Integrated Use of Trichoderma harzianum and Plant Extracts for Managing Fusarium Root Rot and Inducing Defense Genes in Sugar Beet

Fusarium oxysporum f. sp. betae is responsible for damping-off and root rot diseases that affect sugar beet (Beta vulgaris L.), the most important industrial crop in Egypt. Among ten Trichoderma spp. Isolates, which were evaluated against F. oxysporum in vitro, the El-Nubaria-T3 isolate was the most effective. Moringa (Moringa oleifera) and lemongrass (Cymbopogon citratus) extracts at various concentrations (1, 3, 6, and 9%), particularly lemongrass at higher concentrations, were more effective in reducing the linear growth of F. oxysporum compared to the Trichoderma spp. isolates in vitro, which appeared to be resistant to the antifungal activity of both extracts. Maxim fungicide and the combination of T. harzianum with either lemongrass or moringa extract were the most effective treatments in reducing F. oxysporum damping-off and root-rot disease severity, while also increasing plant survival compared to the control in vivo. These treatments significantly increased the expression levels of peroxidase and PAL genes compared to those observed for chitinase SP2 and SE2 gene expressions. High-speed solid-phase microextraction (HS-SPME) coupled with GC-MS was used to analyze and evaluate 32 volatile compounds in lemongrass and 26 components in moringa aqueous extract, respectively. Analysis of the lemongrass extract using High-Performance Liquid Chromatography (HPLC) identified ten phenolic acids and eight flavonoids in the aqueous extract. Under field conditions, the combination of T. harzianum with lemongrass and moringa significantly reduced damping-off, root-rot, and disease severity while improving plant survival, yield, and yield components, including total soluble solids, sucrose content, and purity during the 2021/2022 and 2022/2023 growing seasons.