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.

Figure 1

Genetic linkage map of sorghum showing 61 QTL identified for the grain yield and nine stay-green traits in M35-1 xB35 RIL mapping population. The useful alleles contributed for the traits by M35-1parent are represented by “asterisk” in the QTL name. The length of the vertical bars indicates 1-LOD support interval. Maximum LOD for each QTL is indicated as a beak on the bar which shows QTL position.

Figure 2

Co-location of QTL for stay-green and genes controlling chlorophyll metabolism. SPADB: SPAD values at Booting, SPADM: SPAD values at maturity, GLB: Green leaves at booting, GLM: Green leaves at maturity, PGLM: Percent green leaves retained at maturity, GLAB: Green leaf area at booting, GLAM: Green leaf area at maturity, PGLAM: Per cent green leaf area at maturity, RLS: Rate of leaf senescence, GY: Grain yield per panicle. A. Enzymes involved in Chlorophyll Biosynthesis. B. Enzymes involved in Chlorophyll degradation.