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Role of inoculum sources in Rhynchosporium population dynamics and epidemics on barley

Reference	BB/D015200/1
Principal Investigator / Supervisor	Professor Bruce Fitt
Co-Investigators / Co-Supervisors	Professor John Lucas
Institution	Rothamsted Research
Department	Plant Biology & Crop Science
Funding type	Research
Value (£)	392,078
Status	Completed
Type	Research Grant
Start date	03/04/2006
End date	02/04/2010
Duration	48 months

Abstract

Rhynchosporium secalis causes a polycyclic disease (many pathogen generations per season), which is an increasing problem on both winter and spring barley crops in the UK. Rhynchosporium control has been eroded during the last two decades by the ability of R. secalis to break down host resistance genes and to develop resistance to several classes of fungicides. To achieve more sustainable control, a better understanding of factors affecting R. secalis population dynamics is required. New methods to detect and quantify R. secalis DNA during the long symptomless phase early in epidemics now make it possible to study factors affecting R. secalis population dynamics over the whole season. Task 1 will test the hypothesis that seed-borne inoculum of R. secalis plays an important role in the development of rhynchosporium epidemics on barley crops each season. PCR-based assays will be used to monitor the development of R. secalis in different host plant tissues (seed, roots, stem and leaves) at regular intervals throughout the growing season, even in the absence of disease symptoms. To determine whether sexually-produced ascospores might also be a source of infection and variation in the pathogen population, spore samplers will be used to examine potential production of air-borne ascospores in different locations. AFLP fingerprinting will be used to assess the genetic structure of R. secalis populations in relation to location, cultivar (host resistance factors) and inoculum source (e.g. seed, debris). Virulence testing, using the UK Cereal Pathogen Virulence Survey will also provide genetic information about sources. Task 2 will test whether quantification of early symptomless R. secalis (by PCR) can be used to predict rhynchosporium epidemic severity and understand barley cultivar resistance, irrespective of environmental and agronomic factors. Short-term dynamics will be studied using samples from untreated and fungicide-treated plots in commercial trials (different cultivars at >20 locations in England, Scotland, Ireland) at a few specific stages during the growing season. R. secalis population dynamics will be assessed by observing changes with time in amounts of DNA by quantitative PCR. PCR results will be compared with visual assessments on epidemic (symptom) development in the same plots. To better understand relationships between early symptomless and later symptomatic infection, work will be done with genotypes from a mapping population selected as representative of different resistance phenotypes. Task 3 will test hypotheses (e.g. genetic changes in R. secalis populations) to explain the increase in severity of rhynchosporium epidemics since the mid 20th century. Rothamsted has a long-term experiment on continuous cultivation of spring barley since 1852. At the end of each season, leaf/stem material and grain have been archived. This material will also be used to investigate changes in the incidence of R. secalis in leaf and seed samples and to monitor the frequency of specific alleles associated with important traits (e.g. mating type, virulence) over the 150 year period. Results will be compared with available environmental and agronomic data. Task 4 will use the knowledge gained during this project and other related projects to develop guidelines for improved husbandry and deployment of cultivar resistance and fungicides to achieve a more sustainable control of rhynchosporium epidemics.

Summary

Rhynchosporium leaf blotch of barley, caused by the fungus Rhynchosporium secalis, is of increasing importance in world agriculture. It is the most serious disease on winter and spring barley in the UK, causing substantial losses nationally, despite expenditure of £50M per year on fungicides. The disease is difficult to control with fungicides, as the fungus can exist for a long period in the crop without causing symptoms. A severe epidemic may then emerge without warning. The sources of infection responsible for such epidemics are not well understood. We have recently discovered, for instance, that contaminated seed may be an important primary source of the disease. This project aims to clarify the origin and early dynamics of epidemics using molecular techniques (quantitative PCR) that can detect and quantify the DNA of the pathogen in barley plants before symptoms occur. The same techniques can also detect genetic characteristics of the fungus, such as mating type, virulence, and genes responsible for resistance to fungicides. Each season, epidemics will be monitored on both winter (October-sown) and spring (March-sown) barley. Work will also be done on historical spring barley samples archived at Rothamsted over 150 years, and on samples from current crops from at least 10 sites in England, Scotland and Ireland. We aim to study short-term and long-term changes in the pathogen population. Knowledge from this project will be combined with new information from related projects being funded by BBSRC LINK, Defra, HGCA and SEERAD (at ADAS, and in Scotland, SAC and SCRI) to develop guidelines for crop husbandry and agronomic practices to reduce R. secalis population size and genetic variation to achieve sustainable control of rhynchosporium disease of barley.

Committee	Closed Committee - Agri-food (AF)
Research Topics	Crop Science, Microbiology, Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	LINK: Sustainable Arable Production SAPPIO (SAP) [1998-2010]
Funding Scheme	X – not Funded via a specific Funding Scheme

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