Qtl mapping and phenotypic evaluation of qtl introgression lines for stay-green traits in sorghum (sorghum biocolor (l.) monech)
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Date
2018-02-09
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Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani
Abstract
The progress in genetic improvement of post-rainy sorghum for drought tolerance using traditional plant breeding practices has been slow, and selection has not been much effective due to complex interaction between genotype and environment. Identification of genetic factors involved in stay-green through molecular breeding approaches would provide the basis for genetic improvement for drought tolerance. In this experiment stay-green QTLs were mapped and the effect of environment on stay-green expression was observed. For this a sorghum Recombinant Inbred Line (RIL) population was field evaluated for 2 years during the post-rainy season of 2011 and 2012, under two water regimes, (stress and control). A set of 200 entries, including 180 RILs, parents and checks were sown in a plot of 2 rows of 2m in RCBD design with 3 and 2 replications for stress and control treatments, respectively. Data was recorded for percent green leaf area (%GLA) with a weekly interval basis (7 counts) with starting from 50% flowering till physiological maturity and agronomic traits. This reveals significant genotypic variances along with high heritability. A genetic linkage map based on 176 RILs with 271 markers consisting of SSRs, DArT and two qualitative traits was developed.
For the staygreen weekly scores traits, co-mapped QTLs were identified for %GLA at 14, 21, 28, 35, 42 and 56 (DAF) days after flowering (between markers isep0843 and sb 19216) on SBI-03. All these QTL exhibited a positive additive effect indicating complementary relationships between these pairs oftraits. The staygreen trait %GLA at 21 and 42 DAF was co-mapped with the trait hundred grain mass on SBI-03 (between the markers sb15076 and isep0843).On the SBI-07 (between the markers isep0805 and sb 16413) co-mapped QTLs for %GLA at 14, 21, 28, 35, 42, 49 and 56 DAF were identified. All these QTLs exhibited negative additive effects. On the same linkage group (SBI-07), co-mapped QTLs were identified for the traits, plant height, fresh and dry stover weight, biomass and vegetative growth index (between the markers sb17056 and sb 18227), all the QTLs with positive additive effect. On SBI-06, staygreen traits, %GLA at 14, 21 and 42 DAF were co-mapped with the days to 50% flowering, time to grain physiological maturity, fresh stover weight per plot and harvest index (between the markers sb19610 and sb18296). The staygreen traits were with positive additive effect. The staygreen trait %GLA at 14 DAF was co-mapped with panicle dry weight, grain dry weight, grain number per plot and per panicle, fresh stover weight per plot (between markers sb18296 and sb20374) with negative additive effect for all the QTLs. also detected co-localization of staygreen and grain yield QTL under drought stress.
These study results indicate the existence of genes or gene clusters with major effects on staygreen traits, particularly on SBI-03 and SBI-07, and several single major QTLs for agronomic traits on SBI-07. Hence marker saturation of these regions would be particularly useful for the detection of candidate genes that might be responsible for variation in these traits.
Breeding experiments have shown that any single stay-green QTL alone does not effectively protect sorghum yield from terminal drought. For this study, a combination of 7 and 8 stg Introgression Lines (IL) was developed in half diallel fashion both in R16- and S35- backgrounds, respectively. F2 seed was produced by selfing of confirmed F1s. Resulted 49 progenies (21 and 28 in R16 and S35, respectively) were field evaluated in summer 2013 along with parents and F1s in RCBD design with 3 replications.In R16 background, the double QTL combinations with stg B and stg 3 showed a higher number of transgressive segregants for high green leaf area and grain dry weight and hundred grain mass. While QTL combinations with stg 4 showed more transgressive segregants towards less green leaf area, grain dry weight and hundred grain mass.In S35 background, the double QTL combinations with stg A and stg 1 were with positive transgressive segregants for the trait per cent green leaf area and grain dry weight.For double staygreen QTL combinations, in R16 background, in general stg B is better combination than another. And in S35 background stg A and stg 1 are equally good. So that Pyramiding of these QTLs will be helpful to protect sorghum yield and quality from post flowering drought stress in most environments.
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