Broadening and improving the Turnip yellows virus resistance base in oilseed rape (BITYR)
Oilseed rape (scientific name: Brassica napus)
Oilseed rape is the 3rd most important oil plant in the world after palm and soybean (Sharma et al. 2012). The oil produced from the seed is most commonly used in the production of biodiesels and specialised industrial lubricants but rapeseed oil is also becoming a popular edible oil. The byproduct of oil production, the seed meal, is also used as a protein rich animal feed.
Figure 1: The Triangle of U (Stewart et al. 2003).
Oilseed rape or Brassica napus (AACC) is an amphidiploid species that resulted from the interspecific hybridization of Brassica rapa (AA) and Brassica oleracea (CC) (Fig. 1). Since B. napus shares both the A and C genomes of B. rapa and B. oleracea, respectively, genetic diversity within these relatives can be utilized in oilseed rape breeding.
Turnip yellows virus (TuYV) is a problem
Turnip yellows virus (TuYV, family: Luteoviridae, Genus: Polerovirus) is transmitted by aphids, primarily the peach-potato aphid (Myzus persicae) and can decrease the yield of oilseed rape by as much as 30% in the UK costing the industry up to £69million per year (9% of the crop value) (Nicholls and Stoddart 2014).
A HDC (now AHDB) funded project at the University of Warwick showed that TuYV was also damaging to vegetable brassicas (B. oleracea) with reported yield losses in Brussels sprouts and cabbage of 65% and 30%, respectively (Walsh 2011). TuYV has also been linked to tipburn disorder in stored cabbage (Hunter et al. 2002) which in turn results in an average annual yield loss of 10% in the UK.
TuYV can be symptomless or can cause non-specific symptoms that can be mistaken for plant stress responses to drought or nutrient deficiency (Fig. 2). For this reason, TuYV is hard to diagnose and many brassica growers do not realise they have a problem until harvest.
Figure 2: Oilseed rape (Brassica napus) samples infected with Turnip yellows virus (TuYV). Left: oilseed rape plant showing non-specific symptoms associated with TuYV infection. Right: An oilseed rape leaf heavily infected with TuYV but showing no symtoms (Newbert, unpublished).
Controlling Turnip yellows virus
Insecticide treatments are used to control TuYV by tragetting its aphid vectors. However, strict regulations and bans on insecticide applications and emerging insecticide resistances within aphids have prevented the successful control of TuYV. Consequently, research has been directed towards breeding host genetic resistance to TuYV as this removes the need for heavy insecticide applications, which are damaging to the environment and overcomes the issue of aphid insecticide resistance.
Existing sources of TuYV resistance in oilseed rape
Amalie is a winter oilseed rape variety, bred by Limagrain, which has increased resistance to TuYV compared to other common cultivars. Amalie successfully made the AHDB recommended list in 2015 (AHDB 2015) after showing yield advantages over TuYV-susceptible varieties.
However, the gene(s) responsible for TuYV resistance in Amalie have yet to be identified and the mechanism of resistance is still unknown. Infact, no genes have been implicated in resistance to TuYV or any other viruses of the Luteoviridae family. These uncertanties make it difficult to determine Amalie's effectiveness in controlling TuYV and its durability to resistance breaking.
Broadening and improving TuYV resistance in oilseed rape
As a result of the rapidly evolving nature of TuYV and the availability of only a single commercial resistance source, it is essential to monitor and improve TuYV resistance within oilseed rape to ensure its sustainability.
Sources of TuYV resistance in B. oleracea and B. rapa have already been identified here at the Univeristy of Warwick but they have yet to be characterised and the genes responsible for the resistance identified by genetic mapping. TuYV resistance found in B. oleracea and B. rapa can be deployed in vegetable brassicas by conventional same-species crossing and can also be integrated into oilseed rape using interspecific crossing. Combining TuYV resistance from both the Brassica A and C genome in oilseed rape will produce the first double-layered TuYV resistance that will hopefully be stonger and more durable than single-layered resistances.
My research objectives
- To identify candidate gene(s) responsible for TuYV resistance in commercial oilseed rape varieties.
- To characterise and map novel sources of TuYV resistance in B. oleracea and B. rapa.
- To integrate the novel TuYV resistances found in B. oleracea and B. rapa into B. napus.
- Identify important crop hosts for TuYV.
- Investigate Verticillium longisporum (a fungal pathogen) tolerance in oilseed rape.
AHDB. (2015) AHDB recommended lists for cereals and oilseeds 2016/2017. Retrieved 08.02.2016.
Coleman, A. D. (2014) Control of Turnip yellows virus: Assessing impact on oilseed rape quality traits and dissecting circulative transmission by aphids. Home Grown Cereals Authority, John Innes Centre. Research review: 26: 26-28.
Hunter P J, Jones J E and Walsh J A (2002) Involvement of Beet western yellows virus, Cauliflower mosaic virus, and Turnip mosaic virus in internal disorders of stored white cabbage. Phytopathology 92, 816-826.
Nicholls C and Stoddart H. (2014) Restriction of neonics; restriction on crop protection? Retrieved 10.05.2016
Sharma, M., Gupta, S. K., Mondal, A. K., Yadava, D. K., Vasudev, S., Singh, N., Mohapatra, T. and Prabhu, K. V. (2012) Technological innovations in major world oil crops. Springer New York. Volume 1. Pages 4-7.
Stewart, C. N., Halfhill, M. D. and Warwick, S. I. (2003) Transgene introgression from genetically modified crops to their wild relatives. Nature Reviews Genetics, 4, 806-817.
Walsh J, Richards A, Sharpe C, Kevitt-Jack J, Jones J D G and Mead A (2011) The incidence of Turnip yellows virus (TuYV) in overwintered cauliflower and Brussels sprout and the effect of the virus on yield quality and storage - Phase 1. AHDB. Final report - FV 365.