Effect of Foliar Application of Macroalgae Aqueous Extracts on the Nutrient Status and Fruit Quality of "Valencia" Orange

Abstract

Macroalgae contain macro- and microelements, vitamins, amino acids, and phytohormones. These compounds contribute to the development of plants, making macroalgae highly promising as a biofertilizer for different crops. This study aimed to evaluate the potential of three local macroalgae available along the Mediterranean coast, Egypt, two of which are green algae (Ulva flexusoa and Enteromorpha intestinalis), and one of red algae (Griffithsia teges), on nutrition status and fruit quality of "Valencia" orange (Citrus sinensis, Osbeck). Aqueous extracts of the three macroalgae were prepared at 0 (control), 5, 10, and 15% concentrations and applied three times as a foliar application throughout the growing period. Results revealed that the macroalgae under investigation contain significant levels of various phytohormones, such as IAA, GA3 ABA, and CK; green algae contain the highest concentrations of GA3, whereas cytokine was observed only in G. tege. Macroalgae possess various amounts of essential macro- and microelements, containing Na > Ca >Mg >Mn in addition to Zn, CU, Fe, K, and P. Applying macroalgae extracts significantly affected the mineral composition of orange leaves and the chlorophyll content (presented as SPAD values). Green algae notably impacted fruit quality characteristics, including weight, length and width, juice volume, TSS, and peel color. However, no significant effect was detected on peel thickness or titratable acidity. We concluded that macroalgae extracts could be utilized as an eco-friendly biofertilizer, providing an alternative source for required nutrients in citrus and other fruit orchards.