ICRISAT Archival Report 2006 - The seedlings of success in the ...

esistance QTLs are being developed. Simultaneously, studies are being undertaken to enhance the understanding of
sorghum seed supply systems and to ensure the effective integration of seven Striga-resistant FPSVs into farming
systems in Eritrea, Kenya, Mali and Sudan. The extent of outcrossing rates and gene flow are being determined in
five selected FPSVs.
So far, 712 plants were genotyped from two backcross generations (BC 1 F 1 and BC 2 F 1 ) at the BecA research
platform (ILRI; Nairobi, Kenya) using a total of 10 foreground SSR markers and 16 background SSR markers.
Genotyping revealed that 256 plants from the second backcross generation (BC 2 F 1 ) were heterozygous for 1 to 3
QTLs.
In Kenya, 43 BC 2 F 1 plants were selfed and genotyped to select for segregating homozygous BC 2 S 1 plants that have
been taken through another selfing generation (BC 2 S 2 ) to fix the QTLs. Plans are now underway to genotype the
BC 2 S 2 plants, and those confirmed to contain one to three QTLs will then be multiplied and evaluated for Striga
resistance in artificially infested fields.
The selfing of 73 BC 2 F 1 plants in Mali and 103 BC 2 F 1 plants in Sudan has been completed and genotyping of the
BC 2 S 1 is now planned. The segregating homozygous BC 2 F 1 plants will be selfed to fix the QTLs. Preliminary
studies have revealed some variability in FPSVs with outcrossing rates ranging between 3 and 5%. Initial gene flow
studies have shown pollen dispersal for distances of up to 100 m in multiple directions, with a marked decrease after
40 m from the center.
Activity A2.2: Develop Sorghum varieties resistant to Midge through marker-assisted selection.
Milestone A2.2.1: Markers segregating with traits associated with resistance to midge identified and linkage map of
the F2 population of AF28 Seredo generated by 2007 (DK, TH)
Sorghum midge (Stenodiplosis sorghicola Coquillet), spotted stem borer (Chilo partellus Swinhoe) and sorghum
shoot fly (Atherigona soccata Rond.) are the three most destructive insect pests of sorghum in the ASARECA
(Association for Strengthening Agricultural Research in East and Central Africa) region. Midge control in sorghum,
therefore, is one of the research priorities in ECARSAM (the Eastern and Central Africa Regional Sorghum and
Millet Network), the sorghum and millet network of ASARECA.
Midge resistance in sorghum is location specific and the identification of sorghum genotypes with stable resistance
to sorghum midge is therefore hampered by genotype × environment interactions. Identifying DNA markers closely
linked to midge resistance loci and using these markers in marker–assisted selection (MAS) will aid breeding for
sorghum midge resistance. The objectives of this project are therefore to 1) identify SSR markers that segregate with
traits associated with resistance to sorghum midge and 2) initiate MAS towards the development of midge resistant
sorghum varieties to improve sorghum production in East Africa. The project aims to map midge resistance QTL in
order to identify SSR markers closely linked to these QTL and to initiate the development of sorghum varieties with
resistance to sorghum midge through MAS. So far the project, generated a segregating sorghum population for
midge resistance using the highly resistant, locally adapted sorghum landrace from Africa AF 28 and Seredo, a highyielding,
drought tolerant, midge susceptible Kenyan sorghum cultivar. The resulting F 1 ’s are now being genotyped
in the ICRISAT/BecA lab using SSR markers to confirm their heterozygosity.
D Kiambi, D Hoisington, T Hash, S de Villiers
Output Target A3: Genetically diverse and regionally adapted germplasm and breeding populations of
sorghum and millet developed and disseminated [2011]
Activity A3.1: Develop and evaluate traits and end use specific sorghum and millet populations and breeding
lines for adaptation to specific environments and resistance to biotic stresses
Milestone A3.1.2: Conventionally bred midge, stem borer and leaf disease resistant lines for sorghum and millets
evaluated in advanced trials for yield and adaptability by 2008
Sorghum midge [Contarinia sorghicola] is the most widely distributed of all sorghum insect pets. Host plant
resistance and time of planting are some of the important components for the management of the pest. Several
sources of resistance have been identified, however the levels of resistance vary from location to location. This calls
105