Soil-borne Diseases Research Articles

Trichoderma virens XZ11-1 producing siderophores inhibits the infection of Fusarium oxysporum and promotes plant growth in banana plants

BackgroundBanana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense is a soil-borne fungal disease. Especially, tropical Race 4 (Foc TR4) can infect almost Cavendish subgroup and has a fatal threat to banana industry. Use of antagonistic microbes to manage soil-borne pathogen is viewed as a promising strategy.ResultsStrain XZ11-1 isolated from tropical rainforest has the production ability of high siderophore. By the analysis of physiological and biochemical profiles, construction of phylogenetic tree, and comparative results from the NR database, strain XZ11-1 was identified as Trichoderma virens. A relative content of 79.45% siderophores was produced in the optimized fermentation solution, including hydroxamate and carboxylate-type siderophores. Siderophores were key for inhibiting the growth of Foc TR4 by competing for environmental iron. Similarly, T. virens XZ11-1 also had antagonistic activities against 10 phytopathogenic fungi. Pot experiments demonstrated that T. virens XZ11-1 could colonize in the root system of banana plants. The symbiotic interaction not only improve plant resistance to Foc TR4, but also enhance iron absorption of roots to promote plant growth by secreting siderophores.ConclusionsT. virens XZ11-1 with the high-yield siderophores was isolated and identified. The strain could effectively inhibit the infection of Foc TR4 in banana roots and promote plant growth. It is a promising biocontrol agent for controlling fungal disease.

Development of a qPCR assay for early detection and quantification of Phytopythium vexans in kiwifruit plant and soil affected by Vine Decline Syndrome.

Kiwifruit Vine Decline Syndrome (KVDS) is a soilborne disease affecting Actinidia fruit trees in perennial cropping systems. Since its emergence in 2012, studies have increasingly identified the oomycete Phytopythium vexans as a major causative agent of the disease. P. vexans is also implicated in complex soilborne disease systems of woody perennial crops, including replant disease in apple and pear. To date, most molecular assays for the detection of P. vexans target the nuclear ribosomal internal transcribed spacer (ITS), a region which is ill-suited for distinguishing between closely related oomycete species. The cytochrome oxidase subunit I (COI) mitochondrial gene was targeted for the design of new primers because it was previously identified as a better marker for differentiating oomycete species. The FOR2/REV4RCA primer pair gave the best results regarding PCR specificity and was selected for use in a SYBR Green-based qPCR assay. The specificity of the qPCR assay was evaluated using 29 P. vexans strains (including different phylogenetic groups) as well as a wide variety of closely related off-target species associated with pathogenic soil communities of fruit trees. P. vexans strains were successfully quantified down to 20 fg in water and in DNA extracted from kiwifruit roots. P. vexans was also detected in artificially inoculated Actinidia plant roots as well as in a variety of naturally infected field samples of both kiwi and apple trees. These results suggest that the qPCR assay developed in this study is highly sensitive and specific to target pathogen, regardless of sample matrix.

A Comprehensive Review on Cucurbit Grafting: A Sustainable Approach to Boost Crop Performance

Grafting, which unites the rootstock and scion of a plant, is crucial for combating soil-borne diseases in cucurbitaceous crops such as watermelon, melon, bitter gourd, summer squash and cucumber. Essential due to limited arable land and off-season demand, this technique enhances plant vigour by improving nutrient uptake and providing resistance to soil pathogens, salinity, drought and temperature variations, thereby improving overall yield and fruit quality. Initially implemented in Japan in the late 1990s, grafting significantly affects fruit pH, flavour, sugar content, carotenoids, and texture. Globally, it has been adopted to prevent diseases like fusarium wilt and root-knot nematode. This practice mitigates production losses under adverse conditions and promotes organic, safer vegetables by reducing pesticide residues. Recent advancements in grafting methods and versatile rootstocks further support its widespread use.

Strategies for Selecting Potentially Effective Biofumigant Species for Optimal Biofumigation Outcomes

Soil-borne diseases threaten sustainable agriculture, traditionally managed by chemical fumigants, whose use is now restricted due to environmental and health concerns. This study evaluates the biofumigation potential of Brassicaceae species, specifically Brassica carinata A.Braun., Brassica juncea (L.) Vassiliĭ Matveievitch Czernajew., Raphanus sativus L., and Sinapis alba L., cultivated in central Spain. Field trials across two growing cycles assessed biomass production, glucosinolate (GSL) concentration, photosynthetically active radiation (PAR) interception, and radiation use efficiency (RUE). Biomass production varied across species and sampling dates, with S. alba and R. sativus outperforming other species in shorter cycles, while B. juncea and B. carinata showed a more efficient GSL profile regarding soil-borne disease control, particularly in aliphatic GSLs like sinigrin. Results highlight B. juncea and B. carinata as potent biofumigants due to their high GSL levels, whereas S. alba and R. sativus are more suited to early biomass production. The study also explores the chlorophyll content index (SPAD) as a potential field indicator of GSL concentration, providing a practical approach for optimizing biofumigation timing. These findings support the selection of specific Brassicaceae species adapted to climatic conditions and crop cycles for effective biofumigation in sustainable agricultural practices.

Identification of genetic loci and candidate genes underlying Fusarium crown rot resistance in wheat.

A major locus Qfcr.cau-1B conferring resistance to Fusarium crown rot was identified and validated. The putative gene underlying this locus was pinpointed via virus-induced gene silencing. Fusarium crown rot (FCR), caused by various Fusarium pathogens such as Fusarium pseudograminearum and F. culmorum, is a severe soil-borne disease which significantly affected wheat (Triticum aestivum) production in many arid and semi-arid cropping regions of the world. In this study, a total of 5 QTLs associated with FCR resistance were detected on chromosomes 1B, 2B, 3A, 5A, and 7D using a population of 120 F8 recombinant inbred lines (RIL) derived from a cross between two Chinese germplasm 20828 and SY95-71. A major locus Qfcr.cau-1B, which accounted for up to 28.33% of the phenotypic variation with a LOD value of 10.99, was consistently detected across all three trials conducted. The effect of Qfcr.cau-1B on FCR resistance was further validated using a F5 RIL population between 20828 and BLS2. Integrated transcriptome and sequence variation analysis showed that three genes including TraesCS1B02G017700, TraesCS1B02G016400, and TraesCS1B02G022300 were potential candidate genes for Qfcr.cau-1B. Of these three genes, the virus-induced silencing of TraesCS1B02G022300 significantly promoted FCR severity, indicating its positive role in FCR resistance. Taken together, results from this study expand our understanding on genetic basis of FCR resistance in wheat and will be indicative for cloning genes conferring FCR resistance.

Synergistic role of rootstock and grafting in boosting growth, yield, and quality of cucumber cultivation

Cucumber (Cucumis sativus L.) is a widely grown and highly valued cucurbitaceous vegetable crop, commanding premium prices in the vegetable market. However, intensive cultivation and monocropping practices have led to significant challenges in cucumber production, particularly in greenhouses, due to root-knot nematode and soil-borne diseases. Grafting has emerged as an alternative approach to boost abiotic stress tolerance and mitigate root diseases caused by soil-borne pathogens, thereby improving crop productivity. A study was conducted during 2023-2024 on the farmer’s field to explore the interactive effects of various grafting techniques by grafting a hybrid cucumber scion onto various local rootstocks. The experiment evaluated the performance of the hybrid cucumber scion Emistar, grafted onto four rootstocks: fig-leaf gourd (Cucurbita ficifolia), pumpkin (Cucurbita pepo), ash gourd (Benincasa hispida), and bottle gourd (Lagenaria siceraria). Two grafting techniques-hole insertion and splice grafting, were tested using different scion-rootstock combinations. The study evaluated growth, yield, and fruit quality under controlled environmental conditions. The results indicated that the pumpkin rootstock outperformed the other rootstocks, particularly when grafted using the hole insertion techniques. This combination achieved the earliest flowering (26.33 days), longest plant growth (455.77 cm), and highest fruit yield (8.07 kg). In contrast, splice grafting on bottle gourd resulted in slower growth and lower yields. Additionally, hole insertion grafting on pumpkin produced superior fruit characteristics, including the longest fruits (16.43 cm), largest diameter (9.1cm), highest fruit weight (147.24 g), and the highest TSS content (2.85ºBrix). Correlation and principal component analysis (PCA) highlighted strong positive relationships between yield and growth traits, emphasizing the superiority of the pumpkin rootstock for cucumber grafting. The study showed vigorous rootstocks like pumpkin can significantly enhance cucumber growth and yield through improved nutrient uptake, hormone translocation, and optimized grafting techniques.

Soil fungal networks exhibit sparser interactions than bacterial networks in diseased banana plantations.

Soil microorganisms are pivotal in mitigating soil-borne diseases. The intricate mechanisms underlying the interactions among microbes and their impact on disease occurrence remain enigmatic. This study underscores that a reduction in fungal network interactions correlates with the incidence of soil-borne Fusarium wilt.

Comparative Transcriptome and Weighted Gene Co-Expression Network Analysis of Eggplant (Solanum melongena L.) Reveals Key Genes Responding to Ralstonia solanacearum Infection

Eggplant (Solanum melongena L.) is a widely cultivated vegetable belonging to the family Solanaceae. However, it is highly susceptible to yield reduction owing to soil-borne diseases caused by bacterial wilt (BW) (Ralstonia solanacearum L.). Therefore, understanding the mechanism of bacterial wilt resistance in eggplant is helpful for genetic improvement to create cultivars with strong bacterial wilt resistance. In this study, we conducted a comparative analysis of transcriptomics from eggplant varieties of different genotypes following infection with R. solanacearum. Transcriptome analysis revealed the majority of differentially expressed genes (DEGs) primarily implicated in pathways such as the MAPK signaling pathway, plant hormone signal transduction, and plant–pathogen interactions, as determined using Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The expression profiles of hormone pathway genes suggest that salicylic acid, ethylene, and jasmonic acid may play significant roles in conferring bacterial wilt resistance. DEGs from the leaves, roots, and stems were partitioned into 14 modules. Among these, the black module exhibited the strongest correlation with target traits and 16 hub genes were identified using gene co-expression network analysis. Subsequently, seven hub genes were selected for validation using RT-qPCR, and the results were consistent with the RNA-seq data. Notably, upon gene annotation, a significant proportion of the hub genes were annotated as heat shock proteins (HSPs) or heat shock transcription factors (HSFs). These findings offer valuable insights for advancing research on the molecular genetic mechanisms through which HSPs/HSFs contribute to bacterial wilt resistance in eggplant.

Fusarium Wilt of Banana Latency and Onset Detection Based on Visible/Near Infrared Spectral Technology

Fusarium wilt of banana is a soil-borne vascular disease caused by Fusarium oxysporum f. sp. cubense. The rapid and accurate detection of this disease is of great significance to controlling its spread. The research objective was to explore rapid banana Fusarium wilt latency and onset detection methods and establish a disease severity grading model. Visible/near-infrared spectroscopy analysis combined with machine learning methods were used for the rapid in vivo detection of banana Fusarium wilt. A portable visible/near-infrared spectrum acquisition system was constructed to collect the spectra data of banana Fusarium wilt leaves representing five different disease grades, totaling 106 leaf samples which were randomly divided into a training set with 80 samples and a test set with 26 samples. Different data preprocessing methods were utilized, and Fisher discriminant analysis (FDA), an extreme learning machine (ELM), and a one-dimensional convolutional neural network (1D-CNN) were used to establish the classification models of the disease grades. The classification accuracies of the FDA, ELM, and 1D-CNN models reached 0.891, 0.989, and 0.904, respectively. The results showed that the proposed visible/near infrared spectroscopy detection method could realize the detection of the incubation period of banana Fusarium wilt and the classification of the disease severity and could be a favorable tool for the field diagnosis of banana Fusarium wilt.

Optimization, Characterization, & In vitro Evaluation of Spent Mushroom-Based Bio-fungicide for Tomato (Solanum lycopersicon L.) Disease Management

Aims: This study evaluated the potential of spent mushroom substrate (SMS) as an organic bio-fungicide for managing tomato diseases effectively while promoting sustainable agricultural practices. Study Design: Optimization tests utilized ANOVA (p < 0.05) to assess the effects of fermentation periods and SMS-to-water ratios on the bio-fungicide's effectiveness. Significant differences among treatments were analyzed using LSD, identifying optimal preparation conditions. A T-test compared the physico-chemical properties of fermented and non-fermented SMS-based bio-fungicides. Additionally, In vitro efficacy against various fungal diseases of tomato was evaluated using ANOVA and Tukey’s HSD test for precise treatment comparisons. Place and Duration of Study: The study was conducted at the Mushroom and Crop Protection Laboratory, Surigao del Norte State University (SNSU) – Mainit Campus, Magpayang, Mainit, Surigao del Norte, Philippines. Methodology: Fermentation periods (2, 4, and 7 days) and SMS-to-water ratios (0.5 kg, 1.0 kg, and 2.0 kg per 20 L) were evaluated to optimize beneficial microbial growth. Physico-chemical properties of both fermented and non-fermented SMS-based bio-fungicides were analyzed to determine nutrient composition and microbial activity. In vitro efficacy trials assessed the bio-fungicide’s ability to control soil-borne, foliar, and post-harvest tomato diseases. Results: ANOVA and LSD analyses identified 1.0 kg SMS per 20 L water fermented for 7 days as the optimal formulation, achieving the highest microbial population (41,666.67 CFU/mL) dominated by Trichoderma spp., Penicillium spp., actinomycetes, and Bacillus spp. Fermentation significantly enhanced the nutrient profile, increasing levels of P, Ca, Mg, Fe, and Cu, while reducing N, Zn, and Mn, thereby optimizing microbial activity and nutrient availability. In vitro assays demonstrated superior efficacy of fermented SMS bio-fungicides at 20 mL/100 mL water in managing tomato diseases, significantly outperforming non-fermented formulations. Conclusion: This study highlights SMS as a sustainable and eco-friendly bio-fungicide, aligning with circular economy principles in mushroom production. Its effectiveness in controlling tomato diseases underscores its potential as an innovative solution for sustainable agriculture. Further field validation and application to other crops are recommended to maximize its broader utility.

Biocontrol potential of natamycin-producing Streptomyces lydicus JCK-6019 against soil-borne fungal diseases of cucumber and characterization of its biocontrol mechanism.

Fusarium oxysporum f. sp. cucumerinum and Rhizoctonia solani AG-4 are the two most important fungal pathogens causing soil-borne fungal diseases of cucumber; they are difficult to control and cause serious economic losses. Given the detrimental effects of the indiscriminate use of chemical fungicides, biocontrol emerges as an efficient and ecofriendly alternative for managing soil-borne fungal diseases. Streptomyces lydicus JCK-6019 (hereafter, JCK-6019) was isolated from rhizosphere soil. Its fermentation filtrate and volatile organic compounds exhibited broad-spectrum antifungal activity against various phytopathogenic fungi and oomycetes. JCK-6019 produced natamycin as an agar-diffusible antifungal metabolite. It also produced indole-3-acetic acid and various hydrolytic enzymes. In vivo experiments revealed that a ten-fold-diluted optimized JCK-6019 fermentation broth exhibited 100% control efficiency against cucumber damping-off disease and 62.5% control efficiency against cucumber Fusarium wilt disease. Pretreatment of cucumber seedlings with 1000-fold-diluted optimized JCK-6019 fermentation broth resulted in 68.18% and 23.91% disease control values against cucumber damping-off and Fusarium wilt disease, respectively. Moreover, peroxidase activity in cucumbers after 1 day of treatment was 1.5-fold higher than that in the control. Similarly, polyphenol oxidase activity in cucumbers after 3 days of treatment was 2.34-fold higher than that in the control, indicating that JCK-6019 can induce plant resistance. The natamycin-producing strain JCK-6019 could effectively suppress the development of cucumber Fusarium wilt and damping-off disease by inducing plant resistance and producing antifungal metabolites, including natamycin and volatile organic compounds. Thus, JCK-6019 possesses high potential for application in the development of biocontrol agents against soil-borne fungal diseases of cucumber. © 2024 Society of Chemical Industry.

Untargeted Metabolomic Analysis Reveals a Potential Role of Saponins in the Partial Resistance of Pea (Pisum sativum) Against a Root Rot Pathogen, Aphanomyces euteiches.

In soilborne diseases, the plant-pathogen interaction begins as soon as the seed germinates and develops into a seedling. Aphanomyces euteiches, an oomycete, stays dormant in soil and is activated by sensing the host through chemical signals present in the root exudates. The composition of plant exudates may, thus, play an important role during the early phase of infection. To better understand the role of root exudates in plant resistance, we investigated the interaction between partially resistant lines (PI660736 and PI557500) and susceptible pea cultivars (CDC Meadow and AAC Chrome) against A. euteiches during the pre-invasion phase. The root exudates of the two sets of cultivars clearly differed from each other in inducing oospore germination. PI557500 root exudate not only had diminished induction but also inhibited the oospore germination. The contrast between the root exudates of resistant and susceptible cultivars was reflected in their metabolic profiles. Data from fractionation and oospore germination inhibitory experiments identified a group of saponins that accumulated differentially in susceptible and resistant cultivars. We detected 56 saponins and quantified 44 of them in pea root and 30 from root exudate; the majority of them, especially soyasaponin I and dehydrosoyasaponin I with potent in vitro inhibitory activities, were present in significantly higher amounts in both roots and root exudates of PI660736 and PI557500 compared with Meadow and Chrome. Our results provide evidence for saponins as deterrents against A. euteiches, which might have contributed to the resistance against root rot in the studied pea cultivars. [Formula: see text] Copyright © 2024 His Majesty the King in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada and the National Research Council of Canada. This is an open access article distributed under the CC BY 4.0 International license.

Host genotype-specific rhizosphere protists associate soil-borne viral disease resistance in wheat

Host genotype-specific rhizosphere protists associate soil-borne viral disease resistance in wheat

Trichoderma atroviride isolated from diseased apple stem have possible biocontrol effect and tolerance toward azoxystrobin and difenoconazole

BackgroundApple root rot (ARR) is a typical soil-borne disease that seriously threatens the development of the apple industry. In this study, a biocontrol fungus named AT-1 was screened from the basal tissue of apple stem recovered from root rot infection, and it was identified as Trichoderma atroviride based on morphological characteristics and amplification of the ITS, LSU, and TEF 1 genes. Limited knowledge is present in using Trichoderma against ARR disease.ResultsIn subsequent experiments, a potential biocontrol strain (AT-1) had significant antagonistic activity and easily parasitized a variety of ARR pathogens such as Rosellinia necatrix, Phytopythium vexans, and Athelia rolfsii. The lowest antifungal rate recorded was still more than 40%. In addition, different chemical fungicides were tested against pathogens and biocontrol strains. The control effect was 94.79% in May and 83.41% in August, when T. atroviride AT-1 was applied along with fungicides. Applying chemical fungicides brought more sensitivity against R. necatrix. Trichoderma strains had a good tolerance for azoxystrobin SC and difenoconazole WG fungicides. The antimicrobial strains effectively colonized in apple stem base for more than 1 month, produced many conidia, occupied a favorable niche, and finally, controlled the disease with more than 80% in the field.ConclusionOverall results suggested that T. atroviride AT-1 had a good potential in the prevention and control of ARR and had a good resistance against the applied fungicides, which can provide strain resources and a theoretical basis for ARR control.

Associations Among Cultivar Cropping Sequence, 2,4-Diacetlyphloroglucinol-Producing Pseudomonad Populations, and Take-All Disease of Winter Wheat in Oregon.

Take-all of wheat (Triticum aestivum L.), caused by Gaeumannomyces tritici (syn. G. graminis var. tritici), is perhaps the most important soilborne disease of wheat globally and can cause substantial yield losses under several cropping scenarios in Oregon. Although resistance to take-all has not been identified in hexaploid wheat, continuous cropping of wheat for several years can reduce take-all severity through the development of suppressive soils, a process called "take-all decline" (TAD). Extensive work has shown that TAD is driven primarily by members of the Pseudomonas fluorescens complex that produce 2,4-diacetlyphloroglucinol (DAPG), an antibiotic that is associated with antagonism and induced host resistance against multiple pathogens. Field experiments were conducted to determine the influence of agronomically relevant first-year wheat cultivars on take-all levels and ability to accumulate DAPG-producing pseudomonads within their rhizospheres in second-year field trials and in greenhouse trials. One first-year wheat cultivar consistently resulted in less take-all in second-year wheat and accumulated significantly more DAPG-producing pseudomonads than other cultivars, suggesting a potential mechanism for take-all reduction associated with that cultivar. An intermediate level of take-all suppression in other cultivars was not clearly associated with population size of DAPG-producing pseudomonads, however. The first-year cultivar effect on take-all dominated in subsequent plantings, and its impact was not specific to the first-year cultivar. Our results confirm that wheat cultivars may be used to suppress take-all when deployed appropriately over cropping seasons, an approach that is cost-effective, sustainable, and currently being used by some wheat growers in Oregon to reduce take-all.

Advances in the detection technology of vegetable soil borne fungi and bacteria.

Soil borne diseases are one of the most serious diseases which often results the decline of vegetables quality and loss of production. Moreover, it is difficult for plants to exhibit disease symptoms in the early stages attributing to strong concealment of soil borne pathogens. Therefore, early detection of pathogens and their physiological races plays an important role in reducing the harm of pathogens associated with diseases of vegetable crops. The traditional diagnostic techniques relied on the time consuming and less accurate methods like disease symptom observation, microscopic diagnosis, and culture techniques etc. The development of molecular biology technology has brought revolutionary changes to the diagnosis of vegetable soil borne diseases, improving the accuracy and efficiency of diagnosis. This paper reviews the various molecular detection techniques for vegetable soil borne pathogens (PCR, nested-PCR, multiplex PCR, etc.) and their physiological races (host identification, DNA molecular markers, transposon detection, etc.), explains the advantages and disadvantages of each detection technique. Furthermore, the paper comprehensively introduces the application of molecular detection technology for soil borne pathogen detection in soil, plants, and seeds. Finally, we put forward important perspectives for the future development of rapid detection methods, aiming to promote rapid diagnosis of soil pathogenic microorganisms and provide guidance for the control of biological risks.

The impact of Ricinus straw on tomato growth and soil microbial community.

Returning straw can alter the soil microbial community, reduce the occurrence of soilborne diseases, and promote plant growth. In this study, we aimed to evaluate the effects of Ricinus straw on tomato growth and rhizosphere microbial community. We carried out microcosm experiments to investigate the effects of Ricinus straw with different dosages (0, 1, and 3%) on tomato dry biomass and rhizosphere bacterial and fungal communities. The results indicated that the dry biomass of tomato seedlings with 1% addition of Ricinus straw increased by 53.98%. In addition, Ricinus straw also changed the abundance, diversities, and composition of tomato rhizosphere microbial communities. In detail, the addition of 1% Ricinus straw increased the relative abundance of putative beneficial bacteria and fungi in straw decomposition, such as Ramlibacter sp., Azohydromonas sp., Schizothecium sp., and Acaulium sp., and decreased the relative abundance of Fusarium sp. Meanwhile, Ricinus straw inhibited the growth of putative pathogenic microorganisms. The correlation analysis showed that the changes in fungal community operational taxonomic units stimulated by the addition of Ricinus straw may play a crucial positive regulatory role in tomato growth. Finally, the representative fungal strain Fusarium oxysporum f. sp. Lycopersici (FOL), named TF25, was isolated and cultured. We found that Ricinus straw extract inhibited the growth of TF25 in an in vitro experiment with an inhibition rate of 34.95-51.91%. Collectively, Ricinus straw promoted plant growth by changing the rhizosphere microbial community composition and inhibiting FOL growth, which provides new evidence for understanding the improvement of key microorganism composition in improving crop growth and the sustainability of agriculture.

CHEMICAL CONTROL OF BLACK SHANK (PHYTOPHTHORA NICOTIANAE) IN STRIP-TILLAGE DARK FIRE-CURED TOBACCO

Black shank, a soil-borne disease caused by Phytophthora nicotianae, is one of the most devastating oomycetes affecting dark tobacco worldwide. Field trials were conducted in 2018 and 2022 at an established black shank site near Hopkinsville, KY, to evaluate the efficacy of mefenoxam, fluopicolide, and oxathiapiprolin for management of black shank in dark fire-cured tobacco. Black shank field trials at this location have been conducted each year since 2006. KT D6LC, a dark-fired cultivar with moderate resistance to race 0 and race 1 black shank, was used in 2018 and 2022. Black shank infection was much greater in 2022, resulting in greater stand and yield loss in 2022 compared to 2018. Rainfall amount and timing differences between the 2 years likely contributed to these differences in final stand and yield. Final stand and total yield ranged from 80.7 to 99.3% and 2,374 to 2,882 kg ha−1, respectively, in 2018, and from 10.3 to 81.8% and 238 to 2,637 kg ha−1, respectively, in 2022. In both years, all oomyceticide treatments increased final stand and yield compared to untreated tobacco. In 2018, highest final stand came from tobacco that received mefenoxam or oxathiapiprolin plus mefenoxam at transplanting alone or followed by fluopicolide and mefenoxam after transplanting, or fluopicolide followed by mefenoxam after transplanting. Total yield was similar for tobacco treated with any oomyceticide treatment and higher than the yield of untreated tobacco in 2018. In 2022, tobacco treated with oxathiapiprolin plus mefenoxam in transplant water either alone or followed by fluopicolide and mefenoxam had significantly higher final stand and yield than all other treatments. Across both years, it was evident that oomyceticide applications made in transplant water, particularly oxathiapiprolin plus mefenoxam, had the greatest impact on black shank management in dark fire-cured tobacco.

Harnessing Trichoderma asperellum: Tri-Trophic Interactions for Enhanced Black Gram Growth and Root Rot Resilience.

Root rot caused by Macrophomina phaseolina, a common soil-borne disease in black gram, is managed with chemical fungicides, leading to toxicity and degradation of beneficial soil microbes. Existing bioagents, like talc formulation, cause leaching, clogging, and reduced productivity. The development of liquid bio-formulation via drip irrigation is crucial to mitigate biotic stress and maximize yield. This study aims to investigate the efficacy and survivability of liquid formulation of Trichoderma asperellum against root rot and its growth promotion. The results showed that Tv1 effectively inhibited M. phaseolina (66.67%), under in vitro condition. The vigor index of 4025.00 and the spore load of 1 × 108 cfu/mL were recorded from plant growth promotion and spermosphere study @ 5 mL/kg of seeds with formulation. The study found that combined application of seed treatment @ 5 mL/kg of seed and soil application @ 10 mL/L of water significantly reduced disease incidence (9.1%) against control (74.3%), with increased biomass index. There are 32 mVOCs profiled during the tritrophic interaction in roots of black gram and they were up or downregulated, viz., mollugin, pentadecanoic acid, cyclopropaneoctanoic acid, 2-octyl-, methyl ester, rhodopin, dodecanoic acid, 1,2,3-propanetriyl ester by involved in defense mechanism and biosynthetic pathways like jasmonic acid, glyconeogenic and act as acyl-CoA: acyltransferase 2 inhibitor. The results of this study confirmed that liquid formulation performs better in growth promotion, survivability on seed surface, and managing root rot of black gram compared talc-based formulation.

Evaluating Trichoderma-containing Biofungicide and Grafting for Productivity and Plant Health of Triploid Seedless Watermelon in California’s Commercial Production

Two field experiments were carried out in 2022 and 2023 within commercial watermelon fields in Stockton and Modesto, CA, USA. Two Trichoderma-containing products were applied to the grafted and nongrafted watermelon seedlings through tray soaking or field chemigation. All seedlings were mechanically transplanted into a split-split plot design with the Trichoderma product as the main factor and application method (tray soaking and chemigation) as the sub-plot. The sub-sub-factor included three interspecific hybrid squash rootstocks (Cucurbita maxima × Cucurbita moschata) ‘Cobalt’, ‘Flexifort’, and ‘RS841’ that were grafted with the commercial seedless watermelon scion ‘Summer Breeze’. All treatments were replicated four times. Vine health was visually assessed three times, and canopy coverage was assessed for a total of six measurements for each year. Harvest was conducted three times in 2022 and twice in 2023 to analyze yield and quality differences among treatments. Aboveground and root samples from defective plants were taken amid the harvest and shipped to the University of California, Davis Fungal Pathology Diagnostics Research Laboratory for identification of soilborne fungal pathogens to confirm or rule out their involvement in vine declines initially attributed to nonpathogenic factors. The laboratory diagnosis indicated that Macrophomina was morphologically identified from the foot and root isolations of 67% of the submitted nongrafted, non-Trichoderma-biofungicide–treated plants in 2022. Further sequencing results confirmed the primary pathogen, Macrophomina phaseolina, from 50% of those submitted plant samples. In addition, putative Fusarium root and stem rot (Fusarium oxysporum f. sp. radices-cucurmerinum) and Falciforme crown rot and decline (Fusarium noneumartii) from runners and roots of nongrafted, noninoculated plants in the 2022 experiment were also reported. However, no significant soilborne fungal pathogens were found in the 2023 experiment. In both trials, the effects of Trichoderma-containing biofungicides and their application methods on preventing vine decline, maintaining canopy coverage, and enhancing fruit yield and quality were not as remarkable as grafting. The average grafting effect contributed to 83% and 53% decrease of vine decline compared with the nongrafted plants in 2022 and 2023. Overall, grafted plants yielded 47.6% and 32.4% more than the nongrafted counterpart in 2022 and 2023, respectively. In addition, grafting exerted predominant influence on fruit firmness and rind thickness. The study results indicated that grafting onto multipathogen resistance watermelon rootstocks serves as an effective production tool to maintain fruit yield, quality, and plant health under both pathogenic and disease-free conditions. Further work is still needed to continue evaluating best practical application protocols of Trichoderma-based biofungicides and other biopesticides to enhance product effectiveness and end users’ confidence in reducing soilborne diseases and reliance on conventional fumigants.