As nature's allies: Bee honey outperforms pomegranate and lemon juices in improving physio-biochemistry, antioxidants, RubisCO gene expression, and vase life of Calendula officinalis

Abstract

Honey, pomegranate juice, and lemon juice are natural plant growth biostimulators that contain many bioactive substances that play essential roles in many plants’ physio-biochemical processes, and development. The objectives of this research were to explore how foliar spraying with a 5 % or 10 % diluted pomegranate juice solution (DPJS), a 5 % or 10 % diluted lemon juice solution (DLJS), or a 5 % or 10 % diluted honey solution (BHS), versus a control (distilled water; D-H₂O), positively influenced the growth, pharmaceutical, and ornamental qualities of calendula (Calendula officinalis L.) plants in both the 2021/2022 and 2022/2023 seasons. Foliar spraying with 5 %- or 10 %-DPJS, 5 %- or 10 %-DLJS, or 5 %- or 10 %-BHS significantly increased photosynthesis-related assessments (total chlorophyll and carotenoid contents, the maximum quantum efficiency of photosystem II (Fv/Fm), and net CO₂ assimilation), water use efficiency, RubisCO content and activity, RubisCO gene expression, and sugar fraction (glucose, sucrose, and starch contents). Also, osmoregulatory compounds (K⁺, total soluble sugars, and glycine betaine contents), antioxidant capacity (in terms of total flavonoid, anthocyanin, proline, ascorbate, and glutathione contents), nutrient and hormonal contents were significantly increased by foliar spraying of all the above-mentioned treatments. These positive findings were noticeably reflected in improved growth (fresh and dry plant weights), inflorescence traits (number of inflorescences on plant, fresh and dry petal weights, petal content of soluble sugars, ß-carotene, and total carotenoids), and longevity of inflorescence (vase life and water uptake by inflorescences), while electrolyte leakage and abscisic acid were noticeably decreased compared to foliar spraying with D-H₂O. The second-best treatment was 5 %-DPJS or 10 %-BHS, and they were preceded by 5 %-BHS as the best treatment, which the research results recommended applying in the field to obtain the best pharmaceutical and ornamental qualities of calendula.