8th INTERNATIONAL WHEAT CONFERENCE

ToWARdS A PhySICAL mAP of SST1, A mAJoR LoCuS
CoNfeRRINg SoLId STem exPReSSIoN IN WheAT
C. J. Pozniak 1 , P. J. Hucl 1 , J.M. Clarke 1 , F.R. Clarke 2 ,
R. E. Knox 2 , and A.K. Singh 2
1 Department of Plant Sciences, Crop Development Centre, University of Saskatchewan, Saskatoon,
Canada, S7N5A8
2 Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada, Swift
Current, Canada, S9H3X2
E-mail Address of presenting author: curtis.pozniak@usask.ca
The wheat stem sawfly (Cephus cinctus) causes substantial yield reduction and loss of
quality in durum (Triticum turgidum var durum) and hexaploid (Tritcum aestivum)
wheat. The most effective way to reduce losses from the wheat stem sawfly is through
the deployment of resistant cultivars. In wheat, genotypes expressing solid stems have
better resistance to sawfly cutting. A locus designated as SSt1 controls the solid stemmed
trait and has been localized to chromosome 3BL in both durum and hexaploid wheat.
The recent release of a physical map of chromosome 3B provides the opportunity to better
delineate the SSt1 locus. In this study, approximately 30 polymorphic insertion site
based polymorphism (ISBP) markers were mapped in a durum wheat population of 155
doubled haploid lines derived from the cross Kofa (hollow-stemmed) and W9262-260D3
(solid-stemmed). Stem solidness was assessed on a 1-5 scale in replicated trials. Lines
were classified into two discrete classes (solid:hollow) and data fit a 1:1 ratio expected for
segregation of a single gene. The SSt1 locus was mapped as a Mendelian factor along with
the ISBP markers previously localized to the physical map of 3B. Results indicate that
SSt1 resides in deletion bin 3BL7 0.63-1.0. Three ISBP markers flanking SSt1 were identified
and allowed anchoring of the SSt1 genetic map to the current 3B physical map. In addition,
several wheat expressed sequence tags (ESTs) and rice (Oryza sativa) genes known
to co-locate in the same physical region were also mapped, allowing further delineation
of the SSt1 locus. The markers identified in this study will be useful for wheat breeders selecting
for resistance to the wheat stem-sawfly. We are currently fine-mapping this region
in a population of over 3000 F 2 individuals with the ultimate objective of cloning SSt1.
This will be essential to identify genetic factors that are known to suppress expression of
SSt1 in some genetic backgrounds of hexaploid wheat.
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