Abstract
Key message We performed QTL analysis for SCN resistance in PI 437655 in two mapping populations, characterized CNV of Rhg1 through whole-genome resequencing and evaluated the effects of QTL pyramiding to enhance resistance. Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most serious pests of soybean worldwide. PI 437655 has broader resistance to SCN HG types than PI 88788. The objectives of this study were to identify quantitative trait loci (QTL) underlying SCN resistance in PI 437655, and to evaluate the QTL for their contribution to SCN resistance. Two F6:7 recombinant inbred line populations, derived from cv. Williams 82 × PI 437655 and cv. Hutcheson × PI 437655 crosses, were evaluated for resistance to SCN HG types 1.2.5.7 (PA2), 0 (PA3), 1.3.5.6.7 (PA14), and 1.2.3.4.5.6.7 (LY2). The 1,536 SNP array was used to genotype the mapping populations and construct genetic linkage maps. Two significant QTL were consistently mapped on chromosomes (Chr.) 18 and 20 in these two populations. One QTL on Chr. 18, which corresponds to the known Rhg1 locus, contributed resistance to SCN HG types 1.2.5.7, 0, 1.3.5.6.7, and 1.2.3.4.5.6.7 (PA2, PA3, PA14, and LY2, respectively). Copy number variation (CNV) analysis by whole-genome resequencing showed that PI 437655 and PI 88788 had similar CNV at the Rhg1 locus. The QTL on Chr. 20 contributed resistance to SCN HG types 1.3.5.6.7 (PA14) and 1.2.3.4.5.6.7 (LY2). Evaluation of both QTL showed that pyramiding of Rhg1 and the QTL on Chr. 20 significantly improved the resistance to SCN HG types 1.3.5.6.7 (PA14) and 1.2.3.4.5.6.7 (LY2) in both populations. Our studies provided useful information for deploying PI 437655 as a donor for SCN resistance in soybean breeding through marker-assisted selection.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-014-2409-5) contains supplementary material, which is available to authorized users.
Highlights
Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most important pests of soybean [Glycine max (L.) Merr.] worldwide
We found that plant introductions (PIs) 437655 had a lower Female index (FI) for all tested SCN populations and showed broader spectrum resistance to SCN HG types than PI 88788
A likelihood of odds (LOD) threshold score of 3.0 and a maximum genetic distance of 50 cM were used for the initial linkage grouping of markers
Summary
Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most important pests of soybean [Glycine max (L.) Merr.] worldwide. Two QTL, Rhg on Chr. 18 and Rhg on Chr. 8 (Concibido et al 2004), were commonly mapped in various sources of resistance, primarily plant introductions (PIs). These two QTL have been successfully cloned from PI 88788 and cultivar Forrest, respectively (Cook et al 2012; Liu et al 2012). The SCN resistance conferred by Rhg in PI 88788 was found to be controlled by three genes (Cook et al 2012). The alteration of expression level caused by copy number variation (CNV) rather than sequence mutation for these three genes explained the phenotypic differences between susceptible and resistant varieties (Cook et al 2012). Two point mutations in Forrest altered a key regulatory property of this enzyme, which may disturb the folate homeostasis and lead to a nutritional deficiency preventing life of the nematode (Liu et al 2012)
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