Characterising Barley yellow dwarf virus (BYDV) resistance conferred by the introgression of the gene Bdv2 in wheat cv. RGT Wolverine

Abstract

Barley yellow dwarf virus (BYDV) is an aphid-transmitted pathogen that infects over 150 Poaceae species, including wheat, barley, oats, rice, and maize. Wheat is the most affected crop, with yield losses ranging from 11–33%, but occasionally reaching 80%. Climate change is expected to exacerbate BYDV outbreaks and because of the ban of neonicotinoid seed treatments in the UK, there is an increased need for sustainable control strategies. A promising approach is the deployment of BYDV resistance genes, such as Bdv2, from Thinopyrum intermedium which was introgressed into the commercial variety RGT Wolverine. However, the mechanism underlying Bdv2-mediated resistance remains poorly understood. This PhD project aimed to characterise the resistance conferred by Bdv2 and develop valuable resources/tools for BYDV studies.
A phenotyping protocol for BYDV-PAV resistance was optimised using near-isogenic lines of wheat cv. Skyfall, differing only in the presence (+Bdv2) or absence (–Bdv2) of the resistance locus. Assessment of chlorophyll content, disease severity, growth traits, and viral titre revealed consistent differences between resistant and susceptible lines, leading to a standardised protocol. The results demonstrated that in the varieties RGT Wolverine and Skyfall, Bdv2 confers tolerance rather than true resistance to BYDV-PAV as previously published before this study for other wheat varieties.
An EMS mutagenesis protocol was established for RGT Wolverine to generate a mutant population. A total of 2200 seeds were mutagenised and 744 progressed to the M3 generation where phenotyping was undertaken. Two mutant lines showed BYDV-PAV susceptibility despite retaining the Bdv2 introgression. Whole genome sequencing of one of the BYDV-PAV susceptible mutant line and a non-mutagenised cv. RGT Wolverine was done using the PacBio technology; this represents an invaluable resource to determine the candidate alleles related to BYDV resistance in the future. Whereas, using a short-read Illumina library, two introgressed genomic regions from T. intermedium have so far been identified in RGT Wolverine.
The first UK BYDV whole genome sequence (~5.7 kb) was obtained for the species PAV and used to develop a BYDV infectious clone. Phylogenetic analysis using the UK and the publicly available BYDV-PAV whole genome sequences, revealed a strong geographical clustering of BYDV-PAV isolates, suggesting regional adaptation and cross-continental spread.
Overall, this study provides novel insights into Bdv2-mediated BYDV tolerance in wheat, establishes key genetic and molecular tools, and lays the foundation for future BYDV studies.

Date of Award	20 Jan 2026
Original language	English
Awarding Institution	University of Bristol
Sponsors	RAGT Seeds Ltd
Supervisor	Andy M Bailey (Supervisor), Kim Hammond-Kosack (Supervisor), Christopher Burt (Supervisor) & Lola Gonzalez-Penades (Supervisor)