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Genetic (QTL) mapping approach revealed unexpected patterns of bypassed and sustainable resistances to Microcyclus ulei in rubber tree (Hevea spp.).

Seguin M., Garcia D., Mattos C.R.R., Doare F., Le Guen V.. 2012. In : INRA MetaProgramme SMaCH. Scientific programme and abstracts of the Plant Resistance Sustainability International Conférence 2012, La Colle-sur-Loup, France, 16-19 octobre 2012. s.l. : s.n., p. 88-88. Plant Resistance Sustainability International Conférence 2012, 2012-10-16/2012-10-19, La Colle-sur-Loup (France).

The South American Leaf Blight (SALB), due to the Ascomycota Microcyclus ulei, threatens the world production of natural rubber, based on the cultivation of nearly only one species: the tropical tree Hevea brasiliensis. In connection with a breeding program, conducted in Brazil by Michelin and Cirad and aiming to create resistant cultivars of rubber tree, we analysed the genetic determinism of 3 sources of natural resistance to SALB. We developed a classical approach of QTL mapping on 5 segregating populations issued from crosses implying 3 resistant Hevea accessions, showing contrasting type of resistance: partial or complete, bypassed or sustainable. Disease resistance of the progenies was assessed under natural infestation in field trials, in Brazil and French Guyana, or under controlled inoculations with isolated strains of Microcyclus ulei. Genetic mapping revealed unexpected genetic determinisms underlying the observed resistances: whereas a complex genetic determinism implying major resistance genes and several minor QTLs can be bypassed by the pathogen (Le Guen et al. 2007), a durable partial resistance appeared to be governed by only 2 major resistance loci (Le Guen et al. 2011). These original results constitute a favorable context for a marker?aided selection of cultivars combining high latex yield and SALB tolerance.

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