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

Abstract

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 Claviceps purpurea isolates on wheat reveals complex virulence and host susceptibility relationships

“…There are other wheat genotypes that have been reported to show resistance to C. purpurea, which could be considered for inclusion in a more comprehensive differential set. For instance, the winter wheat line 'Robigus' has recently been shown to have lower average sclerotium weight and sclerotial weight per ear than other winter wheat lines (Gordon et al 2015). It is also important to note that the resistance in our differential wheat lines has not been characterized, and some of these lines may possess more than one gene for resistance, or some of the same genes for resistance.…”

“…Platford et al (1977) studied the genetics of resistance to C. purpurea in 'Kenya Farmer' and determined that a gene or genes for resistance which influence honeydew production and frequency and size of sclerotia was located on chromosome 6b, but genes on other chromosomes also influenced sclerotium size and honeydew production. Gordon et al (2015) studied the resistance to C. purpurea in the winter wheat line 'Robigus' and identified interacting QTL that influence the size and weight of sclerotia, but the majority of the J.G. Menzies et al Claviceps purpurea and wheat relationships genetic variation affecting sclerotium development was not detectable.…”

Genetic and transcriptional dissection of resistance to Claviceps purpurea in the durum wheat cultivar Greenshank

“…Unpublished work in the groups of Boyd and Gordon has shown Cp to induce significant changes in the expression of wheat genes involved in hormonal pathways, in particular gibberellic acid (GA), ethylene, auxin and jasmonic acid. In addition, two QTL for ergot resistance, (mapped in the hexaploid Robigus × Solstice double haploid population), co-located with the semi-dwarfing alleles at the Rht loci Rht-B1 and Rht-D1, implicating a role of DELLA proteins in Cp infection (Gordon et al 2015). The DELLA proteins are regulated by GA, being degraded via the 26S proteasome SCF complex in the presence of GA (Dill et al 2004).…”

“…In Canada, six Cp isolates, originating from Manitoba, Canada (Table 1), were mixed in equal concentrations in distilled water with one drop of Tween 20 (polyethylene glycol sorbitan monolaurate) per litre, making a final concentration of 10 4 conidia per ml (Menzies 2004). In the UK, a single Canadian Cp isolate, EI4, was used (Table 1), and the Cp inoculum was prepared as described by Gordon et al (2015). Fresh conidia were collected as honeydew and diluted in deionised water to a concentration 10 5 conidia per ml.…”

“…Robigus, located on chromosomes 2A and 4B, and two from cv. Solstice on chromosomes 4D and 6A (Gordon et al 2015), while in cv. Carberry and AC Cadillac, ergot resistance QTL were found on chromosomes 2B, 5A and 6A and chromosomes 2A, 3D, 6B and 7B, respectively (Berraies et al 2019).…”