The Use of Biochar for Plant Pathogen Control

Biochar-based Bacillus subtilis inoculants promote plant growth: Regulating microbial community to improve soil properties

Numerous studies support the synergistic use of biochar (BC) and plant growth-promoting rhizobacteria to enhance plant growth. Despite this, the complex and dynamic nature of soil environments necessitates further exploration of the interactions between soil microorganisms and soil properties under BC-based inoculants. This study investigated their combined effects using a BC-based inoculant, Bacillus subtilis SL-44 (BC@SL), to explore the relationship between microorganisms and soil properties. Additionally, differentiating the effects of exogenous auxiliaries BC, SL-44, and BC@SL, which can promote plant growth, enhance plant and soil enzyme activities, regulate microbial communities, and increase soil nutrient content. Compared to BC alone, SL-44 enhances plant superoxide dismutase, peroxidase, and catalase enzyme activities, while BC increases soil cellulase and urease activities. SL-44 elevates Bacillus content, whereas BC boosts overall microbial abundance. Although initial values of most soil properties remain stable under exogenous auxiliaries, by the fourth week, soil pH and organic matter decrease, while electrical conductivity, available phosphorus, and ammonium nitrogen increase significantly across treatments. BC@SL, integrating the advantages of both BC and SL-44, exhibits superior performance. Under BC@SL treatment, Bacillus content rises from 4.36% to 14.96%, and available phosphorus and ammonium nitrogen increase by 81.97% and 53.16%, respectively. Additionally, plant dry weight increases by 51.95%. These results highlight the effectiveness of BC@SL in microbial regulation, soil nutrient enhancement, and plant growth promotion. In summary, BC@SL proves to be a stable and efficient solid soil additive, supporting the advancement of green fertilizer practices.

Biochar reduces containerized pepper blight caused by Phytophthora Capsici

Phytophthora blight caused by Phytophthora capsici is a serious disease affecting a wide range of plants. Biochar as a soil amendment could partially replace peat moss and has the potential to suppress plant diseases, but its effects on controlling phytophthora blight of container-grown peppers have less been explored, especially in combination of biological control using Trichoderma. In vitro (petri dish) and in vivo (greenhouse) studies were conducted to test sugarcane bagasse biochar (SBB) and mixed hardwood biochar (HB) controlling effects on pepper phytophthora blight disease with and without Trichoderma. Sugarcane bagasse biochar and HB were blended with the commercial substrate (CS, peat-based) at 10% (SBB10, by volume), and 10%, 30%, 50%, 70% (HB10, HB30, HB50, and HB70, by volume), respectively, and CS (CS100) was used as the control. Both in vitro and in vivo studies used randomized complete block design with three treatment factors: pathogen (without or with inoculation of P. capsici), biochar (different biochar treatments), and Trichoderma (without or with inoculation). In vitro results showed that Trichoderma inhibited P. capsici growth while biochar did not have significant beneficial effects. In vivo results showed that plants grown in HB30 and HB50 had similar or higher plant growth index and shoot dry weight than the control regardless of pathogen presence. In the presence of the pathogen, plants grown in HB30, HB50, and HB70 had significantly lower disease severity, and disease incidence ratings than the control, while Trichoderma did not show beneficial effects on controlling the disease. In conclusion, HB replacing 30% and 50% peat moss in substrate could reduce pepper blight disease caused by P. capsici without negatively affecting plant growth.

Biochar amendment affects the microbial genetic profile of the soil, its community structure and phospholipid fatty acid contents

Biochar (BC) amendment has been proposed as a promising strategy for mitigating greenhouse gas (GHG) emissions, specifically carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Conducting a meta-analysis to evaluate the impact of biochar on microbial genetic profile, community structure, and phospholipid fatty acid (PLFA) contents can aid in identifying key microbial groups involved in GHG production and consumption, and assessing the overall effectiveness of biochar in reducing GHG emissions. The present meta-analysis revealed that the addition of biochar resulted in a 22 % and 41 % reduction in pmoA and mcrA genes of methanogenic microorganisms, respectively. The mcrA/pmoA ratio significantly increased by 81 %. Gene abundances exhibited a positive response to biochar amendment, with increases observed in nifH, nirK, nirS, nosZ, and nosZ (nirS + nirK) genes by 13 %, 32 %, 37 %, 42 %, and 79 %, respectively. Moreover, biochar amendment influenced the microbial community structure accordingly. The concentration of PLFAs increased in response to BC treatment in the following order: A-bacteria (+49 %) < Fungi (+30 %) < Gram-pb (+21 %) < G-bacteria (+17 %) < Gram-nb (+11 %). These findings indicate that biochar amendment shapes the microbial community structure, further emphasizing its significance in enhancing soil fertility.

Managing tobacco black shank disease using biochar: direct toxicity and indirect ecological mechanisms

Black shank disease in tobacco, caused by Phytophthora nicotianae, can lead to yield losses of 30%-50% upon outbreak. Recently, biochar derived from agricultural waste has shown significant potential in controlling soil-borne diseases, though its mechanisms remain unclear. Over a 3-year observation period, we found that the incidence of black shank was significantly lower in plots amended with biochar compared with normal cultivation plots. To investigate the underlying mechanisms, we studied both the direct and indirect effects of biochar on black shank. Direct antifungal assays indicated that biochar reduced the total number of sporangia by 53.91%. Further pot experiments revealed a 62.34% reduction in the P. nicotianae population in the soil following biochar application. Additionally, biochar application led to notable changes in soil physicochemical properties and microbial community composition. Microbial species analysis showed that biochar promoted the aggregation of beneficial microbes such as Sphingomonas, Flavisolibacter, and Mucoromycota. Functional predictions using the PICRUSt 2 software revealed that biochar enhances bacterial functions related to antimicrobial substance synthesis (Tetracycline biosynthesis), detoxification metabolism (D-arginine and D-ornithine metabolism, arginine and proline metabolism), and lipid and fatty acid metabolism (Lipopolysaccharide biosynthesis, fatty acid biosynthesis), while fungal functions showed no significant changes. This suggests that rhizosphere bacteria play a more prominent role in the suppression of black shank by biochar, a finding supported by partial least squares path modeling analysis. Therefore, we hypothesize that biochar not only directly inhibits P. nicotianae growth but also regulates the composition of the rhizosphere microbial community, inducing the production of antimicrobial substances by rhizosphere bacteria, effectively preventing P. nicotianae invasion.IMPORTANCEBlack shank, a global soil-borne fungal disease in tobacco, currently lacks effective control methods. Notably, biochar derived from agricultural waste has shown significant potential in controlling soil-borne diseases. Over a 3-year observation period, we found that plots amended with biochar had a significantly lower incidence of black shank compared with normal cultivation plots. However, the mechanisms of disease suppression remained unclear. Through in vitro antifungal assays and pot experiments, we discovered that tobacco-derived biochar can directly inhibit the growth of the pathogen. Additionally, biochar regulates the composition of the rhizosphere microbial community, inducing rhizosphere bacteria to produce antimicrobial substances, effectively preventing pathogen invasion. This discovery reveals both the direct and indirect mechanisms by which biochar suppresses black shank in tobacco. It provides a scientific basis for developing green control technologies for black shank and offers theoretical support for the application of biochar in managing soil-borne diseases in tobacco cultivation areas.

A comprehensive review on biochar against plant pathogens: Current state-of-the-art and future research perspectives

Plant pathogens cause a serious menace to food production. The diseases caused by pathogens are estimated to cause a yield loss of about 14.1 %, whereas, in India, up to 26 %. Several plant pathogens like Pythium, Phytophthora, Rhizoctonia, Sclerotinia, Fusarium, and Verticillium can cause 50-75 % yield losses in cereals, cotton, and horticultural crops (fruits, vegetables, and flowers) 10-100 % in pulses, 30-60 % loses in oilseed crops and 40-50 % in plantation crops. Biochar as soil amendment is emerging as an effective environment friendly substitute for fungicides to counter plant pathogens. It has also been reported to induce resistance in plants to combat plant pathogens by activating the two important defense pathways such as salicylic acid, jasmonate/ethylene defense, and triggering the plant's antioxidant enzymatic activities. Biochar promotes soil health and consequently improves the plant health, resulting in reduced incidence of disease. This novel amendment also helps in the priming of expression of genes against foliar fungal pathogen infection. This review paper will summarize the effect of biochar incorporation in the plant disease management as well as on their growth parameters.

Potential of silicon-rich biochar (Sichar) amendment to control crop pests and pathogens in agroecosystems: A review

We reviewed the potential of silicon (Si)-rich biochars (sichars) as crop amendments for pest and pathogen control. The main pathosystems that emerged from our systematic literature search were bacterial wilt on solanaceous crops (mainly tomato, pepper, tobacco and eggplant), piercing-sucking hemipteran pests and soil-borne fungi on gramineous crops (mainly rice and wheat), and parasitic nematodes on other crops. The major pest and pathogen mitigation pathways identified were: i) Si-based physical barriers; ii) Induction of plant defenses; iii) Enhancement of plant-beneficial/pathogen-antagonistic soil microflora in the case of root nematodes; iv) Alteration of soil physical-chemical properties resulting in Eh-pH conditions unfavorable to root nematodes; v) Alteration of soil physical-chemical properties resulting in Eh-pH, bulk density and/or water holding capacity favorable to plant growth and resulting tolerance to necrotrophic pathogens; vi) Increased Si uptake resulting in reduced plant quality, owing to reduced nitrogen intake towards some hemi-biotrophic pests or pathogens. Our review highlighted synergies between pathways and tradeoffs between others, depending, inter alia, on: i) crop type (notably whether Si-accumulating or not); ii) pest/pathogen type (e.g. below-ground/root-damaging vs above-ground/aerial part-damaging; "biotrophic" vs "necrotrophic" sensu lato, and corresponding systemic resistance pathways; thriving Eh-pH spectrum; etc.); iii) soil type. Our review also stressed the need for further research on: i) the contribution of Si and other physical-chemical characteristics of biochars (including potential antagonistic effects); ii) the pyrolysis process to a) optimize Si availability in the soil and its uptake by the crop and b) to minimize formation of harmful compounds e.g. cristobalite; iii) on the optimal form of biochar, e.g. Si-nano particles on the surface of the biochar, micron-sized biochar-based compound fertilizer vs larger biochar porous matrices.

Evaluation of Soil Antagonism against the White Root Rot Fungus Rosellinia necatrix and Pathogen Mycosphere Communities in Biochar-amended Soil

White root rot disease caused by Rosellinia necatrix is a growing issue in orchards, and biochar pyrolyzed from the pruned branch residues of fruit trees has potential as a soil amendment agent with a number of benefits, such as long-term carbon sequestration. However, the effects of pruned branch biochar on white root rot disease remain unclear. Therefore, we compared direct antagonism against R. necatrix between soils with and without pruned pear branch biochar using a toothpick method and then linked soil physicochemical properties and microbial communities with soil antagonism. The results obtained showed that soil antagonism against the pathogen, that is, the extinction zone of R. necatrix in mycelial toothpicks, decreased in soils amended with 20% (v/v) pruned branch biochar. Soil pH was neutralized and aeration was promoted by the biochar amendment, which may be favorable for pathogen growth. An investigation of microbial communities surrounding R. necatrix mycelia indicated that antagonistic fungi affiliated with Chaetomiaceae and Trichoderma were selectively excluded from the mycosphere community in biochar-amended soil. Therefore, the enrichment of these indigenous antagonistic fungi may be important for controlling R. necatrix. Based on the present results, we do not recommend the application of pruned branch biochar to the soil area associated with the roots of fruit trees in order to avoid increasing the risk of white root rot in orchards.

Low cost maize stover biochar as an alternative to inorganic fertilizer for improvement of soil chemical properties, growth and yield of tomatoes on degraded soil of Northern Uganda

BACKGROUND

Soil fertility decline due to nutrient mining coupled with low inorganic fertilizer usage is a major cause of low crop yields across sub-Saharan Africa. Recently, biochar potential to improve soil fertility has gained significant attention but there are limited studies on the use of biochar as an alternative to inorganic fertilizers. In this study, we determined the effect of maize stover biochar without inorganic fertilizers on soil chemical properties, growth and yield of tomatoes (Solanum lycopersicum L.). A field experiment was conducted in 2022 for two consecutive seasons in Northern Uganda. The experiment included five treatments; inorganic fertilizer (control), biochar applied at rates of 3.5, 6.9, 13.8 and 27.6 t ha-1.

RESULTS

In this study, maize stover biochar improved all the soil chemical properties. Compared to the control, pH significantly increased by 27% in the 27.6 t ha-1 while total N increased by 35.6% in the 13.8 t ha-1. Although P was significantly low in the 3.5 t ha-1, 6.9 t ha-1 and 13.8 t ha-1, it increased by 3.9% in the 27.6 t ha-1. Exchangeable K was significantly increased by 42.7% and 56.7% in the 13.8 t ha-1 and 27.6 t ha-1 respectively. Exchangeable Ca and Mg were also higher in the biochar treatment than the control. Results also showed that plant height, shoot weight, and all yield parameters were significantly higher in the inorganic fertilizer treatment than in the 3.5, 6.9, and 13.8 t ha-1 treatments. Interestingly, maize stover biochar at 27. 6 t ha-1 increased fruit yield by 16.1% compared to the control suggesting it could be used as an alternative to inorganic fertilizer.

CONCLUSIONS

Maize stover biochar applied at 27.6 t ha-1 improved soil chemical properties especially pH, N, P and K promoting growth and yield of tomatoes. Therefore, maize stover biochar could be recommended as an alternative to expensive inorganic fertilizers for tomato production in Northern Uganda.

Bamboo charcoal mediated plant secondary metabolites biosynthesis in tomato against South American tomato pinworm (Tuta absoluta)

Introduction

The south American tomato pinworm (Tuta absoluta), an invasive insect pest species, has established itself in more than 33 Chinese prefectures, where it is mainly damaging tomato crops. Immediate efforts have been initiated to find strategies to control this pest. Studies have shown that biochar (BC) amendment to soil can enhance plant growth and resistance to herbivory.

Methods

First, we quantified the morphological performance of tomato plants grown in different coconut bran and bamboo charcoal (v/v) combinations and selected the most beneficial one. Then we checked the T. absoluta survival on the tomato plants grown in the selected bamboo charcoal combination. Finally, we studied the leaf metabolite accumulation and gene expression changes in tomato plants after growing in the selected bamboo charcoal combination.

Results

We found that the 30:1 ratio of bamboo charcoal and coconut bran is the most beneficial to tomato growth as its amendment to soil increased tomato plant height, stem thickness, and chlorophyll content, whereas, the T. absoluta survival decreased. The metabolome profiles of BC tomato leaves showed an increased accumulation of flavonoids, terpenoids, and phenolic acids compared to CK. Transcriptome sequencing resulted in the identification of 244 differentially expressed genes. Most of the upregulated genes were associated with stress-related hub proteins, flavonoid biosynthesis, MAPK and phytohormone signaling, and terpenoid biosynthesis. Additionally, the expression of many genes related to signaling and defense was changed in response to the bamboo charcoal amendment.

Discussion

We conclude that bamboo charcoal induces biosynthesis of flavonoids, terpenoids, and phenolic acids, which improve plant growth and tolerance against T. absoluta, thus reducing the survival of destructive pests.

Effect of incorporation of broccoli residues into soil on occurrence of verticillium wilt of spring-sowing-cotton and on rhizosphere microbial communities structure and function

Cotton verticillium wilt (CVW) represented a typical plant soil-borne disease and resulted in widespread economic losses in cotton production. However, the effect of broccoli residues (BR) on verticillium wilt of spring-sowing-cotton was not clear. We investigated the effects of BR on CVW, microbial communities structure and function in rhizosphere of two cotton cultivars with different CVW resistance using amplicon sequencing methods. Results showed that control effects of BR on CVW of susceptible cultivar (cv. EJ-1) and resistant cultivar (cv. J863) were 58.49% and 85.96%, and the populations of V. dahliae decreased by 14.31% and 34.19%, respectively. The bacterial diversity indices significantly increased in BR treatment, while fungal diversity indices significantly decreased. In terms of microbial community composition, the abilities to recruit bacteria and fungi were enhanced in BR treatment, including RB41, Gemmatimonas, Pontibacter, Streptomyces, Blastococcus, Massilia, Bacillus, and Gibberella, Plectosphaerella, Neocosmospora, Aspergillus and Preussia. However, the relative abundances of Sphingomonas, Nocardioides, Haliangium, Lysobacter, Penicillium, Mortierella and Chaetomidium were opposite tendency between cultivars in BR treatment. According to PICRUSt analysis, functional profiles prediction showed that significant shifts in metabolic functions impacting KEGG pathways of BR treatment were related to metabolism and biosynthesis. FUNGuild analysis indicated that BR treatment altered the relative abundances of fungal trophic modes. The results of this study demonstrated that BR treatment decreased the populations of V. dahliae in soil, increased bacterial diversity, decreased fungal diversity, changed the microbial community structure and function, and increased the abundances of beneficial microorganisms.

Microbial and Plant Derived Low Risk Pesticides Having Nematocidal Activity

Microorganisms, virus, weeds, parasitic plants, insects, and nematodes are among the enemies that induce severe economic losses to agrarian production. Farmers have been forced to combat these enemies using different methods, including mechanical and agronomic strategies, since the beginning of agriculture. The development of agriculture, due to an increased request for food production, which is a consequence to the rapid and noteworthy growth of the world's population, requires the use of more efficient methods to strongly elevate the yield production. Thus, in the last five-to-six decades, a massive and extensive use of chemicals has occurred in agriculture, resulting in heavy negative consequences, such as the increase in environmental pollution and risks for human and animal health. These problems increased with the repetition of treatments, which is due to resistance that natural enemies developed against this massive use of pesticides. There are new control strategies under investigation to develop products, namely biopesticides, with high efficacy and selectivity but based on natural products which are not toxic, and which are biodegradable in a short time. This review is focused on the microbial and plant metabolites with nematocidal activity with potential applications in suitable formulations in greenhouses and fields.

The Suppressive Effects of Biochar on Above- and Belowground Plant Pathogens and Pests: A Review

Soilborne pathogens and pests in agroecosystems are serious problems that limit crop yields. In line with the development of more ecologically sustainable agriculture, the possibility of using biochar to control pests has been increasingly investigated in recent years. This work provides a general overview of disease and pest suppression using biochar. We present an updated view of the literature from 2015 to 2022 based on 61 articles, including 117 experimental case studies. We evaluated how different biochar production feedstocks, pyrolysis temperatures, application rates, and the pathosystems studied affected disease and pest incidence. Fungal pathogens accounted for 55% of the case studies, followed by bacteria (15%), insects and nematodes (8%), oomycetes and viruses (6%), and only 2% parasitic plants. The most commonly studied belowground pathogen species were Fusarium oxysporum f. sp. radicis lycopersici in fungi, Ralstonia solanacearum in bacteria, and Phytophthora capisci in oomycetes, while the most commonly studied pest species were Meloidogyne incognita in nematodes, Epitrix fuscula in insects, and both Phelipanche aegyptiaca and Orobanche crenata in parasitic plants. Biochar showed suppression efficiencies of 86% for fungi, 100% for oomycetes, 100% for viruses, 96% for bacteria, and 50% for nematodes. Biochar was able to potentially control 20 fungal, 8 bacterial, and 2 viral plant pathogens covered by our review. Most studies used an application rate between 1% and 3%, a pyrolysis temperature between 500 °C and 600 °C, and a feedstock based on sawdust and wood waste. Several mechanisms have been proposed to explain disease suppression by biochar, including induction of systemic resistance, enhancement of rhizosphere competence of the microbial community, and sorption of phytotoxic compounds of plant and/or microbial origin. Overall, it is important to standardize biochar feedstock and the rate of application to improve the beneficial effects on plants in terms of disease control.

Overview of the use of biochar from main cereals to stimulate plant growth

The total global food demand is expected to increase up to 50% between 2010 and 2050; hence, there is a clear need to increase plant productivity with little or no damage to the environment. In this respect, biochar is a carbon-rich material derived from the pyrolysis of organic matter at high temperatures with a limited oxygen supply, with different physicochemical characteristics that depend on the feedstock and pyrolysis conditions. When used as a soil amendment, it has shown many positive environmental effects such as carbon sequestration, reduction of greenhouse gas emissions, and soil improvement. Biochar application has also shown huge benefits when applied to agri-systems, among them, the improvement of plant growth either in optimal conditions or under abiotic or biotic stress. Several mechanisms, such as enhancing the soil microbial diversity and thus increasing soil nutrient-cycling functions, improving soil physicochemical properties, stimulating the microbial colonization, or increasing soil P, K, or N content, have been described to exert these positive effects on plant growth, either alone or in combination with other resources. In addition, it can also improve the plant antioxidant defenses, an evident advantage for plant growth under stress conditions. Although agricultural residues are generated from a wide variety of crops, cereals account for more than half of the world's harvested area. Yet, in this review, we will focus on biochar obtained from residues of the most common and relevant cereal crops in terms of global production (rice, wheat, maize, and barley) and in their use as recycled residues to stimulate plant growth. The harvesting and processing of these crops generate a vast number and variety of residues that could be locally recycled into valuable products such as biochar, reducing the waste management problem and accomplishing the circular economy premise. However, very scarce literature focused on the use of biochar from a crop to improve its own growth is available. Herein, we present an overview of the literature focused on this topic, compiling most of the studies and discussing the urgent need to deepen into the molecular mechanisms and pathways involved in the beneficial effects of biochar on plant productivity.