Combatting Sugar Beet Root Rot: Streptomyces Strains’ Efficacy against Fusarium oxysporum

Abstract

Sugar beet root rot disease triggered by <i>Fusarium oxysporum</i> f. sp. <i>radicis-betae</i> is a destructive disease and dramatically affects the production and quality of the sugar beet industry. Employing beneficial microorganisms as a biocontrol strategy represents an eco-friendly and sustainable approach to combat various plant diseases. The distinct aspect of this study was to assess the antifungal and plant growth-promoting capabilities of recently isolated <i>Streptomyces</i> to treat sugar beet plants against infection with the phytopathogen <i>F. oxysporum</i>. Thirty-seven actinobacterial isolates were recovered from the rhizosphere of healthy sugar beet plants and screened for their potential to antagonize <i>F. oxysporum</i> in vitro. Two isolates SB3-15 and SB2-23 that displayed higher antagonistic effects were morphologically and molecularly identified as <i>Streptomyces</i> spp. Seed treatment with the fermentation broth of the selected <i>Streptomyces</i> strains SB3-15 and SB2-23 significantly reduced disease severity compared to the infected control in a greenhouse experiment. <i>Streptomyces</i> SB2-23 exhibited the highest protective activity with high efficacy ranging from 91.06 to 94.77% compared to chemical fungicide (86.44 to 92.36%). Furthermore, strain SB2-23 significantly increased plant weight, root weight, root length, and diameter. Likewise, it improves sucrose percentage and juice purity. As a consequence, the strain SB2-23's intriguing biocontrol capability and sugar beet root growth stimulation present promising prospects for its utilization in both plant protection and enhancement strategies.