Developing genetics and genomics interface to develop strategies for sustainable use of resistance to white rust in oilseed mustard (Brassica juncea)

Oilseed crops are important for the economy and health of people living throughout south Asia. In India, for example, annual imports of edible oil are a staggering 50% of the national consumption, costing of over £ 3.6 billion. The national average dietary intake of fat/oil in India is 9kg/person/year (kpy). In rural India, the intake is 1-7 kpy, which is well below the minimum nutritional recommendation of 14 kpy.
White blister rust caused by the oomycete Albugo candida is one of the most important diseases of oilseed mustard and other vegetable brassicas globally. The pathogen can infect all above-ground parts of the plant, but causes the most severe damage as systemic infections of the inflorescence leading to staghead formation. The disease causes yield losses in oilseed mustard of 20-60% in India, Canada and Australia. With the development of canola quality B. juncea, many countries like Australia and Canada are growing B. juncea more extensively as a crop that is better suited for areas with low rainfall than oilseed rape. However, white rust susceptibility is a major concern, so development of new B. juncea varieties that combine durable white rust resistance and drought tolerance is needed to improve productivity in south Asia and to expand global production of this important oilseed crop.
The integrated use of pathology and molecular genetics can provide an evidence-based strategy for assembling gene combinations around specific broad spectrum R-genes, and ultimately achieve sustainable disease control via anticipatory breeding of new resistant crop cultivars. This strategy is theoretically possible in any crop, including Indian mustard. However, molecular identification of matching host and pathogen determinants (R and AVR genes, respectively) are rate-limiting but nevertheless required to enable whole-genome selection of optimal gene combinations along with other essential traits.
The proposed Indo-UK partnership has a unique opportunity to lead in this research of global importance to food security. This will be achieved by harnessing genomics and bioinformatics tools to extend the on-going efforts towards anticipatory breeding of disease resistance, for sustainable control of white rust in brassicas, and specifically for development of B. juncea varieties that will be adapted for cultivation in India. To date, deployment of the state-of-art genomic approaches for combating white blister rust has been minimal in India and the UK. Similarly, efforts have not yet been initiated to characterize the genome level diversity of the pathogen population. The proposed project is therefore a major opportunity to establish coordinated capability in the genomic characterization of both host and pathogen, which will extend the approaches currently being used in India towards more effective breeding and disease management strategies.
Primary outputs will be aimed at efficient identification of genes that control white blister rust in brassicas. To achieve this, three project objectives will exploit examples of white rust resistance that have already been identified in primary and secondary gene pools, and in the wild relative Arabidopsis thaliana, to enable precise genotyping of resistance in seedlings for marker-assisted breeding of R-gene combinations, and to evaluate transgenic methods for developing sustainable white rust control in B. juncea cultivars of Indian mustard.
A complementary pathology aim will advance capability of using pathogen-based information for evaluating the potential durability of targeted disease resistance genes in optimal combinations for use in Indian mustard varieties of B. juncea. Two project objectives will capitalise on the latest genomic resources available in Albugo, to define the pathotype variability of A. candida in India and to assess the potential emergence of variants that could overcome individual white rust resistance genes.

White blister rust (Albugo candida) is one of the most important diseases of oilseed mustard. The disease causes yield losses of 20-60% in India, Canada and Australia. With the development of canola quality B. juncea, many countries like Australia and Canada are growing B. juncea more extensively as a crop that is better suited for areas with low rainfall than oilseed rape. Development of new B. juncea varieties that combine white rust resistance and drought tolerance is therefore needed to improve productivity in south Asia and elsewhere. The integrated use of pathology and molecular genetics can provide an evidence-based strategy for assembling gene combinations, and ultimately achieve sustainable disease control via anticipatory breeding of new resistant crop cultivars. Molecular identification of matching host and pathogen determinants is rate-limiting but nevertheless required to enable whole-genome selection of optimal gene combinations along with other essential traits.
The proposed Indo-UK partnership will lead in this research of global importance, by harnessing genomics and bioinformatics tools to extend efforts towards anticipatory breeding of white rust resistance in brassicas, and specifically for development of B. juncea varieties that will be adapted for cultivation in India. Primary outputs will be aimed at efficient identification of genes that control white rust. To achieve this, the project will exploit examples of white rust resistance that have already been identified in primary and secondary gene pools, and in Arabidopsis thaliana, to enable genotyping of resistance in seedlings for marker-assisted breeding of R-gene combinations, and to evaluate transgenic methods for white rust control in cultivars of Indian mustard. A pathology aim will advance capability of using pathogen-based information for evaluating the potential durability of targeted disease resistance genes in optimal combinations.

The proposed research will directly underpin the future sustainability of oilseed production in the Indian sub-continent by addressing the reduction of major crop losses due to biotic interactions. Oilseed crops are important for the economy and health of people living in throughout south Asia, as a multi-purpose crop including seeds for edible oil, leaves as a vegetable and for animal fodder, and the dried stems as domestic biofuel. Rapeseed-mustard crops comprise more than one third of the home-grown vegetable oil production in India and covers around 7.0 million hectares. B. juncea occupies more than 80% of this area. Smallholding, resource poor farmers produce most of the crop, and will be direct beneficiaries, with current average seed production of less than 0.4 tonne/ha compared with a yield potential of 2.5-3.0 tons/ha.
White blister rust is a major disease constraint on production, causing yield losses of at least 20-60% in India, Canada and Australia. Durable disease resistance would improve incomes of smallholding resource poor dry-land farmers, by stabilising mustard yields, and as a consequence boosting rural economy and enhancing nutrition of the poorest people in the Indian subcontinent. Thus, the combined aim of our Indo-UK partnership will be to genetically improve cultivars already adapted for low input production in India, particularly in the rainfed areas, as the duration of the crop is relatively short and has low water requirement compared to other crops. The white rust resistance genes will be introduced into hybrids that have been developed at Delhi University, which will already contain other useful seed quality and yield improvements. Similarly, characterization of white rust resistance will also help research programme in UK dealing with vegetable brassicas, and also with the development of canola quality B. juncea for production in dry regions of Canada and Australia.
No international institute currently coordinates research on oilseed brassica crops globally. The proposed Indo-UK partnership, however, will assemble a highly complementary team of crop scientists who will build significantly on previous DFID investment in oilseed brassica production in India, and translation of BBSRC and European Research Council investment in pathogen genomics and molecular genetics of disease resistance from Arabidopsis into brassica crops. The research partners will use knowledge gained from their coordinated effort to advance links with existing links with colleagues and research programmes in Canada, Australia and elsewhere in Asia.
Exchange visits will take place to enable research staff in both countries to develop an active and productive collaboration. This will include UK scientists visiting India in Year 1 for a project meeting and visit to field production sites; and in Year 3 for a knowledge transfer workshop. Indian scientists will visit the UK for training periods, including two PhD students from DU who will each visit for 6 months (one in Year 1 for pathology; and one in Year 2 for gene cloning and pathogen genomics), and two research scientists from AUUP and GBPUAT in Year 1 for pathology. Staff from both India and the UK will also attend the 14th International Rapeseed Congress in Saskatoon, Canada in Year 2, to jointly present results from the Indo-UK partnership to an international audience.
Knowledge gained from fundamental and strategic science will be published in international refereed journals and disseminated at international and regional conferences. The future translation of this knowledge into breeding programmes will be via the National Agricultural Research Systems of India, Pakistan, Nepal, Bhutan and Bangladesh. This will be facilitated by existing interactions amongst South Asian countries.