Evaluation of QTLs for Shoot Fly (Atherigona soccata) Resistance Component Traits of Seedling Leaf Blade Glossiness and Trichome Density on Sorghum (Sorghum bicolor) Chromosome SBI-10L

Abstract

Shoot fly is a major insect pest of sorghum damaging early crop growth, establishment and productivity. Host plant resistance is an efficient approach to minimize yield losses due to shoot fly infestation. Seedling leaf blade glossiness and trichome density are morphological traits associated with shoot fly resistance. Our objective was to identify and evaluate QTLs for glossiness and trichome density using-i) 1894 F 2 s, ii) a subset of 369 F 2-recombinants, and iii) their derived 369 F 2:3 progenies, from a cross involving introgression lines RSG04008-6 (susceptible)×J2614-11 (resistant). The QTLs were mapped to a 37-72 centimorgan (cM) or 5-15 Mb interval on the long arm of sorghum chromosome 10 (SBI-10L) with flanking markers Xgap001 and Xtxp141. One QTL each for glossiness (QGls10) and trichome density (QTd10) were mapped in marker interval Xgap001-Xnhsbm1044 and Xisep0630-Xtxp141, confirming their loose linkage, for which phenotypic variation accounted for ranged from 2.29 to 11.37 % and LOD values ranged from 2.03 to 24.13, respectively. Average physical map positions for glossiness and trichome density QTLs on SBI-10 from earlier studies were 4 and 2 Mb, which in the present study were reduced to 2 Mb and 800 kb, respectively. Candidate genes Glossy15 (Sb10g025053) and ethylene zinc finger protein (Sb10g027550) falling in support intervals for glossiness and trichome density QTLs, respectively, are discussed. Also we identified a subset of recombinant population that will facilitate further fine mapping of the leaf blade glossiness and trichome density QTLs on SBI-10.

Fine-Mapping of Sorghum Stay-Green QTL on Chromosome10 Revealed Genes Associated with Delayed Senescence

“…S9_58757394 ( Sobic.009G253700 ) was annotated as similar to the putative uncharacterized protein, and S9_58295230 was present in the intergenic region. SBI-01 and SBI-09 MTAs did not overlap with Haussmann et al [ 21 ] stay-green QTLs [ 3 ]; nor were the candidate genes’ annotations relevant to any stay-green mechanism.…”

“…The stay-green QTLs on SBI-10 with flanking Xgap001 and Xtxp141 SSR markers were overlapped with the shoot fly resistance QTLs, between the same flanking SSR markers. For better coverage, additional SSRs viz., Is10253, and Xisep1011 were added to capture complete QTL regions, and these flanking markers were utilized in the present study ( Figure 1 ) [ 21 ]. The initial QTL interval reported by Haussmann et al (2002) was 37 cM [ 3 ], which was extended to 72 cM, with additional SSRs mapping as explained above.…”

“…This increased the ability to detect and map recombination events in the relatively large QTL interval, which in turn resulted in the identification of additional QTL (clusters), indicating the involvement of several gene complexes in the regulation of stay-green expression. The experimental design was carried on NIL parents RSG04008-6, a stay-green donor for the stay-green QTLs on sorghum chromosome SBI-10, and the other parent J2614-11 is a shoot fly resistant QTL donor on SBI-10, which overlaps with the stay-green region [ 21 ]. The parents and the population segregated for the overall stay-green expression (including the target region) in this study, focused on the known major QTL on SBI-10L.…”

“…An integrated linkage map with 8 SSR markers for the target flanking region (with 72cM interval with SSRs) was constructed with 152 selfed F 2:4 individuals, with mostly homozygous step introgressions [ 21 ] covering the target region. Allele calls for 8 SSRs and 1515 GBS–SNPs were compared across the parents (RSG04008-6 and J2614-11) and grandparents (E36-1, R16, IS18551, and BTx623) of the population.…”

“…The F 2 population was initially screened with 5 SSRs, across the target QTL interval, including Xgap001 and Xtxp141 SSRs ( Figure 1 A). For better coverage and detecting the possible recombination in the complete stay-green QTL region, three additional SSRs were screened across the complete F 2 population [ 21 ]. Based on the recombination events between target SSRs covering the homozygote recombination events for every interval, a sub-set of 152 F 2 genotypes were selected for population advancement and genotyping (GBS) ( Figure 1 B).…”