Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, ...limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.
The coconut rhinoceros beetle (CRB; Oryctes rhinoceros) is one of the most destructive insect pests of coconut and oil palms in tropical Asia and the Pacific islands. Members of a new variant, known ...as CRB-G (clade I), have recently spread into the Pacific islands, causing significant damage. Biopesticides containing Metarhizium spp. are the strongest candidates for inundative biological control against the emerging CRB threat. Selection of the most virulent and robust isolate may determine the impact of this control option on the pest. In this work, CRB specimens with natural fungal infection were collected in Papua New Guinea (PNG) and Solomon Islands (SI). Putative entomopathogenic fungi were isolated and identified. These new isolates and some previously obtained from other Pacific countries were molecularly identified, characterized, and tested for virulence against CRB larval populations in PNG and SI in laboratory bioassays. Of the new isolates collected, four obtained from SI were identified as Metarhizium majus (conidia length ⁓11–15 μm), and four from PNG were identified as Metarhizium pingshaense (conidia length ⁓4–6 μm). The most virulent isolate was M. majus AgR-F717, which caused 100 % mortality in 20–23 days against a CRB variant from the CRB-S grouping (clade II) in laboratory bioassays carried out in PNG. Isolates of M. pingshaense did not show pathogenicity against CRB larvae. M. majus AgR-F717 was also the most virulent in laboratory bioassays using the mixed SI population (from both CRB-S and CRB-G groupings) and was selected for further evaluation using artificial breeding sites. Under field conditions, this isolate demonstrated its ability to infect CRB, dispersal up to 100 m from treated artificial breeding sites, and persistence in soil for at least four months. The new isolate AgR-F717 of M. majus has demonstrated potential as an augmentative biological control agent for CRB in PNG and SI.
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•Four new Metarhizium majus isolates from Solomon Islands were identified and characterized.•Four new Metarhizium pingshaense isolates from Papua New Guinea were identified and characterized.•New M. pingshaense isolates AgR-F718 and F720 did not infect Oryctes rhinoceros larvae.•M. majus AgR-F717 caused 100 % mortality and was the most virulent against O. rhinoceros larvae.•AgR-F717 dispersed up to 100m from treated sites and persisted in soil for ≥4 months.
Losses in crop yields due to disease need to be reduced in order to meet increasing global food demands associated with growth in the human population. There is a well-recognized need to develop new ...environmentally friendly control strategies to combat bacterial crop disease. Current control measures involving the use of traditional chemicals or antibiotics are losing their efficacy due to the natural development of bacterial resistance to these agents. In addition, there is an increasing awareness that their use is environmentally unfriendly. Bacteriophages, the viruses of bacteria, have received increased research interest in recent years as a realistic environmentally friendly means of controlling bacterial diseases. Their use presents a viable control measure for a number of destructive bacterial crop diseases, with some phage-based products already becoming available on the market. Phage biocontrol possesses advantages over chemical controls in that tailor-made phage cocktails can be adapted to target specific disease-causing bacteria. Unlike chemical control measures, phage mixtures can be easily adapted for bacterial resistance which may develop over time. In this review, we will examine the progress and challenges for phage-based disease biocontrol in food crops.
Fungal diseases result in significant losses of fruits and vegetables during handling, transportation and storage. At present, post-production fungal spoilage is predominantly controlled by using ...synthetic fungicides. Under the global climate change scenario and with the need for sustainable agriculture, biological control methods of fungal diseases, using antagonistic microorganisms, are emerging as ecofriendly alternatives to the use of fungicides. The potential of microbial antagonists, isolated from a diversity of natural habitats, for postharvest disease suppression has been investigated. Postharvest biocontrol systems involve tripartite interaction between microbial antagonists, the pathogen and the host, affected by environmental conditions. Several modes for fungistatic activities of microbial antagonists have been suggested, including competition for nutrients and space, mycoparasitism, secretion of antifungal antibiotics and volatile metabolites and induction of host resistance. Postharvest application of microbial antagonists is more successful for efficient disease control in comparison to pre-harvest application. Attempts have also been made to improve the overall efficacy of antagonists by combining them with different physical and chemical substances and methods. Globally, many microbe-based biocontrol products have been developed and registered for commercial use. The present review provides a brief overview on the use of microbial antagonists as postharvest biocontrol agents and summarises information on their isolation, mechanisms of action, application methods, efficacy enhancement, product formulation and commercialisation.
Crop disease remains a major problem to global food production. Excess use of pesticides through chemical disease control measures is a serious problem for sustainable agriculture as we struggle for ...higher crop productivity. The use of plant growth promoting rhizobacteria (PGPR) is a proven environment friendly way of controlling plant disease and increasing crop yield. PGPR suppress diseases by directly synthesizing pathogen-antagonizing compounds, as well as by triggering plant immune responses. It is possible to identify and develop PGPR that both suppress plant disease and more directly stimulate plant growth, bringing dual benefit. A number of PGPR have been registered for commercial use under greenhouse and field conditions and a large number of strains have been identified and proved as effective biocontrol agents (BCAs) under environmentally controlled conditions. However, there are still a number of challenges before registration, large-scale application, and adoption of PGPR for the pest and disease management. Successful BCAs provide strong theoretical and practical support for application of PGPR in greenhouse production, which ensures the feasibility and efficacy of PGPR for commercial horticulture production. This could be pave the way for widespread use of BCAs in agriculture, including under field conditions, to assist with both disease management and climate change conditions.
We evaluated Fusarium verticillioides and fumonisin contamination in maize samples after application of a non-aflatoxigenic Aspergillus flavus strain in the field. The sampling was performed 150 days ...after planting. The results showed a reduction in F. verticillioides frequency, as well as in fumonisin levels when samples were obtained from field areas treated with non-aflatoxigenic A. flavus strain. These results suggested a competition for substrate or space between fungi reducing the frequency of F. verticillioides and, consequently, fumonisin production.
•Fusarium verticillioides frequency was reduced with an Aspergillus flavus strain.•An Aspergillus flavus strain controled fumonisin contamination.•Non-toxigenic Aspergillus seem to be an alternative for control fumonisin.
While phages hold promise as an antibiotic alternative, they encounter significant challenges in combating bacterial infections, primarily due to the emergence of phage-resistant bacteria. Bacterial ...defence mechanisms like superinfection exclusion, CRISPR, and restriction-modification systems can hinder phage effectiveness. Innovative strategies, such as combining different phages into cocktails, have been explored to address these challenges. This review delves into these defence mechanisms and their impact at each stage of the infection cycle, their challenges, and the strategies phages have developed to counteract them. Additionally, we examine the role of phage cocktails in the evolving landscape of antibacterial treatments and discuss recent studies that highlight the effectiveness of diverse phage cocktails in targeting essential bacterial receptors and combating resistant strains.
•Phages can be an alternative in combating bacterial infections.•The emergence of phage-resistant bacteria hinders the effectiveness of phage therapy.•Bacterial defense mechanisms reduce the effectiveness of phage therapy.•Phage cocktails can overcome the challenges posed by bacterial defenses.•This review examines how phage cocktails can be effective against bacterial defenses.
Rosa multiflora Thunb. is a perennial shrub native to eastern Asia. It is commonly found on habitat margins, such as forest edges, streams, and roadsides (CABI n.d.). Due to its aromatic flowers, its ...usefulness in erosion control, and as a living livestock fence, R. multiflora was introduced to North America as an ornamental in the early 1800's (Hindal and Wong 1988). However, R. multifora, grows rapidly and frequently outcompetes native species, and is therefore considered invasive in North America (Hindal and Wong 1988). In May 2020 Phragmidium rosae-multiflorae Dietel, or rose rust, was collected from R. multiflora in Patton Woods Park, a small residential park in Patton Township, Centre Co., PA, USA (40° 47' 28.40" N; 77° 55' 33.37" W). P. rosae-multiflorae is an autoecious macrocyclic rust fungus known to occur on R. multiflora in the plant's native range. To our knowledge, there are no previously published records of P. rosae-multiflorae in North America. The host exhibited conspicuous aecia on the stems and petioles. Aecia were caeoma form, orange, irregular, erumpant, and pulverulent. Aeciospores were one-celled, verrucose, hyaline to pale yellow, variable in shape, ranging from ellipsoidal to globose (Fig.1), measuring 22.5 ± 3 × 15.5 ± 5 μm (n = 30). Disease symptomology and aecia are consistent with P. rosae-multiflorae Dietel (Wei 1988; Liu et. al 2020). Fungal DNA was extracted from infected petioles. Polymerase chain reaction and sequencing of the 28S region of the nuclear ribosomal DNA repeat was conducted with primers Rust2inv and LR6 following protocols in Aime (2006). The sequence shares 98.77% identity (900 / 487 bp) with P. Rosae-multiflorae from China (MN264739). A voucher specimen has been preserved in the Arthur Fungarium at Purdue University (PUR N23123) with corresponding 28S sequence (GenBank accession #MZ323415). The recorded occurrence of P. rosae-multiflorae on R. multiflora in North America is significant, given the ecological impact of the host plant as an invasive species and need for biocontrol. While no formally published records of this fungus in North America exist, there are putative occurrences across the northeastern United States reported on Global Biodiversity Information Facility (GBIF) and the Maryland Biodiversity Project websites.
Penicillium nordicum is the main ochratoxin A (OTA)-producing species on the surface of dry-fermented sausages, such as the “chorizo”. New antifungal strategies are being developed using biocontrol ...agents (BCAs), such as plant extracts and native microorganisms. This work aimed to evaluate the antiochratoxigenic capacity and the causative modes of action of BCAs (rosemary essential oil (REO), acorn shell extract and the yeast Debaryomyces hansenii (Dh)) in a “chorizo”-based medium (Ch-DS). BCAs were inoculated on Ch-DS together with P. nordicum and incubated at 12 °C for 15 days to collect mycelia for OTA analyses and comparative proteomics. Both REO and Dh alone decreased OTA accumulation up to 99% and affected the abundance of P. nordicum proteins linked to cell wall organisation, synthesis of OTA-related metabolites and ergosterol synthesis. It is worth highlighting the increased abundance of an amidase by REO, matching with the decrease in OTA. The use of REO and Dh as BCAs could be an effective strategy to reduce the OTA hazard in the meat industry. Based on their not fully coincident modes of action, their combined application could be of interest in “chorizo” to maximise their potential against ochratoxigenic strains.
•REO is a valuable strategy for reducing OTA by P. nordicum in “chorizo”.•Dh is an effective biocontrol agent for reducing OTA by P. nordicum in “chorizo”.•The combination of Dh and REO is also successful in reducing OTA.•AE does not affect OTA production in “chorizo”.•REO and Dh affect ergosterol-, secondary metabolites- and CWI-related proteins.
Biocontrol strains from the genera Bacillus and Pseudomonas and their bioactive secondary metabolites may be considered beneficial for plant health, since they act through several mechanisms, ...including direct antibiosis, plant growth promotion and the induction of systemic resistance in the plant hosts. These beneficial bacteria have been proven to be very active against bacterial and fungal phytopathogens, nematodes and different insects. Direct antibiosis, an induced immune system response (ISR) in the host plant and competition for nutrients and space are the most common biocontrol potential of these genera. Species belonging to the Bacillus genus are commonly considered ideal due to their rapid growth, ease of handling and excellent colonizing properties. These endospore‐forming Bacillus strains are capable of suppressing and inhibiting plant pathogens, both indirectly by competing with the pathogens for a niche or nutrient requirements, or directly by producing various lipopeptide compounds such as iturin, surfactin and fengycin, which are active on many plant pathogens. Furthermore, they are also capable of inducing systemic resistance in plants through the production of volatile substances including alcohols, aldehydes, aromatics, sulfides and ketones. Lipopeptides, polyketides and volatiles from Bacillus spp. can stimulate the expression of genes coding for pathogenesis-related (PR) proteins and other defense-related proteins in the plant hosts through the activation of jasmonic acid (JA), salicylic acid (SA) or ethylene (ET) signaling pathways. In addition, inhibition of quorum sensing in competitive bacteria and the capability to downregulate expression of genes involved in mycelial growth, penetration, sporulation and the virulence of a fungal pathogen is another property of Bacillus strains and their volatiles. The Pseudomonas genus is rich in species with the potential for biocontrol with positive effects on plant welfare, which actively participate in complex plant-pathogen-antagonist interaction. The most common molecules involved in this mechanism are, among others, 2,4‐diacetylphloroglucinol, phenazine‐1‐carboxylic acid, phenazine-1-carboxamide, pyoluteorin and pyrrolnitrin. Cyclic lipopeptides from Pseudomonas spp. such as nunamycin, nunapeptin, brasmycin and braspeptin were intensively studied as agents for plant biocontrol and biostimulation in agriculture. Nunamycin, nunapeptin, brasmycin and braspeptin were identified as essential in the antifungal role. Furthermore, phenazines, sessilins and orfamides were shown to have additive roles in the suppression of some fungal diseases. Additionally, Bacillus and Pseudomonas spp. produce chitinases, glucanases and proteases involved in the suppression of many fungal diseases. Their production is mainly induced by the presence of fungal pathogen biomass and their cell wall. This review provides an updated overview of the antimicrobial activity of plant-associated Bacillus and Pseudomonas involved in plant disease suppression via biological control mechanisms, including their molecular basis and direct activity, offering a better understanding in preventing different pests.
•Bacillus and Pseudomonas spp. produce wide array of secondary metabolites.•Secondary metabolites are involved in biocontrol and biofertilization mechanisms.•Numerous phytopathogens are controlled by Bacillus and Pseudomonas isolates.•Molecular mechanisms of biocontrol activity are discussed.
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