Plant growth-promoting microorganisms as biocontrol agents of plant diseases: Mechanisms, challenges and future perspectives

Abstract

Plant diseases and pests are risk factors that threaten global food security. Excessive chemical pesticide applications are commonly used to reduce the effects of plant diseases caused by bacterial and fungal pathogens. A major concern, as we strive toward more sustainable agriculture, is to increase crop yields for the increasing population. Microbial biological control agents (MBCAs) have proved their efficacy to be a green strategy to manage plant diseases, stimulate plant growth and performance, and increase yield. Besides their role in growth enhancement, plant growth-promoting rhizobacteria/fungi (PGPR/PGPF) could suppress plant diseases by producing inhibitory chemicals and inducing immune responses in plants against phytopathogens. As biofertilizers and biopesticides, PGPR and PGPF are considered as feasible, attractive economic approach for sustainable agriculture; thus, resulting in a “win-win” situation. Several PGPR and PGPF strains have been identified as effective BCAs under environmentally controlled conditions. In general, any MBCA must overcome certain challenges before it can be registered or widely utilized to control diseases/pests. Successful MBCAs offer a practical solution to improve greenhouse crop performance with reduced fertilizer inputs and chemical pesticide applications. This current review aims to fill the gap in the current knowledge of plant growth-promoting microorganisms (PGPM), provide attention about the scientific basis for policy development, and recommend further research related to the applications of PGPM used for commercial purposes.

Agroecological Management of the Grey Mould Fungus Botrytis cinerea by Plant Growth-Promoting Bacteria

“…However, there are still some gaps in the knowledge of bacteria-fungus interactions that can better direct their dual action in the field and that do not harm other endemic beneficial organisms. Other precautions that must be taken before releasing a biofungicide were recently proposed by other authors [ 22 ]. Finally, the search and characterisation of new species of PGPB and their anti- Botrytis compounds will continue to be a resource that should be explored with greater effort to have better and more sustainable agricultural practices for the sake of our planet.…”

“…Therefore, alternatives have been sought to eliminate or reduce the use of synthetic chemicals to control B. cinerea , including the use of microbial agents such as Trichoderma harzianum [ 17 ], T. viride , T. virens [ 18 ], Ulocladium spp. [ 19 ], Clonostachys rosea [ 20 ], Gliocladium catenulatum , Saccharomyces cerevisiae , Wickerhamomyces anomalus , Metschnikowia pulcherrima , and Aureobasidium pullulans [ 21 , 22 ], as well as diverse plant growth-promoting bacterial species (PGPB) [ 11 , 23 , 24 , 25 , 26 , 27 ]. This last group of beneficial bacteria, in addition to stimulating plant growth directly, can also antagonise fungal pathogens, such as B. cinerea, through various mechanisms [ 28 ].…”

Study on the Potential for Stimulating Mulberry Growth and Drought Tolerance of Plant Growth-Promoting Fungi

“…The mechanisms employed by plant-beneficial microorganisms to promote growth are involved in various ways. Specifically, they benefit plants directly by phytohormone production and modulation such as indole-3-acetic acid (IAA) and gibberellin (GA) [ 19 ], enhancement of nutrient acquisition including iron, phosphorus, and nitrogen elements, and production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase [ 20 , 21 ]. It was reported that endosymbiont Piriformospora indica could promote tomato growth by elevating putrescine, IAA, and GA levels [ 22 ].…”

Exploration of Antagonistic Fungi From Rhizospheric Soil Against Phytopathogens of Solanum melongena and Citrus sinensis

“…For several years, a great deal of money and manpower is invested to protect the crop plants from fungal pathogens for ensuring good quantitative and qualitative yield, but still, it remains as a burning problem. The potential issues as toxicity, environmental pollution and side effects on human health hinder the applicability of chemical agents for fighting the phytopathogens (1) .…”

“…Commercialization of biological control agents for plant diseases is following a slow pace mainly due to their variable performances under different environmental conditions in the field, their host specificity and low efficacy to manage the disease (5) . The performance of a biocontrol agent depends on the survival rate in the soil, its compatibility with the crop plant, interaction with other soil microbial species and the environmental factors (1) . These limitations can be overcome if we can identify the biologically active compound from the antagonistic organism and extract it in the pure form.…”