Bilateral BBSRC-Embrapa: Exploiting natural and induced variation to increase Fusarium head blight and brusone resistance in wheat

Fusarium head blight (FHB) and wheat blast (brusone) are two devastating diseases of wheat that cause major yield losses in Brazil. Both pathogens severely affect wheat heads with direct damage to the grain, both in terms of quality and yield. In the absence of resistant varieties, current disease control relies heavily on fungicides that are costly, non-sustainable for Brazil, and only partially effective.

Brusone, caused by the fungus Magnaporthe oryzae, was first identified in southern Brazil in 1985 but has since spread into Argentina, Bolivia, and Paraguay. The disease can cause total yield loss of yield and in 2009 brusone cut Brazilian wheat production by up to 30%. Importantly, the susceptibility of Brazilian varieties to brusone precludes their cultivation in the Cerrado region, an unused potential of 5 million ha for expansion that would improve Brazilian self-sufficiency of this essential staple.

Fusarium head blight, caused primarily by the fungus Fusarium graminearum, is a serious disease in both Brazil and the UK. In addition to the very significant yield and quality losses, a major concern with FHB is the contamination of grain with trichothecene mycotoxins such as deoxynivalenol (DON). Both the European Union and Brazil have imposed maximum permissible levels for DON in cereals and cereal products. In Brazil, severe FHB outbreaks have increased in frequency. In 2014 FHB was so severe that more than 60% of wheat yield was lost in the State of Rio Grande do Sul and in the western region in 2014 some farmers lost more than 80% to the combination of brusone + FHB.

There is an urgent need to identify and characterise sources of resistance to both FHB and brusone and ensure that the introduction of genes to control one disease does not compromise resistance to the other.

Moderate levels of resistance to brusone have been identified in Brazilian wheat but the genetic basis of this resistance is unclear. Resistance expressed in seedlings is not always expressed in adult plants making it essential that resistance is assessed in adult plants.
Resistance to FHB is generally controlled by several genes of moderate/weak effect that are defined genetically as quantitative trait loci (QTL). Although Brazilian wheat varieties differ widely in their resistance to FHB with some being moderately resistant, no variety was found to possess the major Fhb1 resistance originating from Asian sources. Thus the genetic basis of the most FHB-resistant Brazilian cultivars is not known and suggests that they contain novel resistances that could be combined with those from elsewhere to breed very highly resistant wheat varieties.

This project will use a range of cutting-edge approaches to identify the genetic basis of resistance to brusone and FHB disease. We will identify which parts of the genome contain genes that increase FHB and/or brusone resistance and determine whether increased resistance to one disease is associated with increased susceptibility to the other.

We will also identify genes in wheat that reduce resistance to the two diseases. This will provide a complementary approach to increasing resistance to FHB and brusone in wheat. We will produce DNA markers to enable plant breeders to follow the presence of the beneficial genes in their breeding programmes and ensure that their varieties are highly resistant to both diseases.
The results from this work will benefit plant breeders in Brazil and elsewhere across the world where these diseases are prevalent. This should lead to reduced risk of crop losses to growers and reduced risk to consumers from mycotoxins accumulating in grain. It will lead to a reduced reliance on fungicides to control these diseases which, in turn will benefit, growers and the environment.

The project will employ a range of approaches to identify loci associated with FHB and brusone resistance in Brazilian wheat germplasm. Genome-wide association surveys (GWAS) for FHB and brusone resistance will be performed. Historic data from Embrapa trials will be combined with high density genotyping (Genotyping by Sequencing (GbS) and Illumina 90K iSelect wheat SNP chip analysis) to reveal loci in Brazilian varieties associated with FHB and/or brusone resistance.

Numerous, large-scale field trials will be performed with bi-parental mapping populations of Brazilian wheat varieties to screen for FHB and brusone resistance under high disease pressure. The populations will be genotyped using a 35K wheat SNP array and data used in QTL analysis to locate loci associated with resistance and determine the extent of trade-off between resistance to the two diseases.

High-throughput PCR-based KASP markers will be produced to enable breeders to introduce and follow resistance loci in their breeding programmes.

A TILLING population of a Brazilian variety has been developed within the Pump-Priming project. The population will be screened for FHB and brusone resistance to identify mutants altered in resistance. Exome-capture will be used to identify the mutations present in selected lines and candidate resistance/susceptibility genes identified. Additional exome-capture characterised hexaploid and tetraploid wheat TILLING populations will be screened to identify lines carrying mutations in candidate genes. These lines will also be screened for altered FHB and brusone resistance to establish whether the genes have a role in disease resistance/susceptibility to FHB and/or brusone. Back-crossing of lines from the original Brazilian TILLING population to the parent will also be undertaken to complement this approach to identify the causal genes.

Fusarium head blight (FHB) and brusone diseases are devastating wheat production in Brazil. Currently, disease control relies upon fungicides that are only partially effective, costly and unsustainable for Brazil. Furthermore, risk of brusone disease prevents the development of the Cerrado region for wheat cultivation, an unused potential of 5 million ha of huge potential for Brazilian food security.
This project brings together UK expertise and cutting edge technologies in host genetics and genomics with the knowledge and expertise of Brazilian partners to significantly increase resistance of wheat to these two diseases.

The project will provide knowledge of the resistances to FHB and brusone in Brazilian wheat germplasm. It will reveal how these resistances are distributed across the different pools of germplasm relating to the growing regions of Brazil. This will enable researchers and breeders to combine resistances from different pools. Importantly, the project will reveal which resistances act antagonistically, either through linkage or pleiotropy, and this information is critical for breeders developing varieties for particular environments.

The markers developed to these resistances will enable researchers and plant breeders to combine and pyramid resistances to the two diseases to produce robust durable disease resistant varieties for use across the highly diverse wheat growing environments of Brazil. The ability to reliably produce highly resistant wheat varieties will reduce reliance upon fungicides and benefit both growers and the environment.

The development of varieties highly resistant to FHB will benefit growers, processors and consumers through increased yields and reduced risks posed by mycotoxins accumulating in grain. Thus, this project has the potential to improve food safety for consumers.

The knowledge gained from this project may enable breeders to produce varieties with sufficiently high levels of brusone resistance to permit deployment in the Cerrado region, thereby providing a dramatic increase in the potential area of wheat production in Brazil. These varieties will enable policy makers to decide upon the viability of expanding wheat production in the Cerrado region where brusone has the potential to devastate yields.

The GWAS and TILLING platforms developed in this project will provide new tools to enable researchers to undertake studies to investigate a wide range of other agronomically important traits such as abiotic stress resistance, yield and grain quality in Brazilian wheat.

Knowledge on the FHB and brusone resistance in Brazilian germplasm may assist researchers and breeders across the globe through the ability to combine novel resistances with those currently deployed to increase disease resistance and food safety.

The knowledge and skills developed by the researchers involved in this project will be extremely valuable to all parties involved. UK and Brazilian scientists will exchange knowledge on wheat genetics, host-pathogen interactions, QTL mapping, next generation sequencing, GWAS, exome-capture and TILLING technologies. Furthermore, it is expected that the knowledge gained from this project in relation to genes involved in resistance and susceptibility to these diseases will provide exciting new avenues of research for the future.

This project will involve collaboration between UK and Brazilian researchers on two important diseases of wheat. This bi-lateral collaboration will provide the scientists involved the opportunity to establish networks of contacts that will prove extremely valuable within their future careers.