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.

Jun Chen,Xianjin Qin,Liuting Zhou,Juanying Wang,Linkun Wu,Israr Ud Din,Wenxiong Lin,Hongmiao Wu,Qian Li,Yasir Arafat,Tingting Wu,Sheng Lin,Ganga Raj Pokhrel

doi:10.3389/fmicb.2021.579920

Abstract

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

Highlights

Due to the allelopathy and the dysbiosis of microorganisms, continuous planting of many Chinese medicinal herbs in the same land results in a significant decrease in yield and quality, which is known as continuous monoculture problem or soil sickness (Zhang and Lin, 2009; Zhao et al, 2015; Wu et al, 2016)
The role of root-associated mutualistic plant symbiont, Trichoderma spp., in activation of R. pseudostellariae immunity by triggering the expression of defense-related genes is never explored. The objectives of this present study are as follows: (1) to analyze the changes of Trichoderma communities in rhizosphere soil under R. pseudostellariae monoculture using denatured gradient gel electrophoresis (DGGE) combined with quantitative PCR technique and (2) further, to study the effect of different Trichoderma strains on the growth and defense response of R. pseudostellariae against the F. oxysporum and to assess the expression level of defense-related genes in R. pseudostellariae treated with the selected Trichoderma isolate
Abundance of Trichoderma spp. was significantly decreased with prolonged monoculture (Figure 3). These results were consistent with the Trichoderma-specific DGGE analysis (Supplementary Figure 2)

Summary

Introduction

Due to the allelopathy and the dysbiosis of microorganisms, continuous planting of many Chinese medicinal herbs in the same land results in a significant decrease in yield and quality, which is known as continuous monoculture problem or soil sickness (Zhang and Lin, 2009; Zhao et al, 2015; Wu et al, 2016). Successive cultivation of R. pseudostellariae on the same piece of land leads to a decline in both the quality and yield owing to poor plant performance and insufficient biotic stress resistance (Lin et al, 2015). Most of researches in continuous monoculture problem of R. pseudostellariae and their potential biological microorganisms are focused on prokaryotes (i.e., Pseudomonas spp. and Burkholderia spp.) (Wu et al, 2016a; Chen et al, 2017). To develop a reliable system of biological control against plant pathogens, we need to explore the antagonizing role of potentially important eukaryotic microorganisms like fungi as well

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