Plants growing in natural environments are exposed to a broad range of biotic (pathogen attack, insect herbivory, etc.) and abiotic factors (drought, extreme temperatures, UV radiation, salinity, etc.) that are known to cause stress symptoms in many species. Biotic and abiotic stress-inducing determinants often adversely impact plant growth and development, frequently leading to severe annual yield losses in agricultural production. The research described in the PhD thesis focuses on study plant responses to different sequential combinations of biotic factors (infection with Botrytis cinerea or herbivory by Pieris rapae) and drought, aiming to identify genes that contribute to tolerance to the aforementioned sequential stress combinations. The study highlights the importance of an array of genes, crucial to the underlying defense processes, as targets for breeding by allele mining, ultimately aimed at improvement of crop tolerance to frequent combinations of stress factors.