Bread wheat (Triticum aestivum L.) has been commercially cultivated in South Africa for more than a century and currently ranks the second most significant cereal crop after maize. The production of wheat in the country remains under threat from various pathogens, with fungal diseases, notably rusts such as Puccinia spp., which continues to present the most significant challenge to wheat cultivation in South Africa.

Therefore, it is important to understand how wheat regulate its defense against pathogen attacks. Thus, our current study aimed to evaluate differences in the metabolites that play important role in metabolic responses to Puccinia striiformis f. sp. tritici (Pst) infection in two wheat varieties at different times using an untargeted metabolomic approach.

The differential changes of metabolites in two wheat varieties, Senqu (resistant) and Morocco (susceptible), caused by the infection with two Pst races (6E22A+ and 6E22A-) at 14- and 21- days post-inoculation (dpi) were analysed using untargeted ultra-high performance liquid chromatography coupled with a quadruple time of flight mass spectrometry (UHPLC-qTOF-MS) analysis.

Multivariate statistical analysis (MVDA) tools, viz. principal component analysis (PCA) and the orthogonal projection to latent structures-discriminant analysis (OPLS-DA) loading scatter plot were used to identify the metabolites that are positively and negatively correlated to Pst infection. PCA and OPLS-DA analysis showed cluster separations between the varieties, infection races and the time-points, thus indicating distinct biochemical changes.

Metabolites were identified belonging class of phenolic acids, carbohydrates and fatty acids among other classes. The study provided the insights on biochemical changes in wheat metabolite expressions following stripe rust infection, thus offering valuable insights for potential applications in crop improvement.