Genetic mapping and identification of QTLs involved in the tolerance of rubber tree (Hevea brasiliensis) to Corynespora cassiicola secreted effectors

Tran Dinh Minh, Clément-Demange André, Soumahoro Mouman, Masson Aurélien, Pujade-Renaud Valérie. 2015. Genetic mapping and identification of QTLs involved in the tolerance of rubber tree (Hevea brasiliensis) to Corynespora cassiicola secreted effectors. In : Proceedings International Rubber Conference 2015: Productivity and quality towards a sustainable and profitable natural rubber sector. Le Quang Khoi (ed.). IRRDB, RRIV. Ho Chi Minh City : Agricultural Publishing House, 198-199. ISBN 978-604-60-2156-8 International Rubber Conference 2015, Ho Chi Minh City, Viet Nam, 2 Novembre 2015/3 Novembre 2015.

Résumé : The CLF (Corynespora Leaf Fall) disease caused by the necrotrophic fungus Corynespora cassiicola has gained increasing importance in most areas of rubber cultivation in Asia and West Africa. To avoid developing susceptible varieties, we want to develop a selection program based on a better understanding of the interaction between the parasite and the plant. In a previous study, we purifieda secreted toxin, cassiicolin, from the culture filtrate of an aggressive C. cassicolastrain (CCP, from Philippines). The amino acid sequence and three-dimensional structure of the toxin were described previously.The application of purified cassiicolin or conidial suspension inoculation from the CCP isolate resulted in the same visual symptoms with similar sensitivity profiles, suggesting that cassiicolin is an important effector of C. cassiicola pathogenicity (Barthe et al. , 2007; Breton, Sanier, & d'Auzac, 2000; Deon et al., 2012a; Deon et al., 2014; Deon et al., 20 I 2b ). The construction of genetic linkage maps for cultivated rubber clones (Hevea brasiliensis) has and continues to be an important research goal to facilitate quantitative trait locus (QTL) analysis for use in a marker-assisted selection in breeding (Le Guen et al., 2011; Lespinasse et al., 2000; Pootakham et al., 2015; Prapan et al., 2006; Souza et al., 2013). Our recently published maps were constructed from the cross of cultivated rubber clones, in which isozyme biochemical markers and molecular markers (RFLP, RAPD, AFLP or SSR or SNP) were used. The objective of the present study was to explore a new genetic map in order to identify QTLs of sensibility/tolerance to C. cassiicola secreted effectors. The FI progenies derived from the cross of two cultivated clones PB260 x RR1M600, planted in two trials in Ivory Coast, were genotyped using SSR markers only. Three saturated genetic maps were constructed: one for each site and one consensus map. Eighteen linkage groups corresponding to the eighteen chromosomes of the haploid rubber tree genome were found, with total coverage distances of 2005, 2021 and 2036 cM, for Site 1, Site 2 and the two sites combined respectively, and an average intermarker distance of 6.6, 7.4 and 6.6 cM respectively. By comparison, there were collinear order of the markers and conservation of all collinear linkage groups between the maps. Phenotyping was conducted through a toxicity test on detached leaves, using crude culture filtrate (isolate CCP) or the purified cassiicolin, with measurement of both the necrosis surface and the electrolyte linkage. The conductivity method seems more effective for quantifying early cellular damages generating electrolyte leakage, while the visual symptoms (necrosis surface) may reflect later events (cell disruption). This toxicity test allowed the identification of three quantitative trait loci (QTLs). Interestingly, two common QTLs were detected for the purified cassiicolin and the CCP culture filtrate, demonstrating the important role of cassiicolin in CCP filtrate toxicity. These two QTLs were found on both sites, demonstrating the stability of the genetic factors involved in the response to cassiicolin in different environments. But effectors other than Cas 1 may also exist in the CCP filtrate. Indeed, one supplementary minor QTL was detected for CCP filtrate in Site 2. Surprisingly, this additional effector was not detected in Site I. This could be explained by different environment or sampling effects between the two sites. The percentages of phenotypic variance QTLs explained by the various QTLs in this study are quite low. This could be explained by the genetic complexity of the Hevea brasiliensis species that is highly heterozygous. The sensitivity/tolerance of rubber against Corynespora seems to be controlled by several genes with minor effect.

Classification Agris : F30 - Génétique et amélioration des plantes
H20 - Maladies des plantes

Auteurs et affiliations

• Tran Dinh Minh, CIRAD-BIOS-UMR AGAP (FRA)
• Clément-Demange André, CIRAD-BIOS-UMR AGAP (FRA)
• Soumahoro Mouman, SAPH (CIV)
• Masson Aurélien, SOGB (CIV)
• Pujade-Renaud Valérie, CIRAD-BIOS-UMR AGAP (FRA)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/579204/)

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