Iron Efficiency in Different Cucumber Cultivars: The Importance of Optimizing the Use of Foliar Iron

The ability of plant cultivars to deal with iron (Fe) deficiency (plant Fe efficiency capabilities) has a significant influence on crop yield and fruit quality. This study investigates Fe efficiency in four cucumber ( Cucumis sativus L.) cultivars (Ashley, Anico, Trópico, and Serena) using a complementary approach. The ability to express the main Fe-stress root responses (rhizosphere acidification, Fe reduction, and specific morphological changes) and grow (dry matter production, nutrient acquisition, and efficiency of photosystem II) under Fe starvation were assessed. Results show that while the four cultivars were able to activate the main Fe-stress root responses, only ‘Ashley’ presented a significant capacity to grow and acquire nutrients under Fe deficiency. This ability to develop under Fe starvation was also reflected in the efficiency of photosystem II. Results suggest the existence of two different but probably inter-regulated mechanisms to deal with Fe deficiency in these plants. One would be related to the control of the expression of Fe-stress responses in the root and the other would be involved in optimizing the use of Fe present in the shoot, which is reflected in the plant's ability to develop under Fe deficiency. Among the cucumber cultivars studied, only ‘Ashley’ presented complete Fe efficiency, expressed in the development of Fe-stress root responses and in the ability to optimize Fe metabolic efficiency in the shoot. Likewise, this study evidences the need to consider Fe-stress root responses and the capacity to optimize the metabolic use of Fe in the shoot in studying plant Fe efficiency.