Location: Hard Winter Wheat Genetics Research
Project Number: 3020-21000-012-028-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: May 1, 2026
End Date: Apr 30, 2028
Objective:
The objective of the project is to identify novel sources of resistance to the wheat stem sawfly (WSS) in USDA-ARS winter wheat breeding germplasm carrying introgressions from wheat ancient ancestor, wild emmer (Triticum dicoccoides), using the cone-tainer method developed in the cooperator’s lab at Colorado State University, Fort Collins. Specifically, the non-preference (antixenosis) and survival (antibiosis) of WSS in the introgression lines will be evaluated. In addition, regional high-throughput phenotyping efforts for WSS resistance will be supported by supplying sawflies and WSS-infested stems to ARS scientists and their cooperators.
Approach:
Plant material and experimental procedures will follow published protocols developed by the cooperator (Peirce et al. 2022). Seeds provided by USDA-ARS will be hand- or mechanically threshed, germinated, and vernalized at 4 °C for seven weeks. Following vernalization, one seedling per accession will be transplanted into cone-tainers (164 mL; Stuewe & Sons) filled with a 7:2 soil-to-perlite mixture with a cotton plug to prevent soil loss. Plants will be grown in a CSU greenhouse under a 16L:8D photoperiod with supplemental high-pressure sodium lighting and day:night temperatures of 23:18 °C. Planting dates will be staggered over three weeks each year to synchronize plant phenology with peak wheat stem sawfly (WSS) flight. Accessions will be randomized within trays, trays will be randomly positioned, checks will be replicated in every rack, and wild wheat accessions will be replicated 10–20 times depending on germination.
Once plants reach Zadoks growth stages 35–45, they will be exposed to natural WSS infestations at New Raymer and Orchard, CO, by placing cone-tainer trays in fields with WSS-infested stubble adjacent to growing wheat. After exposure, adult sawflies will be removed using sweep nets or aspirators, and plants will be returned to the greenhouse. Within 48 h, half of the plants will be dissected to quantify oviposition, recording stem diameter, Zadoks growth stage, egg number, and stem solidness. Stem solidness will be scored on a 1–5 scale per internode (hollow to solid) and summed across up to five internodes. Thirty days post-infestation, remaining stems will be dissected to assess larval presence, frass, and larval mass. Stems will be classified as infested if frass and/or larvae are present.
Host selection (egg counts) will be analyzed using linear mixed models with exposure date as a random effect and wheat genotype, Zadoks growth stage, and stem solidness as fixed effects. Host suitability (infestation) will be analyzed using generalized linear models with a binomial error distribution based on presence or absence of frass.