Maximising the potential of Aegilops ventricosa introgression for Pch1 eyespot resistance and increased grain protein in wheat

Lead Research Organisation: John Innes Centre
Department Name: Crop Genetics

Abstract

Eyespot is the most important disease of the stem base of cereals in the UK causing £12-20 million per annum in lost yield, in addition to significant expenditure on fungicides. Only three sources of resistance to eyespot are known to be present in modern wheat cultivars. The most potent of these is the gene Pch1, which originates from a wild grass. This resistance was introduced into wheat by conventional crossing, replacing a large segment of one of the wheat chromosomes with the equivalent portion from the wild grass (so-called 7DV segment). The two other eyespot resistances (Pch2 and QTL5A) both come from the variety Cappelle Desprez but they both have only moderate effects on eyespot resistance.

Wheat varieties carrying the 7DV segment are highly resistant to eyespot and it has also been observed that varieties containing the 7DV segment have a higher grain protein content. Unfortunately varieties carrying this 7DV segment suffer a yield penalty and it is only relatively recently that Pch1 carrying varieties have been developed that also possess high yield potential. We have shown that most of these varieties carry the full size original segment and so it appears that the negative yield effect of the 7DV segment is compensated by other factors in these new varieties.

Efforts to separate the desirable eyespot resistance and protein content traits from the deleterious yield effect have been seriously hindered by two factors: an apparent reduction in recombination between the native wheat chromosome and the 7DV segment and a lack of suitable DNA markers. However, recent advances in marker technology have made it possible to characterise the 7DV segment and identify lines carrying much smaller segments.

In this project we aim to isolate the Pch1 gene and also identify the part of the7DV segment that confers the increased grain protein content. This will enable plant breeders to develop wheat varieties that carry the desirable parts of the 7DV segment (Pch1 eyspot resistance and the part responsible for increased grain protein content) without the undesirable (yield penalty) parts.

Pch1 lies in a region of 7DV that is similar to that of the moderately effective eyespot resistance gene Pch2 from Cappelle Desprez. These two resistances are potentially due to 'sister' genes and we will determine whether this is the case or whether they are in similar but not identical positions.

Technical Summary

The most potent gene for eyespot resistance in modern wheat cultivars is Pch1, which originates from the wheat relative Aegilops ventricosa. This resistance was introduced into wheat by introgression of a chromosomal segment from Ae. ventricosa (7DV segment).

The 7DV segment confers potent eyespot resistance as well as increased grain protein content but varieties carrying this 7DV segment suffer a yield penalty.

Efforts to separate the desirable eyespot resistance and protein content traits from the deleterious yield effect and to locate their relative positions on the 7DV segment have been seriously hindered by two factors: an apparently reduced recombination rate between the native wheat 7D and Ae. ventricosa 7DV regions and a lack of suitable co-dominant DNA markers. However, advances in DNA marker technology have overcome the latter and we have used these to demonstrate recombination within the 7DV segment as a prelude to cloning the Pch1 gene.

Within this project we will exploit the new DNA marker technologies to fine-map the Pch1 locus in a very large population segregating for Pch1. This will be complemented by cytogenetic and mutational approaches to delimit the locus and identify candidate genes for Pch1. Candidates will be validated by transformation into an eyespot susceptible wheat variety.

We will collaborate with plant breeders to phenotype a population of 7DV recombinants to identify the regions of 7DV responsible for increased grain protein content and the the yield penalty.

Pch1 lies in a region of 7DV that is similar to that of the gene Pch2 from Cappelle Desprez located on chromosome 7A of wheat, providing evidence that the two resistances are potentially homoeologues. We will undertake genetic mapping of a large new population segregating for Pch2 and combine this with disease phenotyping to precisely locate the position of Pch2 and establish whether Pch1 and Pch2 are homoeologous.

Planned Impact

Eyespot is the most important disease of the stem base of cereals in the UK causing £12-20 million per annum in lost yield, in addition to significant expenditure on fungicides. Furthermore, impending EU legislation on pesticide application will impact on the availability of chemicals suitable for the control of eyespot making the use of host resistance even more important.

We demonstrated previously that, whereas fungicides provided a yield benefit for varieties highly and moderately susceptible to eyespot, no fungicide application produced a yield benefit in varieties carrying the Pch1 eyespot resistance gene. This demonstrates the potency of this resistance whereby its presence removes the need for fungicide application to control eyespot.

Significantly, eyespot facilitates entry of secondary invaders responsible for brown foot rot (e.g. Fusarium species). This indicates that the deployment of Pch1 would also contribute to control of brown foot rot which is, itself an important inoculum source for Fusairum head blight of wheat.

This project will provide plant breeders with the knowledge and plant materials to develop high yielding winter wheat varieties that do not require fungicide application to control eyespot.

The project will also enable plant breeders to efficiently exploit the potential of the 7DV segment to increase grain protein content in future varieties.

In the longer term, the ability of plant breeders to reliably produce high yielding wheat varieties with potent eyespot resistance will benefit growers who will need to make fewer fungicide applications to achieve maximum profitability.

The project will provide a benchmark for the exploitation of 'alien' introgressed chromosomal segments to separate beneficial from deleterious elements. Such a demonstration will encourage plant breeders to deploy the numerous beneficial traits available in grass species in wheat breeding programmes but which they are currently very reluctant to use because ofthe effects of deleterious linkage drag.

Publications

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Pasquariello M (2017) The eyespot resistance genes Pch1 and Pch2 of wheat are not homoeoloci. in TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik

 
Description Two genes for eyespot resistance are widely used in wheat: Pch1 and Pch2. Previous research suggested that these may be different versions of a similar gene (termed a homoeologue). We have carried out numerous experiments on wheat lines carrying the two genes and found that this is not the case. The two genes lie in different positions on their respective chromosomes.

A physical map has been generated for the region containing Pch1 and candidate genes identified. New research has identified that the region containing Pch1 contains a cluster of genes similar to classical resistance genes. No such cluster is present in this region of the genome in wheat.

The relationship between a perceived yield penalty and grain protein content has been clarified and it has been shown that the Pch1 resistance can be safely used without risking a yield penalty.

Preliminary investigation indicates that Pch1 may not be a single gene but that the resistance is the effect of a number of related and closely linked genes that each has a differential effect on the two fungal species that cause eyespot.
Exploitation Route Our findings can be used by others to guide them towards the grain protein and yield penalty genes to produce markers to follow their presence in wheat breeding programmes.
Sectors Agriculture, Food and Drink

 
Description New DNA markers have been produced to define the regions containing Pch1 and Pch2. These markers are freely available to plant breeders to follow the resistances in their breeding programmes. The demonstration that the Pch1 eyespot resistance gene is located away from the region associated with yield penalty now provides confidence to breeders to use this gene in their breeding programmes without fear of compromising grain yield. DNA markers have been developed to a new eyespot resistance gene that could not previously be tracked in breeding programmes because of a deletion in the region used for tracking. This will potentially provide plant breeders with a new and potent source of eyespot resistance that can be used on both durum and bread wheat.
First Year Of Impact 2016
Sector Agriculture, Food and Drink
Impact Types Economic

 
Description RAGT 
Organisation RAGT Seeds
Country United Kingdom 
Sector Learned Society 
PI Contribution Knowledge of genetics of disease resistance in wheat including new sources of resistance and associated genetic markers
Collaborator Contribution germplasm, DNA marker information, breeder know-how
Impact iCASE PhD studentship and scientific publications
 
Description AHDB Pch1 project 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact The latest findings relating to eyespot resistance of wheat were provided to a panel from AHDB and selected scientists. We have yet to receive formal feedback but the panel were impressed by the progress being made and the potential significance of new resistances.
Year(s) Of Engagement Activity 2018
 
Description AHDB presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Presentation of knowledge on genes controlling eyespot resistance and association with yield penalty and increased grain protein
Year(s) Of Engagement Activity 2014,2015,2016,2017
 
Description Breeder day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Presentations to invited individuals from the wheat breeding and food/feed beverage supply chain
Year(s) Of Engagement Activity 2015,2016,2017
 
Description School teacher education 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact The activity involved a presentation and discussion with school teachers on the importance and relevance of plant disease in a historical and current context. The activity is aimed at providing teachers who are not experts in plant pathology to effectively provide all the relevant information required within the A-level curriculum to their students
Year(s) Of Engagement Activity 2018
 
Description eyespot industry partners 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact informed wheat breeders on genetics of eyespot resistance and candidate resistance genes and potential trade-off between yield and protein content of grain
Year(s) Of Engagement Activity 2015,2016,2017
 
Description school visit 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Delivery of the plant disease and host disease resistance components of the A level curriculum to A'level students. This was delivered alongside a presentation on the impact of plant disease on human civilisation throughout history and efforts to combat disease through plant breeding.
Year(s) Of Engagement Activity 2018