During the last seven years, Wheat Improvement Team (WIT) breeding populations were enriched for tolerance to bird-cherry oat aphid (BCOA) feeding, followed by the development of experimental lines with seedling tolerance to heavy infestations. This massive effort constituted a breeding project within a breeding program. Experimental lines were entered into the final stages of statewide testing, and for the 2020-21 Oklahoma Wheat Research Foundation funding cycle, we conducted a final field validation study of lines previously identified with tolerance to BCOA and desirable agronomic characteristics. 

 

In a replicated small-plot field trial in Perkins, the effect of fall plus spring infestations was investigated for progenies previously selected for BCOA seedling tolerance and for an additional set of experimental lines and susceptible varieties. Our fall plus spring infestation strategy was designed to test whether seedling tolerance extended to winter-long BCOA feeding.  

              

For this intensive field study, and following planting, we immediately placed fine-mesh cages over each 14”x 27” plot, then after-emergence thinned plots to 61 seedlings to ensure uniform evaluation of yield response among entries (Figure 1). Control plots (no-aphids) were maintained with regular insecticide applications and visual monitoring. To ensure that plants within the aphid-infested plots had winter-long BCOA infestations above known economic injury levels, we placed laboratory reared BCOA directly on plants during the fall and early spring and allowed them to reproduce. Plots were then monitored to ensure adequate aphid numbers per seedling among entries. During the spring, the mesh cages were removed, and all plots were treated with insecticide to prevent any further aphid infestations. Plots were harvested by hand, and yields were measured. A few entries were heavily infected with leaf rust and could not be included for this summary, but the remaining entries experienced low levels of rust infection.

 

From fall to spring, densities of BCOA per plant in all infested plots increased well above economic injury levels, but fortunately, they were lower than levels that would have killed plants. Therefore, our comparison of yields between un-infested and infested plots provide evidence of how well entries tolerated severe BCOA infestations (Table 1). Several entries that were previously not tested in the laboratory for BCOA tolerance performed quite well with acceptable levels of yield reduction under intense aphid feeding pressure. Entries previously identified as having tolerance to BCOA also performed well with yield reduction being less than the susceptible entry. 

 

This project may allow for direct commercialization of varieties with acceptable tolerance to BCOA feeding. A forward breeding strategy has already commenced to further distribute BCOA tolerance throughout the WIT variety development program, using OK19105126 as the principal donor. OK19105126, OK19105122 and OK19105130F are promising lines and have performed well in statewide yield trials. Interestingly, in preliminary laboratory trials, OK19105126 also shows consistent cross-resistance to greenbug by reducing their reproductive capacity. We expect that each of these lines would perform best with the typically low aphid infestations seen in Oklahoma. In addition, OK19105126 and OK19105122 have a strong disease resistance package with acceptable end-use quality. OK19105130F, with the same pedigree, is a soft red winter wheat and is undergoing continued quality evaluation with the Wheat Quality Council. 

Figure 1. Caged experiments conducted at Perkins in 2021 to determine and validate bird-cherry oat aphid tolerance.