Characterization of Tomato Seed Endophytic Bacteria as Growth Promoters and Potential Biocontrol Agents

Abstract

Endophytic bacteria residing within plant seeds are increasingly recognized for their potential to enhance plant growth and provide biocontrol against pathogens. Despite this, seed-borne endophytes remain underexplored in many crops, including tomato. In this study, we isolated and characterized bacterial endophytes from tomato seeds and evaluated their plant growth-promoting traits and antifungal activities. The taxonomic analysis of the Hawaii 7996 tomato seed endophyte collection revealed a diverse community, predominantly from the phylum Bacillota, with Paenibacillaceae and Bacillaceae as the most abundant families. Among the 35 unique strains identified, 19 produced indole-3-acetic acid, four exhibited siderophore production, and 12 could solubilize phosphate. These traits contribute to growth promotion and disease suppression in plants. In the plant growth promotion assay, several bacterial strains, notably Streptomyces olivaceus (BHM1), Streptomyces variegatus (BHM3), Bacillus stercoris (BHR2), and Moraxella osloensis (YHT4-1), demonstrated significant potential for tomato cultivation by positively affecting fresh weight, stem length, and root length. These strains consistently promoted growth across all three parameters evaluated in this study. Furthermore, several strains exhibited strong antifungal activity against major tomato pathogens, including Fusarium oxysporum race 1 and 2, and Botrytis cinerea. Notably, Bacillus subtilis (BHN1), Bacillus stercoris (BHR2), and Paenibacillus peoriae (YHR2-1) showed broad-spectrum antifungal efficacy. Our findings highlight the potential of seed-associated endophytic bacteria as growth promoters and biological control agents, offering promising avenues for sustainable agricultural practices.