The Role of Endophytes in Combating Fungal- and Bacterial-Induced Stress in Plants

Abstract

Plants are subjected to multifaceted stresses that significantly jeopardize crop production. Pathogenic microbes influence biotic stress in plants, which ultimately causes annual crop loss worldwide. Although the use of pesticides and fungicides can curb the proliferation of pathogens in plants and enhance crop production, they pollute the environment and cause several health issues in humans and animals. Hence, there is a need for alternative biocontrol agents that offer an eco-friendly mode of controlling plant diseases. This review discusses fungal- and bacterial-induced stress in plants, which causes various plant diseases, and the role of biocontrol defense mechanisms, for example, the production of hydrolytic enzymes, secondary metabolites, and siderophores by stress-tolerant fungi and bacteria to combat plant pathogens. It is observed that beneficial endophytes could sustain crop production and resolve the issues regarding crop yield caused by bacterial and fungal pathogens. The collated literature review indicates that future research is necessary to identify potential biocontrol agents that can minimize the utility of synthetic pesticides and increase the tenable agricultural production.

Keywords: antagonism; biocontrol mechanism; endophytes; induced stress.

Figure 1

Endophytic biocontrol mode of defense mechanisms against pathogens. Stage 1: Bacteria and fungi invade the plant through a wound or stomatal opening. Stage 2: Both bacteria and fungi degrade the plant cell wall with the aid of enzymes, secondary metabolites, or virulent factors. Bacteria proliferate through the intercellular space, whereas fungi invade the plant by a biotrophic or necrotrophic mechanism using appressorium (A), germ tube (G.T.), and spore and proliferate in the cells of the plant. Endophytes provide defense against pathogens through various modes of action, such as (a) hydrolytic enzyme; (b) mycoparasitism; (c) siderophore; and (d) SAR and ISR modes of action. Note: ISR, induced systemic resistance; JA, jasmonic acid; MAMPs, microbe-associated molecular patterns; NPR1, non-expressor of pathogenesis-related genes 1; PAMPs, pathogen-associated molecular patterns; PRRs, pattern recognition receptors; PTI, pathogen-triggered immunity; SA, salicylic acid; SAR, systemic acquired resistance.