GENOMIC MAPPING FOR DROUGHT TOLERANCE IN SORGHUM

IntroductionDrought 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 Sukumaran1, Yuye Wu1, Raymond Mutava1, P. V. Vara Prasad1, Guihua Bai2, Mitchell R. Tuinstra3, Tesfaye Tesso1 and Jianming Yu1 1Department of Agronomy, Kansas State University, Manhattan, KS; 2USDA-ARS and Department of Agronomy, Kansas State University,

Manhattan, KS; 3Department 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., 2008. Community Resources and Strategies for Association Mapping in Sorghum.Crop Science 48:30-40.• Yu, J. et al., 2006. A unified mixed-model method for association mapping that accounts for multiple levels of relatedness. Nature Genetics 38:203-208.

Traits G E G×EHeritability

2008 2009 Combined

Grain yield ** ** ** 0.57† - -

Flowering time ** ** NS 0.69 0.68 0.76

Chlorophyll content ** ** NS 0.23 0.25 0.29

Leaf temperature ** ** ** 0.42 0.04 0.03

Leaf fluorescence ** ** NS 0.31 0.22 0.12

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..)

Traits Mean Range

Grain yield (1000 kg/ha) 3.08 0.56 - 7.80Flowering time (day) 58.80 46 - 75

Chlorophyll content 53.27 32.2 - 71.0

Leaf temperature (oC) 28.53 18.2 - 35.1

Leaf fluorescence (Fv/Fm) 0.734 0.512 - 0.856

Grain moisture (%) 12.12 6.5 - 17.9

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

a b

a b c

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