Biocontrol of pistachio gummosis using encapsulated Pseudomonas chlororaphis VUPF5.

Abstract

In this study, the biocontrol and plant growth-promoting properties of Pseudomonas chlororaphis VUPF5 were comprehensively evaluated using a series of in vitro biochemical assays. The strain showed strong enzymatic activities, such as the production of cellulase and protease, which contribute to nutrient recycling and degradation of pathogenic fungal structures. In addition, the ability to solubilize phosphate, produce siderophores, HCN, and indole-3-acetic acid (IAA) underscores its versatile potential to promote plant health and control pathogens through both direct and indirect mechanisms. To improve the viability and efficiency of the VUPF5 strain under environmental stress, it was encapsulated with a composite matrix of sodium alginate and soy protein isolate (SPI). Structural characterization by XRD, FTIR, and SEM confirmed the formation of a stable, biocompatible microcapsule with high encapsulation efficiency (approx. 84%) and controlled release over 55 days. These capsules protected the bacteria from environmental fluctuations while allowing their gradual release, ensuring sustained bioactivity in the soil. Greenhouse trials with pistachio seedlings infected with Phytophthora drechsleri showed that plants treated with microcapsules had an 87% disease control rate, outperforming both the free bacterial suspension and control groups. Interestingly, even empty capsules showed moderate protection, likely due to the bioactive nature of SPI, suggesting an additive effect in strengthening plant defenses. Overall, VUPF5 is a promising dual-function bioinoculant that improves plant growth and disease control. Encapsulation enhances its survival, release, and contribution to plant resistance, thus supporting sustainable agriculture.