Marker-Assisted Selection for Resistance to the

Wheat Stem Sawfly

Jason Cook, Phil Bruckner, Jack Martin, Julie Elser, Phil Fox, and Luther Talbert*

Dep. Of Plant Sciences and Plant Pathology, Montana State University,

Bozeman, MT, USA 59717

*Corresponding Author: PH: (406) 994-5060; E-mail: usslt@montana.edu

ABSTRACT

The major insect pest of wheat in Montana and contiguous portions of North Dakota and Saskatchewan is the wheat stem sawfly (Cephus cinctus Nort.). The sawfly hatches in late spring, and adults lay eggs in developing wheat stems. Resulting larvae cause yield loss by feeding on the inside of the stem. At the end of the season, larvae cut the plant stem at its base resulting in harvest difficulties. Pith-filled, or solid, stems provide the only reliable control measure for the sawfly. The trait is poorly-expressed in heterozygous individuals and in less than optimum light (such as greenhouse conditions). Thus, molecular markers for key genes would allow more rapid progress in breeding for resistance. A single locus on 3BL was found to control 76% of the variation for stem solidness in a double haploid population developed from a solid- by hollow-stemmed cross. However, lines with this major gene were often not solid enough to provide an acceptable level of resistance. A second cross between a semi-solid line and a solid line (both fixed for the major gene) allowed identification of a secondary gene that may improve stem-solidness to the point that MAS will be useful for transferring solid stems into high yielding cultivars. Additionally, replicated yield trials have shown no negative relationship between the solid-stem genes and other traits, suggesting that high-yielding solid-stemmed cultivars are a reasonable goal.