During the last six years, segregating 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. A few experimental lines have now entered the final stages of line testing. For the 2019-2020 Oklahoma Wheat Research Foundation funding cycle, two research activities were emphasized: a) quantitative analyses of the phenotyping protocol and b) field evaluation of five lines with tolerance to BCOA and desirable agronomic characteristics.

 

From multiple years of laboratory phenotyping data, a model was developed to describe the most influential measures on final resistant scores. Percent chlorosis and leaf height were most influential on final phenotype score, and not surprisingly, aphid count per leaf was the least important measure for tolerance evaluations. This analysis will allow for more rapid phenotyping procedures for BCOA by focusing on factors that most strongly correlate with plant survival.

 

In a replicated small-plot field trial in Perkins, the effect of season-long infestation was investigated for five progenies previously selected for BCOA tolerance in controlled assays. During the fall and winter, densities of BCOA per plant in infested plots increased exponentially to levels well beyond those that could be tolerated, and unfortunately, any relative measures of tolerance could not be determined. However, in planned, uninfested plots, natural infestations of BCOA occurred during seedling and early tiller stages at levels high enough to reduce yield, based on published economic injury levels. In these “lightly” infested plots, estimated yields for lines previously classified as tolerant or moderately tolerant were measurably higher than the susceptible check (Table 1). These preliminary results were compelling and were the basis for a final planned evaluation of 16 entries for the 2020-2021 field season. For this expanded evaluation, BCOA densities will be carefully controlled in caged field plots to ensure infestations are relevant to managed production systems.

 

This 7-year project is likely to result in direct commercialization of tolerant cultivars and has already produced crossing schemes that combine barley yellow dwarf and other disease-resistant traits with BCOA tolerance. OK19105122 is the most coveted progeny of those listed in Table 1 for its statewide yield performance in 2020 breeding nurseries. This line demonstrated the strongest disease resistance package with acceptable end-use quality and has the pedigree TCI012160/OK08413//OK10132. OK19105130F, with the same pedigree, is a soft red winter wheat and is undergoing a three-year quality evaluation in the USDA-ARS Soft Wheat Quality Laboratory in Wooster, Ohio. These two progenies, plus four other siblings with desirable BCOA tolerance from controlled assays, were advanced for final statewide testing in 2020-2021.