Award details

Targeting symptomless pathogen growth to control fungal plant diseases

Reference	BB/E001610/1
Principal Investigator / Supervisor	Professor Bruce Fitt
Co-Investigators / Co-Supervisors	Professor Ian Crute, Professor Graham King
Institution	Rothamsted Research
Department	Plant Biology & Crop Science
Funding type	Research
Value (£)	336,070
Status	Completed
Type	Research Grant
Start date	01/01/2007
End date	30/11/2010
Duration	47 months

Abstract

This project will test two hypotheses relating to symptomless growth of plant pathogens in host tissues, using oilseed rape (Brassica napus)/ Leptosphaeria maculans (phoma stem canker disease) as a model host/pathogen system. 1. A crucial component of plant QTL-mediated (quantitative, field) resistance operates against symptomless pathogen growth; 2. Effects of crop fungicides on symptomless pathogen growth are crucial to their control of disease; We will determine the contribution of resistance to symptomless growth as a potential component of QTL associated with race non-specific quantitative resistance identified in reference segregating populations, for which near-isogenic lines with or without the QTL are now available. Timing and effects on pathogen extension growth and pathogen biomass of resistance to symptomless spread will be established in controlled environment experiments by use of GFP-labelled pathogen strains and qPCR detection methods, respectively. We will establish the relationship between the CE data on growth of the pathogen and the resistance phenotype in field trials. Refined phenotype assays will be used to resolve the genetic control of quantitative resistance and loci will be resolved by use of additional recombinants from the reference population. Interactions between fungicide (the triazole fluzilazole) and genetic resistance effects on symptomless spread of L. maculans will be determined in controlled environment and field experiments. Results of these experiments will be used to characterise the quantitative resistance to L.maculans, so that it can be easily exploited in resistance breeding programmes, and determine the effects of fungicides more precisely so that timing of application can be optimised.

Summary

Symptomless pathogen spread in host tissues is a crucial stage in the development of diseases, including most plant diseases. Better understanding of this symptomless spread is essential to devise effective measures for control of such diseases, whether it be through host resistance or application of fungicide sprays. Phoma stem canker is the most important disease of oilseed rape in the world, including the UK. Whilst the pathogen initially infects the leaves, it then grows symptomlessly down their petioles (stalks) to reach plant stems, where the damaging phase of epidemics occurs. Recent evidence suggests that field (quantitative) resistance to the pathogen operates during the symptomless phase of the disease and that treatment of crops with fungicides when infections are symptomless is crucial to effective disease control. The recent development at Rothamsted of pathogen strains expressing the jellyfish green fluorescent protein (GFP) gene and quantitative polymerase chain reaction (qPCR) methods to quantify the biomass of the pathogen in symptomless tissues provides a unique opportunity to investigate the symptomless phase of this disease. Furthermore, these methods can be used on host material recently produced by INRA (Rennes, France) that provides greater genetic resolution of the chromosomal regions containing genes contributing to quantitative resistance. This work, supported as an IPA application by DuPont, who have interests in both crop breeding and fungicides, will aim to answer two questions. 1. Is oilseed rape resistance restricting symptomless growth of the phoma stem canker pathogen down the leaf stalk and into the plant stem the key component of field resistance to the disease? 2. Are current fungicides effective against the pathogen (Leptosphaeria maculans) only if applied before the pathogen causes stem symptoms? This will involve four tasks. Task 1 will address question 1 by comparing results obtained in controlled environment (CE) experiments (GFP, qPCR) on resistance to symptomless spread of the pathogen in leaf stalks with data from field experiments (qPCR, stem canker severity assessed by sampling stems before harvest). Task 2 will address question 1 by comparing results obtained in controlled environment (CE) experiments (GFP, qPCR) on resistance to symptomless spread of the pathogen in plant stems with data from field experiments. Thus it should be possible to determine whether the main component of quantitative resistance occurs during growth down the leaf stalk or during colonisation of stem tissues. Task 3 will investigate the genetic control of resistance to symptomless growth of the pathogen in leaf stalks and plant stems, exploiting results of field and controlled environment experiments in relation to existing and new genetic mapping information. Task 4 will address question 2 by examining interactions between fungicide and genetic resistance effects on symptomless pathogen growth in leaf stalks and plant stems. It will involve CE experiments (GFP) with resistant and susceptible lines. Fungicide applications will be made at different times in relation to inoculation (determined by results of task 2) and the effects on symptomless growth in a number of genetically different host lines observed. CE experiments will be complemented by field experiments with a range of fungicide timings. Results of these experiments will be used to identify and characterise the quantitative resistance to L.maculans, so that it can be easily exploited in resistance breeding programmes. They will also enable timing of fungicide applications to be optimised.

Committee	Closed Committee - Agri-food (AF)
Research Topics	Crop Science, Microbiology, Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	Industrial Partnership Award (IPA)

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