Influence of Rhizopheric H2O2 on Growth, Mineral Absorption, Root Anatomy and Nematode Infection of Ficus deltoidea

Hydrogen peroxide (H₂O₂) is a broad-range chemical catalyst that is receiving rapidly increasing attention recently due to its role as a signaling molecule in various plant physiological and biochemical processes. A study was carried out to investigate the effects of H₂O₂ on the plant physiology, root growth, mineral nutrient accumulation, root anatomy, and nematode control of Ficus deltoidea, a slow growing shade tolerant and nematode susceptible medicinal plant. H₂O₂ at 0 (control), 15, 30, 60, and 90 mM was injected into the root zone of plants weekly. The results showed that the treatment of H₂O₂ enhanced the accumulation of pigments, photosynthetic characteristics, and quantum yield (Fᵥ/Fₘ) of F. deltoidea. H₂O₂ at a 90 mM treatment significantly increased seedling height, leaf number, syconium number, biomass yield, relative water content, leaf dry matter, leaf moisture, and live line fuel moisture of the plant by 1.35-, 3.02-, 3.60-, 5.13-, 1.21-, 1.12-, 1.79- and 1.06-fold, respectively, over the control plant. In addition, root growth, which includes root crown diameter, root length, root volume, root tips, number of roots and root biomass, also exhibited the highest values with an application of 90 mM of H₂O₂. Heavy metals arsenic (As⁺) and antimony (Sb⁺) content in the leaves decreased by 4.08-and 1.63-fold, respectively, in the 60 mM H₂O₂ treated plant when compared to the control plant. In addition, 90 mM H₂O₂ was the best treatment for magnesium (Mg²⁺), calcium (Ca²⁺), and sodium (Na⁺) mineral accumulation in the syconium of F. deltoidea. Treatments with 60 mM H₂O₂ increased magnesium (Mg²⁺), calcium (Ca²⁺), and potassium (K⁺) content in leaves by 14%, 19%, and 15%, respectively, over the control plant. In the study of controlling root-knot nematode, both control and 15 mM treatments produced many root galls, whereas, 60 mM H₂O₂ treatment produced fewer tiny root galls and 90 mM of H₂O₂ showed no root gall formation. H₂O₂ treatments reduced root gall size, root/shoot ratio, and increased the shoot biomass of plants. The treated root developed an epidermal suberin, root periderm, resin duct, cortex, druses, and a well-developed vascular system compared to the control plants. Furthermore, no nematodes were observed in the roots of treated plants with 30–90 mM H₂O₂. The study concluded that injections of 60–90 mM H₂O₂ to the root zone weekly improved plant physiology, increased mineral accumulation, root growth and development, reduced root gall formation, improved root cellular structure, and controlled root-knot nematode of F. deltoidea plants.