ARS | Publication request: Interactions Between QTL SAP6 and SU91 on Resistance to Common Bacterial Blight in Red Kidney Bean and Pinto Bean Populations

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 2009
Publication Date: December 8, 2009
Citation: Vandemark, G.J., Fourie, D., Larsen, R.C., Miklas, P.N. 2009. Interactions Between QTL SAP6 and SU91 on Resistance to Common Bacterial Blight in Red Kidney Bean and Pinto Bean Populations. Euphytica. 170:371-381.

Interpretive Summary: Molecular markers that are closely associated with important agronomic traits such as disease resistance are widely used by plant breeders to accelerate breeding progress. Most molecular markers are ‘dominant’ markers, which means that they can only be used to determine if a plant has at least one copy of the gene of interest. Breeders need to be able to identify plants that have two copies of a gene of interest in order to identify parents that breed true for a trait. Common bacterial blight is a severe disease of bean for which resistance is controlled by multiple genes, called ‘Quantitative Trait Loci (QTL)’.We used a pinto bean population and a dark red kidney bean population to determine how two QTL, SAP6 and SU91, interact to cause CBB resistance. We determined that resistance to CBB in these two populations was conferred by the presence of at least a single SU91 QTL and that SAP6 did not appreciably contribute to improved disease resistance. This paper describes a method for simultaneously evaluating plants at the seedling stage for SAP6 and SU91. Plants can be evaluated at the seedling stage, resulting in considerable cost savings per breeding cycle. These results also provide basic information on how different QTL interact to confer disease resistance that can be used to develop more efficient strategies for developing improved varieties.

Technical Abstract: Resistance to common bacterial blight in common bean is a complex trait that is quantitatively inherited. We examined the interaction between two independent QTL, SAP6 and SU91, which condition resistance to CBB.The QTL were studied in a pinto bean F2 population a cross between Othello (sap6 sap6 //su91 su91) x ABCP-8 (SAP6 SAP6//SU91 SU91). Interactions between QTL were also examined in a dark red kidney bean F2 population from a cross between Red Hawk (sap6 sap6 //su91 su91) x USBK CBB-15 (SAP6 SAP6//SU91 SU91).The disease reaction of each F2 was scored at several time points after inoculations. The dominant SCAR markers SAP6 and SU91 were simultaneously genotyped as codominant markers using a multiplex real time PCR assay. In both populations, at each time point plants having genotypes of su91 su91//SAP6 SAP6; su91 su91//SAP6 sap6, and su91 su91//sap6 sap6 were significantly more susceptible to CBB than plants with any of the six other possible genotypes (SU91 -//- -). Very few examples were observed across both populations and all time points in which mean disease reactions were significantly different between any of the six (SU91 -//- -). For both populations, at no time was the mean CBB reaction of SU91 SU91//sap6 sap6 plants significantly different than SU91 SU91//SAP6 SAP6 plants. These results suggest that in these two populations CBB resistance is conditioned by the presence of at least a single copy of the SU91 QTL. Breeders can realize gains in breeding for resistance to CBB by focusing on marker assisted selection for SU91.