Genotype-dependent architectural and physiological responses regulate the strategies of two oregano cultivars to water excess and deficiency regimes

Abstract Plants can exhibit alternative strategies to cope with water stress regimes by reconfiguring different morphophysiological processes. Nonetheless, the physiological bases that define the response of oregano genotypes to water stress are still poorly understood. A pot experiment in a greenhouse was conducted to evaluate the changes in the configuration of plant architecture and physiological traits and the strategies displayed by two novel oregano cultivars (Origanum vulgare ssp. hirtum ‘Alpa Sumaj FCA-INTA’ and Origanum x majoricum Cambess. ‘Aguanda FCA-INTA’) in response to two water stress regimes (water excess and deficit) in vegetative phenological stages. To do this, water relations and morphological, developmental, and physiological traits were measured. The architectural and physiological responses were dependent upon stressful water regimes and oregano cultivars. Two strategies were found to face water excess regime: Alpa Sumaj remained quiescent whereas Aguanda followed an escape strategy. Biomass production of Alpa Sumaj was halved since physiological and architectural traits were mostly reduced, especially the leaf area. In contrast, Aguanda was more tolerant because of its altered biomass allocation pattern, leading to taller plants with mild reductions of the leaf area and transpiration rate. Therefore, relative water content and biomass yield were preserved. Contrastingly, the strategy to face water deficit regime in both cultivars was dehydration avoidance. All traits were reduced in a similar way, but interesting genotypic differences in water relation traits were observed. Thereby, leaf water potential decrease was highlighted in Alpa Sumaj cultivar, whereas the lessening in transpiration rate as the leaf area is reduced represented the outstanding physiological trait of Aguanda.