Exploring Two Streptomyces Species to Control Rhizoctonia solani in Tomato

Marzieh Ebrahimi-Zarandi,Essaid Ait Barka,Roohallah Saberi Riseh,Mohamed El-Shetehy,Ismail Saadoun,Gholam Hosein Shahidi Bonjar

doi:10.3390/agronomy11071384

Abstract

Streptomyces species are effective biocontrol agents toward many plant pathogens. These microorganisms are well known for producing secondary metabolites, promoting plant growth and inducing plant defense mechanisms. In this study, the ability of tomato root-colonizing Streptomyces strains to trigger the resistance against Rhizoctonia solani (J.G. Kühn) AG4 was investigated. For this goal, we evaluated the pattern of LOXB and PAL1 genes expression changes upon pathogen inoculation in primed tomato plants. The results revealed that Streptomyces globisporous (Krasil’nikov) strain F8 and S. praecox (Millard and Burr) strain R7 were able to enhance the expression of lipoxygenase and phenylalanine ammonia lyase in tomato plants. This finding suggests that Streptomyces strains F8 and R7 may trigger jasmonic acid and phenyl propanoid signaling pathways in plants, therefore, resulting an induced defense status in tomatoes against R. solani. Biochemical characterization of these Streptomyces strains showed that they were strong producers of siderophores. S. praecox strain R7 produced siderophores of hyderoxamate and catechol types and S. globisporous strain F8 produced a phenolic siderophore. Moreover, they also produced protease while only the S. praecox strain R7 was able to produce amylase. Taken together, these results indicate that S. globisporous strain F8 and S. praecox strain R7 promote plant growth and reduces disease and hence are suitable for future in depth and field studies with the aim to attain appropriate biocontrol agents to protect tomatoes against R. solani.

Highlights

We investigated PAL1 gene expression changes in leaves and roots and LOXB gene expression changes in leaves at different time intervals upon pathogen inoculation in tomato plants that were treated with Streptomyces strains R7 and F8, primarily
The present study demonstrated that S. globisporus and S. praecox are able to enhance the expression of plant defense genes encoding enzymes such as phenylalanine ammonia lyase (PAL) and lipooxygenase (LOX) in tomato seedlings
Despite the level of gene expression being low during the interaction between S. globisporous strain F8 or S. praecox strain R7 and pathogen in the tomato plant, it may suggest the involvement of jasmonic acid (JA) and salicylic acid (SA) signaling pathways upon the strain’s perception, as reflected by the increased expression of LOX, which is a key element of the oxylipin synthesis, and an induced expression of PAL gene, which was found to be induced by SA

Summary

Introduction

Investigation on the relationship between microbiota and their host plants is crucial for innovative sustainable agriculture. In addition to managing abiotic and biotic stresses in plants, Plant Growth Promoting Rhizobacteria (PGPR) affect the plants fitness and growth in two different manners, which are directly or indirectly. While PGPR are able to trigger plant growth by mobilizing nutrients in soils or producing numerous growth regulators, they protect plants from plant pathogens either by controlling invaders or by triggering plant defense mechanisms. During last decades, “induced resistance” to diseases or plant “immunization” has received interesting attention. Colonization of plant roots by PGPR can induce a systemic resistance in plants [1]. Primed plants respond faster and stronger defense responses to future stresses, which is a process named priming [2,3,4,5]

Methods

Results

Discussion

Conclusion