Talukder Zahirul Islam. 2002. Mapping quantitative trait loci for rice blast resistance: stability across fungal isolates and leaf nitrogen environments. Aberdeen : University of Aberdeen, 245 p. Thesis Ph. D. : University of Aberdeen
Encadrement : Pirce, Adam
Résumé : Rice blast disease, caused by the fungal pathogen Magnaporthe grisea, is one of the most devastating diseases of rice in the World. The use of resistant cultivars is the most economical and effective method of controlling the disease. Partial resistance genes are known to play a vital role in the durability of the resistance. Quantitative trait locus (QTL) mapping using DNA markers is an effective approach for studying partial disease résistance, and it also provides a framework for marker assisted selection (MAS) and positional cloning of partial résistance genes. Partial disease résistance conferred by minor genes are known to be non-specific to pathogen races and effective against almost all races of the pathogen. Race non- specificity of partial résistance genes are, therefore, particularly valuable for the construction of MAS breeding programme for the development of durable resistance varieties. Nitrogen fertilization is essential for increased yield particularly in upland rice ecosystem which is often poor in soil nutrient status. However, results of many experiments over a long period have shown that high nitrogen fertilization always induces a heavy incidence of blast disease, suggesting an interaction between nitrogen concentration in leaves and blast résistance. The objective of this study is to address two major questions. Firstly, to what extent are partial resistance QTLs effective against different fungal isolates? Secondly, to what extent are partial résistance QTLs stable under conditions which result in contrasting leaf nitrogen status? Answers to these questions should elucidate the nature of partial resistance genes, characterize their potential value in breeding and identify target regions of the genome useful for the application of marker assisted selection in the production of durably resistant varieties. A population of 100 F6 recombinant inbred (RI) lines produced from a cross between Azucena (a japonica type tropical upland rice from Philippines) and Bala (an indica type upland rice from Eastern India) was evaluated for partial resistance to blast disease in the green house against three diverse sources of fungal isolates, one from the Philippines and two from Africa. A genetic map developed from this population containing 142 molecular markers was used to map main-effect and epistatic QTLs with composite interval mapping. A total of twenty genomic locations on eleven chromosomes where main-effect QTLs for different traits related to partial blast résistance were detected against ail three isolates. The majority of the QTLs appeared as race specific QTLs. At nine genomic regions, QTLs were detected against single isolates. Similarly, at another nine genomic regions, QTLs were detected with two isolates. In only two genomic locations on chromosomes 6 and 12 were QTLs detected against ail three isolates, suggesting that these QTLs are not isolate specific and can be used in MAS breeding programme. There was evidence of epistatic gene interactions in almost all screens. However, no consistent pattern emerged, with different pairwise interactions occuring in each screen. This pattern of epistasis can not, therefore, be used to guide future breeding strategies. The genomic location of certain QTLs were found to coincide with previously mapped blast résistance major genes, resistant gene analogues/homologues and expressed sequence tags (ESTs) with disease resistance gene or defense-response gene like sequences, suggesting that some might be relies of major resistance genes, while others might be defense genes. When plants were grown under contrasting nitrogen feeding regimes, major differences in mean leaf nitrogen content and mean disease severity were observed, in agreement with common observations that high plant nitrogen status increases disease severity. However, no major differences in the location of QTLs for disease severity were observed between these two treatments. This suggests that the increase
Classification Agris : F30 - Génétique et amélioration des plantes
H20 - Maladies des plantes
Auteurs et affiliations
- Talukder Zahirul Islam, University of Aberdeen (GBR)
Autres liens de la publication
Source : Cirad - Agritrop (https://agritrop.cirad.fr/570989/)
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