resistance in Kentucky bluegrass are not well established. A large scale disease assessment trial was established to compare within-year and year-to-year variability among measures of ergot incidence or severity in Kentucky bluegrass and to determine the most efficient approaches for cultivar evaluation. The susceptibility of 104 Kentucky bluegrass cultivars (78 commercial and 26 experimental) to ergot was assessed, based on percentage of panicles with sclerotia (incidence), sclerotia per panicle (severity), percentage of seeds replaced by sclerotia, or percentage of sclerotia among seed by weight. Cultivar ranking for susceptibility within years was similar for all methods of ergot assessment. Yearly mean incidence of ergot among cultivars ranged from 1.0 to 97.5% for susceptible cv. HV102 to 0.0 to 2.5% for resistant cv. Huntsville, with remaining cultivars distributed between the extremes. Yearly mean values of ergot incidence and severity differed among years. Much of this variability was due to days with rain during the period from flower initiation to maturity (period of susceptibility). Disease incidence was correlated (P ≤ 0.05) with days with rain in 22 of the cultivars. Duration of flowering was correlated (P ≤ 0.05) with ergot incidence in 11 cultivars. Results from this study suggest that variability in host and environment would likely offset any gain in precision of severity data. In large trials in particular, collection of incidence data (percentage of panicles with ergot) would provide the most timely and efficient means for ergot assessment.