THE EFFECT OF TWO BACILLUS ISOLATES ON ROOT ELONGATION OF WHEAT SEEDLINGS

Wheat is grown on 20% of the cultivated land area of the world and is a main food resource for 40% of the world’s population (Braun et al., 2010). In 2019, the forecast of wheat production is at nearly 771 million tonnes, 5.6 percent high than previous year’s (FAO, 2019). In 2050, the world’s population is expected to reach 9 billion, thus it is estimated that cereal production needs to increase by 50% by 2030 (Alexandratos and Bruinsma, 2012). The wheat production is suffering substantial losses of biotic and abiotic stress factors (Elad and Pertot, 2014; Kan et al., 2017). PGPRs (Plant Growth Promoting Rhizobacteria) are a group of beneficial bacteria living in the rhizosphere, the phyllosphere, or in the plant tissues as entophytes (Ahemad and Kibret, 2014; Miliutė et al., 2015). PGPRs can promote plant growth against stresses by direct and indirect mechanisms or a combination of both (Ertürk et al., 2010; Siddikee et al., 2010; Kusek and Çınar, 2012; Imriz et al., 2014; Unlu and Aysan, 2016; Telek et al., 2019). Indirect mechanisms comprise the suppression of pathogens through the production of antibiotics and extracellular hydrolytic enzymes and the action of siderophores, Inducing Systemic Resistance (ISR), exo-polysaccharides production. Direct mechanisms involve making the natural nutrition source ready to use for plants including fixation of atmospheric nitrogen, solubilisation of phosphorus, potassium and iron; production of siderophores; producing phytohormones like auxins, cytokinins and gibberellins, (Ahemad and Kibret, 2014) or by the activity of 1-aminocyclopropane-1carboxylate (ACC)-deaminase, an enzyme which can hinder the “plant stress ethylene” that is typically arose by a number of environmental stresses such as flooding, extreme temperature, the presence of organic and inorganic toxicants, phytopathogens, drought or high salt concentrations (Cheng et al., 2007; Glick, 2014; Gamalero and Glick, 2015).