Antagonistic Activity of Trichoderma spp. Against Fusarium oxysporum in Rhizosphere of Radix pseudostellariae Triggers the Expression of Host Defense Genes and Improves Its Growth Under Long-Term Monoculture System

Abstract

Under consecutive monoculture, the abundance of pathogenic fungi, such as <i>Fusarium oxysporum</i> in the rhizosphere of <i>Radix pseudostellariae</i>, negatively affects the yield and quality of the plant. Therefore, it is pertinent to explore the role of antagonistic fungi for the management of fungal pathogens such as <i>F. oxysporum.</i> Our PCR-denatured gradient gel electrophoresis (DGGE) results revealed that the diversity of <i>Trichoderma</i> spp. was significantly declined due to extended monoculture. Similarly, quantitative PCR analysis showed a decline in <i>Trichoderma</i> spp., whereas a significant increase was observed in <i>F. oxysporum</i>. Furthermore, seven <i>Trichoderma</i> isolates from the <i>R. pseudostellariae</i> rhizosphere were identified and evaluated <i>in vitro</i> for their potentiality to antagonize <i>F. oxysporum</i>. The highest and lowest percentage of inhibition (PI) observed among these isolates were 47.91 and 16.67%, respectively. In <i>in vivo</i> assays, the <i>R. pseudostellariae</i> treated with four <i>Trichoderma</i> isolates, having PI > 30%, was used to evaluate the biocontrol efficiency against <i>F. oxysporum</i> in which <i>T. harzianum</i> ZC51 enhanced the growth of the plant without displaying any disease symptoms. Furthermore, the expression of eight defense-related genes of <i>R. pseudostellariae</i> in response to a combination of <i>F. oxysporum</i> and <i>T. harzianum</i> ZC51 treatment was checked, and most of these defense genes were found to be upregulated. In conclusion, this study reveals that the extended monoculture of <i>R. pseudostellariae</i> could alter the <i>Trichoderma</i> communities in the plant rhizosphere leading to relatively low level of antagonistic microorganisms. However, <i>T. harzianum</i> ZC51 could inhibit the pathogenic <i>F. oxysporum</i> and induce the expression of <i>R. pseudostellariae</i> defense genes. Hence, <i>T. harzianum</i> ZC51 improves the plant resistance and reduces the growth inhibitory effect of consecutive monoculture problem.