GENOMIC MAPPING FOR DROUGHT TOLERANCE IN SORGHUM Introduction Drought is a major abiotic factor limiting crop production. Sorghum is one of the most drought tolerant crops in the world and it is a suitable candidate to study complex traits. QTL mapping and association mapping are the two common methods for dissecting complex traits. Objectives To identify QTLs for drought tolerance in sorghum with a bi-parental cross population. To identify genes for drought tolerance in sorghum through candidate gene association mapping. Materials and Methods  QTL mapping 190 Recombinant Inbred Lines (RIL) were developed from a cross of Tx436/00MN7645. The testcrosses of 190 RILs with ATx3042 was phenotyped with a randomized complete block design with 2 replications, 3 locations over 2 years. Data were analyzed using SAS 9.1 proc mixed to obtain entry mean based heritability for the traits.  Association mapping Sorghum bicolor panel: a collection of 300 diverse sorghum lines consisting of lines from SCP (sorghum conversion program) and elite US breeding lines. This panel was phenotyped for a set of drought tolerant traits at 6 locations over 2 years. Single nucleotide polymorphism (SNP) discovery in candidate genes, a subset of 24 diverse lines. Fig. 1. (a) SPAD-502 meter; (b) Handheld Infrared Thermometer; (c) OS-30p Chlorophyll fluorometer Sivakumar Sukumaran 1, Yuye Wu 1, Raymond Mutava 1, P. V. Vara Prasad 1, Guihua Bai 2, Mitchell R. Tuinstra 3, Tesfaye Tesso 1 and Jianming Yu 1 1 Department of Agronomy, Kansas State University, Manhattan, KS; 2 USDA-ARS and Department of Agronomy, Kansas State University, Manhattan, KS; 3 Department of Agronomy, Purdue University, West Lafayette, IN Genes sequenced: 41 DNA sequenced: ~50 kb SNPs identified: 543 SNP frequency: 1 SNP per 95 bp Future Work  Genotyping will be done on the RILs with 1536 random SNPs distributed across the genome to identify QTLs for drought tolerance in sorghum.  For candidate gene association mapping, candidate SNPs identified will be genotyped on the large Sorghum bicolor panel. Key References Casa, A. M. et al., Community Resources and Strategies for Association Mapping in Sorghum. Crop Science 48: Yu, J. et al., A unified mixed-model method for association mapping that accounts for multiple levels of relatedness. Nature Genetics 38: TraitsGE G×EG×E Heritability Combined Grain yield** 0.57 † -- Flowering time** NS Chlorophyll content** NS Leaf temperature** Leaf fluorescence** NS Grain moisture** 0.15 † -- Results This work is supported by Kansas Grain Sorghum Commission, and Center for Sorghum Improvement, Kansas State University Acknowledgements Results (contd..) TraitsMeanRange Grain yield (1000 kg/ha) Flowering time (day) Chlorophyll content Leaf temperature ( o C) Leaf fluorescence (Fv/Fm) Grain moisture (%) G = Genotype, E = Environment, ** Indicates p value < 0.001, * p value < 0.05, NS = not significant, † Indicates the data is from 2 locations. Fig. 2. (a) Sorghum bicolor panel; and (b) Field view of 190 RIL testcrosses Table 2. Heritability of different traits based on 190 RIL testcrosses Table 1. Different trait characteristics of 190 RIL testcrosses ab abc Zeaxanthin Antheraxanthin aba1 All-trans-violoxanthin xanthoxin vp14 Abscissic aldehyde aba3 Xanthoxic acid ABSCISSIC ACID Abscissic aldehyde oxidase aba2 Fig. 3. ABA pathway and the genes sequenced c