Quantitative Trait Locus Mapping of Resistance to Turnip Yellows Virus in Brassica rapa and Brassica oleracea and Introgression of These Resistances by Resynthesis Into Allotetraploid Plants for Deployment in Brassica napus
Abstract:Turnip yellows virus (TuYV) is aphid-transmitted and causes considerable yield losses in oilseed rape (OSR, Brassica napus, genome: AACC) and vegetable brassicas. Insecticide control of the aphid vector is limited due to insecticide resistance and the banning of the most effective active ingredients in the EU. There is only one source of TuYV resistance in current commercial OSR varieties, which has been mapped to a single dominant quantitative trait locus (QTL) on chromosome A04. We report the identification,… Show more
“…For example, developing broadspectrum TuYV resistance must include challenging lines with genetically diverse isolates. Studies that have identi ed, characterised and/or created pre-breeding tools for sources of TuYV resistance thus far have used just a single isolate which risks development of less durable strain-speci c resistance [12,29,30,36].…”
Turnip yellows virus (TuYV; family Solemoviridae, genus Polerovirus, species Turnip yellows virus) is a genetically diverse virus that infects a broad range of plant species across the world. Due to its global economic significance, most attention has been given to the impact of TuYV on canola (syn. oilseed rape; Brassica napus). In Australia, a major canola exporting country, TuYV isolates are highly diverse with most variation concentrated in open reading frame 5 (ORF 5) which encodes the readthrough domain (P5) component of the readthrough protein (P3P5) which plays an important role in host adaptation and aphid transmission. When analysing ORF 5, Australian TuYV isolates form three phylogenetic groups with just 45 to 49% aa identity; variants P5-I, P5-II and P5-III. Despite the possible implications for TuYV epidemiology and management, research examining phenotypic differences between TuYV variants is scarce. This study was designed to test the hypothesis that three TuYV isolates, representing each of the Australian P5 variants, differ phenotypically. In particular, the host range, vector species, transmissibility, and virulence of isolates 5414 (P5-I5414), 5509 (P5-II5509) and 5594 (P5-III5594) were examined in a series of glasshouse experiments. Only P5-I5414 readily infected faba bean (Vicia faba), only P5-II5509 infected chickpea (Cicer arietinum), and only P5-I5414 and P5-III5594 infected lettuce (Lactuca sativa). Myzus persicae transmitted each isolate, but Brevicoryne brassicae and Lipaphis pseudobrassicae did not. When using individual M. persicae to inoculate canola seedlings, P5-I5414 had significantly higher transmission rates (82%) than P5-II5509 (62%) and P5-III5594 (59%). As indicated by enzyme-linked immunosorbent assay absorbance values, P5-I5414 reached higher virus titers in canola than P5-II5509 which, in turn, reached higher titers than P5-III5594. P5-I5414 was also more virulent in canola than P5-II5509 and P5-III5594, inducing more severe foliar symptoms, stunting and, in one of two experiments, seed yield loss. Results from this study compared to those of previous studies suggest that analysis of ORF 5 alone is insufficient to assign isolates to coherent strain categories, and further sequencing and phenotyping of field isolates is required.
“…For example, developing broadspectrum TuYV resistance must include challenging lines with genetically diverse isolates. Studies that have identi ed, characterised and/or created pre-breeding tools for sources of TuYV resistance thus far have used just a single isolate which risks development of less durable strain-speci c resistance [12,29,30,36].…”
Turnip yellows virus (TuYV; family Solemoviridae, genus Polerovirus, species Turnip yellows virus) is a genetically diverse virus that infects a broad range of plant species across the world. Due to its global economic significance, most attention has been given to the impact of TuYV on canola (syn. oilseed rape; Brassica napus). In Australia, a major canola exporting country, TuYV isolates are highly diverse with most variation concentrated in open reading frame 5 (ORF 5) which encodes the readthrough domain (P5) component of the readthrough protein (P3P5) which plays an important role in host adaptation and aphid transmission. When analysing ORF 5, Australian TuYV isolates form three phylogenetic groups with just 45 to 49% aa identity; variants P5-I, P5-II and P5-III. Despite the possible implications for TuYV epidemiology and management, research examining phenotypic differences between TuYV variants is scarce. This study was designed to test the hypothesis that three TuYV isolates, representing each of the Australian P5 variants, differ phenotypically. In particular, the host range, vector species, transmissibility, and virulence of isolates 5414 (P5-I5414), 5509 (P5-II5509) and 5594 (P5-III5594) were examined in a series of glasshouse experiments. Only P5-I5414 readily infected faba bean (Vicia faba), only P5-II5509 infected chickpea (Cicer arietinum), and only P5-I5414 and P5-III5594 infected lettuce (Lactuca sativa). Myzus persicae transmitted each isolate, but Brevicoryne brassicae and Lipaphis pseudobrassicae did not. When using individual M. persicae to inoculate canola seedlings, P5-I5414 had significantly higher transmission rates (82%) than P5-II5509 (62%) and P5-III5594 (59%). As indicated by enzyme-linked immunosorbent assay absorbance values, P5-I5414 reached higher virus titers in canola than P5-II5509 which, in turn, reached higher titers than P5-III5594. P5-I5414 was also more virulent in canola than P5-II5509 and P5-III5594, inducing more severe foliar symptoms, stunting and, in one of two experiments, seed yield loss. Results from this study compared to those of previous studies suggest that analysis of ORF 5 alone is insufficient to assign isolates to coherent strain categories, and further sequencing and phenotyping of field isolates is required.
“…Due to the evolutionary history of the Brassica genus, valuable traits of interest already identified in diploid Brassica genomes have the potential to be exploited in amphidiploid Brassica species through modern genetic editing techniques, or via interspecific crossing/resynthesis. This approach was used to great effect when introducing clubroot disease resistance from B. rapa into B. juncea material, wherein natural resistance is not evident ( Hasan and Rahman, 2018 ) and to introduce turnip yellows virus resistance from Brassica oleracea and B. rapa into B. napus ( Greer et al, 2021 ). Potential therefore exists for the generation of enhanced TuMV-resistant B. juncea cultivars using resistances already identified on the “A” genome of other Brassica species via resynthesis.…”
Turnip mosaic virus (TuMV) induces disease in susceptible hosts, notably impacting cultivation of important crop species of the Brassica genus. Few effective plant viral disease management strategies exist with the majority of current approaches aiming to mitigate the virus indirectly through control of aphid vector species. Multiple sources of genetic resistance to TuMV have been identified previously, although the majority are strain-specific and have not been exploited commercially. Here, two Brassica juncea lines (TWBJ14 and TWBJ20) with resistance against important TuMV isolates (UK 1, vVIR24, CDN 1, and GBR 6) representing the most prevalent pathotypes of TuMV (1, 3, 4, and 4, respectively) and known to overcome other sources of resistance, have been identified and characterized. Genetic inheritance of both resistances was determined to be based on a recessive two-gene model. Using both single nucleotide polymorphism (SNP) array and genotyping by sequencing (GBS) methods, quantitative trait loci (QTL) analyses were performed using first backcross (BC1) genetic mapping populations segregating for TuMV resistance. Pairs of statistically significant TuMV resistance-associated QTLs with additive interactive effects were identified on chromosomes A03 and A06 for both TWBJ14 and TWBJ20 material. Complementation testing between these B. juncea lines indicated that one resistance-linked locus was shared. Following established resistance gene nomenclature for recessive TuMV resistance genes, these new resistance-associated loci have been termed retr04 (chromosome A06, TWBJ14, and TWBJ20), retr05 (A03, TWBJ14), and retr06 (A03, TWBJ20). Genotyping by sequencing data investigated in parallel to robust SNP array data was highly suboptimal, with informative data not established for key BC1 parental samples. This necessitated careful consideration and the development of new methods for processing compromised data. Using reductive screening of potential markers according to allelic variation and the recombination observed across BC1 samples genotyped, compromised GBS data was rendered functional with near-equivalent QTL outputs to the SNP array data. The reductive screening strategy employed here offers an alternative to methods relying upon imputation or artificial correction of genotypic data and may prove effective for similar biparental QTL mapping studies.
“…Greer et al (2021) found and mapped new sources of TuYV resistance in B. rapa (ABA15005) and B. oleracea (JWBo12) and proceeded to resynthesise allotetraploid AACC plants (SER19001) through an interspecific cross of the TuYV‐resistant B. rapa and B. oleracea individuals. This was the first report of a B. napus with resistance to TuYV in both the A and C genomes, as well as the first report of a C genome‐associated resistance.…”
Section: The First Example Of Resistance To Tuyv In the Two Diploid B...mentioning
confidence: 99%
“…A resynthesised allotetraploid B. napus was created through the interspecific hybridisation of a resistant B. rapa with a resistant B. oleracea and resynthesised plants were confirmed to contain TuYR3 , TuYR4 , TuYR5 , and TuYR6 . Genome wide LOD thresholds ( α ≤ .05) of 1000 permutations are indicated as dashed horizontal lines. Source : Figure from Greer et al (2021). …”
Section: The First Example Of Resistance To Tuyv In the Two Diploid B...mentioning
confidence: 99%
“…Greer et al (2021) successfully rescued embryos from an interspecific cross between the resistant B. rapa and B. oleracea and after colchicine treatment and selfing, the progeny were confirmed to be allotetraploid AACC. Phenotyping of the resynthesised population (SER19001) showed that the resynthesised line was uniformly resistant, did not show significantly different viral titre from either diploid resistant parent but had a significantly lower titre than that of the susceptible lines used in the diploid mapping.…”
Section: The First Example Of Resistance To Tuyv In the Two Diploid B...mentioning
Turnip yellows virus (TuYV; previously known as beet western yellows virus) causes major diseases of Brassica species worldwide resulting in severe yield‐losses in arable and vegetable crops. It has also been shown to reduce the quality of vegetables, particularly in cabbage where it causes tip burn. Incidences of 100% have been recorded in commercial crops of winter oilseed rape (Brassica napus) and vegetable crops (particularly Brassica oleracea) in Europe. This review summarises the known sources of resistance to TuYV in B. napus (AACC genome), Brassica rapa (AA genome) and B. oleracea (CC genome). It also proposes names for the quantitative trait loci (QTLs) responsible for the resistances, Turnip Yellows virus Resistance (TuYR), that have been mapped to at least the chromosome level in the different Brassica species. There is currently only one known source of resistance deployed commercially (TuYR1). This resistance is said to have originated in B. rapa and was introgressed into the A genome of oilseed rape via hybridisation with B. oleracea to produce allotetraploid (AACC) plants that were then backcrossed into oilseed rape. It has been utilised in the majority of known TuYV‐resistant oilseed rape varieties. This has placed significant selection pressure for resistance‐breaking mutations arising in TuYV. Further QTLs for resistance to TuYV (TuYR2‐TuYR9) have been mapped in the genomes of B. napus, B. rapa and B. oleracea and are described here. QTLs from the latter two species have been introgressed into allotetraploid plants, providing for the first time, combined resistance from both the A and the C genomes for deployment in oilseed rape. Introgression of these new resistances into commercial oilseed rape and vegetable brassicas can be accelerated using the molecular markers that have been developed. The deployment of these resistances should lessen selection pressure for resistance‐breaking isolates of TuYV and thereby prolong the effectiveness of each other and extant resistance.This article is protected by copyright. All rights reserved.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
