title: Detection and validation of stay-green QTL in post-rainy sorghum involving widely adapted cultivar, M35-1 and a popular stay-green genotype B35.
abstract: BACKGROUND
  Sorghum [Sorghum bicolor (L.) Moench] is an important dry-land cereal of the world providing food, fodder, feed and fuel. Stay-green (delayed-leaf senescence) is a key attribute in sorghum determining its adaptation to terminal drought stress. The objective of this study was to validate sorghum stay-green quantitative trait loci (QTL) identified in the past, and to identify new QTL in the genetic background of a post-rainy adapted genotype M35-1.
  
  
  RESULTS
  A genetic linkage map based on 245 F9 Recombinant Inbred Lines (RILs) derived from a cross between M35-1 (more senescent) and B35 (less senescent) with 237 markers consisting of 174 genomic, 60 genic and 3 morphological markers was used. The phenotypic data collected for three consecutive post-rainy crop seasons on the RIL population (M35-1 × B35) was used for QTL analysis. Sixty-one QTL were identified for various measures of stay-green trait and each trait was controlled by one to ten QTL. The phenotypic variation explained by each QTL ranged from 3.8 to 18.7%. Co-localization of QTL for more than five traits was observed on two linkage groups i.e. on SBI-09-3 flanked by S18 and Xgap206 markers and, on SBI-03 flanked by XnhsbSFCILP67 and Xtxp31. QTL identified in this study were stable across environments and corresponded to sorghum stay-green and grain yield QTL reported previously. Of the 60 genic SSRs mapped, 14 were closely linked with QTL for ten traits. A genic marker, XnhsbSFCILP67 (Sb03g028240) encoding Indole-3-acetic acid-amido synthetase GH3.5, was co-located with QTL for GLB, GLM, PGLM and GLAM on SBI-03. Genes underlying key enzymes of chlorophyll metabolism were also found in the stay-green QTL regions.
  
  
  CONCLUSIONS
  We validated important stay-green QTL reported in the past in sorghum and detected new QTL influencing the stay-green related traits consistently. Stg2, Stg3 and StgB were prominent in their expression. Collectively, the QTL/markers identified are likely candidates for subsequent verification for their involvement in stay-green phenotype using NILs and to develop drought tolerant sorghum varieties through marker-assisted breeding for terminal drought tolerance in sorghum.
authors.forename: Nagaraja Reddy
authors.initials: NR
authors.lastname: Rama Reddy
authors.affiliation: Marker-assisted selection Lab, ICAR-Directorate of Sorghum Research (DSR), Rajendranagar, Hyderabad 500 030, India. madhu@sorghum.res.in.
authors.forename: Madhusudhana
authors.initials: M
authors.lastname: Ragimasalawada
authors.forename: Murali Mohan
authors.initials: MM
authors.lastname: Sabbavarapu
authors.forename: Seetharama
authors.initials: S
authors.lastname: Nadoor
authors.forename: Jagannatha Vishnu
authors.initials: JV
authors.lastname: Patil
mesh_terms: D065567:Absorption, Physiological / Q000235:genetics*; D002734:Chlorophyll / Q000378:metabolism; D002874:Chromosome Mapping; D005838:Genotype; D010858:Pigmentation / Q000235:genetics*; D018515:Plant Leaves / Q000378:metabolism; D040641:Quantitative Trait Loci / Q000235:genetics*; D015203:Reproducibility of Results; D045868:Sorghum / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*
chemical_list: D002734:Chlorophyll