GENETIC MAPPING OF A RESISTANCE GENE TO NEMATODE Heterodera sacchari IN RICE

¹ CIAT - Biotechnology Unit and Rice Program - AA6713 - CALI - Colombia

² IRD - Rice Genomics Research Unit - BP 64501 - 34394 Montpellier cedex 05 - France

³ IRD - LEST - 32, avenue Henri Varagnat - 93143 Bondy Cedex - France

Inheritance of resistance to cyst nematode (Heterodera sacchari) in Oryza sativa was investigated by inoculation tests with isolate 244 from Congo in segregating populations derived from hybridisation between O. sativa and its African sister cultivated species, O. glaberrima. We found that the resistance was controlled by one major gene, Hsa-1Og, with codominance of susceptible and resistant alleles. To map Hsa-1Og on the rice genome, we pooled the data obtained from segregation of the resistance trait and microsatellite markers in three kinds of progeny: BC1F3, BC1F4, and pseudo-F2 populations. Hsa-1Og was unambiguously located between Cornell University's RM206 and RM254 markers on chromosome 11. Two additional microsatellite markers derived from Monsanto publicly available sequences were found to be tightly linked to the Hsa-1Og gene. It is possible that numerous plant resistances to a pathogen in fact exhibit a codominant inheritance, possibly explaining misleading conclusions in several reports on resistance segregation.