The Influence of Arbuscular Mycorrhiza Fungi and Seaweed Extract Application on Some of Morpho-Physiological Characteristics and Nutrient content of Okra (Abelmoschus esculentus L.) Transplants

Okra (Abelmoschus esculentus) is a tropical and sub-tropical vegetable that is mainly grown by transplantation. Technological advances in agriculture have also contributed to the progress of the transplanting industry because they have reduced the cost of transplant production. Arbuscular mycorrhizal fungi (AMF) have symbiotic relationship with many plants’ root and their importance in growth and yield improvement has been proven. Mycorrhizal symbiosis is one of the most common symbiosis in plants. The main advantage of AMF for host plants is the expansion of the root penetration zone. Also, seaweed extract (SWE) acts as a bio-stimulant to plant growth enhancement. These products are widely used in improving agricultural sustainability and can actually facilitate the production process by reducing environmental effects. And, the co-application of AMF and SWE could be attributed to promoting the growth and yield of agricultural crops.

In order to study the effect of SWE foliar application and AMF inoculation on okra transplants, a factorial experiment was conducted based on a completely randomized design with two factors and four replications under greenhouse condition. The first factor was AMF (Glomus mosseae) inoculation at two levels included 0 (as control) and 5 g kg-1 and the second factor was SWE (Ascophyllum Nodosum) foliar application at four levels included 0 (as control), 1, 2 and 4 g L-1. The morphological traits of the transplants such as plant height, number of leaves, length and width of the leaves, fresh and dry weight of the root and shoot, and stem diameter were measured. Also, in order to assess physiological responses of transplants to used treatments, some important traits such as photosynthesis pigments content, total soluble carbohydrates, total soluble proteins, total antioxidant activity and some macro- and micronutrients were evaluated.

The results showed that the morphological, physiological, and biochemical characteristics, as well as the nutrient content of okra were significantly affected by SWE spraying and AMF inoculation. These treatments improved the growth parameters, photosynthetic pigments content, osmolytes (total soluble carbohydrates and total soluble protein), total antioxidant activity, and macro and micro-nutrients of okra transplants. The foliar spraying of 4 g L-1 SWE along with AMF increased the stem diameter, plant height and leaf length by 72, 85 and 55%, respectively, compared to the control plants. AMF inoculation improved the leaf width by 12.83% compared to control. Foliar application of SWE at 4 g L-1 concentration increased the leaf width by 25% compared to control. The treatment of 4 g L-1 SWE along with AMF inoculation caused an increase in fresh and dry weight of root by 132.83 and 204.54 %, respectively. The highest content of chlorophyll a (36.51 and 35.79 mg g-1 FW) was observed in transplants treated with SWE 2 and 4 g L-1 and AMF, respectively, and the lowest content (12.01 mg g-1 FW) was observed in control. The highest content of chlorophyll b (22.21 mg g-1 FW) was obtained in transplants treated with SWE 4 g L-1 and AMF, and the lowest value was recorded in control (6.51 mg g-1 FW). Foliar spraying of SWE and AMF inoculation led to a 2.7-fold enhancement in total soluble protein compared to control. The highest antioxidant activity (35.89 %) was recorded in transplants treated with SWE 2 g L-1 and the lowest value (25.44 %) was for control plants.

The results of the current study have shown that application of SWE and AMF as separate or combined treatments led to a significant improvement in okra transplants morphological characteristics such as plant height, leaf length, number of leaves, stem diameter, leaf width, and stem and root fresh and dry weight, as well as enhanced physiological traits such as protein content, chlorophyll a and b content, antioxidant activity rate, carbohydrate and carotenoid content, and the amounts of macro- and micro-nutrients. Based on obtained results of this study, foliar application of SWE at concentration of 4 g L-1 along with AFM inoculation could be recommended as useful treatment to produce okra transplants with suitable morpho-physiological characteristics.