Inoculum Level Research Articles

Allelopathic interactions of Carthamus oxyacantha, Macrophomina phaseolina and maize: Implications for the use of Carthamus oxyacantha as a natural disease management strategy in maize.

Fungicides are used to control phytopathogens but all these fungicides have deleterious effects. Allelopathic interactions can be harnessed as a natural way to control the pathogens but there are no reports that show the allelopathic interactions of donor plant, recipient crop, as well as the target plant pathogen and the material used for inoculum production. So, in the present study, the suitability of Carthamus oxyacantha M. Bieb. was assessed against Macrophomina phaseolina, the cause of charcoal rot in maize. Among the various treatments in pot experiment, a negative control, 3 concentrations of inoculum (1.2×105, 2.4×105, and 3.6×105 colony forming units (CFU) mL-1, 3 concentrations (0.5, 1.0, and 1.5% w/w) of C. oxyacantha along with an autoclaved M. phaseolina (Mp) and C. oxyacantha alone were included to investigate their allelopathic effects on maize, not investigated earlier. Maximum suppression of the disease was observed by 1.5% (w/w) concentration of C. oxyacantha. Soil amendment with C. oxyacantha significantly suppressed the disease incidence (DI) and disease severity index (DSI) in charcoal rot of maize up to 40 and 55%, respectively over the strongest level of inoculum (Mp3). C. oxyacantha not only reduced area under disease incidence progress curve (AUDIPC) and area under disease severity progress curve (AUDSPC), but also improved the morphological, biochemical and physiological parameters of maize. The maximum increase of 48, 65, and 75% in values of shoot length (SL), shoot dry mass (SDM), and root dry mass (RDM), respectively was observed by application of the highest concentration of C. oxyacantha in the treatment Mp1+Co3, over infested control (Mp1). Photosynthetic pigments, such as chlorophyll a, chlorophyll b and carotenoids were increased to 58, 64, and 46%, respectively over Mp1, by the application of C. oxyacantha. Carbon assimilation rate (A), stomatal conductance (gs), rate of transpiration (E), and internal carbon dioxide concentration (Ci) were significantly increased to 58, 48, 48, and 20%, respectively over infested control (Mp3), by application of C. oxyacantha concentration 1.5 (w/w). Moreover, defense enzymes like superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were boosted up to 27, 28, and 28% over Mp3, respectively. Positive allelopathy of C. oxyacantha towards maize and negative allelopathy towards M. phaseolina makes C. oxyacantha a suitable candidate for charcoal rot disease control in maize.

In-Furrow Application of Biologicals for Control of Rhizoctonia Diseases in Snap Bean

Florida ranks first in the production of fresh-market snap bean in the United States. Rhizoctonia diseases, including damping-off and root rot caused by Rhizoctonia solani, are important diseases in snap bean, 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 (Howler, Theia, and Double Nickel LC) 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./acre and Double Nickel LC at 16 fl. oz./acre each applied as an in-furrow spray at seeding significantly ( P < 0.05) reduced disease incidence compared with 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./acre in the 2022 trial, and 32.8% for Double Nickel LC was observed at 16 fl. oz./acre in 2023. Both biologicals also significantly increased the pod yield, by 85.6% with Howler in 2022 and doubled by Double Nickel LC in 2023 when compared with 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.

Evaluation of the antibacterial activity of selenium nanoparticles and those conjugated with lysozyme against Bacillus cereus spiked in pasteurized skim milk

Selenium nanoparticles (SeNPs) and SeNPs conjugated with lysozyme (SeNPs-lysozyme) were synthesized via sodium selenite reduction with ascorbic acid and polysorbate-80 stabilization. These were physiochemically characterized to impart antibacterial properties. X-ray diffraction analysis (XRD) revealed that both formulations had hexagonal crystalline structures. Fourier transform infrared (FT-IR) confirmed the successful conjugation of lysozyme to SeNPs through the emergence of amine peaks at 1542 cm−1. Dynamic light scattering (DLS) showed lysozyme conjugation increased nanoparticle size from 76.6 to 92.4 nm and charge from − 12.6 to + 17.6 mV. Transmission electron microscopy (TEM) images confirmed that spherical morphologies and size increased from 73–79 nm for SeNPs to 84–98 nm for SeNPs-lysozyme after lysozyme capping. Both formulations exhibited identical minimum inhibitory concentrations (MIC) of 125 μg/mL. However, lysozyme conjugation reduced SeNPs cytotoxicity by 2.4-fold based on IC50 values from an MTT (Thiazolyl Blue Tetrazolium Bromide) assay. When tested in phosphate-buffered saline (PBS), SeNPs and SeNPs-lysozyme fully inhibited Bacillus cereus (B. cereus) proliferation up to 6 log10 CFU/mL inoculums over 24 h of incubation. However, at (7 log10 CFU/mL) inoculum, only partial inhibition occurred, with (2.5 ± 0.3 log10 CFU/mL) growth still detected for SeNPs and (2.2 ± 0.2 log10 CFU/mL) for SeNPs-lysozyme. At all inoculum levels (5, 6, and 7) log10 CFU/mL, B. cereus grew a lot in milk (more than 8 log10 CFU/mL). This was probably because SeNPs or SeNPs-lysozyme tend to aggregate around milk components, making them less effective.

SARS-CoV-2 surrogate bacteriophage φ6 cross-contamination between fruits and gloves, survival on discarded gloves and inactivation by photodynamic treatment

This study assessed the SARS-CoV-2 surrogate bacteriophage φ6 cross-contamination between high-density polyethylene or polyvinyl chloride gloves and fruits (tomato and cucumber) using different inoculum levels (6.0 and 4.0 log PFU/sample). Bacteriophage φ6 survival on contaminated gloves was assessed over 9 days at 25 °C. The effectiveness of photodynamic treatment using curcumin as a photosensitizer to inactivate φ6 on fruits was determined. The fruit type and the glove material influenced the φ6 transfer. Longer contact times resulted in greater φ6 transfer. The highest φ6 transfer occurred from tomato to HDPE glove (0.8% or −1.1 log % transfer) after 30 s of contact at the higher inoculum level. Bacteriophage φ6 was detected on cross-contaminated HDPE gloves for up to 6 days. Bacteriophage φ6 survived better on vinyl gloves cross-contaminated by cucumber vs. tomato (detected up to 6 vs 3 days). Photodynamic inactivation of φ6 was time-dependent and varied with the tested fruit but was not influenced by viral starting concentration. Photodynamic treatment decreased the φ6 titer by 3.0 and 2.2 log PFU/sample in tomato and cucumber, respectively. Transmission electronic microscopy showed that photodynamic treatment changed the structure of the φ6 capsid. These findings may help in the management of SARS-CoV-2 contamination risks in fruit handling. They may also help in the establishment of effective measures to manage cross-contamination risk.

Effect of Nitrite-Embedded Packaging Film on Growth of Listeria monocytogenes in Nitrite-free and Conventionally-cured Bologna Sausage

Listeria monocytogenes is a pathogen frequently associated with ready-to-eat (RTE) meat and poultry products. Nitrite is a key antimicrobial additive that can offer some degree of protection against L. monocytogenes when included in meat product formulations. The objectives of this study were to determine the potential of nitrite-embedded film to affect the growth of L. monocytogenes following postthermal processing of conventionally-cured and nitrite-free bologna. Two bologna treatment formulations, a conventionally-cured control formulation (CON) and a nitrite-free formulation (UCC), were manufactured, packaged in conventional (CF) or nitrite-embedded (NEF) film, inoculated with 3.5 log CFU/cm2 of a cocktail of L. monocytogenes strains, and stored at 10 ± 1 °C. CON-NEF and UCC-NEF treatments had significantly slower (P < 0.05) growth of L. monocytogenes than CON-CF and UCC-CF, with populations in UCC-CF (which contained no nitrite) increasing by 3.4 logs after 10 d of storage in UCC-CF and 3.6 logs after 50 d in CON-CF (which had formulated nitrite only), while in the NEF-packaged samples, with or without formulated nitrite, they did not exceed the inoculum level until after day 40. Initial (day 0) residual nitrite was significantly greater (P < 0.05) in the control formulation. Packaging in NEF, however, resulted in an increase of 27–28 ppm by day 3, regardless of formulation, after which it decreased rapidly. Results suggest NEF can be used as a post-lethality antimicrobial intervention in food safety intervention strategies, in both cured and uncured processed meat products.

Production of Amylase by Solid State Fermentation Using Agricultural Waste

This study presents a comprehensive investigation into the production of amylase, a crucial enzyme with wide-ranging industrial applications, using locally sourced substrates from Kachchh, Gujarat. The research employed the Bacillus licheniformis strain and substrates such as coconut, rice husk, wheat bran, paddy straw, and maize straw. The study found paddy straw to be the most promising substrate for amylase production. The research also systematically optimized various process parameters for amylase production in Solid-State Fermentation (SSF) using the One Variable at a Time (OVAT) method. These parameters included incubation period, temperature, inoculum level, additional carbon sources, starch concentrations, additional nitrogen sources, initial pH, different mineral salt ions, initial moisture level, and surfactants. The results showed that the optimal conditions for maximum amylase yield were an incubation period of 48 hours, an incubation temperature of 35°C, an inoculum level of 10%, starch as the additional carbon source, a starch concentration of 2.5%, yeast extract as the additional nitrogen source, an initial pH of 7, NaCl as the mineral salt, an initial moisture level of 75%, and Tween 80 as the surfactant. This research provides a reliable and sustainable approach to enzyme production, offering valuable insights for the optimization of the solid-state fermentation process for maximum amylase production.

Machine learning-assisted optimization of food-grade spirulina cultivation in seawater-based media: From laboratory to large-scale production

The shortage of food and freshwater sources threatens human health and environmental sustainability. Spirulina grown in seawater-based media as a healthy food is promising and environmentally friendly. This study used three machine learning techniques to identify important cultivation parameters and their hidden interrelationships and optimize the biomass yield of Spirulina grown in seawater-based media. Through optimization of hyperparameters and features, eXtreme Gradient Boosting, along with the recursive feature elimination (RFE) model demonstrated optimal performance and identified 28 important features. Among them, illumination intensity and initial pH value were critical determinants of biomass, which impacted other features. Specifically, high initial pH values (>9.0) mainly increased biomass but also increased nutrient sedimentation and ammonia (NH3) losses. Both batch and continuous additions could decrease nutrient losses by increasing their availability in the seawater-based media. When illumination intensity exceeded 200 μmol photons/m2/s, it amplified the growth of Spirulina by mitigating the light attenuation caused by a high initial inoculum level and counteracted the negative effect of low temperature (<25 °C). In large-scale cultivation, production efficiency would be reduced if illumination was not maintained at a high level. High salinity and sodium bicarbonate (NaHCO3) addition promoted carbohydrate accumulation, but suitable dilution could keep the required protein content in Spirulina with relatively low media and production costs. These findings reveal the interactive influence of cultivation parameters on biomass yield and help us determine the optimal cultivation conditions for large-scale cultivation of Spirulina-based seawater system based on a developed graphical user interface website.

Pigeonpea cyst nematode (Heteroderacajani Koshy) pathogenicity in black gram (Vigna mungo L.): Quantitative and qualitative yield losses, and bio- organic management

The pigeonpea cyst nematode (PCN) Heterodera cajani Koshy infects black gram (Vigna mungo L.), causing significant yield losses. However, there is a lack of systematic information on PCN pathogenicity, as well as quantitative and qualitative yield losses in black gram under various inoculum levels and soil conditions. Therefore, we have assessed the threshold inoculum level(s), estimated the yield and protein losses caused by PCN, and evaluated eco-friendly management option(s) with botanicals (neem cake, neem seed powder) and a microbial agent (Trichoderma harzianum). The results revealed a gradual and significant decline in crop growth parameters as the inoculum levels increased from 0 to 3000 juveniles (J2s)(2 kg soils). The severity of PCN infestation was notably higher in alluvial soils compared to lighter soils, exhibiting higher cyst counts (+63%) in plant roots. The threshold inoculum level(s) causing a 25% reduction in various agronomic parameters was significantly lower in alluvial soil(176–1262 J2s; mean = 921) compared to light soil (720–1444 J2s, mean = 1308), indicating that alluvial soil conditions favored increased PCN infestation over light soils, leading to more substantial growth inhibition. Strong positive correlations were found between initial inoculum levels and final populations of PCN. Inoculum levels ranging from 90 to 120 thousand J2s (representing 45–60 J2s per 100 cc soils) resulted in yield losses of 26–78% (p < 0.001). Additionally, there was a corresponding decrease in grain protein content by 9–22% (p < 0.01), subsequently reducing protein productivity by 11–83% (p < 0.001). In the PCN management experiment, among the different bio-organic components, neem cake at 1.0 t ha−1 exhibited the highest efficacy against PCN at crop harvest stage, leading to significant improvements in both dry shoot weight (4.3 g) and dry root weight (1.0 g)/plant compared to the inoculated check. Also, neem seed powder (at 0.1 t ha−1) and T. harzianum + farmyard manure (1 kg in 100 kg farmyard manure ha−1) showed increased effectiveness against the nematode. This study emphasizes the substantial influence of nematode infection on crop performance, particularly in alluvial soils, resulting in significant losses in both yield and protein content. Neem cake emerges as a promising eco-friendly management for managing the PCN in black gram.

Multivariate analysis for understanding spoilage in cooked Turkey ham

SummaryThis study aimed to comprehend the spoilage of cooked turkey ham caused by various Leuconostoc species using multivariate analysis to link the growth of these microorganisms, pH kinetics, and mesophilic counts for predicting ham spoilage at 8 and 12 °C. The methodology assesses changes in Leuconostoc spp. growth behaviour using the Baranyi and Roberts model, pH kinetics employing the Weibull model, and milkiness and swelling through quantitative descriptive analysis during storage at 8 and 12 °C, with artificial contamination of Leuconostoc carnosum and L. mesenteroides at 102 and 104 CFU g−1. Multivariate analysis encompasses linear quadratic discriminant and Pearson correlation analysis. Biokinetic growth parameters do not significantly differ among Leuconostoc species, temperatures, or inoculum levels. In discriminant analysis, pH is the most influential variable in spoilage grade classification, followed by LAB log counts. Furthermore, correlation analysis reveals a strong positive correlation between the rate of pH reduction and the storage time for spoilage onset.

Impact of Different Inoculum Levels of Cereal Cyst Nematode (Heterodera avenae) on the Physiological Traits of Wheat (Triticum aestivum)

This study aimed to examine the effects of various inoculum levels of H. avenae on wheat physiology. The experiments were conducted in the screenhouse at the Department of Nematology, CCSHAU, Hisar, with inoculum levels set at 5, 10, and 15 eggs and juveniles per gram of soil. Observations on physiological parameters were made 30 days post-sowing. It was found that increasing inoculum levels led to significant decreases in total chlorophyll, carotenoid content, chlorophyll fluorescence, photosynthetic rate, transpiration rate, and stomatal conductance. The highest inoculum level showed the most pronounced reductions, with respective decreases of 39.71%, 30.55%, 7.90%, 39.75%, 51.58%, and 64.86%. Highest nematode inoculum level also resulted in the highest reduction in gaseous exchange parameters, biomass and leaf pigments concentrations and maximum increment in nematode population density.

Pathogenicity of Root-knot Nematode, Meloidogyne incognita on Tuberose (Polianthes tuberosa L.)

A pot experiment was carried out in the net house of Department of Nematology, Assam Agricultural University, Jorhat, to study the pathogenicity of root-knot nematode, Meloidogyne incognita, on tuberose. The study found that as the inoculum level of M. incognita increased from 10 to 10,000 second-stage juveniles (J2) per pot (containing 1 kg of sterilized soil), all plant growth parameters of tuberose decreased progressively. At the highest inoculum level, the plants became severely stunted, chlorotic, and produced very few bulblets. It was noted that at the highest inoculum level, the root systems were significantly reduced, with larger and mostly coalescent galls. The treatments with no nematode (check and associated check) were free from galls and eggmasses. An initial inoculum level of 100 J2 of M.incognita per kg of soil caused significant reduction in all growth parameters and proved to be pathogenic to the tuberose plants. The number of galls and eggmasses increased gradually in the plants with an initial inoculum level of 10 to 1000 J2 of M.incognita per kg of soil, but it declined at highest inoculum level of 10,000 J2 per kg of soil. The experiment also recorded the variation in nematode population in the soil as well as their reproductive rates. These findings can be used to develop effective, targeted methods for minimizing the damage caused by root-knot nematode in tuberose crops.

Modeling the growth behavior of Salmonella spp. in grated carrots inoculated with different inoculum levels stored at various temperatures

AbstractThe consumption of fresh and fresh‐cut fruits and vegetables, such as carrots, has increased for the last decades for a healthy life and an adequate diet, but concerns regarding the microbial safety of them have been raised. The present study was conducted to develop predictive models for Salmonella spp. in grated carrots. The results showed that Salmonella spp. did not display growth at 5°C, but it grew in grated carrots at other temperatures (10, 15, 20, 25, and 37°C) for both inoculum levels. Also, the inoculum levels affected the growth of this pathogen in grated carrots when the storage temperatures ranged from 15 to 25°C. The theoretical minimum temperatures calculated using the Huang model were 3.48 and 5.79°C for inoculum levels of 101 and 102 CFU/g, respectively. The primary and secondary models performed well in terms of agreement between experimental and estimated values. Furthermore, compared to the Ratkowsky model, the theoretical minimum temperature was given a more reasonable value using the Huang model. The models developed in the present study will be a useful input for future quantitative microbial risk assessment to appraise the proliferation of Salmonella spp. in grated carrots throughout the production process, storage, and distribution.

Production of low-cost lactic acid from dairy wastes and dates wastewater and bioactive silver-poly (lactic acid) nanocomposite for biological applications

L-Lactic acid-producing Lactobacillus lactis and L. plantarum were isolated from date wastes. The fermentation process was optimized using a one-variable-at-a-time approach. Dairy wastewater and wastewater from the date industry were utilized as low-cost culture media to produce lactic acid. The selected two bacterial strains were co-cultured in wastewater medium to produce L-lactic acid and D-lactic acid. Lactic acid production was significantly improved by glucose (carbon source), yeast extract (nitrogen source), initial inoculum level, and polysorbate 80. A central composite design and response surface methodology were used to optimize the variables and their levels to improve lactic acid yield. The supplemented yeast extract, glucose, and polysorbate 80 improved lactic acid. The predicted variables and their levels for maximum lactic acid production were glucose (67.5 g/L), yeast extract (10.28 g/L), and polysorbate 80 (0.48 mL/L). The prepared nanocomposites exhibited antibacterial activity against foodborne bacterial pathogens. The structural properties of the silver-polylactic acid nano compost materials were determined. The characterized compost materials exhibited a peak absorption wavelength of 430 nm. The silver and poly(lactic acid) were characterized using X-ray diffraction analysis and were 30 to 50 nm in size.

Resilience of Canola to Plasmodiophora brassicae (Clubroot) Pathotype 3H under Different Resistance Genes and Initial Inoculum Levels.

In this study, we explored the resilience of a clubroot resistance (CR) stacking model against a field population of Plasmodiophora brassicae pathotype 3H. This contrasts with our earlier work, where stacking CRaM and Crr1rutb proved only moderately resistant to pathotype X. Canola varieties carrying Rcr1/Crr1rutb and Rcr1 + Crr1rutb were repeatedly exposed to 3H at low (1 × 104/g soil) and high (1 × 107/g soil) initial resting spore concentrations over five planting cycles under controlled environments to mimic intensive canola production. Initially, all resistant varieties showed strong resistance. However, there was a gradual decline in resistance over time for varieties carrying only a single CR gene, particularly with Crr1rutb alone and at the high inoculum level, where the disease severity index (DSI) increased from 9% to 39% over five planting cycles. This suggests the presence of virulent pathotypes at initially low levels in the 3H inoculum. In contrast, the variety with stacked CR genes remained resilient, with DSI staying below 3% throughout, even at the high inoculum level. Furthermore, the use of resistant varieties, carrying either a single or stacked CR genes, reduced the total resting spore numbers in soil over time, while the inoculum level either increased or remained high in soils where susceptible Westar was continuously grown. Our study demonstrates greater resistance resilience for stacking Rcr1 and Crr1rutb against the field population of 3H. Additionally, the results suggest that resistance may persist even longer in fields with lower levels of inoculum, highlighting the value of extended crop rotation (reducing inoculum) alongside strategic CR-gene deployment to maximize resistance resilience.

Effect of Different Treatments on Chemical Components of Fermented Probiotic Millet Dried Mix

Aims: The purpose of this study was to develop fermented probiotic millet dried mix by incorporating a probiotic Lactobacillus acidophilus and to ascertain how different processes used in the product's development affected its chemical components. Study Design: Fermented probiotic millet dried mix was developed by fermentation of germinated finger millet flour and Reconstituted Skim Milk (RSM) with L. acidophilus. The impact of various treatments on moisture, crude protein, crude fiber, total ash, alcoholic acidity and phytate content were investigated. Place and Duration of Study: Department of Dairy Microbiology, Dairy Science College, Hebbal, Bengaluru, Karnataka, India between June 2023 and April 2024. Methodology: Moisture, crude protein, crude fiber, total ash, alcoholic acidity and phytate content were examined after various treatments such as soaking, germination, autoclaving, fermentation and drying of millet dried mix. Results: At 10% L. acidophilus inoculum level and a 1:1.5 millet to RSM ratio, a maximum viability of 9.52 log10 cfu/g was reported after 30 h of fermentation. After freeze drying of fermented probiotic millet mix with 2% Skim Milk Powder (SMP) as a cryoprotective agent, viability was retained to 9.50 log10 cfu/g. The optimized fermented probiotic millet dried mix had 4.76% moisture, 11.94% crude protein, 6.50% crude fiber, 4.74% total ash, 1.90% alcoholic acidity and 1.73 mol/kg of phytate. Conclusion: The resultant fermented probiotic millet dried mix was rich in nutrients and the probiotic L. acidophilus helps to improve gut health. Thus, the product had combined therapeutic and nutritional benefits of probiotics with millet.

Pomegranate (Punica granatum L.) growth and biochemical alterations in response to meloidogyne incognita infection, minerals, and nano-fertilizers

The effects of four inoculum levels (500, 1,000, 2,000, or 4,000 second-stage juveniles (J2) per plant) of the root-knot nematode, Meloidogyne incognita, on two pomegranate cultivars (‘Manfalouty’ and ‘Wonderful’) were investigated under greenhouse conditions in response to plant inorganic and organic chemical concentrations. Furthermore, the effects of six commercial chemical fertilizers (inorganic fertilizers and nano-fertilizers) on plant growth and nematode reproduction were also studied. Both cultivars recorded the highest gall formation, embedded stages, and final nematode population at the inoculum dosage of 2,000 J2/plant. The highest reproductive rate was achieved with 500 J2/plant, while the lowest rate was observed with 4,000 J2/plant on both cultivars. ‘Wonderful’, at all M. incognita inoculum levels, was more sensitive to nematode infestation than ‘Manfalouty’. ‘Wonderful’ showed a greater reduction in fresh and dry plant weights than ‘Manfalouty’ at 2,000 and 4,000 J2/plant. In both cultivars, the concentrations of N, P, and K decreased with increasing nematode inoculum levels. This decline was more pronounced in ‘Manfalouty’ than in ‘Wonderful’. The nano-fertilizers, Hyper Feed®, and Hyper Feed Solo® reduced all nematode parameters but only in ‘Wonderful’. Treatment with Hyper Feed® resulted in the highest percentage increases in all plant growth parameters in ‘Wonderful’. Total carbohydrate concentration was increased in ‘Manfalouty’ treated with the nano-fertilizers, especially with Hyper Feed®. Also, concentrations of total phenols and tannins increased in ‘Wonderful’ when treated with either nano-fertilizer. Generally, both nano-fertilizers showed an increase in plant N levels. We recommend using nano-fertilizers in integrated pest management (IPM) programs on pomegranate where they improved plant growth parameters and reduced nematode multiplication parameters more markedly than inorganic fertilizers.

Survival of Salmonella enterica and Enterococcus faecium on Abiotic Surfaces During Storage at Low Relative Humidity

Currently, there is limited knowledge on the survival of bacteria on surfaces during postharvest handling of dry products such as onions. Extended survival of microorganisms, coupled with a lack of established and regular, validated cleaning or sanitation methods could enable cross-contamination of these products. The aim of the study was to evaluate the survival of a potential surrogate, Enterococcus faecium, and Salmonella enterica on typical onion handling surfaces, polyurethane (PU), and stainless steel (SS), under low relative humidity. The influence of onion extract on the survival of E. faecium and Salmonella on PU and SS was also investigated. Rifampin-resistant E. faecium NRRL B-2354 and a five-strain cocktail of Salmonella suspended in 0.1% peptone or onion extract were separately inoculated onto PU and SS coupons (2 × 2 cm), at high, moderate, or low (7, 5, or 3 log CFU/cm2) levels. The inoculated surfaces were stored at ∼34% relative humidity and 21°C for up to 84 days. Triplicate samples were enumerated at regular intervals in replicate trials. Samples were enriched when populations fell below the limit of detection by plating (0.48 log CFU/cm2). Scanning electron microscopy was used to observe the cell distribution on the coupons. Reductions of E. faecium of less than ∼2 log were observed on PU and SS over 12 weeks at all inoculum levels and with both inoculum carriers. In 0.1% peptone, Salmonella populations declined by 2 to 3 log over 12 weeks at the high and moderate inoculum levels; at the low inoculum level, Salmonella could not be recovered by enrichment at 84 days. Survival of E. faecium and Salmonella was significantly (P < 0.05) enhanced over 84 days of storage when suspended in onion extract, where cells were covered by a layer of onion extract. E. faecium might have utility as a conservative surrogate for Salmonella when evaluating microbial survival on dry food-contact surfaces.

Evaluating the efficacy of peroxyacetic acid in preventing Salmonella cross-contamination on tomatoes in a model flume system

The use of flume tanks for tomato processing has been identified as a potential source of cross-contamination, which could result in foodborne illness. This study's objective was to assess the efficacy of peroxyacetic acid (PAA) at a concentration of ≤80 mg/L in preventing Salmonella enterica cross-contamination under various organic loads in a benchtop model tomato flume tank. The stability of 80 mg/L PAA at different chemical oxygen demand (COD) levels was also tested. Tomatoes were spot inoculated with a five-serovar rifampin-resistant (rif+) Salmonella cocktail (106 or 108 colony forming unit (CFU)/tomato). Inoculated (n = 3) and uninoculated (n = 9) tomatoes were introduced into the flume system containing 0–80 mg/L PAA and 0 or 300 mg/L COD. After washing for 30, 60, or 120 s, uninoculated tomatoes were sampled and analyzed for cross-contamination. All experiments were conducted in triplicate. Increasing the organic load (measured as COD) affected the stability of PAA in water with significantly faster dissociation when exposed to 300 mg/L COD. The concentration of PAA, inoculum level, COD levels, and time intervals were all significant factors that affected cross-contamination. Cross-contamination occurred at the high inoculum level (108 CFU/tomato) even when 80 mg/L PAA was present in the model flume tank, regardless of the organic load level. When the tomatoes were contaminated at a level of 106 CFU/tomato, concentrations as low as 5 mg/L of PAA were effective in preventing cross-contamination at 0 mg/L COD; however, 100 % tomatoes (9/9) were positive when the organic load increased to 300 mg/L COD. When the PAA concentration was increased to 10 mg/L, it effectively prevented cross-contamination in the tank, regardless of the presence of organic load. These results suggest that using PAA at concentrations below the maximum limit remains effective in limiting bacterial cross-contamination and offers a more environment-friendly option for tomato packinghouse operators.

Strategy to identify common beans with resistance to white mould for dry‐irrigated areas: Additional evidence

AbstractIn a previous study, common bean (Phaseolus vulgaris L.) genotypes were selected in the field for reactions to white mould (WM), caused by Sclerotinia sclerotiorum. These genotypes, along with the resistant control A195, were then evaluated in both field and greenhouse (straw test) conditions. The results showed that field trials effectively identified high‐yielding WM‐resistant genotypes for dry‐irrigated conditions. Here we challenge the results of this study with new data and methodology by conducting six sprinkler‐irrigated trials from 2015 to 2017 with five genotype groups (G). Three groups comprised genotypes previously studied: G1, seven partially resistant; G4, two intermediately resistant; and G5, three susceptible. G2 consisted of four lines selected for partial resistance in the current study. The resistant control group, G3, comprised the genotypes A195, G122, Cornell605, and Ouro Branco. WM was absent (one trial), or pressure was either low/moderate (two trials) or moderate/high (three trials). The average seed yield ranged from 2207 (G3) to 3178 kg/ha (G1). The contrast G1, G2 versus G3 was nonsignificant for incidence and severity index, indicating that genotypes selected for resistance in the field were as resistant as the resistant control genotypes. Additionally, the groups selected for resistance yielded 43% more and produced 33% less sclerotia weight compared with the control group. Our results reinforce the effectiveness of selecting WM‐resistant genotypes using beans originally bred for purposes other than WM‐resistance, specifically targeting dry‐irrigated areas. Furthermore, our results suggest that the use of genotypes selected for partial resistance reduces inoculum levels in the soil.

Predicting airborne ascospores of Sclerotinia sclerotiorum through machine learning and statistical methods

AbstractA main biological constraint of dry bean (Phaseolus vulgaris) production in Canada is white mould, caused by the fungal pathogen Sclerotinia sclerotiorum. The primary infectious propagules of S. sclerotiorum are airborne ascospores and monitoring the air for inoculum levels could help predict the severity of white mould in bean fields. Daily air samples were collected in commercial dry bean fields in Alberta, Manitoba and Ontario and ascospores were quantified using quantitative PCR. Daily weather data was obtained from in‐field weather stations. The number of ascospores on a given day was modelled using 63 different environmental variables and several modelling methods, both regression and classification approaches, were implemented with machine learning (ML) (random forests, logistic regression and support vector machines) and statistical (generalized linear models) approaches. Across all years and provinces, ascospores were most highly correlated with ascospore release from the previous day (r ranged from 0.15 to 0.6). This variable was also the only variable included in all models and had the greatest weight in all models. Models without this variable had much poorer performance than those with it. Correlations of ascospores with other environmental variables varied by province and sometimes by year. A comparison of ML and statistical models revealed that they both performed similarly, but that the statistical models were easier to interpret. However, the precise relationship between airborne ascospore levels and in‐field disease severity remains unclear, and spore sampling methods will require further development before they can be deployed as a disease management tool.