Trichoderma/pathogen/plant interaction in pre-harvest food security

Large losses before crop harvesting are caused by plant pathogens, such as viruses, bacteria, oomycetes, fungi, and nematodes. Among these, fungi are the major cause of losses in agriculture worldwide. Plant pathogens are still controlled through application of agrochemicals, causing human disease and impacting environmental and food security. Biological control provides a safe alternative for the control of fungal plant pathogens, because of the ability of biocontrol agents to establish in the ecosystem. Some Trichoderma spp. are considered potential agents in the control of fungal plant diseases. They can interact directly with roots, increasing plant growth, resistance to diseases, and tolerance to abiotic stress. Furthermore, Trichoderma can directly kill fungal plant pathogens by antibiosis, as well as via mycoparasitism strategies. In this review, we will discuss the interactions between Trichoderma/fungal pathogens/plants during the pre-harvest of crops. In addition, we will highlight how these interactions can influence crop production and food security. Finally, we will describe the future of crop production using antimicrobial peptides, plants carrying pathogen-derived resistance, and plantibodies.     

Can microbial-based insecticides replace chemical pesticides in agricultural production?

Extensive use of chemical insecticides to control insect pests in agriculture has improved yields and production of high-quality food products. However, chemical insecticides have been shown to be harmful also to beneficial insects and many other organisms like vertebrates. Thus, there is a need to replace those chemical insecticides by other control methods in order to protect the environment. Insect pest pathogens, like bacteria, viruses or fungi, are interesting alternatives for production of microbial-based insecticides to replace the use of chemical products in agriculture. Organic farming, which does not use chemical pesticides for pest control, relies on integrated pest management techniques and in the use of microbial-based insecticides for pest control. Microbial-based insecticides require precise formulation and extensive monitoring of insect pests, since they are highly specific for certain insect pests and in general are more effective for larval young instars. Here, we analyse the possibility of using microbial-based insecticides to replace chemical pesticides in agricultural production.     

Arbuscular mycorrhizas and biological control of soil-borne plant pathogens – an overview of the mechanisms involved

 Biological control of plant pathogens is currently accepted as a key practice in sustainable agriculture because it is based on the management of a natural resource, i.e. certain rhizosphere organisms, common components of ecosystems, known to develop antagonistic activities against harmful organisms (bacteria, fungi, nematodes etc.). Arbuscular mycorrhizal (AM) associations have been shown to reduce damage caused by soil-borne plant pathogens. Although few AM isolates have been tested in this regard, some appear to be more effective than others. Furthermore, the degree of protection varies with the pathogen involved and can be modified by soil and other environmental conditions. This prophylactic ability of AM fungi could be exploited in cooperation with other rhizospheric microbial angatonists to improve plant growth and health. Despite past achievements on the application of AM in plant protection, further research is needed for a better understanding of both the ecophysiological parameters contributing to effectiveness and of the mechanisms involved. Although the improvement of plant nutrition, compensation for pathogen damage, and competition for photosynthates or colonization/infection sites have been claimed to play a protective role in the AM symbiosis, information is scarce, fragmentary or even controversial, particularly concerning other mechanisms. Such mechanisms include (a) anatomical or morphological AM-induced changes in the root system, (b) microbial changes in rhizosphere populations of AM plants, and (c) local elicitation of plant defence mechanisms by AM fungi. Although compounds typically involved in plant defence reactions are elicited by AM only in low amounts, they could act locally or transiently by making the root more prone to react against pathogens. Current research based on molecular, immunological and histochemical techniques is providing new insights into these mechanisms. Accepted: 29 October 1996     

Bacillus amyloliquefaciens GA1 as a source of potent antibiotics and other secondary metabolites for biocontrol of plant pathogens

Background  

Phytopathogenic fungi affecting crop and post-harvested vegetables are a major threat to food production and food storage. To face these drawbacks, producers have become increasingly dependent on agrochemicals. However, intensive use of these compounds has led to the emergence of pathogen resistance and severe negative environmental impacts. There are also a number of plant diseases for which chemical solutions are ineffective or non-existent as well as an increasing demand by consumers for pesticide-free food. Thus, biological control through the use of natural antagonistic microorganisms has emerged as a promising alternative to chemical pesticides for more rational and safe crop management.     

AM真菌在植物病虫害生物防治中的作用机制

丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与大约80%的陆生高等植物形成共生体。由土传病原物侵染引起的土传病害被植物病理学界认定为最难防治的病害之一。研究表明,AM真菌能够拮抗由真菌、线虫、细菌等病原体引起的土传性植物病害,诱导宿主植物增强对病虫害的耐/抗病性。当前,利用AM真菌开展病虫害的生物防治已经引起生态学家和植物病理学家的广泛关注。基于此,围绕AM真菌在植物病虫害生物防治中的最新研究进展,从AM真菌改变植物根系形态结构、调节次生代谢产物的合成、改善植物根际微环境、与病原微生物直接竞争入侵位点和营养分配、诱导植株体内抗病防御体系的形成等角度,探究AM真菌在植物病虫害防治中的作用机理,以期为利用AM真菌开展植物病虫害的生物防治提供理论依据,并对本领域未来的发展方向和应用前景进行展望。     

Fungal entomopathogens: new insights on their ecology

An important mechanism for insect pest control should be the use of fungal entomopathogens. Even though these organisms have been studied for more than 100 y, their effective use in the field remains elusive. Recently, however, it has been discovered that many of these entomopathogenic fungi play additional roles in nature. They are endophytes, antagonists of plant pathogens, associates with the rhizosphere, and possibly even plant growth promoting agents. These findings indicate that the ecological role of these fungi in the environment is not fully understood and limits our ability to employ them successfully for pest management. In this paper, we review the recently discovered roles played by many entomopathogenic fungi and propose new research strategies focused on alternate uses for these fungi. It seems likely that these agents can be used in multiple roles in protecting plants from pests and diseases and at the same time promoting plant growth.     

Plant protection and growth stimulation by microorganisms: biotechnological applications of Bacilli in agriculture

The increasing demand for a steady, healthy food supply requires an efficient control of the major pests and plant diseases. Current management practices are based largely on the application of synthetic pesticides. The excessive use of agrochemicals has caused serious environmental and health problems. Therefore, there is a growing demand for new and safer methods to replace or at least supplement the existing control strategies. Biological control, that is, the use of natural antagonists to combat pests or plant diseases has emerged as a promising alternative to chemical pesticides. The Bacilli offer a number of advantages for their application in agricultural biotechnology. Several Bacillus-based products have been marketed as microbial pesticides, fungicides or fertilisers. Bacillus-based biopesticides are widely used in conventional agriculture, by contrast, implementation of Bacillus-based biofungicides and biofertilizers is still a pending issue.     

Mechanisms of action and biocontrol potential of Trichoderma against fungal plant diseases - A review

Plant diseases are among the major causes of the low productivity of crops, causing yield losses of up to 30%, heralding an enormous threat to global food security. Indiscriminate use of chemical-based fungicides for controlling fungal diseases has raised severe concerns about ecosystem health. Moreover, pathogens have become insensitive against these chemicals necessitating excessive use of chemicals for adequate control. The resulting accumulation of these chemicals in the food chain has provoked numerous health complications. For combating the adversaries of chemical-based fungicides, biological control of fungal pathogens is proposed as an eco-friendly alternative. Among various biological controls, Trichoderma-based biological control agents (BCAs) are widely used in agriculture for controlling soil-borne pathogens. These BCAs are commercialized and known as; stimulators of resistance in plants, growth enhancers, bio-fertilizers, and bio-pesticides. Biological management of plant pathogens has yielded valuable results in the sustainability of ecosystems and compelling improvements in the quality and quantity of agricultural produce. These BCAs exhibit potential against pathogens, remarkably improve photosynthesis, plant growth, and nutrient use efficiency for impressive crop yields. Despite these peculiarities, Trichoderma's mechanisms against pathogens and their growth promotional effects are not thoroughly investigated, hence formulating the prime objective of the current review. Along with these, Trichoderma-based fungicides marketed in different geographical locations are encompassed in this review. Finally, the knowledge gaps and future research directions for improving the efficacy of Trichoderma-based BCAs are discussed.     

Biotechnological approaches to develop bacterial chitinases as a bioshield against fungal diseases of plants

Fungal diseases of plants continue to contribute to heavy crop losses in spite of the best control efforts of plant pathologists. Breeding for disease-resistant varieties and the application of synthetic chemical fungicides are the most widely accepted approaches in plant disease management. An alternative approach to avoid the undesired effects of chemical control could be biological control using antifungal bacteria that exhibit a direct action against fungal pathogens. Several biocontrol agents, with specific fungal targets, have been registered and released in the commercial market with different fungal pathogens as targets. However, these have not yet achieved their full commercial potential due to the inherent limitations in the use of living organisms, such as relatively short shelf life of the products and inconsistent performance in the field. Different mechanisms of action have been identified in microbial biocontrol of fungal plant diseases including competition for space or nutrients, production of antifungal metabolites, and secretion of hydrolytic enzymes such as chitinases and glucanases. This review focuses on the bacterial chitinases that hydrolyze the chitinous fungal cell wall, which is the most important targeted structural component of fungal pathogens. The application of the hydrolytic enzyme preparations, devoid of live bacteria, could be more efficacious in fungal control strategies. This approach, however, is still in its infancy, due to prohibitive production costs. Here, we critically examine available sources of bacterial chitinases and the approaches to improve enzymatic properties using biotechnological tools. We project that the combination of microbial and recombinant DNA technologies will yield more effective environment-friendly products of bacterial chitinases to control fungal diseases of crops.     

Food webs obscure the strength of plant diversity effects on primary productivity

Plant diversity experiments generally find that increased diversity causes increased productivity; however, primary productivity is typically measured in the presence of a diverse food web, including pathogens, mutualists and herbivores. If food web impacts on productivity vary with plant diversity, as predicted by both theoretical and empirical studies, estimates of the effect of plant diversity on productivity may be biased. We experimentally removed arthropods, foliar fungi and soil fungi from the longest‐running plant diversity experiment. We found that fungi and arthropods removed a constant, large proportion of biomass leading to a greater reduction of total biomass in high diversity plots. As a result, the effect of diversity on measured plant productivity was much higher in the absence of fungi and arthropods. Thus, diversity increases productivity more than reported in previous studies that did not control for the effects of heterotrophic consumption.     

Not all GMOs are crop plants: non-plant GMO applications in agriculture

Since tools of modern biotechnology have become available, the most commonly applied and often discussed genetically modified organisms are genetically modified crop plants, although genetic engineering is also being used successfully in organisms other than plants, including bacteria, fungi, insects, and viruses. Many of these organisms, as with crop plants, are being engineered for applications in agriculture, to control plant insect pests or diseases. This paper reviews the genetically modified non-plant organisms that have been the subject of permit approvals for environmental release by the United States Department of Agriculture/Animal and Plant Health Inspection Service since the US began regulating genetically modified organisms. This is an indication of the breadth and progress of research in the area of non-plant genetically modified organisms. This review includes three examples of promising research on non-plant genetically modified organisms for application in agriculture: (1) insects for insect pest control using improved vector systems; (2) fungal pathogens of insects to control insect pests; and (3) virus for use as transient-expression vectors for disease control in plants.     

Recent advances in bio‐chemical,molecular and physiological aspects of membrane lipid derivatives in plant pathology

Plant pathogens pose a significant threat to the food industry and food security accounting for 10–40% crop losses annually on a global scale. Economic losses from plant diseases are estimated at $300B for major food crops and are associated with reduced food availability and accessibility and also high food costs. Although strategies exist to reduce the impact of diseases in plants, many of these introduce harmful chemicals to our food chain. Therefore, it is important to understand and utilize plants' immune systems to control plant pathogens to enable more sustainable agriculture. Lipids are core components of cell membranes and as such are part of the first line of defense against pathogen attack. Recent developments in omics technologies have advanced our understanding of how plant membrane lipid biosynthesis, remodelling and/or signalling modulate plant responses to infection. Currently, there is limited information available in the scientific literature concerning lipid signalling targets and their biochemical and physiological consequences in response to plant pathogens. This review focusses on the functions of membrane lipid derivatives and their involvement in plant responses to pathogens as biotic stressors. We describe major plant defense systems including systemic‐acquired resistance, basal resistance, hypersensitivity and the gene‐for‐gene concept in this context.     

Finished genome of the fungal wheat pathogen Mycosphaerella graminicola reveals dispensome structure, chromosome plasticity, and stealth pathogenesis

The plant-pathogenic fungus Mycosphaerella graminicola (asexual stage: Septoria tritici) causes septoria tritici blotch, a disease that greatly reduces the yield and quality of wheat. This disease is economically important in most wheat-growing areas worldwide and threatens global food production. Control of the disease has been hampered by a limited understanding of the genetic and biochemical bases of pathogenicity, including mechanisms of infection and of resistance in the host. Unlike most other plant pathogens, M. graminicola has a long latent period during which it evades host defenses. Although this type of stealth pathogenicity occurs commonly in Mycosphaerella and other Dothideomycetes, the largest class of plant-pathogenic fungi, its genetic basis is not known. To address this problem, the genome of M. graminicola was sequenced completely. The finished genome contains 21 chromosomes, eight of which could be lost with no visible effect on the fungus and thus are dispensable. This eight-chromosome dispensome is dynamic in field and progeny isolates, is different from the core genome in gene and repeat content, and appears to have originated by ancient horizontal transfer from an unknown donor. Synteny plots of the M. graminicola chromosomes versus those of the only other sequenced Dothideomycete, Stagonospora nodorum, revealed conservation of gene content but not order or orientation, suggesting a high rate of intra-chromosomal rearrangement in one or both species. This observed "mesosynteny" is very different from synteny seen between other organisms. A surprising feature of the M. graminicola genome compared to other sequenced plant pathogens was that it contained very few genes for enzymes that break down plant cell walls, which was more similar to endophytes than to pathogens. The stealth pathogenesis of M. graminicola probably involves degradation of proteins rather than carbohydrates to evade host defenses during the biotrophic stage of infection and may have evolved from endophytic ancestors.     

Diseases of insects and other arthropods: results of diagnostic research over 55 years

Arthropods and especially insects are attacked by many arthropod-pathogenic organisms belonging to viruses, bacteria including rickettsiae, fungi, microsporidia, protists, and nematodes. They may cause lethal or chronic diseases. For 55 years, research on all kinds of arthropod diseases was conducted at the Institute for Biological Control, Darmstadt, formerly belonging to the Federal Biological Research Centre for Agriculture and Forestry (BBA) that became part of the newly founded Julius Kühn-Institute. Special attention is still being paid to diagnostics. During this period, about 1900 accessions comprising many thousands of dead or diseased specimens from 21 different arthropod orders were examined and the causative agents diagnosed. In the present paper, about 450 arthropod species, mainly insects, are listed together with the group and scientific name of the diagnosed arthropod pathogens and the origin (country) of the accession.     

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

The rhizosphere is a hot spot of microbial interactions as exudates released by plant roots are a main food source for microorganisms and a driving force of their population density and activities. The rhizosphere harbors many organisms that have a neutral effect on the plant, but also attracts organisms that exert deleterious or beneficial effects on the plant. Microorganisms that adversely affect plant growth and health are the pathogenic fungi, oomycetes, bacteria and nematodes. Most of the soilborne pathogens are adapted to grow and survive in the bulk soil, but the rhizosphere is the playground and infection court where the pathogen establishes a parasitic relationship with the plant. The rhizosphere is also a battlefield where the complex rhizosphere community, both microflora and microfauna, interact with pathogens and influence the outcome of pathogen infection. A wide range of microorganisms are beneficial to the plant and include nitrogen-fixing bacteria, endo- and ectomycorrhizal fungi, and plant growth-promoting bacteria and fungi. This review focuses on the population dynamics and activity of soilborne pathogens and beneficial microorganisms. Specific attention is given to mechanisms involved in the tripartite interactions between beneficial microorganisms, pathogens and the plant. We also discuss how agricultural practices affect pathogen and antagonist populations and how these practices can be adopted to promote plant growth and health.     

Plant biodiversity: phytochemicals and health

Biodiversity may be defined as the variability occuring among living organisms and affecting all species of animals and plants, their genetics and their environment. Biological diversity of plants also relies on the chemical diversity deriving from their specialized metabolites which possess a wide range of different chemical structures as a result of plant evolution. They are responsible for the plant ecological properties and are required for the plant-environment interactions. In addition, many of them display important pharmacological properties. In the recent years, the growing interest in using plant metabolites to treat diseases in humans and animals and the high request of health products originating from natural sources rather than synthetic has revived the research on plant biodiversity to identify new bioactive molecules. Based on our studies on the chemical and biological characterization of rare or less studied plant species, the present paper aims to describe a selection of botanical species with phytopharmaceutical importance in order to highlight the chemical polymorphism deriving from their biodiversity along with its implications on bioactivity.     

Evolving challenges and strategies for fungal control in the food supply chain

Fungi that spoil foods or infect crops can have major socioeconomic impacts, posing threats to food security. The strategies needed to manage these fungi are evolving, given the growing incidence of fungicide resistance, tightening regulations of chemicals use and market trends imposing new food-preservation challenges. For example, alternative methods for crop protection such as RNA-based fungicides, biocontrol, or stimulation of natural plant defences may lessen concerns like environmental toxicity of chemical fungicides. There is renewed focus on natural product preservatives and fungicides, which can bypass regulations for ‘clean label’ food products. These require investment to find effective, safe activities within complex mixtures such as plant extracts. Alternatively, physical measures may be one key for fungal control, such as polymer materials which passively resist attachment and colonization by fungi. Reducing or replacing traditional chlorine treatments (e.g. of post-harvest produce) is desirable to limit formation of disinfection by-products. In addition, the current growth in lower sugar food products can alter metabolic routing of carbon utilization in spoilage yeasts, with implications for efficacy of food preservatives acting via metabolism. The use of preservative or fungicide combinations, while involving more than one chemical, can reduce total chemicals usage where these act synergistically. Such approaches might also help target different subpopulations within heteroresistant fungal populations. These approaches are discussed in the context of current challenges for food preservation, focussing on pre-harvest fungal control, fresh produce and stored food preservation. Several strategies show growing potential for mitigating or reversing the risks posed by fungi in the food supply chain.     

Biological and molecular events associated with simultaneous transmission of plant viruses by invertebrate and fungal vectors

Viruses are likely to be the most dangerous parasites of living organisms because of their widespread occurrence, possible deleterious effects on their hosts and high rates of evolution. Virus host‐to‐host transmission is a critical step in the virus life cycle, because it enables survival in a given environment and efficient dissemination. As hosts of plant viruses are not mobile, these pathogens have adopted diverse transmission strategies involving various vector organisms, mainly arthropods, nematodes, fungi and protists. In nature, plants are often infected with more than one virus at a time, thereby creating potential sources for vectors to acquire and transmit simultaneously two or more viruses. Simultaneous transmission can result in multiple infections of new host plants, which become subsequent potential sources of the viruses, thus enhancing the spread of the diseases caused by these pathogens. Moreover, it can contribute to the maintenance of viral genetic diversity in the host communities. However, despite its possible significance, the problem of the simultaneous transmission of plant viruses by vectors has not been investigated in detail. In this review, the current knowledge on multiple viral transmissions by aphids, whiteflies, leafhoppers, planthoppers, nematodes and fungi is outlined.     

The genus Pythium in Taiwan, China (1) — a synoptic review

The genus Pythium,with slightly over 280 described species,has been classified traditionally with other filamentous,coenocytic,sporangia-producing fungi as "Phycomyetes".However,with recent advances in chemical,ultrastructural and molecular studies,Pythium spp.are now considered as "fungus-like organisms" or "pseudo-fungi" and are placed in the Kingdom Chromista or Kingdom Straminopila,distinct from the true fungi of the Kingdom Fungi or Kingdom Mycota.They are widely distributed throughout the world as soil saprophytes or plant pathogens.Because of the warm moist maritime climate,Taiwan,China,is especially rich in Pythium species.To date,48 species of Pythium have been reported from Taiwan,China,with the dominant species being Py.vexans,Py.spinosum,Py.splendens,Py.aphanidermatum,Py.dissotocum and Py.acanthicum.There is no definite geographical distribution of Pythium spp.in Taiwan,China.Twenty nine species of Pythium have proven to be plant pathogens attacking a wide variety of woody and herbaceous plants primarily causing pre-and post-emergence seedling damping-off,root rot,stem rot and rotting of fruits,tubers and ginger rhizomes,resulting in serious economic losses.The most important plant pathogenic species include Py.aphanidermatum and Py.Myriotylum,which are most active during the hot and wet summer months;whereas Py.splendens,Py.spinosum,Py.ultimum and Py.irregulare cause the greatest damage in the cool winter.Most Pythium spp.are non-specific pathogens,infecting mainly juvenile or succulent tissues.This review attempts to assess the taxonomic position of the genus Pythium and provide details of the historical development of the study of Pythium as pathogens in Taiwan,China,causing diseases of sugarcane,trees,vegetables,fruits,specialty crops and flowering plants,as well as measures to control these diseases.Of special note is the introduction of the S-H mixture which,when used as soil amendment,effectively controls many soil-borne Pythium diseases during the early stages of plant growth.The diversity of Pythium species in Taiwan,China,is discussed in comparison with the situation in the mainland of China and suggestions are made to fully utilize Pythium spp.as agents for biological control,in industry and medicine.     

Arbuscular mycorrhizal fungi and nitrogen uptake

Nitrogen (N) is among the most important macro-nutrients significantly affecting plant growth and yield production. Accordingly, N must be supplied adequately so that optimum amounts of yield are resulted. There are different ways of supplying N to the plant including the use of chemical and biological fertilization. The chemical properties of N make it very mobile, especially under humid conditions. Hence, N must not be overfertilized with respect to the economical and environmental points of view. N Biological fertilization includes the use of plant growth-promoting rhizobacteria (PGPR) including the N-fixing bacteria, rhizobium. There are also arbuscular mycorrhizal (AM) fungi in the soil, which are symbiotic to most terrestrial plants enhancing plant growth and yield production through increasing the uptake of water and nutrients by the host plant. Numerous experiments have indicated the important role of AM fungi in enhancing P uptake by plant. However, it is yet a matter of debate that how AM fungi may affect soil N dynamic and hence plant N uptake. Some of the most important and recent aspects regarding such effects by AM fungi are highlighted, which can be of significance to health and productivity of the ecosystem.