Trichoderma Biological Control to Protect Sensitive Maize Hybrids against Late Wilt Disease in the Field

Phylogenetic analysis of plant-pathogenic and non-pathogenic Trichoderma isolates on maize from plants, soil, and commercial bio-products

Fungi of the genus Trichoderma are primarily associated with the mycobiome of dead wood but can also be occasionally found in soil and plant rhizospheres. Several Trichoderma spp. are used in crop health management to promote growth and control plant diseases. Although widely considered beneficial to plants, some members have been reported to be pathogenic to maize, causing a disease called Trichoderma ear rot. Since 2018, Trichoderma afroharzianum has caused significant infections of maize cobs in Germany, France, and Italy. This study aimed to investigate the pathogenicity and phylogenetic relationships among different Trichoderma strains from diverse sources and geographical origins. While previous studies primarily identified T. afroharzianum as the main species causing Trichoderma ear rot, this study found that isolates of T. asperellum, T. atroviride, and T. guizhouense may also exhibit pathogenicity on maize cobs. Additionally, Trichoderma strains from commercial biocontrol products displayed unexpected pathogenicity inducing up to 92% disease severity on maize cobs. Most T. afroharzianum strains induced high levels of disease severity, although some isolates of the same species did not cause any disease, indicating a large heterogeneity in pathogenicity within the species. Notably, phylogeny reconstruction based on the tef1-α and rpb2 genes did not result in any discernible clustering between pathogenic and non-pathogenic isolates. A further novel finding is the isolation of pathogenic Trichoderma isolates from agricultural soil, demonstrating that soil can serve as a reservoir for pathogenic species. This study highlights the need for biosecurity assessment and monitoring of Trichoderma strains for agricultural use, considering their beneficial and pathogenic potential.IMPORTANCEIn this study, we explored the ability of different Trichoderma species to infect maize plants. Trichoderma is a group of fungi known for its beneficial role in agriculture, often used as a biological pesticide to control fungal plant diseases. However, some species within this genus can also act as pathogens, causing infections in crops like maize. We found that one species, T. afroharzianum, is particularly aggressive, capable of infecting maize without the plant being wounded first. This makes it a potentially serious threat to crop health. In contrast, other species, such as T. atroviride and T. asperellum, only caused infections when maize plants were injured before. Our research suggests that pathogenic Trichoderma species not only effectively infect plants but can also survive well in soil, making their control difficult. These findings highlight the need for better understanding of how these fungi operate in order to manage the risks they pose to important crops like maize, while still taking advantage of their beneficial uses in agriculture.

Co-inoculation of Trichoderma viride with Azospirillum brasilense could suppress the development of Harpophora maydis-infected maize in Egypt

Plant diseases caused by fungal pathogens are responsible for severe damage to strategic crops worldwide. Late wilt disease (LWD) is a vascular disease that occurs late in maize development. Harpophora maydis, the causative agent of maize LWD, is responsible for significant economic losses in Egypt. Therefore, the aim of this study was to control LWD of maize using an alternative approach to reduce the use of chemical pesticides. A combination of Trichoderma viride, a fungal biocontrol agent, and Azospirillum brasilense, a bacterial endophytic plant growth promoter, was applied in vitro and in planta. T. viride showed high mycoparasitic potential against H. maydis via various antagonistic activities, including the production of lytic enzymes, secondary metabolites, volatile compounds, and siderophores. A. brasilense and T. viride filtrates were also shown to suppress H. maydis growth, in addition to their ability to produce gibberellic and indole acetic acids. A significant change in the metabolites secreted by T. viride was observed using GC/MS in the presence of H. maydis. A field experiment was conducted on susceptible and resistant hybrids of maize to evaluate the antagonistic activity of T. viride combined with A. brasilense on LWD incidence as well as plant growth promotion under field conditions. The data revealed a significant decrease in both disease incidence and severity in maize plants treated with T. viride and/or A. brasilense. Further, there was a noticeable increase in all plant growth and yield parameters. An anatomical examination of the control and inoculated maize roots was also reflective of plant responses under biotic stress. Taken together, the obtained results provide successful eco-friendly management strategies against LWD in maize.

Trichoderma-Bioenriched Vermicompost Induces Defense Response and Promotes Plant Growth in Thai Rice Variety "Chor Khing"

Vermicompost (VC) produced by African nightcrawler earthworms (Eudrilus eugeniae) is a natural fertilizer with a rich microbial community. Trichoderma asperelloides PSU-P1 is an effective antagonistic microorganism with multifaceted activity mechanisms. This research aimed to develop Trichoderma-bioenriched vermicompost (TBVC) to promote plant growth and induce the defense response in the Thai rice variety "Chor Khing". T. asperelloides PSU-P1 was tested against Rhizoctonia solani, the pathogen of sheath blight disease, using a dual-culture assay. The results showed that T. asperelloides PSU-P1 effectively inhibited R. solani in vitro growth by 70.48%. The TBVC was prepared by adding a conidial suspension (108 conidia/mL) to vermicompost. The viability of Trichoderma persisted in the vermicompost for 6 months and ranged from 1.2 to 2.8 × 107 CFU/mL. Vermicompost water extracts significantly enhanced seed germination, root length, and shoot length compared to a control group (p < 0.05). Plants that received the TBVC displayed significantly longer shoot and root lengths and higher total chlorophyll content than control plants (p < 0.05). The TBVC induced defense response by increasing the enzyme activity of peroxidase (POD) and polyphenol oxidase (PPO) in comparison with control plants. Rice grown in the TBVC had a significantly reduced incidence of sheath blight caused by R. solani in comparison with control rice (p < 0.05). Furthermore, the fungal community of rice plants was analyzed via the high-throughput next-generation sequencing of the internal transcribed spacer (ITS). The fungal community in the TBVC had greater alpha diversity than the community in the VC. Phylum Ascomycota was dominant in both samples, and a heat map showed that Trichoderma was more prevalent in the TBVC than in the VC. Our results indicate that the enrichment of VC with Trichoderma increases growth, enhances the defense response, and reduces the incidence of sheath blight disease in the Thai rice variety "Chor Khing".

Antagonistic interactions between maize seeds microbiome species and the late wilt disease agent, Magnaporthiopsis maydis

Magnaporthiopsis maydis is a maize pathogen that causes severe damage to commercial corn fields in the late growth stages. Late wilt disease (LWD) has spread since its discovery in the 1960s in Egypt and is now reported in about 10 countries. The pathogen has a hidden endophytic lifecycle in resistant corn plants and secondary hosts such as green foxtail, watermelon lupin and cotton. At the same time, it could be an opportunist and hinder the host development under the right conditions. This study uncovered M. maydis interactions with newly identified maize endophytes. To this end, six fungi were isolated from the seeds of three sweet corn cultivars having varying susceptibility to LWD. These isolates were identified using colony morphology and microscopic characterization, universal internal transcribed spacer (ITS) molecular targeting and phylogenetic analysis. Most of them belonged to pathogenic species. Compared to three previously identified bioprotective microorganisms, the new species were tested for their ability to secrete metabolites that repress M. maydis in vitro and to antagonize it in a solid media confront test and a seedlings pathogenicity assay. The opportunistic fungal species Aspergillus flavus (ME1), Aspergillus terreus (PE3) and the reference biocontrol bacteria Bacillus subtilis (R2) achieved the highest M. maydis inhibition degree in the plates tests (74-100% inhibition). The seedlings' pathogenicity assay that predicts the seeds' microflora resistance to M. maydis highlighted the bio-shielding potential of most species (23% or more epicotyl elongation over the infected control). Fusarium sp. (ME2) was the leading species in this measure (43% enhancement), and B. subtilis gave the best protection in terms of seeds' germination (50%) and sprouts' biomass (34%). The results of this study could enhance our understanding of the pathobiome's role in the context of LWD and represent a first step in using the seeds' natural protective microflora to develop novel management strategies.

Integrated Management of the Cotton Charcoal Rot Disease Using Biological Agents and Chemical Pesticides

Charcoal rot disease (CRD), caused by the phytopathogenic fungus Macrophomina phaseolina, is a significant threat to cotton production in Israel and worldwide. The pathogen secretes toxins and degrading enzymes that disrupt the water and nutrient uptake, leading to death at the late stages of growth. While many control strategies were tested over the years to reduce CRD impact, reaching that goal remains a significant challenge. The current study aimed to establish, improve, and deepen our understanding of a new approach combining biological agents and chemical pesticides. Such intervention relies on reducing fungicides while providing stability and a head start to eco-friendly bio-protective Trichoderma species. The research design included sprouts in a growth room and commercial field plants receiving the same treatments. Under a controlled environment, comparing the bio-based coating treatments with their corresponding chemical coating partners resulted in similar outcomes in most measures. At 52 days, these practices gained up to 38% and 45% higher root and shoot weight and up to 78% decreased pathogen root infection (tracked by Real-Time PCR), compared to non-infected control plants. Yet, in the shoot weight assessment (day 29 post-sowing), the treatment with only biological seed coating outperformed (p < 0.05) all other biological-based treatments and all Azoxystrobin-based irrigation treatments. In contrast, adverse effects are observed in the chemical seed coating group, particularly in above ground plant parts, which are attributable to the addition of Azoxystrobin irrigation. In the field, the biological treatments had the same impact as the chemical intervention, increasing the cotton plants' yield (up to 17%), improving the health (up to 27%) and reducing M. phaseolina DNA in the roots (up to 37%). When considering all treatments within each approach, a significant benefit to plant health was observed with the bio-chemo integrated management compared to using only chemical interventions. Specific integrated treatments have shown potential in reducing CRD symptoms, such as applying bio-coating and sprinkling Azoxystrobin during sowing. Aerial remote sensing based on high-resolution visible-channel (RGB), green-red vegetation index (GRVI), and thermal imaging supported the above findings and proved its value for studying CRD control management. This research validates the combined biological and chemical intervention potential to shield cotton crops from CRD.

Physiological Effects of Microbial Biocontrol Agents in the Maize Phyllosphere

In a world with constant population growth, and in the context of climate change, the need to supply the demand of safe crops has stimulated an interest in ecological products that can increase agricultural productivity. This implies the use of beneficial organisms and natural products to improve crop performance and control pests and diseases, replacing chemical compounds that can affect the environment and human health. Microbial biological control agents (MBCAs) interact with pathogens directly or by inducing a physiological state of resistance in the plant. This involves several mechanisms, like interference with phytohormone pathways and priming defensive compounds. In Argentina, one of the world's main maize exporters, yield is restricted by several limitations, including foliar diseases such as common rust and northern corn leaf blight (NCLB). Here, we discuss the impact of pathogen infection on important food crops and MBCA interactions with the plant's immune system, and its biochemical indicators such as phytohormones, reactive oxygen species, phenolic compounds and lytic enzymes, focused mainly on the maize-NCLB pathosystem. MBCA could be integrated into disease management as a mechanism to improve the plant's inducible defences against foliar diseases. However, there is still much to elucidate regarding plant responses when exposed to hemibiotrophic pathogens.

Bacterial and Fungal Biocontrol Agents for Plant Disease Protection: Journey from Lab to Field, Current Status, Challenges, and Global Perspectives

Plants are constantly exposed to various phytopathogens such as fungi, Oomycetes, nematodes, bacteria, and viruses. These pathogens can significantly reduce the productivity of important crops worldwide, with annual crop yield losses ranging from 20% to 40% caused by various pathogenic diseases. While the use of chemical pesticides has been effective at controlling multiple diseases in major crops, excessive use of synthetic chemicals has detrimental effects on the environment and human health, which discourages pesticide application in the agriculture sector. As a result, researchers worldwide have shifted their focus towards alternative eco-friendly strategies to prevent plant diseases. Biocontrol of phytopathogens is a less toxic and safer method that reduces the severity of various crop diseases. A variety of biological control agents (BCAs) are available for use, but further research is needed to identify potential microbes and their natural products with a broad-spectrum antagonistic activity to control crop diseases. This review aims to highlight the importance of biocontrol strategies for managing crop diseases. Furthermore, the role of beneficial microbes in controlling plant diseases and the current status of their biocontrol mechanisms will be summarized. The review will also cover the challenges and the need for the future development of biocontrol methods to ensure efficient crop disease management for sustainable agriculture.

The cotton charcoal rot causal agent, Macrophomina phaseolina, biological and chemical control

The fungus Macrophomina phaseolina causes charcoal rot disease (CRD) in cotton, whose symptoms develop in the late stages of growth and result in wilting and death. Despite significant research efforts to reduce disease incidences, effective control strategies against M. phaseolina are an ongoing scientific effort. Today's CRD control tends toward green options to reduce the chemicals' environmental footprint and health risks. Here, different Trichoderma species were examined separately and in combination with Azoxystrobin (AS) in semi-field open-enclosure pots and a commercial field throughout a full season. In the pot experiment, the T. asperellum (P1) excelled and led to improvement in growth (13%-14%, day 69) and crops (the number of capsules by 36% and their weight by 78%, day 173). The chemical treatment alone at a low dose had no significant impact. Still, adding AS improved the effect of T. longibrachiatum (T7507) and impaired P1 efficiency. Real-time PCR monitoring of the pathogen DNA in the plants' roots at the harvest (day 176), revealed the efficiency of the combined treatments: T. longibrachiatum (T7407 and T7507) + AS. In a commercial field, seed dressing with a mixture of Trichoderma species (mix of P1, T7407, and Trichoderma sp. O.Y. 7107 isolate) and irrigation of their secreted metabolites during seeding resulted in the highest yields compared with the control. Applying only AS irrigation at a low dose (2,000 cc/ha), with the sowing, was the second best in promoting crops. The molecular M. phaseolina detection showed that the AS at a high dose (4,000 cc/ha) and the biological mix treatments were the most effective. Reducing the AS chemical treatment dosages by half impaired its effectiveness. Irrigation timing, also studied here, is proven vital. Early water opening during the late spring suppresses the disease outburst and damages. The results demonstrated the benefits of CRD bio-shielding and encouraged to explore the potential of a combined bio-chemo pest control approach. Such interphase can be environmentally friendly (reducing chemical substances), stabilize the biological treatment in changing environmental conditions, achieve high efficiency even in severe CRD cases, and reduce the development of fungicide resistance.

Trichoderma as a powerful fungal disease control agent for a more sustainable and healthy agriculture: recent studies and molecular insights

Molecular studies have elucidated Trichoderma's biocontrol mechanisms. Since fungicides have limited use, Trichoderma could control disease by new metabolic routes and epigenetic alterations. Due to environmental and health hazards, agrochemicals have been a concern since they were introduced in agriculture. Trichoderma, a well-known fungal genus with different mechanisms of action, is an alternative to pesticides and a great tool to help minimize disease incidence. Trichoderma-treated plants mainly benefit from disease control and growth promotion through priming, and these fungi can modulate plants' gene expression by boosting their immune system, accelerating their response to threats, and building stress tolerance. The latest studies suggest that epigenetics is required for plant priming and could be essential for growth promotion, expanding the possibilities for producing new resistant plant varieties. Trichoderma's propagules can be mass produced and formulated depending on the delivery method. Microsclerotia-based bioproducts could be a promising way of increasing the reliability and durability of marketed products in the field, as well as help guarantee longer shelf life. Developing novel formulations and selecting efficient Trichoderma strains can be tiresome, but patent search indicates an increase in the industrialization and commercialization of technologies and an expansion of companies' involvement in research and development in this field. Although Trichoderma is considered a well-known fungal genus, it still attracts the attention of large companies, universities, and research institutes around the world.

Trichoderma and its role in biological control of plant fungal and nematode disease

Trichoderma is mainly used to control soil-borne diseases as well as some leaf and panicle diseases of various plants. Trichoderma can not only prevent diseases but also promotes plant growth, improves nutrient utilization efficiency, enhances plant resistance, and improves agrochemical pollution environment. Trichoderma spp. also behaves as a safe, low-cost, effective, eco-friendly biocontrol agent for different crop species. In this study, we introduced the biological control mechanism of Trichoderma in plant fungal and nematode disease, including competition, antibiosis, antagonism, and mycoparasitism, as well as the mechanism of promoting plant growth and inducing plant systemic resistance between Trichoderma and plants, and expounded on the application and control effects of Trichoderma in the control of various plant fungal and nematode diseases. From an applicative point of view, establishing a diversified application technology for Trichoderma is an important development direction for its role in the sustainable development of agriculture.

Diversity of Trichoderma species associated with soil in the Zoige alpine wetland of Southwest China

The ecology of soil fungi is poorly understood, and recent comprehensive reports on Trichoderma are unavailable for any region, including the Zoige alpine wetland ecological region in China. One hundred soil samples were collected from different soil types and soil layers in Zoige alpine wetland ecological regions. Using the traditional suspension plating method, 80 Trichoderma strains were chosen to analyze species diversity. After a preliminary classification of morphological characteristics and the genes glyceraldehyde-3-phosphate dehydrogenase (gpd), 57 representative strains were selected and eventually identified as seven species via phylogenetic analyses of multilocus sequences based on the genes transcription elongation factor 1 alpha (tef1), encoding RNA polymerase II subunit B (rpb2) and ATP citrate lyase (acl1). Among them, T. harzianum was the dominant species isolated from five soil layers and four soil types, and had the highest isolation frequency (23%) in this zone, while T. polysporum and T. pyramidale were rare species, with isolation frequencies of less than 1%. Our detailed morphological observation and molecular phylogenetic analyses support the recognition of Trichoderma zoigense was described for the first time as a new species, while T. atrobrunneum as a new record for China was found. Our results will be used as a reference for a greater understanding of soil microbial resources, ecological rehabilitation and reconstructions in the Zoige alpine wetland.

Aggressive strains of the late wilt fungus of corn exist in Israel in mixed populations and can specialize in disrupting growth or plant health

Maize late wilt disease caused by the fungus Magnaporthiopsis maydis significantly damages crops in Israel and in other countries. Resistant maize cultivars are the preferred method for disease restraining. However, the pathogen populations of Spain and Egypt have varying aggressiveness, and virulent strains can overcome host resistance. In 2001 and from 2016 to -2019, 17 M. maydis strains were isolated from infected maize fields in Israel. The isolates' effects on seed germination, plant development, and disease symptoms severity were evaluated. The isolates from Israel display a diverse degree of aggressiveness that is not linked to their geographic distribution. The virulent strains are found in mixed populations, whereas less virulent M. maydis isolates exist. Aggressive strains harmed the development of plants and ears and caused severe wilting and death. In contrast, plants inoculated with less virulent strains exhibited only mild dehydration signs, and crop yield was similar to that of the non-infected control. Interestingly, different host cultivars can evoke specific virulence of M. maydis strains. Moreover, some pathogen strains significantly repress plant development, while the impact of other strains was evidenced by wilting symptoms. The current research further increases our understanding of the pathogen and our ability to control it.

Crop Rotation and Minimal Tillage Selectively Affect Maize Growth Promotion under Late Wilt Disease Stress

In recent years, worldwide scientific efforts towards controlling maize late wilt disease (LWD) have focused on eco-friendly approaches that minimize the environmental impact and health risks. This disease is considered to be the most severe threat to maize fields in Israel and Egypt, and a major growth restraint in India, Spain, and Portugal. Today’s most commonly used method for LWD control involving resistant maize genotypes is under constant risk from aggressive pathogen lines. Thus, this study’s objectives were to evaluate the effect of crop rotation and avoiding tillage on restraining the disease. Such an agrotechnical approach will support the continuity of soil mycorrhiza networks, which antagonize the disease’s causal agent, Magnaporthiopsis maydis. The method gained positive results in previous studies, but many knowledge gaps still need to be addressed. To this end, a dual-season study was conducted using the LWD hyper-susceptible maize hybrid, Megaton cv. The trials were performed in a greenhouse and in the field over full dual-growth seasons (wheat or clover as the winter crop followed by maize as the summer crop). In the greenhouse under LWD stress, the results clearly demonstrate the beneficial effect of maize crop rotation with clover and wheat on plant weight (1.4-fold), height (1.1–1.2-fold) and cob yield (1.8–2.4-fold), especially in the no-till soil. The clover-maize growth sequence excels in reducing disease impact (1.7-fold) and pathogen spread in the host tissues (3-fold). Even though the wheat-maize crop cycle was less effective, it still had better results than the commercial mycorrhizal preparation treatment and the uncultivated non-infected soil. The results were slightly different in the field. The clover-maize rotation also achieved the best growth promotion and disease restraint results (2.6-fold increase in healthy plants), but the maize rotation with wheat showed only minor efficiency. Interestingly, pre-cultivating the soil with clover had better results in no-till soil in both experiments. In contrast, the same procedure with wheat had a better impact when tillage was applied. It may be concluded that crop rotation and soil cultivation can be essential in reducing LWD, but other factors may affect this approach’s benefits in commercial field growth.

Biological Control of Plant Pathogens: A Global Perspective

The increase in the world population has generated an important need for both quality and quantity agricultural products, which has led to a significant surge in the use of chemical pesticides to fight crop diseases. Consumers, however, have become very concerned in recent years over the side effects of chemical fungicides on human health and the environment. As a result, research into alternative solutions to protect crops has been imposed and attracted wide attention from researchers worldwide. Among these alternatives, biological controls through beneficial microorganisms have gained considerable importance, whilst several biological control agents (BCAs) have been screened, among them Bacillus, Pantoea, Streptomyces, Trichoderma, Clonostachys, Pseudomonas, Burkholderia, and certain yeasts. At present, biopesticide products have been developed and marketed either to fight leaf diseases, root diseases, or fruit storage diseases. However, no positive correlation has been observed between the number of screened BCAs and available marketed products. Therefore, this review emphasizes the development of biofungicides products from screening to marketing and the problems that hinder their development. Finally, particular attention was given to the gaps observed in this sector and factors that hamper its development, particularly in terms of efficacy and legislation procedures.

Effects of Marine Antagonistic Fungi against Plant Pathogens and Rice Growth Promotion Activity

Ten marine-derived fungi crude extracts, namely Emericella stellatus KUFA0208, Eupenicillium parvum KUFA0237, Neosartorya siamensis KUFA0514, N. spinosa KUFA 0528, Talaromyces flavus KUFA 0119, T. macrosporus KUFA 0135, T. trachyspermus KUFA0304, Trichoderma asperellum KUFA 0559, T. asperellum KUFA 0559 and T. harzianum KUFA 0631 were determined for their fungicidal activity against five rice pathogens in vitro. The results showed that the extracts of E. stellatus KUFA0208 and N. siamensis KUFA0514 exhibited the best antifungal activity, causing complete cessation of the mycelial growth of Alternaria padwickii, Bipalaris oryzae, Fusarium semitectum, Pyricularia oryzae and Rhizoctonia solani at 10 g/L. The N. siamensis KUFA0514 extract was fractioned and antifungal compounds were found in the fractions derived from petroleum-ether and chloroform (7: 3) evidenced by inhibition zones against the mycelial growth of A. padwickii around the disc containing each fraction. Moreover, in rice growth promotion tests, diluted cultural broth of T. asperellum KUFA 0559 and T. harzianum KUFA 0631 were found to strongly promote rice shoot and root elongation; however, higher concentrations of all marine fungal broths resulted in significantly reduced rice seedling growth rather than promotion. Meanwhile, Trichoderma showed great indole-3-acetic acid (IAA) production leading to the optimum IAA values of 45.38 and 52.30 µg/ml at 11 and 13 days after inoculation, respectively. The results of this study indicated that marine fungi are promising agents having antagonistic mechanisms involving antibiosis production and plant growth promotion and may be developed as novel biocontrol agents for rice disease management.

Trichoderma asperelloides PSU-P1 Induced Expression of Pathogenesis-Related Protein Genes against Gummy Stem Blight of Muskmelon (Cucumis melo) in Field Evaluation

Gummy stem blight caused by Stagonosporopsis cucurbitacearum is the most destructive disease of muskmelon cultivation. This study aimed to induce disease resistance against gummy stem blight in muskmelon by Trichoderma asperelloides PSU-P1. This study was arranged into two crops. Spore suspension at a concentration of 1 × 10⁶ spores/mL of T. asperelloides PSU-P1 was applied to muskmelon to investigate gene expression. The expression of PR genes including chitinase (chi) and β-1,3-glucanase (glu) were determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR), and enzyme activity was assayed by the DNS method. The effects of T. asperelloides PSU-P1 on growth, yield, and postharvest quality of muskmelon fruit were measured. A spore suspension at a concentration of 1 × 10⁶ spore/mL of T. asperelloides PSU-P1 and S. cucurbitacearum was applied to muskmelons to determine the reduction in disease severity. The results showed that the expression of chi and glu genes in T. asperelloides PSU-P1-treated muskmelon plants was 7–10-fold higher than that of the control. The enzyme activities of chitinase and β-1,3-glucanase were 0.15–0.284 and 0.343–0.681 U/mL, respectively, which were higher than those of the control (pathogen alone). Scanning electron microscopy revealed crude metabolites extracted from T. asperelloides PSU-P1-treated muskmelon plants caused wilting and lysis of S. cucurbitacearum hyphae, confirming the activity of cell-wall-degrading enzymes (CWDEs). Application of T. asperelloides PSU-P1 increased fruit weight and fruit width; sweetness and fruit texture were not significantly different among treated muskmelons. Application of T. asperelloides PSU-P1 reduced the disease severity scale of gummy stem blight to 1.10 in both crops, which was significantly lower than that of the control (2.90 and 3.40, respectively). These results revealed that application of T. asperelloides PSU-P1 reduced disease severity against gummy stem blight by overexpressed PR genes and elevated enzyme activity in muskmelon plants.

Characterization and Control of Thielaviopsis punctulata on Date Palm in Saudi Arabia

Date palm (Phoenix dactylifera L.) is the most important edible fruit crop in Saudi Arabia. Date palm cultivation and productivity are severely affected by various fungal diseases in date palm-producing countries. In recent years, black scorch disease has emerged as a devastating disease affecting date palm cultivation in the Arabian Peninsula. In the current survey, leaves and root samples were collected from deteriorated date palm trees showing variable symptoms of neck bending, leaf drying, tissue necrosis, wilting, and mortality of the entire tree in the Al-Ahsa region of Saudi Arabia. During microscopic examination, the fungus isolates growing on potato dextrose agar (PDA) media produced thick-walled chlamydospores and endoconidia. The morphological characterization confirmed the presence of Thielaviopsis punctulata in the date palm plant samples as the potential agent of black scorch disease. The results were further confirmed by polymerase chain reaction (PCR), sequencing, and phylogenetic dendrograms of partial regions of the ITS, TEF1-α, and β-tubulin genes. The nucleotide sequence comparison showed that the T. punctulata isolates were 99.9-100% identical to each other and to the T. punctulata isolate identified from Iraq-infecting date palm trees. The pathogenicity of the three selected T. punctulata isolates was also confirmed on date palm plants of Khalas cultivar. The morphological, molecular, and pathogenicity results confirmed that T. punctulata causes black scorch disease in symptomatic date palm plants in Saudi Arabia. Furthermore, seven commercially available fungicides were also tested for their potential efficacy to control black scorch disease. The in vitro application of the three fungicides Aliette, Score, and Tachigazole reduced the fungal growth zone by 86-100%, respectively, whereas the in vivo studies determined that the fungicides Aliette and Score significantly impeded the mycelial progression of T. punctulata with 40% and 73% efficiency, respectively. These fungicides can be used in integrated disease management (IDM) strategies to curb black scorch disease.

Control Strategies to Cope with Late Wilt of Maize

Control of maize late wilt disease (LWD) has been at the forefront of research efforts since the discovery of the disease in the 1960s. The disease has become a major economic restraint in highly affected areas such as Egypt and Israel, and is of constant concern in other counties. LWD causes dehydration and collapsing at a late stage of maize cultivation, starting from the male flowering phase. The disease causal agent, Magnaporthiopsis maydis, is a seed- and soil-borne phytoparasitic fungus, penetrating the roots at sprouting, colonizing the vascular system without external symptoms, and spreading upwards in the xylem, eventually blocking the water supply to the plant’s upperparts. Nowadays, the disease’s control relies mostly on identifying and developing resistant maize cultivars. Still, host resistance can be limited because M. maydis undergoes pathogenic variations, and virulent strains can eventually overcome the host immunity. This alarming status is driving researchers to continue to seek other control methods. The current review will summarize the various strategies tested over the years to minimize the disease damage. These options include agricultural (crop rotation, cover crop, no-till, flooding the land before sowing, and balanced soil fertility), physical (solar heating), allelochemical, biological, and chemical interventions. Some of these methods have shown promising success, while others have contributed to our understanding of the disease development and the environmental and host-related factors that have shaped its outcome. The most updated global knowledge about LWD control will be presented, and knowledge gaps and future aims will be discussed.

A Review: Late Wilt of Maize-The Pathogen, the Disease, Current Status, and Future Perspective

Late wilt (LWD) is a vascular wilt disease that outbursts late in maize development, usually during or after flowering. The disease causal agent, the soil and seed-borne fungi, Magnaporthiopsis maydis, causes significant economic losses in Egypt, Israel, Spain, Portugal, and India. Since its discovery in the early 1960s in Egypt, the knowledge base of the disease was significantly expanded. This includes basic information on the pathogen and its mode of action, disease symptoms and damages, methods to study and monitor the pathogen, and above all, control strategies to restrain M. maydis and reduce its impact on commercial maize production. Three approaches stand out from the various control methods inspected. First, the traditional use of chemical pesticides was investigated extensively. This approach gained attention when, in 2018-2020, a feasible and economical treatment based on Azoxystrobin (alone or in combination with other fungicides) was proven to be effective even in severe cases of LWD. Second, the growing trend of replacing chemical treatments with eco-friendly biological and other green protocols has become increasingly important in recent years and has already made significant achievements. Last but not least, today's leading strategy to cope with LWD is to rely on resistant maize genotypes. The past two decades' introduction of molecular-based diagnostic methods to track and identify the pathogen marked significant progress in this global effort. Still, worldwide research efforts are progressing relatively slowly since the disease is considered exotic and unfamiliar in most parts of the world. The current review summarizes the accumulated knowledge on LWD, its causal agent, and the disease implications. An additional important aspect that will be addressed is a future perspective on risks and knowledge gaps.

Trichoderma asperellum Secreted 6-Pentyl-α-Pyrone to Control Magnaporthiopsis maydis, the Maize Late Wilt Disease Agent

Simple Summary

The maize (Zea mays L.) late wilt disease, caused by the fungus Magnaporthiopsis maydis, is considered the most severe threat to commercial maize production in Israel and Egypt. Various control strategies have been inspected over the years. The current scientific effort is focusing on eco-friendly approaches against the disease. The genus Trichoderma, a filamentous soil and plant root-associated fungi, is one of the essential biocontrol species, demonstrating over 60% of all the listed biocontrol agents used to reduce plant infectious diseases. They produce different enzymes and elicit defense responses in plants, playing a significant role in biotic and abiotic stress tolerance, hyphal growth, and plant growth promotion. Trichoderma asperellum was found to have biocontrol ability and protect crops against various plant pathogenic fungi, including the maize late wilt disease causal agent. This research aimed at isolating and identifying T. asperellum secondary metabolites with antifungal action against M. maydis. From T. asperellum growth medium, the 6-Pentyl-α-pyrone secondary metabolite was isolated and identified with high potent antifungal activity against M. maydis. This compound previously exhibited antifungal activities towards several plant pathogenic fungi. Achieving clean and identified T. asperellum active ingredient(s) secreted product(s) is the first step in revealing their commercial potential as new fungicides. Follow-up studies should test this component against the LWD pathogen in potted sprouts and the field.

Abstract

Late wilt disease (LWD) is a destructive vascular disease of maize (Zea mays L.) caused by the fungus Magnaporthiopsis maydis. Restricting the disease, which is a significant threat to commercial production in Israel, Egypt, Spain, India, and other countries, is an urgent need. In the past three years, we scanned nine Trichoderma spp. isolates as biological control candidates against M. maydis. Three of these isolates showed promising results. In vitro assays, seedlings pathogenicity trials, and field experiments all support the bio-control potential of these isolates (or their secretions). Here, a dedicated effort led to the isolation and identification of an active ingredient in the growth medium of Trichoderma asperellum (P1) with antifungal activity against M. maydis. This Trichoderma species is an endophyte isolated from LWD-susceptible maize seeds. From the chloroform extract of this fungal medium, we isolated a powerful (approx. 400 mg/L) active ingredient capable of fully inhibiting M. maydis growth. Additional purification using liquid chromatography–mass spectrometry (LC–MS) and gas chromatography–mass spectrometry (GC–MS) separation steps enabled identifying the active ingredient as 6-Pentyl-α-pyrone. This compound is a potential fungicide with high efficiency against the LWD causal agent.

Crop Cycle and Tillage Role in the Outbreak of Late Wilt Disease of Maize Caused by Magnaporthiopsis maydis

The destructive maize late wilt disease (LWD) has heavy economic implications in highly infected areas such as Israel, Egypt, and Spain. The disease outbreaks occur near the harvest, leading to total yield loss in severe cases. Crop rotation has long been known as an effective means to reduce plant diseases. Indeed, agricultural soil conservation practices that can promote beneficial soil and root fungi have become increasingly important. Such methods may have a bioprotective effect against Magnaporthiopsis maydis, the LWD causal agent. In this two-year study, we tested the role of crop rotation of maize with either wheat or clover and the influence of minimum tillage in restricting LWD. In the first experiment, wheat and clover were grown in pots with LWD infected soil in a greenhouse over a full winter growth period. These cultivations were harvested in the spring, and each pot's group was split into two subgroups that underwent different land processing practices. The pots were sown with LWD-sensitive maize cultivar and tested over a whole growth period against control soils without crop rotation or soil with commercial mycorrhizal preparation. The maize crop rotation with wheat without tillage achieved prominent higher growth indices than the control and the clover crop cycle. Statistically significant improvement was measured in the non-tillage wheat soil pots in sprout height 22 days after sowing, in the healthy plants at the season's end (day 77), and in shoot and cob wet weight (compared to the control). This growth promotion was accompanied by a 5.8-fold decrease in pathogen DNA in the plant stems. The tillage in the wheat-maize growth sequence resulted in similar results with improved shoot wet-weight throughout the season. In contrast, when maize was grown after clover, the tillage reduced this parameter. The addition of commercial mycorrhizal preparation to the soil resulted in higher growth measures than the control but was less efficient than the wheat crop cycle. These results were supported by a subsequent similar experiment that relied on soil taken from commercial wheat or clover fields. Here too, the wheat-maize growth cycle (without permanent effect for the tillage) achieved the best results and improved the plants' growth parameters and immunity against LWD and lowered pathogen levels. In conclusion, the results of this study suggest that wheat and perhaps other crops yet to be inspected, together with the adjusted tillage system, may provide plants with better defense against the LWD pathogen.

Trichoderma longibrachiatum and Trichoderma asperellum Confer Growth Promotion and Protection against Late Wilt Disease in the Field

Late wilt disease (LWD) of maize, caused by Magnaporthiopsis maydis, is considered a major threat to commercial fields in Israel, Egypt, Spain, and India. Today's control methods include chemical and agronomical intervention but rely almost solely on resistant maize cultivars. In recent years, LWD research focused on eco-friendly biological approaches to restrain the pathogen. The current study conducted during two growing seasons explores the potential of three Trichoderma species as bioprotective treatments against LWD. These species excelled in preliminary assays performed previously under controlled conditions and were applied here in the field by directly adding them to each seed with the sowing. In the first field experiment, Trichoderma longibrachiatum successfully rescued the plants' growth indices (weight and height) compared to T.&nbsp;asperelloides and the non-treated control. However, it had no positive effect on yield and disease progression. In the subsequent season, this Trichoderma species was tested against T. asperellum, an endophyte isolated from susceptible maize cultivar. This experiment was conducted during a rainy autumn season, which probably led to a weak disease burst. Under these conditions, the plants in all treatment groups were vivid and had similar growth progression and yields. Nevertheless, a close symptoms inspection revealed that the T. longibrachiatum treatment resulted in a two-fold reduction in the lower stem symptoms and a 1.4-fold reduction in the cob symptoms at the end of the seasons. T.&nbsp;asperellum achieved 1.6- and 1.3-fold improvement in these parameters, respectively. Quantitative Real-time PCR tracking of the pathogen in the host plants' first internode supported the symptoms' evaluation, with 3.1- and 4.9-fold lower M. maydis DNA levels in the two Trichoderma treatments. In order to induce LWD under the autumn's less favorable conditions, some of the plots in each treatment were inoculated additionally, 20 days after sowing, by stabbing the lower stem section near the ground with a wooden toothpick dipped in M. maydis mycelia. This infection method overrides the Trichoderma roots protection and almost abolishes the biocontrol treatments' protective achievements. This study suggests a biological Trichoderma-based protective layer that may have significant value in mild cases of LWD.

In Vitro and In Vivo Antifungal Activity of Sorbicillinoids Produced by Trichoderma longibrachiatum

In the search for antifungal agents from marine resources, we recently found that the culture filtrate of Trichoderma longibrachiatum SFC100166 effectively suppressed the development of tomato gray mold, rice blast, and tomato late blight. The culture filtrate was then successively extracted with ethyl acetate and n-butanol to identify the fungicidal metabolites. Consequently, a new compound, spirosorbicillinol D (1), and a new natural compound, 2',3'-dihydro-epoxysorbicillinol (2), together with 11 known compounds (3-13), were obtained from the solvent extracts. The chemical structures were determined by spectroscopic analyses and comparison with literature values. The results of the in vitro antifungal assay showed that of the tested fungal pathogens, Phytophthora infestans was the fungus most sensitive to the isolated compounds, with MIC values ranging from 6.3 to 400 µg/mL, except for trichotetronine (9) and trichodimerol (10). When tomato plants were treated with the representative compounds (4, 6, 7, and 11), bisvertinolone (6) strongly reduced the development of tomato late blight disease compared to the untreated control. Taken together, our results revealed that the culture filtrate of T. longibrachiatum SFC100166 and its metabolites could be useful sources for the development of new natural agents to control late blight caused by P. infestans.