Antagonistic bioagent mechanisms of controlling potato soft rot

Bacterial antagonists are effective as an alternative to synthetic bactericides in the control of potato soft rot. The use of bioagents reduces the application of synthetic bactericides, which are harmful to humans and the environment. However, the mechanisms of some bioagents, such as some fungi and bacteria, are not yet understood. This paper reviews the current situation of potato soft rot, biological controls, antagonistic bioagents and their mechanisms, application strategies and future directions in today’s agriculture. These mechanisms include mycoparasitism, competition, rhizosphere colonisation, synthesis and release of metabolites. Bioagents increased the defensive system of plants by increasing the antioxidants genes, such as superoxide dismutase, peroxidase (POD) and catalase (CAT), and eventually increased the plant growth and yield production.

Epiphytic Bacteria from Sweet Pepper Antagonistic In Vitro to Ralstonia solanacearum BD 261, a Causative Agent of Bacterial Wilt

Biological control of plant pathogens, particularly using microbial antagonists, is posited as the most effective, environmentally-safe, and sustainable strategy to manage plant diseases. However, the roles of antagonists in controlling bacterial wilt, a disease caused by the most devastating and widely distributed pathogen of sweet peppers (i.e., R. solanacearum), are poorly understood. Here, amplicon sequencing and several microbial function assays were used to depict the identities and the potential antagonistic functions of bacteria isolated from 80 red and green sweet pepper fruit samples, grown under hydroponic and open soil conditions, with some plants, fungicide-treated while others were untreated. Amplicon sequencing revealed the following bacterial strains: Bacillus cereus strain HRT7.7, Enterobacter hormaechei strain SRU4.4, Paenibacillus polymyxa strain SRT9.1, and Serratia marcescens strain SGT5.3, as potential antagonists of R. solanacearum. Optimization studies with different carbon and nitrogen sources revealed that maximum inhibition of the pathogen was produced at 3% (w/v) starch and 2,5% (w/v) tryptone at pH 7 and 30 °C. The mode of action exhibited by the antagonistic isolates includes the production of lytic enzymes (i.e., cellulase and protease enzymes) and siderophores, as well as solubilization of phosphate. Overall, the results demonstrated that the maximum antimicrobial activity of bacterial antagonists could only be achieved under specific environmental conditions (e.g., available carbon and nitrogen sources, pH, and temperature levels), and that bacterial antagonists can also indirectly promote crop growth and development through nutrient cycling and siderophore production.

Potential Bacterial Antagonists from Cowshed Air for the Management of Fusarium Pathogens in Stored Rice

Rice is the principal staple food for more than half population of earth which is infested by many pathogens including Fusarium . Numbers of Fusarium species are responsible for causing pathogenic implications in rice like bakanae, rot, blight, etc. Majority of them produce mycotoxins which are responsible for human and animal toxicity and the cause of cancer disease. Adoption of biological control methods utilizing microbial antagonists might be an eco-friendly option. Bacterial species including Bacillus species have been isolated from various sources for utilisation as biocontrol agents to combat crop pathogens. Cow dung and the cow shed air have been a good source of such antagonistic bacteria. Hence, in the current study eighteen bacteria (BC1 to BC18) including Bacillus species have been isolated from cow shed air and paddy seeds stored in cowshed of Odisha, India. Bacteria isolated from domestic cowshed showed excellent inhibitory capacity than those of commercial cowshed against pathogenic Fusarium F90 and pathogenic as well as fumonisin producing Fusarium F55. Non-fumonisin producer Fusarium F90 was inhibited relatively with higher degree by all the antagonistic bacteria even it was completely suppressed by BC6 after three days of interaction. Paddy seeds stored in cowshed were found to be saturated with cowshed antagonistic bacteria. These bacterial antagonists hold potential to be utilized as Biological Control Agents (BCA) for safeguarding rice production. Investigation on more number of bacterial species from more cowsheds will definitely give more insights in the pattern and mode of inhibition.

Evaluation of Rhizosphere Bacterial Antagonists for the Management of Fusarium Wilt in Tomato Plants

Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici is a serious problem limiting tomato production worldwide. The intent of the study was to evaluate potential of bacterial antagonists to suppress fusarium wilt disease development and evaluate the role of the strains as plant growth-promoting rhizobacteria (PGPR) in tomato. Among fifty-two bacterial strains isolated from rhizoplane and rhizosphere of healthy tomato roots, five isolates viz. isolate-01, isolate-17, isolate-23, isolate-24 and isolate-32 were found highly inhibitory against mycelial growth of Fusarium sp., in dual cultures. Highest inhibition of radial mycelial growth of pathogen in dual culture was induced by isolate-24 (72.2%) followed by isolate-32 (71.9%). In greenhouse experiments percent disease incidence (PDI) was lower in artificially inoculated tomato plants treated with isolate-32 (7.8%) and isolate-24 (8.9%), with percent disease reduction over control of 85.6% and 83.6%, respectively. These isolates also exhibited significant difference in seed germination percentage under artificial inoculation along with pathogen, highest germination percentage was recorded by isolate-32 (91%) followed by isolate-24 (89%) as compared to pathogen inoculated control (24%). The study concluded that the two native rhizobacteria isolated from root zone of healthy tomato plants could successfully protect the tomato plants from the lethal infection by Fusarium sp. while enhancing the germination of the treated plants.