Control Of Soil-borne Pathogens Research Articles

In-furrow application of biologicals for control of Rhizoctonia diseases in snap bean

Florida ranks first in the production of fresh-market snap beans in the United States. Rhizoctonia diseases, including damping-off and root rot, caused by Rhizoctonia solani, are important diseases in snap beans, particularly if there is heavy rainfall during the first month after seeding. Growers usually use seeds treated with fungicides to control soilborne pathogens including R. solani. However, there are concerns about resistance development in R. solani and the impacts of chemicals on the environment. In this study, three biological products, including Howler, Theia, and Double Nickle applied as an in-furrow spray at seeding and/or foliar sprays after emergence, were evaluated in the field for their efficacy in controlling R. solani on snap bean. When nontreated seeds were used, Howler at 5 lb/A and Double Nickle at 16 fl oz/A each applied as an in-furrow spray at seeding significantly (P < 0.05) reduced disease incidence compared to the untreated control. However, weekly foliar sprays after emergence showed effectiveness in disease reduction only at a high inoculum level. The highest disease reduction of 95.4% was observed in the treatment with Howler at 5 lb/A in the 2022 trial, and 32.8% for Double Nickle at 16 fl oz/A in 2023. Both biologicals also significantly increased the pod yield, by 85.6% with Howler in 2022 and doubled by Double Nickle in 2023 when compared to the untreated control. Results from these field trials reveal the potential of these biologicals in the control of Rhizoctonia root rot in snap bean production.

Long-Acting Sustained-Release Hydrogel for Soil-Borne Pathogen Control in Chinese Herbal Medicine

Long-Acting Sustained-Release Hydrogel for Soil-Borne Pathogen Control in Chinese Herbal Medicine

Encapsulated allyl isothiocyanate improves soil distribution, efficacy against soil-borne pathogens and tomato yield.

Crop quality, yield and farmer income are reduced by soil-borne diseases, nematodes and weeds, although these can be controlled by allyl isothiocyanate (AITC), a plant-derived soil fumigant. However, its efficacy against soil-borne pathogens varies, mainly because of its chemical instability and uneven distribution in the soil. Formulation modification is an effective way to optimize pesticide application. We encapsulated AITC in modified diatomite granules (GR) and measured the formulation's loading content and stability, environmental fate and efficacy against soil-borne pathogens, and its impact on the growth and yield of tomatoes. We observed that an AITC loading content in the granules of 27.6% resulted in a degradation half-life of GR that was 1.94 times longer than 20% AITC emulsifiable concentrate in water (EW) and shorter than AITC technical (TC) grade. The stable and more even distribution of GR in soil resulted in relatively consistent and acceptable control of soil-borne pathogens. Soil containing AITC residues that remained 10-24 days after GR fumigation were not phytotoxic to cucumber seeds. GR significantly reduced soil-borne pest populations, and tomato growth and yield increased as AITC dosage increased. GR containing an AITC dose of 20 g m-2 effectively controlled pathogens in soil for about 7 months and improved tomato yield by 108%. Our research demonstrates the benefits of soil fumigation with loaded AITC over other formulations for effective pest control, and improved tomato plant growth and fruit yield. Fumigant encapsulation appears to be a useful method to improve pest and disease control, environmental performance and fumigant commercial sustainability. © 2024 Society of Chemical Industry.

Improvement in Biocontrol Ability of Trichoderma Through Chemical Mutation and Gamma Irradiation for The Control of Soil Borne Pathogens

Biocontrol agent like Trichoderma viride was acclaimed as effective, eco-friendly and cheap, nullifying the ill effect of chemicals, These biocontrol agents are identified to act against on array of important soil borne plant pathogens viz.,Sclerotium rolfsii, Rhizoctonia bataticola and Fusarium oxysporum f. sp. ciceri etc.” Improvement in biocontrol ability of Trichoderma viride through mutation” was carried at Department of Plant Pathology, during 2019-2020. The antagonistic ability of a biocontrol agent was determined by its physiological state so that change in physiological or genetically conditions could alter the antagonism. Hence the genetic modification using mutagenesis offers the potential for producing improved bio-protection is likely to enhance their biocontrol capabilities against soil borne pathogen. Mutagenesis by chemical i.e. Ethyl Methyl Sulphonate (EMS) @ 100, 150, 200 and 250 µl/ml and time interval at 30, 45 and 60 minutes. The influence of gamma irradiation on improving production of antifungal metabolites and biological proficiency of the biocontrol agent against soil borne pathogen. Trichoderma viride were irradiated in different dose of gamma radiation (cobalt-60) @ 0, 20, 30, 40 and 50 k-rad. for induced mutation. Sixteen Trichoderma viride mutants were obtained after chemical mutagenesis and gamma irradiation and tested for their antagonistic activities in vitro. Morphological character of efficient mutants was tested up to six generation to check their stability. Among these, four stable mutants viz., TVME 2b, TVME 2c, TVME 3c and TVGM1 were proved as effective antagonists against Sclerotium rolfsii, Rhizoctonia bataticola and Fusarium oxysporum f.sp. ciceri basis of their maximum bioefficiency. Mutants TVME2b, TVME2c, TVME3c and TVGM1 exhibited the highest inhibition to mycelial growth of Sclerotium rolfsii with an inhibition percentage 64.76, 64.22, 63.08 and 62.93% respectively. Rhizoctonia bataticola was inhibited to the extent of 63.47, 60.87, 61.93 and 61.02% by relative mutants, while Fusarium oxysporum f. sp. ciceri was restricted and recorded 63.50, 62.88, 62.03 and 60.74% respectively. The highest chitinase enzyme units/mg of protein i.e. 0.64, 0.63, 0.63 and 0.62 was exerted in TVME2b, TVME2c, TVME3c and TVGM1 having respectively. However, TVME1c contains 0.37 enzyme units; it showed maximum ability against pathogens. hence present study proved that mutagenesis is the efficient tool for improving bioefficiency of Trichoderma viride, a biocontrol agent.

Application of bio-surfactants as bio-control agents against soil-borne and plant root pathogens

Biosurfactants are the chemicals that microorganisms produce and are widely used to control plant diseases and industrial level, such as to produce nanoparticles, water purification, molecular imaging etc. Soil-borne pathogens live in the soil for a long time by forming their resting structures such as sclerotia which remain dormant during unfavorable conditions and become active as conditions become favorable. Different fungi form different types of resting structures. Chemical and cultural methods can control these pathogens by applying biocontrol agents and biosurfactants. Biosurfactants are more reliable to control soilborne pathogens because they have low toxicity, biodegradability, control environmental, and specific to their target. Keywords: biosurfactants, soilborne pathogens, management, biocontrol, application, advantages.

Biological control of soil-borne pathogens in arid lands: a review

Biological control of soil-borne pathogens in arid lands: a review

Preplant Application of Allyl Isothiocyanate Controls Weeds and Pathogens in Eastern North Carolina Strawberry (Fragaria ×ananassa cv. Camarosa) with and without Addition of Soil-applied Steam

Allyl isothiocyanate (AITC) is a colorless aliphatic oil that naturally occurs in many plants of the cabbage and mustard family (Brassicaceae). It has antimicrobial activity and is used as pesticide for a variety of applications. However, AITC as a soil disinfectant has exhibited inconsistent weed and pathogen control, mainly because of its higher viscosity and low vapor pressure (5 mmHg at 25 °C). Steam, however, effectively controls soil-borne pathogens if soil temperatures of 65 °C or more are reached for a minimum duration of 30 minutes. We hypothesized that steam applications targeting lower temperatures, when combined with soil-injected AITC, will provide sufficient weed and pathogen control. We further hypothesized that the combination of AITC and steam will lead to higher strawberry yields compared with either of the components on their own. Two strawberry (Fragaria ×ananassa cv. Camarosa) trials were conducted during two consecutive seasons (2020–21 and 2021–22). The trials were conducted at the Central Crops Research Station in Clayton, NC, USA, and the Horticulture Research Station in Castle Hayne, NC, USA. Eight treatments and a nontreated control were established in a randomized complete block design (four replicates each). The treatments were Pic-Clor 60, AITC, AITC followed by 60 minutes of steam injection, AITC followed by 30 minutes of steam injection, AITC followed by 10 minutes of steam injection, 60 minutes of steam injection, 30 minutes of steam injection, and 10 minutes of steam injection. Soilborne pathogen control efficacy was assessed using wet Pythium sp. plating assays. Weed control was assessed through weed seed/tuber germination assays. Our results showed that combining ATIC with steam did not reduce weed or pathogen levels or improve yield when compared with AITC alone or Pic-Clor 60. Moreover, treatment comprising steam alone did not provide sufficient control. However, AITC alone controlled weeds and pathogens as effectively as Pic-Clor 60 during both years and both locations of the study. These results showed that AITC alone could be a potential alternative soil disinfectant for Eastern North Carolina strawberry production.

Effectiveness of integrated solarization technology in managing soil-borne pathogens and weeds in citrus seedlings under greenhouse conditions

Solarization Technology utilizes solar radiation to kill soil-borne pests, diseases, and weeds in an environmentally and eco-friendly way. In this study, we assessed the efficacy of integrating solarisation with sticky traps on two potting mixtures (sawdust and soil) for three Citrus species (Citrus sinensis, C. reticulata, and C. limon). Eight treatments were tested viz., non-solarized sawdust, non-solarized soil, solarized soil, solarized soil with sticky traps, non-solarized soil with sticky traps, non-solarized sawdust with sticky traps, solarized sawdust, and solarized sawdust with sticky traps, each replicated thrice and were arranged in a randomized complete block design (RCBD). Thirty sterilized seeds of each Citrus species were sown per treatment and monitored for one year in 2019. Analysis of variance (ANOVA) revealed a significant difference in weed control between the treatments at p ≤ 0.05. Tukey’s post hoc test showed weed growth differences between treatments with sawdust and ones with soil as media. More weeds grew in non-solarized soil (32%), compared to non-solarized soil with sticky traps (30%), solarized soil with sticky traps (21%), solarized soil (17%), and treatments with sawdust media did not allow weed growth (0%). A Kruskal Wallis test revealed a significant effect of treatments on the survival percentage of Citrus seedlings (X2 = 36.008, df = 7, p< 0.001), mean of chewed leaves (X2 = 20.850, df = 7, p = 0.004) and percentage levels of low chlorophyll (X2 = 21.073, df = 7, p =0.004) at the p ≤ 0.05 level. Highest number of Citrus seedlings with folded leaves were observed in non-solarized sawdust with sticky traps (mean rank = 119.50), followed by non-solarized soil with sticky traps (112.22), and solarized sawdust (107.69), while the lowest in non-solarized sawdust (90.96), solarized soil (90.91), non-solarized soil (88.25), solarized sawdust with sticky traps (85.44) and lastly solarized soil with sticky traps (82.54). Citrus seedlings with sawdust media were observed to be nitrogen deficient (Mean ranks 118.43 - 141.63). Solarized soil with sticky traps had the least number of Citrus seedlings with leaf miner symptoms (Mean rank = 12.50). Therefore, solarized soil with sticky traps was the most suitable treatment for the control of soil-borne pathogens. Treatments with sawdust media effectively stopped weed growth while those with solarized soil media reduced their growth. Integration of sticky traps was very pivotal in the management of whiteflies and other honey dew secreting insects. We recommend a similar study under field conditions.

Susceptibility and plant immune control-a case of mycorrhizal strategy for plant colonization, symbiosis, and plant immune suppression.

Plants and microbes (mycorrhizal fungi to be precise) have evolved together over the past millions of years into an association that is mutualist. The plants supply the fungi with photosynthates and shelter, while the fungi reciprocate by enhancing nutrient and water uptake by the plants as well as, in some cases, control of soil-borne pathogens, but this fungi-plant association is not always beneficial. We argue that mycorrhizal fungi, despite contributing to plant nutrition, equally increase plant susceptibility to pathogens and herbivorous pests' infestation. Understanding of mycorrhizal fungi strategies for suppressing plant immunity, the phytohormones involved and the signaling pathways that aid them will enable the harnessing of tripartite (consisting of three biological systems)-plant-mycorrhizal fungi-microbe interactions for promoting sustainable production of crops.

Evaluation of Growth Promotion Traits of Ridge Gourd in Vitro and In Vivo Conditions Using Soil Rhizobacteria as Green Bioinoculants

Abstract: Plant growth-promoting bacteria (PGPB) are now a days an important source of biofertilizers, due to increasing trend of organic fertilizers and ill effects of chemical fertilizers. PGPBs are efficient soil microbes which enhance the nutrient utilization efficiency, growth of several crops and controlling soil borne pathogens. Ridge gourd (Luffa acutangula L.) is a potential horticulture crop due to its high economic value and belongs to the family, Cucurbitaceae. In the present study, PGPB were isolated from the rhizospheric soil of 3 different crop fields (sugarcane, mustard and wheat) from Meerut, Uttar Pradesh were used to investigate their effect on growth pattern of ridge gourd. The isolates were screened for morphological, biochemical, and plant growth-promoting characterstics. Under in-vitro condition, inoculation of Ridge gourd with the P1, P2, B2, B3, B4, B5, R2, , R5, A2, A3, A5, A6, A7 showed a significant increase in seed germination and enhancement in elongation of root and shoot compared to control. Then isolated PGPB inoculated with Ridge gourd for Pot experiment and P1, P2, B2, B3, B4, B5, R2, R5, A2, A3, A4, A6, A7 showed the enhanced growth parameters as appearance of first leaf, flower and fruit as compared to the control. Hence, it can be concluded that application of PGPB has immense potential to be used as agricultural crop inoculants as they promote plant growth as well as improve the health and yield of the plants.

Anaerobic digestion for degrading saponins from Panax notoginseng root and applying biogas slurry to promote degradation of autotoxic saponins in continuous cropping soil

Anaerobic digestion degrades complex organic matter and biogas slurry can control soilborne pathogens. However, the potential and efficiency of anaerobic digestion and biogas slurry in degrading autotoxins need further investigation. In this study, we investigated the efficiency of saponin degradation in anaerobic digestion systems (with increasing amounts of Panax notoginseng root powder in groups G1, G4, and G8), and analyzed changes in microbial communities after fermentation. We also determined the degradation efficiency of autotoxic saponins in continuous cropping soil treated with biogas slurry. The degradation rate of saponins (R1, Rg1, and Rb1) in the three anaerobic digestion systems exceeded 80%, and the biogas slurry from these anaerobic digestion systems enhanced autotoxic saponin degradation in continuous cropping soil to over 95%. Microbiome diversity decreased and its structure and composition were altered in anaerobic digestion groups G4 and G8. The predominant methanogenesis pathway in G4 was the acetoclastic pathway of Methanothrix, while that in G8 was the hydrogenotrophic pathway of Methanosarcina. Both G4 and G8 enriched potentially saponin-degrading taxa and shared 33 taxa. In conclusion, anaerobic digestion can enrich specific microbial taxa that degrade saponins, and biogas slurry can promote the degradation of autotoxic saponins in continuous cropping soil.

Microbial-Based Products to Control Soil-Borne Pathogens: Methods to Improve Efficacy and to Assess Impacts on Microbiome

Microbial-based products (either as biopesticide or biofertilizers) have a long history of application, though their use is still limited, mainly due to a perceived low and inconsistent efficacy under field conditions. However, their efficacy has always been compared to chemical products, which have a completely different mechanism of action and production process, following the chemical paradigm of agricultural production. This paradigm has also been applied to regulatory processes, particularly for biopesticides, making the marketing of microbial-based formulations difficult. Increased knowledge about bioinocula behavior after application to the soil and their impact on soil microbiome should foster better exploitation of microbial-based products in a complex environment such as the soil. Moreover, the multifunctional capacity of microbial strains with regard to plant growth promotion and protection should also be considered in this respect. Therefore, the methods utilized for these studies are key to improving the knowledge and understanding of microbial-based product activity and improving their efficacy, which, from farmers' point of view, is the parameter to assess the usefulness of a treatment. In this review, we are thus addressing aspects related to the production and formulation process, highlighting the methods that can be used to evaluate the functioning and impact of microbial-based products on soil microbiome, as tools supporting their use and marketing.

Studies on Cleft Grafting in Brinjal (Solanum melongena L.) with Solanum Rootstocks, Their Compatibility and Growth Performance under Open Field Condition

Grafting in brinjal is an alternative technology for chemical treatments to control soilborne pathogens with minimum impact on product quality and environment. The present study was carried out to determine the graft compatibility of brinjal scions (Dhruva and CO 2) with five wild Solanum rootstocks and their growth performance in open field condition. The cleft grafting method was adopted in this study. The non-grafted plants were used as control under open field condition. Solanum torvum recorded less number of days for graft union with Dhruva (10.36) and CO 2 (10.54) followed by Solanum capsicoides and Solanum chrysotrichum. The results on grafting success at 30 days after grating revealed that the highest success percentage was observed in Dhruva (83.42%) and CO 2 (82.08%) grafted with Solanum torvum rootstock followed by Solanum capsicoides and Solanum chrysotrichum. The field survival rate was higher in Dhruva (88.75%) and CO 2 (85.20%) grafted onto Solanum trovum followed by Solanum capsicoides and Solanum chrysotrichum. Dhruva (90.52cm, 9.15) and CO 2 (80.17cm, 7.29) grafted onto Solanum torvum recorded maximum plant height and more number of primary branches per plant respectively followed by Solanum chrysotrichum. Though Solanum capsicoides performed well throughout the grafting process their growth performance was poor in open field condition. Hence Solanum torvum followed by Solanum chrysotrichum could be used as compatible rootstock for grafting with brinjal scions.

The effect of circular soil biosolarization treatment on the physiology, metabolomics, and microbiome of tomato plants under certain abiotic stresses.

Soil biosolarization (SBS) is an alternative technique for soil pest control to standard techniques such as soil fumigation and soil solarization (SS). By using both solar heating and fermentation of organic amendments, faster and more effective control of soilborne pathogens can be achieved. A circular economy may be created by using the residues of a given crop as organic amendments to biosolarize fields that produce that crop, which is termed circular soil biosolarization (CSBS). In this study, CSBS was employed by biosolarizing soil with amended tomato pomace (TP) residues and examining its impact on tomato cropping under conditions of abiotic stresses, specifically high salinity and nitrogen deficiency. The results showed that in the absence of abiotic stress, CSBS can benefit plant physiological performance, growth and yield relative to SS. Moreover, CSBS significantly mitigated the impacts of abiotic stress conditions. The results also showed that CSBS impacted the soil microbiome and plant metabolome. Mycoplana and Kaistobacter genera were found to be positively correlated with benefits to tomato plants health under abiotic stress conditions. Conversely, the relative abundance of the orders RB41, MND1, and the family Ellin6075 and were negatively correlated with tomato plants health. Moreover, several metabolites were significantly affected in plants grown in SS- and CSBS-treated soils under abiotic stress conditions. The metabolite xylonic acid isomer was found to be significantly negatively correlated with tomato plants health performance across all treatments. These findings improve understanding of the interactions between CSBS, soil ecology, and crop physiology under abiotic stress conditions.

Interspecific and Intraspecific Hybrid Rootstocks to Improve Horticultural Traits and Soil-Borne Disease Resistance in Tomato.

Tomato rootstocks are important to increase yield and control soil-borne pathogens, increasing vigor for a longer crop cycle and tolerance to biotic and abiotic stress. This study, conducted in the greenhouse of Sunchon National University during the period from 2019 to 2022, aimed to identify local soil-borne-disease resistant interspecific and intraspecific tomato hybrid rootstocks. The 71 interspecific hybrids (S. lycopersicum × S. habrochaites) showed that the germination vigor (GV) was less than Maxifort, except for several combinations. The germination rate (GP) of cross-species hybrids showed a different pattern according to the hybrid combinations, of which three combinations showed less than 30%. The horticultural traits, such as GV and GP, of the intraspecies hybrid (S. l × S. l) combination were significantly improved compared to that of Maxifort. In 71 combinations (S. l × S. h) and 25 combinations (S. l × S. l), MAS was used to evaluate the resistance of eight genes related to soil-borne pathogens, four genes related to vector-mediated pathogens, and three genes related to air-borne pathogens. The results showed that the new hybrid combination had improved resistance over the commercial-stock Maxifort. Therefore, interspecies and intraspecies hybrid techniques for breeding commercial rootstocks can be utilized as a way to improve horticultural properties and resistance to soil-borne diseases in tomato.

Spatial and Temporal Changes of Soil Microbial Communities in Field Tomato Production as Affected by Anaerobic Soil Disinfestation

Anaerobic soil disinfestation (ASD) has been demonstrated as an effective alternative to pre-plant chemical soil fumigation (CSF) commonly used to control soilborne pathogens. However, the ASD effects on spatial and temporal changes in soil microbial communities remain poorly understood in production systems with low soilborne disease pressure. The objective of this study was to assess the influence of ASD treatments on soil microbial community composition at different soil depths during the spring tomato production season in Florida. Soil treatments included ASD using 6.9 m3 ha−1 of molasses with 11 Mg ha−1 of composted poultry litter (CPL) (ASD0.5), ASD with 13.9 m3 ha−1 of molasses and 22 Mg ha−1 CPL (ASD1.0), and chemical soil fumigation (CSF) using a mixture of 1,3-dichloropropene and chloropicrin. Soil microbial community composition was measured at soil depths of 0–15 and 15–30 cm using phospholipid fatty acid (PLFA) analysis at 0, 36, 76, and 99 days after transplanting (DAT). Fatty acid methyl esters were categorized into biomarker groups including total microbial biomass (TMB), G+ bacteria (G+), G− bacteria (G−), actinomycetes (Actino), arbuscular mycorrhizal fungi (AMF), protozoa, and general fungi (F). Soil concentrations of G+, Actino, F, AMF, and the ratio of F:bacteria (B) were significantly impacted by a soil treatment × soil depth × sampling time three-way interaction. All the microbial biomarkers were significantly affected by soil treatment × sampling depth two-way interactions except for protozoa and F:B ratio. Concentrations of TMB, Actino, AMF, F, G+, and G− bacteria were significantly increased in ASD treated soils at both 0–15 and 15–30 cm soil depths across different sampling times compared with CSF. In addition, the concentrations of G+ and G− bacteria, AMF, F, and TMB were higher at 0–15 vs. 15–30 cm soil depth under ASD treatments, whereas no soil depth differences were observed in CSF. Discriminant analysis further confirmed that soil microbial community composition was distinctly different in CSF compared with ASD treatments. The soil microbial profile was well-differentiated between the two soil depths under ASD treatments but not in CSF, while the enhancement of PLFA biomarkers by ASD decreased with increasing soil depth.

Understorey biodiversity supports multiple ecosystem services in mature Mediterranean forests

Overstorey biodiversity is known to drive multiple ecosystem functions in mature forests. However, the role of understorey biodiversity in regulating the soil microbiome and ecosystem multiservices of these ecosystems is virtually unknown. Here, we collected vegetation and soil data from mature plantation Mediterranean pine forests (100 years old) with different combinations of tree and understorey plant species to explore the contribution of overstorey and understorey biodiversity for explaining soil microbiomes and ecosystem multiservices. We found that while overstorey diversity is important for supporting soil-borne pathogen control, forest understorey biodiversity is critical for explaining soil nutrient availability, tree production, and soil-plant mutualistic relationships. Our results highlight the importance of understorey biodiversity for maintaining ecosystem multiservices in mature forests, which should be considered in forest management programs.

The Proportion of Soil-Borne Fungal Pathogens Increases with Elevated Organic Carbon in Agricultural Soils.

ABSTRACTSoil-borne fungal phytopathogens are important threats to soil and crop health. However, their community composition and environmental determinants remain unclear. Here, we explored the effects of agricultural fertilization regime (i.e., organic material application) on soil fungal phytopathogens, using data sets from a combination of field survey and long-term experiment. We found that soil organic carbon was the key factor that affected the diversity and relative abundance of fungal phytopathogens in agricultural soils. The dominant genera of phytopathogens including Monographella was also strongly associated with soil organic carbon. In addition, the elevated soil organic carbon enhanced the node proportion of phytopathogens and the positive interactions within the fungal community in the network. Results of the long-term experiment revealed that applications of crop straw and fresh livestock manure significantly increased the proportion of phytopathogens, which were associated with the elevated soil organic carbon. This work offers new insights into the occurrence and environmental factors of fungal phytopathogens in agricultural soils, which are fundamental to control their impacts on the soil and crop systems.IMPORTANCE Fungal phytopathogens are important threats to soil and crop health, but their community composition and environmental determinants remain unclear. We found that soil organic carbon is the key factor of the prevalence of fungal phytopathogens through a field survey, which is also supported by our long-term (6-year) experiment showing the applications of crop straw and fresh livestock manure significantly increased the proportion of fungal phytopathogens. These findings advance our understanding of the occurrence and environmental drivers of soil-borne fungal phytopathogens under agricultural fertilization regime and have important implications for the control of soil-borne pathogens.

Extracellular self‐DNA plays a role as a damage‐associated molecular pattern (DAMP) delaying zoospore germination rate and inducing stress‐related responses in Phytophthora capsici

AbstractPhytophthora capsici is a highly destructive pathogen of crops. Although chemical pesticides are the most widely used strategy to counter phytopathogens, they have been inefficient to combat P. capsici and have produced significant environmental and health problems. Therefore, sustainable alternatives to control soilborne pathogens, such as the inhibitory effect of self‐extracellular DNA (eDNA), have been proposed. This inhibition phenomenon has been attributed to the action of self‐eDNA as a damage‐associated molecular pattern (DAMP). Here, we describe the effect of self‐eDNA on P. capsici zoospore germination rate, antioxidant enzymes activity and MAPK gene expression. Also, the effect of P. capsici eDNA on the protection of chilli pepper (Capsicum annuum) plants against P. capsici was investigated. The results highlight that P. capsici can sense 2–500 µg/ml self‐eDNA and induce stress‐related responses like SAK1 gene expression, and superoxide dismutase and catalase activities. Moreover, in vitro zoospore germination rate was suppressed with self‐eDNA concentrations ranging from 50 to 500 µg/ml. Interestingly, drench applications of P. capsici eDNA at 60 and 100 µg/ml on chilli pepper plants did not show any protective effect against the phytopathogen, whereas 2 µg/ml of P. capsici eDNA drench application showed a lower percentage of plants with symptoms and lower disease severity. Moreover, phenols and total flavonoids were increased in chilli pepper plants, therefore inducing plant immunity. This study showed that self‐eDNA acts as a DAMP in P. capsici and provides insight into the use of eDNA for the protection of crops of agronomic interest.

Quantifying the effects of anaerobic soil disinfestation and other biological soil management strategies on nitrous oxide emissions from raised bed plasticulture tomato production.

Soilborne pests are a major obstacle that must be overcome for the production of horticultural crops. Methyl bromide (MBr) was an effective preplanting soil broad-spectrum biocide, but its use has been banned due to its role in depleting the ozone layer. As a result, sustainable alternative methods for controlling soilborne pathogens and pests are needed. Nitrous oxide (N2 O) emissions are of concern in crop production due to the role of N2 O as a greenhouse gas. Agricultural lands are known sources for emission of N2 O into the atmosphere. Emissions are related to many environmental factors as well as fertilization and fumigation practices. This study evaluated the influence of different alternatives to MBr on N2 O emissions throughout a tomato production season in two locations representative of southern and northern Florida. We evaluated eight soil management practices, including (a) untreated controls; (b) chemical soil fumigation; (c) anaerobic soil disinfestation using molasses (M) + composted poultry litter and (d and e) M + composted yard waste (CYW, at two rates); (f) Soil Symphony Amendment (SSA), a commercially available mix of microbes and nutrients; (g) CYW alone; and (h) CYW + SSA. Nitrous oxide emissions were measured throughout the cropping season. Emissions were highest on the day of planting (Day 21), ranging from 213 to 1,878μg m-2 h-1 , likely due to the release of N2 O that had accumulated under the totally impermeable film when it was punctured for planting. However, statistical significance varied between sites. Estimated cumulative emissions of N2 O throughout the production season ranged from 1.3 to 4.8kg N2 O-N ha-1 .