The Genetic Control of Resistance to Turnip Mosaic Virus (TuMv) and Turnip Yellows Virus (TuYv) in Brassica

Turnip mosaic virus (TuMV) and Turnip yellows virus (TuYV) detrimentally affect cultivated plant species of high socioeconomic importance. Both plant viruses cause losses through diminished harvest yields and quality of produce worldwide. They particularly impact species of the Brassica genus. Few viral disease management strategies exist, and most are considered neither viable nor durable for long-term protection of important brassica crops. Genetic sources of resistance against TuMV and TuYV have been identified previously, although remain unexploited. Through the development of these resistance sources, use of various genotyping strategies, linkage mapping approaches and quantitative trait loci (QTL) analyses, genomic regions associated with TuYV and TuMV resistances have been defined here. In Brassica juncea, pairs of significant QTLs for two sources of recessive TuMV resistance have been elucidated. Complementation testing of these resistances indicated one resistance gene is shared by the two plant lines investigated. Three Brassica rapa TuMV resistance mapping populations have also been generated. These sources of TuMV resistance proved effective against isolates of TuMV known to overcome most current major sources of resistance; this germplasm represents valuable and highly sought after broad-spectrum TuMV resistance. In Brassica oleracea, a major and a minor QTL accounting together for 46.3% of quantitative TuYV resistance with QTL intervals of 24.2cM and 6cM, respectively, were identified using just 93 first backcross plants. A robust marker loci-filtering strategy has also been developed here. Based upon successive filtering without the need to employ standard measures of marker quality (such as read depth for sequencingbased genotyping), or imputation and correction of genotypic data, unreliable genotyping by sequencing data was rendered useful where conventional filtering strategies could not achieve this. B. oleracea genome-editing (GE) using the CRISPR/Cas9 system to induce TuMV resistance was also explored; edits were introduced but appeared to be lethal, highlighting potential challenges for future GE.