Okra, or Abelmoschus esculentus (L.), is a member of the Malvaceae family and is considered a valuable crop due to its nutritional importance because its fruit contains minerals, antioxidants, vitamins, carbohydrates, and proteins (Agregán et al., 2022; Dubey, P. and Mishra, S., 2017). In manufacturing medicine, the mucilage of okra is used. Furthermore, it contains approximately 20% of edible oil and protein along with vitamin B6, K, and C, and other mineral contents such as phosphorus, iron, calcium, folates, and pyridoxin to carry the important physiological functions of the body (Petropoulos et al., 2018). However, the okra production is damaged by nutrient losses, unavailability of nutrients, disease attacks, and other environmental changes (Saima et al., 2022).
Use of agricultural chemicals like as excessive fertilizers, pesticides, and herbicides gained momentum after the green revolution in agricultural production, to compete with the demand for food items and minimize the risk to food security along with posing the harmful effect to the environment (Armanda et al., 2019; Ait El Mokhtar et al., 2019a). The application of these agrochemicals is also threatening to the ecosystem due to adding a considerable amount of heavy metal residues and ultimately entering into the food chain (Ouachoua and Al Karkouri, 2020). Furthermore, intensive agricultural practices, overgrazing, salinization, deforestation, and intensive use of agrochemicals result in a considerable decrease in soil fertility. Climate change is also worsening the problem (Kouba et al., 2018). Loss of stable soil organic carbon decreases soil fertility and increases plant vulnerability to diseases and nutritional imbalances (Mainville et al., 2006). Therefore, the researchers try to find alternative economical and eco-friendly approaches to improve soil fertility and quality production through microbial application and organic amendments (Daniel et al., 2022).
Organic supplements, agronomic techniques, nutrient-efficient cultivars, compost, rhizobacteria and arbuscular mycorrhizal fungus work together to help plants thrive. Only some of the methods used to boost phosphorus availability (Kunwar et al., 2018). Symbiotic microorganisms have been demonstrated to boost crop growth and output, soil fertility, and the regeneration of damaged soils, all while decreasing the need for synthetic agrochemicals (Cavagnaro et al., 2015; Raklami et al., 2019). Increases in photosynthetic rate, water and nutrient absorption, and soil biological and physicochemical qualities are only a few of the ways in which AMF are known to boost plant development (Pii et al., 2015; Boutasknit et al., 2020). Because of the symbiotic link between plant roots and AMF, plants are better able to absorb minerals from the soil. In exchange, fungi receive energy from plants (Bona et al., 2016). The roots of the plants extend only 1–2 mm where mycorrhizae are not present, but AMF’s hyphae increase up to 8 cm and more which increases phosphorus availability for host plants. AMF assists the plant to absorb the essential mineral nutrient from the soil particularly phosphorus which is less available for plants (Begum et al., 2019). As a result of increasing the availability of mineral elements including nitrogen, phosphorus, and potassium, mycorrhizal fungi play a crucial role in nutrient cycling in soil and plants (Ait-El-Mokhtar et al. 2019b; Richardson et al., 2001).
PGPR increases the expansion and maturation of food crops by phytohormones production and mineralization of nutrients to increase their availability (Ilangumaran and Smith, 2017). Microbes can solubilize inorganic phosphate and potassium (El-Shaikh and Mohammed, 2009) and produce soil-active chemicals like auxin (Zhang et al., 2015) and exopolysaccharides (Sharma et al., 2013). Production of Auxin can encourage root development and architecture while exopolysaccharides influence the soil structure and maintain water film required for plant growth and photosynthetic activity (Gonawala and Jardos, 2018). The integrated application of AMF and PGPR seems to be very effective in sustainable farming via restoring the fertility of degraded lands and increasing plant growth (Das and Pradhan, 2016).
AMF interact with a variety of soil microorganisms and boost their activity while they are present in the rhizosphere. This leads to an increase in the number of positive impacts that AMF has on plant growth. According to Mbarki et al.'s research from 2020, the development of plants receives more benefits from the combination inoculation of AMF and PGPR than from the individual inoculation of either pathogen. According to Nanjundappa et al. (2019), the combination of AMF and PGPR increases the availability of nutrients, the permeability of root hyphae, and the plant's defense against biotic and abiotic stresses in plant tissues and soil, which in turn promotes the growth and development of the plant.
Compost and other organic materials are helpful because they promote microbial activity and supply essential nutrients (nitrogen, phosphorus, and potassium). Plants' crude fibers, crude lipids, and soluble carbon are all enhanced by composting (Hashem et al., 2019). Improved soil fertility can boost plant growth, yield, and nutritional content (Jaber et al., 2019). Producing organic acid soil, compost contributes 20–40% of phosphorus (Doan et al., 2015).
Compost and plant-associated microorganisms (AMF and/or PGPR) have been shown to increase plant growth, development, and yield by several studies (Zhu et al., 2016). To our knowledge, however, no data exist for the tripartite combination of the components on okra development and its physiology, and the joint influence of AMF, PGPR, and compost on plant performances has been seldom investigated (Campanelli et al., 2013). The goal of this study is to learn more about the biochemical and physiological mechanisms at play when native AMF and PGPR work together to promote okra development.