Effects of Arbuscular Mycorrhizal Fungi on Chlorophyll Content and Foliar Nutrient Yield of Amaranthus hybridus under Fusarium oxysporum Stress

Abstract

Background: The genus Amaranthus has gained global attention for its nutritionally important species cultivated as leafy vegetables and grains. However, despite their role in diversifying diets in Nigeria, the capacity of arbuscular mycorrhizal fungi (AMF) to mitigate pathogen stress in sandy loam soils remains poorly understood. Aim: This study evaluated the effects of AMF on chlorophyll content and foliar nutrient yield of Amaranthus hybridus under Fusarium root rot stress in a pot experiment. Study Design:  The experiment was structured as an 8 × 3 completely randomized design, consisting of eight treatments with three replicates each, resulting in a total of 24 pots. Place and duration of study: The study was conducted in Calabar, located in the south-south region of Nigeria, between February and May 2025. Methodology: Amaranthus hybridus seedlings were inoculated with two arbuscular mycorrhizal fungi (AMF) strains, Glomus mosseae and Glomus gigaspora. The inocula comprised spores, mycelia, and infected root fragments. Prior to sowing, 50g of crude inoculum was applied 3cm below the soil surface in AMF-treated pots. Following thinning at one week after emergence, uniform seedlings height was selected and inoculated with 50mL of Fusarium spore suspension under field conditions. Results: Inoculation of Amaranthus hybridus seedlings with arbuscular mycorrhizal fungi (AMF) reduced the severity of Fusarium root rot. Seedlings treated with the combined AMF inoculation of Glomus mosseae and Glomus gigaspora in the presence of Fusarium (Gm+Gg+Fo) recorded the lowest disease severity among infected plants, indicating effective suppression of pathogen activity. Plants treated with Glomus mosseae in combination with Fusarium (Gm+Fo) showed improved chlorophyll b and total chlorophyll contents, with mean values of 105.66μg/g⁻¹FW and 206.48μg/g⁻¹FW, respectively, compared with pathogen-inoculated plants. In contrast, seedlings inoculated with Fusarium alone exhibited marked reductions in chlorophyll a, chlorophyll b, and total chlorophyll contents. Furthermore, seedlings treated with Gm+Gg+Fo showed significant (P ≤ 0.05) increases in foliar phosphorus, potassium, and magnesium yields compared with inoculated seedlings under pathogen stress conditions. Similarly, AMF-pathogen treatments (Gm+Fo and Gg+Fo) reduced pathogen effects and produced the highest foliar nitrogen and calcium yields, with values of 14.45 and 8.07g/plant⁻¹, respectively. Conversely, Fusarium stress alone reduced foliar nutrient yield in all measured parameters. Enhanced foliar nutrient accumulation, particularly phosphorus, appears to be a key mechanism underlying disease resistance in mycorrhizal plants. Conclusion: The findings indicate that the combined application of the AMF species Glomus mosseae and Glomus gigaspora with Fusarium oxysporum was the most effective treatment for suppressing root rot disease and improving overall plant nutrition. In contrast, the combination of Glomus mosseae and Fusarium oxysporum (Gm+ Fo) was more effective in enhancing leaf chlorophyll content. These results reinforce the potential of AMF species as a biological means of protecting plants against soil-borne pathogens.