Soil Populations Research Articles

Divergent Aspergillus flavus corn population is composed of prolific conidium producers: Implications for saprophytic disease cycle

ABSTRACT The ascomycete fungus Aspergillus flavus infects and contaminates corn, peanuts, cottonseed, and tree nuts with toxic and carcinogenic aflatoxins. Subdivision between soil and host plant populations suggests that certain A. flavus strains are specialized to infect peanut, cotton, and corn despite having a broad host range. In this study, the ability of strains isolated from corn and/or soil in 11 Louisiana fields to produce conidia (field inoculum and male gamete) and sclerotia (resting bodies and female gamete) was assessed and compared with genotypic single-nucleotide polymorphism (SNP) differences between whole genomes. Corn strains produced upward of 47× more conidia than strains restricted to soil. Conversely, corn strains produced as much as 3000× fewer sclerotia than soil strains. Aspergillus flavus strains, typified by sclerotium diameter (small S-strains, <400 μm; large L-strains, >400 μm), belonged to separate clades. Several strains produced a mixture (M) of S and L sclerotia, and an intermediate number of conidia and sclerotia, compared with typical S-strains (minimal conidia, copious sclerotia) and L-strains (copious conidia, minimal sclerotia). They also belonged to a unique phylogenetic mixed (M) clade. Migration from soil to corn positively correlated with conidium production and negatively correlated with sclerotium production. Genetic differences correlated with differences in conidium and sclerotium production. Opposite skews in female (sclerotia) or male (conidia) gametic production by soil or corn strains, respectively, resulted in reduced effective breeding population sizes when comparing male:female gamete ratio with mating type distribution. Combining both soil and corn populations increased the effective breeding population, presumably due to contribution of male gametes from corn, which fertilize sclerotia on the soil surface. Incongruencies between aflatoxin clusters, strain morphotype designation, and whole genome phylogenies suggest a history of sexual reproduction within this Louisiana population, demonstrating the importance of conidium production, as infectious propagules and as fertilizers of the A. flavus soil population.

Greenhouses represent an important evolutionary niche for Alternaria alternata.

Greenhouses have become increasingly important for food production and food security. However, our understanding of how greenhouses may contribute to genetic variations in soil microbial populations is very limited. In this study, we obtained and analyzed soil populations of the cosmopolitan fungal pathogen Alternaria alternata in seven greenhouses in Shijiazhuang, northeast China. Our analyses revealed high proportions of isolates being resistant to agricultural triazole fungicides and medical triazole drugs, including cross-resistance to both groups of triazoles. In addition, we found that greenhouse populations of A. alternata located within a few kilometers showed similar levels of genetic differentiation as those separated by over 2,000 km between northeast and southwest China. Our study suggests that greenhouse populations of this and potentially other fungal pathogens represent an important ecological niche and an emerging threat to food security and human health.

Potential Role of the Yeast Papiliotrema terrestris Strain PT22AV in the Management of the Root-Knot Nematode Meloidogyne incognita

Potential Role of the Yeast Papiliotrema terrestris Strain PT22AV in the Management of the Root-Knot Nematode Meloidogyne incognita

Stress response and phytoextraction potential of two Noccaea caerulescens populations in multicontaminated soil

AbstractMulticontamination of soils by various organic and inorganic pollutants is considered as an obstacle for the development of hyperaccumulator plants and phytoextraction of metals. The aim of this study was to investigate the effect of polycyclic aromatic hydrocarbons (PAHs) in combination with trace elements on the antioxidant response and phytoextraction efficiency of two populations of the hyperaccumulator Noccaea caerulescens from either a metalliferous (Ganges) or a nonmetalliferous (Chavignée) site. Plants were grown for 17 days in soil containing moderate concentrations of trace elements and under the effect of phenanthrene (PHE), a PAH stress model. In general, exposure to PHE resulted in a reduction of growth parameters, together with the upregulation of antioxidant enzymes and compounds and limitations in nutrient uptake and heavy metal extraction in N. caerulescens. Variations were observed in the extent of enzymatic activities and the amount of metals extracted between the two populations studied. Plants from Chavignée exhibited a slightly more tolerant response to PHE stress than those from Ganges. The presence of PHE in the soil proved highly toxic to N. caerulescens, resulting in low numbers of survivors. Nevertheless, the differences observed between the two populations with regard to growth, metal extraction, and antioxidant defense responses suggest that the difference in defense capacity may ensure different tolerance. This difference may be linked to adaptations acquired by each population according to the soil type from which it originates. However, these results need to be confirmed by further experiments.

Pre-soil fumigation with ammonium bicarbonate and lime modulates the rhizosphere microbiome to mitigate clubroot disease in Chinese cabbage.

Plasmodiophora brassicae is an ever-increasing threat to cruciferous crop production worldwide. This study investigated the impact of pre-soil fumigation with ammonium bicarbonate (N) and lime (NB) to manage clubroot disease in Chinese cabbage through 16S rRNA gene amplification sequencing. We found that soil fumigation with N and NB suppressed disease incidence by reducing the soil acidity and population of P. brassicae in the rhizosphere. Minimum disease incidence and maximum relative control effect of about 74.68 and 66.28% were achieved in greenhouse and field experiments, respectively, under the combined application of ammonium bicarbonate and lime (LNB) as compared with N, NB, and control (GZ). Microbial diversity analysis through Miseq sequencing proved that pre-soil fumigation with N, NB, and LNB clearly manipulated rhizosphere microbial community composition and changed the diversity and structure of rhizosphere microbes compared with GZ. Bacterial phyla such as Proteobacteria, Bacteriodetes, and Acidobacteria and fungal phyla including Olpidiomycota and Ascomycota were most dominant in the rhizosphere of Chinese cabbage plants. Soil fumigation with N and NB significantly reduced the abundance of clubroot pathogen at genus (Plasmodiophora) level compared with GZ, while decreased further under combined application LNB. Microbial co-occurrence network analysis showed a highly connected and complex network and less competition for resources among microbes under combined application LNB. We conclude that for environmentally friendly and sustainable agriculture, soil fumigation with combined ammonium bicarbonate and lime plays a crucial role in mitigating Chinese cabbage clubroot disease by alleviating soil pH, reducing pathogen population, and manipulating the rhizosphere microbiome.

Development of a Large-Scale Soil DNA Extraction Method for Molecular Quantification of Fusarium oxysporum f. sp. fragariae in Soil.

The most common soilborne diseases affecting the strawberry industry in California include Verticillium wilt due to Verticillium dahliae, charcoal root rot due to Macrophomina phaseolina, and Fusarium wilt due to Fusarium oxysporum f. sp. fragariae. Detection of these pathogens in soil is an important facet of disease management and fumigation recommendations. Whereas the soil populations of both M. phaseolina and V. dahliae can be readily quantified with quantitative PCR (qPCR) assays using DNA extractions with 500 mg of soil, the single-cell nature of the F. oxysporum chlamydospore does not provide enough pathogen DNA from 500-mg extractions to be reliably quantified. Here, we describe an improved DNA extraction protocol from 10 to 15 g of soil that allows for the quantification of F. oxysporum f. sp. fragariae populations below 10CFU/g. The relationship between results from the TaqMan qPCR assay and pathogen population density in soil was determined by using this extraction method in pathogen-free soils artificially infested with a hygromycin-resistant strain of F. oxysporum f. sp. fragariae to facilitate accurate colony counts when plated on a selective medium. Although the protocol was developed for F. oxysporum f. sp. fragariae, it is applicable for detection and quantification of other soilborne pathogens.

Effect of Bio Control Agents in the Management of Citrus Nematode (T. semipenetrans) on Khasi Mandarin Seedling

Studies on the effect of Purpureocillium lilacinum, Glomus fasciculatum, Trichoderma harzianum, vermicompost and carbofuran 3G in the management of Tylenchulus semipenetrans on Khasi mandarin under pot condition showed that all thetreatments were effective in increasing plant growth parameters of Khasi mandarin. All the treatments significantly decreased the final nematode population in soil and root over control. The treatment with vermicompost @ 15g/plant+ T. harzianum 10g/plant was found to be most effective in plant growth parameters of Khasi mandarin. The treatment with carbofuran 3G@ 4g/plant was found to be best in suppressing the final nematode population in soil and root followed by the treatment with G. fasciculatum@ 150spores/plant + P. lilacinus@10g/plant.

Management of Root Knot Nematode Meloidogyne incognita on Carrot

A pot experiment was conducted in the net house, Department of Nematology, during the rabi season to know the efficacy of  certain botanicals, Azadiracta indica, Azeratum conizoides, Tagetes erecta, Ricinus Communis, Lantana camara and Parthenium hysterophorus each @  1.0 and 1.5%(w/w) against Meloidogyne incognita on carrot. The result revealed that all the treatments were effective in increasing plant growth parameters with corresponding decreased in number of galls, eggmasses per root system and final nematode population in soil over control. The treatment with Azadiracta indica @1.5%(w/w) was most effective in increasing plant growth characters, reducing number of galls, eggmasses per root system and final nematode population in soil. A microplot experiment was conducted during rabi season to study the efficacy of Glomus fasciculatum, consortia (T. harzianum, T. viride and Pseudomonas fluorescenes) and vermicompost for the management of M.incognita on carrot. All the treatments were effective in increasing plant growth parameters and  yield with corresponding decreased in number of galls, eggmasses per root system and final nematode population in soil over control. The treatment with G. fasciculatum @ 300 spores/m2 + consortia @ 5ml/lt + vermicompost @ 1.25t/ha was found most effective in increasing plant growth parameters, yield of carrot and reducing number of galls and egg masses and final nematode population in soil.

Assessment of Common Factors Associated with Droplet Digital PCR (ddPCR) Quantification of Paratrichodorus allius in Soil.

This research investigated the factors associated with the quantitative detection of Paratrichodorus allius in soil using droplet digital PCR (ddPCR). Small-sized nematodes exhibited significantly lower DNA quantities compared to their medium and large counterparts. Soil pre-treatments (room temperature drying and 37 °C oven-drying) demonstrated no substantial impact on ddPCR detection, and soil storage (0-3 months at 4 °C) exhibited negligible alterations in DNA quantities. A commercial DNA purification kit improved the resulting quality of ddPCR, albeit at the cost of a notable reduction in DNA quantity. Upon assessing the impact of inhibitors from soil extracts, a higher inhibitor concentration (5%) influenced ddPCR amplification efficiency. Incorporating bovine serum albumin (BSA) (0.2 μg/μL or 0.4 μg/μL) into the ddPCR setup mitigated the issue. In brief, while ddPCR exhibits minimal sensitivity to soil pre-treatments and storage, higher concentrations of PCR inhibitors and the DNA purification process can influence the results. Despite ddPCR's capability to detect nematodes of all sizes, quantification may not precisely reflect soil population. Incorporating BSA into the ddPCR setup enhances both detection and quantification capacities. This study represents the first comprehensive investigation of its kind for plant-parasitic nematodes, providing crucial insights for application of ddPCR in nematode diagnosis directly from the soil DNA.

Phosphorus drives adaptive shifts in membrane lipid pools and synthesis between soils

Phospholipids are key constituents of microbial membranes and account for a substantial fraction of microbial P, while P-free betaine lipids provide a pathway for membrane synthesis independent of P. The aim of this study was to test if modulation of relative amounts of phospholipids vs P-free betaine lipids is a response to P availability. To examine responses of membrane lipids to P availability, we added P or P + C to an extremely P-poor sandstone-derived soil (total P = 41 μg g−1) and a higher P shale-derived soil (total P = 201 μg g−1). By using D2O labelling and LC-MS we were able to disentangle membrane lipid synthesis dependent on P (i.e. 2H incorporation into phospholipids) from membrane lipid synthesis independent of P (i.e. 2H incorporation into P-free betaine lipids). In unamended soils, P-free betaine lipids were almost 60% of the membrane lipid pool of the P-poor sandstone-derived soil, but only 10% of the higher-P shale-derived soil. Hence, to produce a unit of membrane lipid, the microbial population of sandstone soil required only 54% as much P as the microbial population of shale soil. Four days after adding P to the sandstone soil, phospholipids accounted for a larger proportion of the pool and synthesis of membrane lipids while pool and synthesis of P-free betaine lipids decreased. The increased allocation to phospholipids in sandstone soil amended with P likely reflected amelioration of P limitation given that P addition did not affect pools or synthesis of phospholipids versus betaine lipids in the higher-P shale soil. Collectively these data support the idea that having membranes with a high proportion of P-free betaine lipids is a key adaptive trait of microbial populations of P-poor soil, while the plasticity afforded by membrane lipid remodelling enables short-term fine-tuning of membrane lipid composition to P availability.

Characterization and Effect of a Nematophagous Fungus Talaromyces cystophila sp. nov. for the Biological Control of Corn Cyst Nematode.

The dynamic of plant-parasitic nematode populations in soil is closely related to soil microorganisms. Fungi from Heterodera zeae cysts were isolated to explore the phenomenon of decline in the H. zeae population in the soil. Phylogenetic study of partial ITS, BenA, CaM, and RPB2 gene sequences, in addition to morphological investigations, was utilized to identify a nematode-destroyingfungus. The nematicidal activity of a novel strain GX1 against H. zeae was assessed in vitro and in the greenhouse. Our findings revealed that strain GX1 is a new species of Talaromyces, named Talaromyces cystophila. It has a strong parasitic and lethal effect on H. zeae cysts, with 91.11% parasitism on cysts at 3 days after treatment. The contents of second-stage juveniles (J2s) and eggs inside the cysts were degraded and formed dense vacuoles, and the damaged eggs could not hatch normally. The spore suspension exhibited high nematophagous activity against nematodes, and fermentation filtrate exhibited marked inhibition of egg hatching and nematicidal activities on J2s. The hatching inhibition rates of eggs exposed to 1 × 108 CFU/ml spore suspensions or 20% 1-week fermentation filtrate (1-WF) for 15 days were 98.56 and 100%, respectively. The mortality of J2s exposed to 1 × 108 CFU/ml spore suspension reached 100% at 24 h; exposure to 50% 2-WF was 98.65 and 100% at 24 and 48 h, respectively. Greenhouse experiments revealed that the spore suspension and fermentation broth considerably decreased H. zeae reproduction by 56.17 to 78.76%. T. cystophila is a potential biocontrol strain with nematophagous and nematicidal activity that deserves attention and application.

Assessing the utility of SoilGrids250 for biogeographic inference of plant populations.

Inclusion of edaphic conditions in biogeographical studies typically provides a better fit and deeper understanding of plant distributions. Increased reliance on soil data calls for easily accessible data layers providing continuous soil predictions worldwide. Although SoilGrids provides a potentially useful source of predicted soil data for biogeographic applications, its accuracy for estimating the soil characteristics experienced by individuals in small-scale populations is unclear. We used a biogeographic sampling approach to obtain soil samples from 212 sites across the midwestern and eastern United States, sampling only at sites where there was a population of one of the 22 species in Lobelia sect. Lobelia. We analyzed six physical and chemical characteristics in our samples and compared them with predicted values from SoilGrids. Across all sites and species, soil texture variables (clay, silt, sand) were better predicted by SoilGrids (R 2: .25-.46) than were soil chemistry variables (carbon and nitrogen, R 2 ≤ .01; pH, R 2: .19). While SoilGrids predictions rarely matched actual field values for any variable, we were able to recover qualitative patterns relating species means and population-level plant characteristics to soil texture and pH. Rank order of species mean values from SoilGrids and direct measures were much more consistent for soil texture (Spearman r S = .74-.84; all p < .0001) and pH (r S = .61, p = .002) than for carbon and nitrogen (p > .35). Within the species L. siphilitica, a significant association, known from field measurements, between soil texture and population sex ratios could be detected using SoilGrids data, but only with large numbers of sites. Our results suggest that modeled soil texture values can be used with caution in biogeographic applications, such as species distribution modeling, but that soil carbon and nitrogen contents are currently unreliable, at least in the region studied here.

Cotton host resistance as a tool for managing Rotylenchulus reniformis in Louisiana.

The reniform nematode, Rotylenchulus reniformis, is a major yield-limiting pest of upland cotton (Gossypium hirsutum) in the United States that has been steadily increasing in incidence in many states. Reniform nematode-resistant cotton cultivars have recently become commercially available for cotton producers; however, few field trials have evaluated their efficacy as a nematode management tool. The aim of this study was to evaluate reniform nematode population development, plant growth, and seed cotton yield of reniform nematode-resistant cotton cultivars in two nematode-infested fields in Louisiana. Replicated small-plot field trials were conducted in St. Joseph, LA (NERS field) and Winnsboro, LA (MRRS field) during the 2022 and 2023 growing seasons. In 2022, cultivars evaluated included: (1) DP 1646 B2XF (susceptible/tolerant), (2) DP 2141NR B3XF (resistant), (3) PHY 332 W3FE (resistant), (4) PHY 411 W3FE (resistant), and (5) PHY 443 W3FE (resistant). In 2023, an additional susceptible cotton cultivar, PHY 340 W3FE, was also included. All nematode-resistant cotton cultivars evaluated provided suppression of reniform nematode population development relative to that of the susceptible cotton cultivars, with suppression of nematode soil population densities at harvest ranging from 49 - 81% relative to DP 1646 B2XF. The resistant cultivar PHY 411 W3FE provided the most consistent suppression of reniform nematode population development, reducing reniform nematode soil population densities at harvest in both field locations and both trial years. In contrast, DP 2141NR B3XF only reduced soil population densities at harvest in the NERS field in 2023. Despite relatively consistent nematode suppression and improvements in plant vigor ratings and canopy coverage associated with the resistant cotton cultivars, a yield increase was only observed with PHY 332 W3FE and PHY 411 W3FE planted at the NERS field in 2023. Despite strong resistance to reniform nematode in the evaluated cotton cultivars, nematode soil population densities still increased during the growing season in plots planted with resistant cotton cultivars, emphasizing the need for additional management tactics to use alongside host resistance. This study indicates that new reniform nematode-resistant cotton cultivars show promising potential to reduce nematode population development during the growing season in Louisiana.

The effect of paraquat dichloride and carbosulfan on soil conditions and population dynamic of soil microbes in a cornfield: a case study in Sumedang, West Java

Paraquat dichloride (PC) is one of the herbicides active ingredients that is widely used by farmers to control various types of weeds, while carbosulfan (CS) is one of the insecticide’s active ingredients that is widely used to control various types of insect pests. The objective of this study is to analyze the impact of pesticides for PC and CS on the chemical and physical conditions of the soil and the dynamics of fungi and soil bacteria population in a corn field in Sumedang district, West Java. The experiment took place between August and October, during the dry season, concluding just as the rainy season began. The PC concentrations used were 0 mL/L, 3.33 mL/L, 4 mL/L, 4.66 mL/L and 5.33 mL/L, while the CS concentrations used were 0 mL/L, 0.5 mL/L, 1 mL/L, 1.5 mL/L and 2 mL/L. Soil sampling was conducted before and after the application of pesticides. The total abundance of fungi and bacteria was analyzed using the total plate count (TPC) method. The application of PC to the cornfield slightly decreased soil bulk density from 1.354 g/cm3 to 0.816 g/cm3, while the application of CS slightly increased soil bulk density. A decrease in bulk density is considered positive for the physical conditions of the soil for plant cultivation. In general, the result indicated that the application of PC and CS did not show a significant effect on the chemical characteristics of the soil, and also it did not affect the population of fungi and bacteria. Weather conditions, i.e. dry season (June-September) and rainy season (started from October) seem to affect more on soil conditions as well soil microbial population than the application of the pesticides.

In vivo Evaluation of Silver Nanoparticles on the Management of Meloidogyne incognita in Green Gram

In the investigations, on the effect of Ag NPs on the management of M. incognita in green gram, the results showed that all the treatments were found to be effective in increasing all growth parameters. Maximum growth parameter viz., plant height, fresh and dry weight of shoot and root were recorded in the treatment with 0.15 ppm Ag NPs + M. incognita. Maximum reduction in galls, egg masses and final nematode population in soil were recorded in the treatment with 0.15 ppm Ag NPs. All the treatments significantly differed from control except the treatment with 0.0015 ppm Ag NPs + M. incognita.

Microbial Populations of Agricultural Soil Polluted With Crude Oil

Crude oil pollution of the soil has become a public health and environmental concern. It impacts soil microbial diversity and population. In this study, the microbial population of crude oil polluted soil and unpolluted were determined. The potential for the indigenous organisms to utilize hydrocarbon as a source of carbon was also determined. A soil sample was obtained from an agricultural field and polluted with a defined amount of crude oil for 12 weeks. The microbial population in the polluted soil and unpolluted soil were estimated and characterized following standard microbiological methods. The heterotrophic bacterial and fungal counts in the unpolluted and polluted soil were 6.5 x 104CFU/g and 4.7 x 104 CFU/g, and 6.3 x104 CFU/g and 3.5 x104 CFU/g respectively. Total hydrocarbon utilizing bacterial and fungal counts in the polluted soil was 4.6 x 104 CFU/g and 2.8 x 104 CFU/g. The genera of bacteria and fungi identified in the soil samples were Bacillus, Enterococcus, Micrococcus, Escherichia, Pseudomonas, Staphylococcus, Serratia, Proteus, Klebsiella, Arthrobacter, Aspergillus, Candida, Penicillium, Fusarium, Trichoderma, Cladosporium and Hyphopichia. The preliminary screening for hydrocarbon utilization shows that Bacillus cereus, Bacillus subtilis, Aspergillus niger and Hypopichia burtonii were excellent hydrocarbon utilizers and can be used in bioaugmentation.

Effect of Microbial Consortia on Soil Health, Nutrient Uptake and Yield of Soybean Grown in a Vertisol of Central India

A field experiment was carried out in the research farm of the Jawaharlal Nehru Krishi Vishwa Vidhyalaya, Jabalpur, Madhya Pradesh, India during Kharif season of 2021-22. The experiment was performed with nine treatments comprised by Rhizobium, Pseudomonas, EM and their consortia with FUI and UFUI (absolute control) in randomized block design. The soybean crop was grown in the field along with recommended package of practices. The result showed that the yield of soybean was 43% higher (2351 kg ha -1) than control FUI and better uptake of N (145 kg ha-1 by seed and 125.6 kg ha-1 by straw), P (7.9 kg ha-1 by seed and 14.9 kg ha-1 by straw) and K (42.3 kg ha-1 by seed and 65.0 kg ha-1 by straw) by soybean were found due to inoculation of microbial consortia of Rhizobium, Pseudomonas and EM culture. The Physico-chemical properties (pH, EC and OC), availability of nutrients (NPK with vales of 288, 29 and 335 kg ha-1 respectively), enzymatic activities (Acid phosphatase, alkaline phosphatase and  dehydrogenase activities with values of 42.2, 69. 8 µg PNG h-1 g-1 of  soil  and 12.9 μg TPF hr-1 g-1 of soil, respectively) and microbial population (Rhizobium by 35.1×106, total bacteria by 39.3×107, fungi by 41.9×104 and actinomycetes by 38.7×103 cfu g-1 soil) in soil also improved with the same treatment as compared to FUI. It is strongly recommended that the inoculation of microbial consortia improved the soil health and soybean production too instead of single inoculation by modulating microbial population which improves the soil health by nutrient fixation, solubilization and mobilization and plant growth promotion.

Impact of microplastics on microbial-mediated soil sulfur transformations in flooded conditions

As emerging environmental pollutants, microplastics have become a crucial focus in environmental science research. Despite this, the impact of microplastics on soil in flooding conditions remains largely unexplored. Addressing this gap, our study examined the influence of polystyrene (PS) and polyphenylene sulfide (PPS) on the microbial populations in black soil, meadow soil, and paddy soil under flooded conditions. Given the significant regulatory influence exerted by microorganisms on sulfur transformations, our study was primarily focused on evaluating the microbial contributions to alterations in soil sulfur species. Our findings revealed several notable trends: In black soil, both PS and PPS led to a marked increase in the abundance of γ-proteobacteria and Subgroup_6, while reducing Clostridia. Ignavibacteria were found to be lower under PPS compared to PS. In meadow soil, the introduction of PPS resulted in increased levels of KD4–96 and γ-proteobacteria, while α-proteobacteria decreased. Chloroflexia under PPS was observed to be lower than under PS conditions. In paddy soil, our study identified a significant rise in Bacteroidia and Ignavibacteria, accompanied by a decrease in α-proteobacteria and γ-proteobacteria. γ-proteobacteria levels under PPS were notably higher than those under PS conditions. These shifts in microbial communities induced by both PS and PPS had a direct impact on adenosine 5′-phosphosulfate reductase, sulfite reductase, and polysulfide dioxygenase. Consequently, these changes led to soil organic sulfur decrease and sulfide increase. This study not only offers a theoretical framework but also provides empirical evidence for understanding the effects of microplastics on soil microorganisms and their role in regulating nutrient cycling, particularly in flood-prone conditions. Furthermore, this study underscores the importance of ensuring an adequate supply of sulfur in agricultural practices, such as rice and lotus root cultivation, to support optimal crop growth in the presence of microplastic pollution.

Influence of Seasonal Variations on Population Dynamics of Phyto-Parasitic Nematodes in Soil and Roots of Bell Pepper (Capsicum annuum L.) in Otari, Rivers State, Nigeria

Weather instability affects nematode proliferation in soil, affecting plant growth. Identifying endemic species and favourable seasons can guide farmers in cultivating crops during specific seasons, minimizing infections and improving yield. A survey to evaluate the influence of seasonal disparity on plant parasitic nematodes population in soil and roots of bell pepper (Capsicum annuum L.) was carried out during dry and rainy seasons in Otari, Abua/Odual Local Government Area of Rivers State, Nigeria. Five bell pepper cultivated fields were randomly selected and a total of 300 soil samples were collected and assayed for soil nematodes. The soil samples were collected using a soil auger at 0-15 cm depth, and roots were collected by the use of sterilized kitchen knife simultaneously for the isolation of nematode. The modified sieve plate method was employed for the extraction of nematodes. Nematode identification was carried out using a pictorial key. A total of 2,220 nematodes from 11 genera were reported in this study, among which 1,290 (58.1%) were recovered during the rainy season while the dry season showed 930 (41.9%) nematodes. Nematode population vary significantly between seasons in soil (P = .13) and roots of bell pepper (P = 3.90), with Heterodera species having higher density (1.44 and 1.03) during the rainy and dry seasons respectively in the soil. High density of Meloidogyne (0.97) was recorded during the rainy season and Radopholus spp (1.40) during the dry season in the root of bell pepper plant. The study showed that seasonal variations impacted on nematode population abundance in fields, establishing that nematodes are responsive to every unsteady condition of the soil environment resulting from seasonal disparity, and only species who adapt rapidly survive. Farmers should increase crop cultivation during the rainy season to boost yield, as nematodes population decline as rainfall increases.

Cover Crop and Crop Rotation Effects on Tissue and Soil Population Dynamics of Macrophomina phaseolina and Yield Under No-Till System.

The effects of crop rotation and winter cover crops on soybean yield and colony-forming (CFU) units of Macrophomina phaseolina, the causal agent of charcoal rot (CR), are poorly understood. A field trial was conducted from 2011 to 2015 to evaluate (i) the impact of crop rotation consisting of soybean (Glycine max [L.] Merr.) following cotton (Gossypium hirsutum L.), soybean following corn (Zea mays L.), and soybean following soybean over a 2-year rotation and its interaction with cover crop and (ii) the impact of different cover crops on a continuous soybean crop over a 5-year period. This trial was conducted in a field with 10 subsequent years of cover crop and rotation treatments. Cover crops consisted of winter wheat (Triticum aestivum L.) and Austrian winter pea (Pisum sativum L. subsp. sativum var. arvense), hairy vetch (Vicia villosa Roth), and a fallow treatment was evaluated with and without poultry litter application (bio-cover). Tissue CFU of M. phaseolina varied significantly between crop rotation treatments: plots where soybean was grown following cotton had significantly greater tissue CFU than plots following soybean. Poultry litter and hairy vetch cover cropping caused increased tissue CFU, though this effect differed by year and crop rotation treatment. Soil CFU in 2015 was substantially lower compared with 2011. However, under some crop rotation sequences, plots in the fallow treatment had significantly greater soil CFU than plots where hairy vetch and wheat was grown as a cover crop. Yield was greater in 2015 compared with 2011. There was a significant interaction of the previous crop in the rotation with year, and greater yield was observed in plots planted following cotton in the rotation in 2015 but not in 2011. The result from the continuous soybean planted over 5 years showed that there were no significant overall effects of any of the cover crop treatments nor was there interaction between cover crop treatment and year on yield. The lack of significant interaction between crop rotation and cover crop and the absence of significant differences between cover crop treatments in continuous soybean planting suggest that cover crop recommendations for midsouthern soybean growers may need to be independent of crop rotation and be based on long-term crop needs.