Conditional QTL underlying resistance to late blight in a diploid potato population

Abstract

A large number of quantitative trait loci (QTL) for resistance to late blight of potato have been reported with a "conventional" method in which each phenotypic trait reflects the cumulative genetic effects for the duration of the disease process. However, as genes controlling response to disease may have unique contributions with specific temporal features, it is important to consider the phenotype as dynamic. Here, using the net genetic effects evidenced at consecutive time points during disease development, we report the first conditional mapping of QTL underlying late blight resistance in potato under five environments in Peru. Six conditional QTL were mapped, one each on chromosome 2, 7 and 12 and three on chromosome 9. These QTL represent distinct contributions to the phenotypic variation at different stages of disease development. By comparison, when conventional mapping was conducted, only one QTL was detected on chromosome 9. This QTL was the same as one of the conditional QTL. The results imply that conditional QTL reflect genes that function at particular stages during the host-pathogen interaction. The dynamics revealed by conditional QTL mapping could contribute to the understanding of the molecular mechanism of late blight resistance and these QTL could be used to target genes for marker development or manipulation to improve resistance.

SSR and e-PCR Provide a Bridge Between Genetic Map and Genome Sequence of Potato for Marker Development in Target QTL Region

“…The same trait values, i.e., the AUDPCs of late blight evaluated in the five environments for mapping above mentioned QTLs (Li et al 2012), were used for the QTL analysis to validate the new markers in this study.…”

“…The PCR was conducted as described (Li et al 2012) and the PCR products were separated by polyacrylamide gel electrophoresis and detected by silver staining (Han et al 2008). Polymorphic SSR and DM candidate gene markers were integrated into the genetic map of CIP301071.3 using Joinmap® 4 (Van Ooijen 2006) as previously described (Li et al 2012).…”

“…Six markers (STI0014, STM1021, At3g24160f, DMC42152b, DMC42144a and Rpi_svnt1_367) around the 2-LOD support interval of the QTL dPI09c (Li et al 2012) were located in the DM pseudomolecules by reverse e-PCR (Schuler 1997) utilizing the primer sequences detailed by Li et al (2012), and, allowing one mismatch and one gap for each given primer pair. The region in the DM genome corresponding to the QTL dPI09c interval, from 50,807,510 to 52,141,421 bp (basepair) on pseudomolecule of chromosome 9, was then scanned for SSR markers.…”

“…Ninety-six individuals of the original B3C1HP population (Li et al 2012) were used for the marker screening and construction of the new genetic map of the chromosome 9 region of interest. The same trait values, i.e., the AUDPCs of late blight evaluated in the five environments for mapping above mentioned QTLs (Li et al 2012), were used for the QTL analysis to validate the new markers in this study.…”

“…In a diploid population B3C1HP derived from advanced potato germplasm, with the AUDPC (Area Under the Disease Progress Curve) data investigated in five environments in Peru, we previously mapped six QTLs underlying late blight resistance. Among the six QTLs, dPI09c is the most stable and strongest QTL across environments with an average 2-LOD support interval of 2.6 cM on chromosome 9. dPI09c controls late blight resistance that originates from the resistant female parent CIP301071.3 (Li et al 2012). CIP301071.3 combines late blight resistance from native Andean cultivated species S. tuberosum ssp.…”