The Quest for Durable Plant Disease Resistance

Abstract: Recessive strain-specific resistance to a number of plant viruses in the Potyvirus genus (largest genus of plant viruses) has been found to be based on mutations in the eukaryotic translation initiation factor 4E (eIF4E) and its isoform eIF(iso)4E. Potyvirus isolates have been found that overcome most of these resistances. The VPg (viral protein genome-linked) of potyviruses is attached to the 5’ end of the +ve sense ssRNA viral genome and has been shown to bind to eIF4E and / or eIF(iso)4E host plant proteins in yeast two-hybrid assays.

In this talk I will present some of our research on the potyvirus Turnip mosaic virus (TuMV) and our quest for durable resistance to this virus. Following screens of a large number of lines of a number of brassica species, we eventually found broad-spectrum resistance to TuMV in an accession of Chinese cabbage (Brassica rapa var pekinensis). Initial genetic analysis indicated the resistance was controlled by one recessive and one dominant gene. In the absence of whole genome sequence, triplication in the B. rapa genome and the difficulty in transforming this species, identification of the resistance genes was challenging. Transformation of candidates for the recessive allele from a TuMV-susceptible B. rapa line in to a knockout line of Arabidopsis thaliana proved misleading. Eventually we did identify the genes involved in the resistance and the novel mechanism was patented. Syngenta are introgressing the resistance in to commercial plant varieties using marker-assisted selection and anticipate commercial release of F₁ hybrid varieties in 2019. 

The broad-spectrum nature and the mechanism of the resistance indicate that it could be durable. In an attempt to manage the resistance we are working on further sources of broad-spectrum TuMV resistance to reduce the selection pressure for resistance breaking virus isolates.