Variation of Osmolytes, Photosynthetic Pigments, Growth, Water Status and Gas Exchange in Green Kohlrabi under Drought and Rehydration Conditions

The objective of this work was to study the effect of water stress on the physio-morphological and biochemical characters of green kohlrabi ( Brassica oleracea var. gongylodes L.) and to identify its various adaptive strategies to counter stress. The greenhouse germination and cultivation of kohlrabi were conducted under various water stress conditions (0, 25, 50, and 75% Field Capacity (FC)) or without as a control. A rehydration (100% FC) of the treated plants was carried out, in order to highlight the capacity of the growth recovery and normal development in this variety. The adaptive strategies, tolerance mechanisms and resistance limits of this plant to drought were discussed. The results have shown that B. oleracea var. gongylodes adopts several strategies to counter water stress. It activates the tolerance mechanisms by actuating the biosynthetic pathways of osmolytes, such as proline and soluble sugars to ensure osmotic adjustment, as well as phenolic compounds and flavonoids. It also adopts the avoidance strategy as a mechanism for countering drought stress. In fact, kohlrabi limits the losses of water by perspiration (decrease of the number and surface of the leaves and reduction of the stomatic conductance), and it improves the absorption of water, by the establishment of a long and vigorous root system.