Effect of Selected Bio-stimulants and Organic Fertilizers on the Flowering, Yield, and Quality of White-Fleshed Dragon Fruit Plants (Hylocereus undatus) under Sandy Soil Conditions

Abstract

This study was conducted over two consecutive growing seasons (2023 and 2024) in a private orchard located in Belbis City, Alsharqia Governorate, Egypt. The primary objective was to evaluate the physiological and physiochemical responses of two-year-old white-fleshed dragon fruit (Hylocereus undatus) plants to five organic and biological treatments: seaweed extract (5 cm/L), Spirulina extract (3 cm/L), chitosan extract (4 cm/L), tea compost (150 ml/L), and humic acid (1.5 gm/L), alongside an untreated control group. The treatments were applied three times per season (March, May, and July) to plants grown under drip irrigation in sandy soil. The experimental results revealed significant variations in growth, reproductive dynamics, and fruit quality traits. Spirulina extract demonstrated superior consistency in enhancing fruit biochemical properties, achieving the highest total phenolic content across both seasons, maximizing total soluble solids (TSS, °Brix), and producing the thinnest peels. However, antioxidant activity showed high seasonal fluctuation, with Spirulina dominating the first season and seaweed extract dominating the second. Structurally, humic acid exerted the most stable and superior influence on vegetative growth, significantly optimizing plant height, stem diameter, and the fruit shape index (Height/Diameter ratio) over the two-year period. Regarding reproductive biology, all evaluated bio-stimulants significantly enhanced flower numbers and fruit set percentages compared to the control group. However, a distinct physiological trade-off emerged between reproductive success and final tree productivity. Due to resource depletion caused by heavy, induced flowering, most biostimulants (particularly seaweed and tea compost) resulted in a significant reduction in overall yield. The untreated control group maintained the highest final tree productivity. Notably, chitosan extract emerged as the optimum and most balanced treatment. Chitosan successfully broke the negative correlation by significantly boosting flowering and fruit set while maintaining a high yield that was statistically equal to the control group. Furthermore, chitosan was highly effective in increasing edible pulp weight and maximizing initial fruit firmness. In conclusion, the strategic application of specific biostimulants particularly chitosan and Spirulina presents a highly effective, sustainable approach to improving dragon fruit quality and commercial viability in semi-arid, light-soil regions.