Biopolymers as Seed-Coating Agent to Enhance Microbially Induced Tolerance of Barley to Phytopathogens

Abstract

Infections of agricultural crops caused by pathogen ic fungi are among the most widespread and harmful, as they not only reduce the quantity of the harvest but also significantly deteriorate its quality. This study aims to develop unique seed-coating formulations incorporating biopolymers (polyhydroxyalkanoate and pullulan) and beneficial microorganisms for plant protection against phytopathogens. A microbial association of biocompatible endophytic bacteria has been created, including Pseudomonas flavescens D5, Bacillus aerophilus A2, Serratia proteamaculans B5, and Pseudomonas putida D7. These strains exhibited agronomically valuable properties: synthesis of the phytohormone IAA (from 45.2 to 69.2 µg mL^-1), antagonistic activity against Fusarium oxysporum and Fusarium solani (growth inhibition zones from 1.8 to 3.0 cm), halotolerance (5-15% NaCl), and PHA production (2.77-4.54 g L^-1). A pullulan synthesized by Aureobasidium pullulans C7 showed a low viscosity rate (from 395 Pa·s to 598 Pa·s) depending on the concentration of polysaccharide solutions. Therefore, at 8.0%, w/v concentration, viscosity virtually remained unchanged with increasing shear rate, indicating that it exhibits Newtonian flow behavior. The effectiveness of various antifungal seed coating formulations has been demonstrated to enhance the tolerance of barley plants to phytopathogens.

Keywords: beneficial microorganisms; biocontrol; dynamic viscosity; polyhydroxyalkanoate; polysaccharides; seed coating.

Figure 1

Inhibition of the growth of the phytopathogenic fungus Fusarium solani by strains (a) Bacillus simplex B9 and (b) Serratia proteamaculans B5.

Figure 2

Growth of bacterial strains on medium containing (a) 5% NaCl and (b) 15% NaCl. D5—Pseudomonas flavescens D5, A2—Bacillus aerophillus A2, B5—Serratia proteamaculans B5, B9—Bacillus simplex B9, D7—Pseudomonas putida D7.

Figure 3

Viscosity of exopolysaccharide solutions produced by B. thuringiensis C8 in different concentrations.

Figure 4

Viscosity of pullulan solutions produced by A. pullulans C7 in different concentrations.

Figure 5

Scheme of pot experiments.

Figure 6

Influence of various pre-sowing treatments on barley seed germination energy and germination capacity.

Figure 7

Barley growth under phytopathogenic stress with different seed treatment variants: (a) T2—untreated, (b) T3—treatment with bacterial suspension, (c) T5—seed coating in polymer mixture with bacterial suspension.