A sorghum linkage map and predicted response to phenotypic and marker selection for resistance to Striga in sorghum

The genetics of Striga resistance in sorghum has not been clearly demonstrated. Expression of field resistance to Striga appears to be quantitative suggesting the involvement of quantitative trait loci (QTL). However, many of these loci including the one responsible for the production of low germination stimulant (lgs) have not been mapped. The objectives of this study were to (i) construct a molecular map of the sorghum genome and to map the (lgs) gene, (ii) estimate heritability and response to selection of resistance to these two Striga species (iii) estimate genetic correlation between field resistance to these two Striga species (iv) identify and map quantitative trait loci (QTL) involved in resistance to two species of Striga in sorghum (v) compare the efficiency of predicted response to marker-based selection (MBS) and marker-assisted (MAS) selection relative to phenotypic selection for resistance to Striga. A sorghum linkage map based on one 168 RI lines and 236 molecular marker loci was constructed. The population was mapped using RAPDs, RFLPs, I-SSR and SSR markers. The estimated map size was 1628 cM, with an average interval of 9.5 cM between adjacent loci. The lgs gene mapped 11.8 cM from RFLP marker PI0200725. Narrow sense heritability (h2) of field resistance to S. asiatica was estimated at 0.35 and that of resistance to S. hermonthica at 0.24. Predicted response to selection for resistance to the two Striga species was the same. Significant genetic correlation (0.52) was found between resistance to S. hermonthica and S. asiatica. Single marker analysis linking field resistance to marker data detected six QTL for resistance to S. hermonthica and five QTLs for resistance to S. asiatica. QTL detected for resistance accounted for 37% of the variation in resistance to S. hermonthica and 49% of the variation in resistance to S. asiatica. Interval mapping confirmed most of the QTL detected by single marker analysis. Analysis of predicted response to selection indicated that marker-based selection was 24% more efficient in selecting for S. hermonthica and 37% more when selecting for resistance to S. asiatica. Marker-assisted selection was 41% more efficient in selecting for resistance to S. hermonthica and 43% more efficient for selecting resistance to S. asiatica