Using genetics, genomics, and diagnostic RenSeq, we demonstrate that the major NB-LRR gene R8 explains the field resistance against potato late blight in the QTL dPI09c
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.
The aim of this study was to increase marker density in a previously identified late blight resistance QTL in a diploid potato population. SSR markers from the reference potato genome sequence were located by e-PCR in the QTL region in the chromosome 9 genetic map of the diploid potato population B3C1HP, and utilized to identify more candidate genes locating between the SSR markers. After verified by PCR and genetic mapping, two SSR markers and two DM candidate genes were mapped in the QTL peak in the maternal genetic map of B3C1HP. The new markers narrowed down the average 2-LOD support interval from 2.6 to 1.4 cM. The new markers on the LOD peak are valuable for fine mapping and positional cloning of the alleles in late blight resistance QTL. This study proves that combination of SSR and e-PCR is an effective way to develop markers in target QTL region.Resumen El objetivo de este estudio era aumentar la densidad de marcadores en un QTL de resistencia a tizón tardío previamente identificado en una población diploide de papa cultivada. Marcadores de SSR de la secuencia del genoma de la papa fueron localizados por e-PCR en la región QTL en el mapa genético del cromosoma 9 del diploide población B3C1HP, y utilizadas para identificar más genes candidatos con la localización entre los marcadores de SSR. Después de verificación por PCR y mapeo genético dos marcadores de SSR y dos genes candidatos DM fueron asignadas en el pico de QTL en el mapa genético de B3C1HP. Los nuevos marcadores redujeron el intervalo medio de soporte 2-LOD de 2.6 a 1.4 cM. Los nuevos marcadores en el pico LOD son valiosos para el mapeo fino y la clonación posicional de los alelos de QTL de resistencia al tizón tardío. Este estudio demuestra que la combinación de SSR y e-PCR es una manera eficaz para desarrollar marcadores en la región QTL.
Tuber shape is one of the most important traits for potato breeding. Since poor or irregular shape increases the difficulty of handling and processing, researching the inheritance of potato tuber shape for potato breeding is highly important. To efficiently identify QTL for tuber shape, a diploid potato population (PM7) was generated by self-pollinated M6 (S. chacoense). A QTL TScha6 for tuber shape was identified by the QTL-seq approach at 50.91-59.93 Mb on chromosome 6 in the potato DM reference genome. To confirm TScha6, four SSR and twenty CAPS markers around the QTL were developed and the TScha6 was narrowed down to an interval of ~ 1.85 Mb. The CAPS marker C6-58.27_665 linked to TScha6 was then used to screen 86 potato cultivars and advanced breeding lines. The tuber length/width (LW) ratio was significantly correlated with the presence/absence of C6-58.27_665, and the correlation coefficient was r = 0.55 (p < 0.01). These results showed that C6-58.27_665 could be applied in marker-assisted selection (MAS) for tuber shape breeding in the future. Our research sets the important stage for the future cloning of the tuber shape gene and utilities of the marker in the breeding program.
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