Genomic regions influencing resistance to the parasitic weed Striga hermonthica in two recombinant inbred populations of sorghum

Abstract

Molecular markers for resistance of sorghum to the hemi-parasitic weed Striga hermonthica were mapped in two recombinant inbred populations (RIP-1, and -2) of F(3:5) lines developed from the crosses IS9830 x E36-1 (1) and N13 x E36-1 (2). The resistant parental lines were IS9830 and N13; the former is characterized by a low stimulation of striga seed germination, the latter by "mechanical" resistance. The genetic maps of RIP-1 and RIP-2 spanned 1,498 cM and 1,599 cM, respectively, with 137 and 157 markers distributed over 11 linkage groups. To evaluate striga resistance, we divided each RIP into set 1 (116 lines tested in 1997) and set 2 (110 lines evaluated in 1998). Field trials were conducted in five environments per year in Mali and Kenya. Heritability estimates for area under the striga number progress curve (ASNPC) in sets 1 and 2 were respectively 0.66 and 0.74 in RIP-1 0.81 and 0.82 in RIP-2. Across sites, composite interval mapping detected 11 QTL (quantitative trait loci) and nine QTL in sets 1 and 2 of RIP-1, explaining 77% and 80% of the genetic variance for ASNPC, respectively. The most significant RIP-1 QTL corresponded to the major-gene locus lgs (low stimulation of striga seed germination) in linkage group I. In RIP-2, 11 QTL and nine QTL explained 79% and 82% of the genetic variance for ASNPC in sets 1 and 2, respectively. Five QTL were common to both sets of each RIP, wtih the resistance alleles deriving from IS9830 or N13. Since their effects were validated across environments, years and independent RIP samples, these QTL are excellent candidates for marker-assisted selection.

Genotypic Variation for Low Striga Germination Stimulation in Sorghum “<i>Sorghum bicolor</i> (L.) Moench” Landraces from Eritrea

“…These accessions may be useful potential sources of resistance to Striga as such or in a backcross breeding program. It would be interesting to confirm whether the mechanical type of Striga resistance that has been mapped using Quantitative Trait Loci (QTL) and reported elsewhere [10] would be found in genotypes with low stimulants production. In order to consolidate this resistance, these accessions of low stimulant production could be crossed with the already identified backcrosses with intro-gressed Striga resistance QTL from a previous study [6].…”

“…Several mechanisms of resistance to Striga in sorghum have been reported that probably operate singly or in various combinations [9] [10]. Using in-vitro laboratory techniques, four specific mechanisms of resistance to Striga which included low production of germination stimulant, low production of the haustoria initiation factor, hypersensi-tive response, and incompatible response were reported in cultivated sorghums and some wild accessions [5] [11].…”

Striga

“…QTL mapping for Striga resistance has resulted in identification of many genes/QTLs spread across the genome. Haussmann et al (2004) mapped several QTLs for Striga resistance in sorghum and reported 9 and 11 QTLs explaining respectively 77% and 82% of the phenotypic variation in a recombinant inbred line (RIL) population. The most significant QTL has been identified to correspond to the major gene locus lgs, which was recently fine-mapped on the chromosome 5 (Satish et al, 2012).…”

First products of DNA marker-assisted selection in sorghum released for cultivation by farmers in sub-saharan Africa

“…The invention of molecular markers has enhanced the effectiveness of breeding for resistance. Five genomic regions (QTLs) with linked markers associated with Striga resistance were mapped in sorghum variety N13 by [10]. In this study, to increase the efficiency of marker-assisted selection (MAS), 27 EST-SSR markers in close association with Striga resistance QTLs were also identified and mapped.…”

“…In the past, five QTLs underlying different Striga resistant phenotypes and molecular SSR markers associated with specific region have been identified and assigned to their specific chromosomal location [10]. These regions and associated SSR markers have been used in advanced backcross populations allowing exploitation of diverse resistance sources [20].…”