CONICET | Buscador de Institutos y Recursos Humanos

Soybean Stem Canker (SSC), caused by the fungus Diaporthe phaseolorum var. meridionalis (Dpm) is a very important disease of soybean crops in Argentina. There are at least five known dominant genes in soybean that confer resistance to SSC, Rdm1 to Rdm5. Particularly, the Rdm2 gene was first identified in cv. Tracy-M and then stabilized in JII breeding line. The Rdm4 gene was identified in cv. Hutcheson, linked to Rdm5, defining the Rdm4-5 resistance locus. The objective of this work was to characterize the behavior of Rdm2 and Rdm4-5 resistance loci, segregating in two different susceptible genetic backgrounds, the cv. RA702 and the line J77-339, in the specific interaction with CE109 and CE112 local physiological races of Dpm. The results demonstrated that Rdm2 and the Rdm4-5 locus segregated phenotypically as expected for complete dominant genes, in both susceptible backgrounds, in the specific interactions: Rdm2- CE109, Rdm4-CE109 and Rdm5-CE112. Interestingly, in the specific interaction JII-CE112 the observed segregation fitted well the 1R: 3S ratio, in both susceptible backgrounds, suggesting that in this case, the resistance in JII was determined by a novel and single recessive gene. This is the first discovered gene, with recessive behavior, that confers resistance to Dpm. Also, in each specific interaction the disease progress and the latency period was analyzed in the susceptible individuals. The segregation analysis of the Rdm, and up to now the rdm genes, in different susceptible genetic backgrounds and the study of their behavior in specific interactions with different local races of the pathogen are basic in the selection of proper parental genotypes for breeding programs aimed to incorporate resistance to SSC.