Efficiency of foliar application of different sources of calcium in tomatoes: understanding and bypassing low phloem mobility

Abstract

Several studies demonstrate that calcium (Ca) presents low mobility in the phloem, hence it is supplied to plant tissues mainly by the xylem. Since transpiration is the driving force of the xylem flow, Ca supply can be compromised in organs, such as fruits, which have low transpiration rate. Low productivity, disorders in fruits, and reduced shelf life are associated with Ca deficiency. The literature shows that the application of Ca-based foliar fertilizers, or even fruit treatment, can prevent these problems. Conversely, the influence of Ca sources on the rate of leaf absorption and translocation, as well as Ca exports to the fruits is still unknown. In this scenario, X-Ray Fluorescence spectrometry (XRF) emerges as a simpler, cheaper, and safer alternative for monitoring the movement of nutrients in plant tissues. This project aims at employing XRF to determine the absorption and translocation rates of Ca sources applied via foliar treatment in tomato (Solanum lycopersicum), such as CaCl2 (frequently reported in the literature) and Ca chelated with citrate and EDTA. The source of Ca with the greatest translocation capacity in the phloem will be selected in a next phase of the study, characterizing the foliar absorption, transport and exportation to tomato fruit using micro and nano XRF and X-ray absorption spectroscopy. From plant physiology/nutrition standing point, the major expected outputs are to contribute to the understanding of the Ca movement limitation in the phloem, identify potential Ca sources with a higher mobility than CaCl2 and able to increase the export efficiency of Ca from foliar fertilizers to fruits. (AU)