INTEGRATING PHOSPHORUS SOLUBILIZATION AND FUNGAL PATHOGENS BIOCONTROL: STREPTOMYCES SPP. AS A DUAL-SOLUTION FOR SUSTAINABLE TOMATO PRODUCTION IN EGYPT

Abstract

Phosphorus (P) deficiency and fungal plant diseases critically limit tomato productivity in Egypt’s P-deficient soils. This study investigated the dual potential of indigenous Streptomyces spp. to enhance P bioavailability and suppress fungal diseases. Seventeen actinobacterial isolates from tomato rhizospheres were screened for P-solubilization and antifungal activity. Streptomyces sp. BK5 demonstrated superior rock phosphate (RP) solubilization (phosphate solubilization index: 1.77) via acidification, releasing 130 mg mL⁻¹ P at 4 g/L RP. Pot trials revealed that the BK5 isolate inoculation significantly increased tomato fresh weight (5.65 vs. 4.89 g control) and tissue P concentration (0.20% vs. 0.18% control), particularly with rock phosphate (RP), highlighting microbial-mediated P mobilization. Factorial ANOVA confirmed P application rate (≤75% recommended dose) as the primary growth driver, while the isolate BK5 enhanced P assimilation without affecting dry biomass. In addition to the positive effect to solubilize P, Confrontation experiment was assessed. Results of the in vitro experiment revealed that Streptomyces sp.BK5 inhibited Fusarium oxysporum (27%), F. solani (32%), Alternaria solani (53%), and Rhizoctonia solani (45%) through antifungal metabolites. Detached leaf assays validated the isolate BK5’s crude extract suppressed pathogen growth by 58-67%. These findings underscore Streptomyces sp. BK5’s dual agrobiotechnological role in sustainable P management and broad-spectrum disease suppression, advocating integrated biofertilizer-biocontrol strategies to reduce reliance on synthetic inputs, optimize tomato yields, and advance eco-friendly agriculture in P-stressed ecosystems.