Changes in leaf gas exchange of kale (Brassica oleracea var. acephala) landraces under drought stress

One of the principles of organic agriculture is a reduced use of resources such as water and the cultivation of stress-resistant cultivars. Recently, kale (Brassica oleracea var. acephala) has gained attention as an abiotic stress-resilient crop, as well as a potential superfood. It is mainly produced in the Mediterranean region; therefore, its production could be greatly impacted by drought stress. Kale is grown on the Croatian Adriatic coast for centuries, which resulted in a great number of local landraces. Therefore, high variability in abiotic stress adaptation traits could be expected. Since photosynthesis is the first-line process that is altered by drought stress, this experiment aimed to test two kale landraces for their photosynthetic response to drought stress alongside physiological parameters such as SPAD value and proline content. Two landraces were subjected to water deficit and measurements were made after 7 days of water withholding. Water withholding significantly reduced the assimilation rate, transpiration rate, and intercellular CO₂ while leaf temperature and stomatal conductance were not affected. The SPAD value and proline content were increased under water shortage. Differences between landraces in measured traits were found and significant interaction of landrace and water shortage was observed. A correlation was found between photosynthetic parameters and proline content, in which proline content increased with the decrease of transpiration rate. Landrace ‘Vis’ exhibited traits that indicate better tolerance to water withholding due to high photosynthetic productivity under water shortage. Kale landraces, which display drought-resistant mechanisms, are necessary for areas whose production is greatly impacted by drought.