Iron‑Supplemented Alginate Beads of Pseudomonas chlororaphis Improves Charcoal Rot Disease Resistance and the Productivity in Tomato Plants

Abstract

Charcoal rot disease, caused by Macrophomina phaseolina, poses a major threat to tomatoes. Encapsulating biocontrol bacteria in alginate offers a novel and effective solution with advantages in viability, shelf life, and controlled release. The current research was conducted to develop alginate beads of biocontrol bacteria and to evaluate their inhibitory capacity against M. phaseolina in combination with essential metal iron (Fe) using in vitro and in planta tests. In vitro, Pseudomonas chlororaphis subsp. chlororaphis (PCC-01) exhibited 71% antifungal activity. It also had plant growth-promoting traits of indole-3-acetic acid, hydrogen cyanide, phosphate, and mineral solubilization. FTIR and UV–vis spectra specified good affinity of PCC-01 and alginate, as revealed by changes in the intensity of peaks, particularly at the protein regions (1600– 1200 cm− 1). The bacterial-loaded alginate beads had excellent properties of encapsulation efficiency (96.20%), swelling ratio (66.47%), moisture content (92.50%), size [1.31 mm (wet) and 0.70 mm (dry)], and ensured slow release of entrapped bacteria up to 120 days. PCA-based biplot, hierarchical clustering, and heat map analysis for in vitro bioassays verified that the antifungal activity of PCC-01-alginate beads improved in nutrient medium supplemented with Fe (91–98%), followed by Mn (74–86%) and Zn (60–76%) via dual culture and modified dual culture methods. In planta, multivariate statistical analyses based on 18 traits related to growth parameters, yield, and biochemical indices of the tomato plants confirmed the greater disease-managing potential of Fe-amended alginate beads of PCC-01 through maximal economic benefits. Therefore, different formulations of PCC-01 and Fe could be prepared and commercialized as a single application product for sustainable and profitable tomato crop production.