••• Project Information

TITLE OF THE PROJECT :

Exploring the genetic diversity of rice-blast host-pathogen interactions in China : a tool to improve breeding for resistance to blast disease
Acronym of the project : RESIDIV
Type of contract : shared cost RTD
Contract number : ICA4-CT-2000-30021
Starting date : 01/10/00
Ending date : 31/12/03
Projet coordinator :
Didier THARREAU
CIRAD, TA A-54 / K, 34398 Montpellier Cedex 5, France
Telephone : (33) 4 99 62 48 39
Telefax : (33) 4 99 62 48 48
E-mail address : tharreau@cirad.fr
Key words : Rice, Magnaporthe grisea, resistance, avirulence, China



OBJECTIVES :

The objective of the RESIDIV project is to identify and characterize genes conferring resistance to blast disease (caused by the fungus Magnaporthe grisea) in Chinese rice varieties. Chinese traditional rice varieties have a large biodiversity and characterization of this material should lead to the identification of new resistance genes. The project aims at improving our knowledge of resistance diversity in Chinese rice varieties and of the diversity of the pathogen in its ability to attack resistant varieties (avirulence/virulence). This knowledge will be of important value for breeders to introduce the appropriate resistance genes by classical methods or by marker assisted selection to obtain durable resistance. The results of the RESIDIV project will be exploited through conventional breeding methods using natural defence systems.


ACTIVITIES :

- WP1 Characterization of Chinese rice varieties resistance spectrum to Chinese blast isolates
The aim of WP1 is to explore the diversity of resistance genes in Chinese rice varieties through inoculation with chosen isolates and to compare the observed reaction patterns with reaction patterns of differential varieties with known resistance genes.
The detailed objectives are :
1. Definition of a working collection of Chinese and international differential rice varieties
2. Characterization of the resistance spectrum to blast by inoculation of these rice varieties with isolates of the pathogen
3. Definition of groups of varieties showing the same pattern of reaction to the isolates
4. Comparison of these patterns with patterns of varieties containing known resistance genes

- WP2 Identification of blast avirulence genes and of corresponding rice resistance genes
The aim of WP2 is to use crosses between isolates of Magnaporthe grisea to identify avirulence genes and to find molecular markers tightly linked to these genes. These crosses will then be used to identify resistance genes in Chinese varieties and to facilitate WP3.
The detailed objectives are :
1. Achievement of crosses between isolates of the fungus
2. Genetic study of avirulence of several Chinese blast isolates by inoculation of blast progeny from several crosses between these isolates
3. Characterization of resistance gene diversity and distribution
4. Comparison of resistance genes in Chinese varieties with known resistance genes
5. Identification of molecular markers linked to the avirulence genes and construction of genetic maps of crosses to prepare cloning of these genes.

- WP3 Molecular characterization of avirulence gene alleles in Chinese populations of the rice blast fungus : Evolution of avirulence genes in relation to the durability of resistance in rice
The aim of WP3 is to clone new avirulence genes present in Chinese populations of the rice blast fungus in order to characterize the diversity at these loci. WP3 will focus on avirulence genes either already cloned by partner 1 and 2 (Avr-Irat7) or identified in WP2. PCR strategies will be used to survey the molecular diversity at these avirulence gene loci. Alleles conferring either avirulence or virulence will be compared at the nucleotide level to reconstruct their evolution. PCR markers will be developed to estimate the frequency of these different alleles in Chinese populations. These data will be useful to predict the occurrence of virulent races and evaluate the durability of the corresponding resistance genes. The detailed objectives are :
1. Positional cloning of avirulence genes mapped in WP2
2. Survey and characterization of alleles at avirulence loci
3. Analysis of the diversity at avirulence loci in the Chinese Rice Blast Fungus populations

- WP4 Genetics of resistance of Chinese rice varieties
The aim of WP4 is to use different rice populations with available genetic maps to identify positions of the resistance genes with different responses to different isolates, and to define the identities of these genes. It will be valuable for the evaluation of the diversity and distribution of the resistance genes for blast (RGBs) in China and for the breeding of new rice varieties with broad resistance spectrum by marker assisted selection. The detailed objectives are :
1. Characterization of RGB distribution in the parents of rice mapping populations
2. Genetic study of RGBs in different populations
3. Identification of the resistance gene loci corresponding to different Chinese isolates in different mapping populations
4. Identification of new RGBs by comparison of the RGB loci with the mapping positions of known resistance genes
5. Identification of molecular markers closely linked to RGBs.


MILESTONES AND EXPECTED RESULTS :

- Milestones WP1
Define a working collection of Chinese rice varieties and a set of Magnaporthe grisea isolates with a wide genetic basis.
Characterize the resistance gene diversity in Chinese varieties by use of a set of isolates with different virulence spectra.
Identify resistance genes in Chinese varieties through comparison with resistance spectrum of varieties with known resistance genes.

- Milestones WP2
Use the hybridization potential of the rice blast fungus to generate progeny with different and known avirulence genotypes.
Identify and characterize resistance genes in Chinese varieties with rice blast progeny of crosses.
Genetic mapping and identification of tightly linked markers to avirulence genes of the blast fungus.

- Milestones WP3
Analyse the polymorphism at avr1-Irat7 locus loci in Chinese Rice Blast Populations.
Clone and characterize new avirulence genes from Chinese Rice Blast Populations.
Design primers to survey the polymorphism at these new loci in Chinese Rice Blast Populations.

- Milestones WP4
Map resistance genes to blast in different populations.
Compare newly mapped resistance gene position with positions of known resistance genes.
Provide molecular markers closely linked to resistance genes to facilitate marker-assisted.


BENEFITS AND BENEFICIARIES :

The outcomes of the project are an extensive characterization of resistance gene diversity in Chinese rice varieties, the identification of new resistance genes, and the characterisation of avirulence gene diversity in the Chinese populations of the pathogen. The information provided by the project will be of real importance and easily exploited in resistance breeding. First, results obtained during the project will provide strategic information on the isolates to be used to characterization the resistance of Chinese rice varieties. Second, the project will provide a rather complete characterization of resistance genes in Chinese varieties, allowing breeders to improve the choice of resistance donor parents for crosses. Third, the mapping of resistance gene will provide molecular markers closely linked to these resistance genes, preparing the way for Marker Assisted Selection. Finally, the characterization of genetic diversity of avirulence in the fungal population will provide important information on the best way to utilize the resistance gene identify and on the way to combine them to create varieties with durable resistance.