Organic agriculture has expanded worldwide. Numerous papers were published in the past 20 years comparing plant diseases in organic and conventional crops. Root diseases are generally less severe ...owing to greater soil health, whereas some foliar diseases can be problematic in organic agriculture. The soil microbial community and nitrogen availability play an important role in disease development and yield. Recently, the focus has shifted to optimizing organic crop production by improving plant nutrition, weed control, and plant health. Crop-loss assessment relating productivity to all yield-forming and -reducing factors would benefit organic production and sustainability evaluation.
The effect of cattle manure and slurry application on percolation and survival of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium was investigated for different soil depths after ...the addition of water. Four treatments were chosen for the first set of experiments: (i) addition of inoculated farmyard manure on the soil surface, (ii) mixing of inoculated farmyard manure with the top 10 cm of soil, (iii) addition of inoculated slurry on the soil surface, and (iv) injection of inoculated slurry into the top 10 cm of the soil. Homogeneity of water distribution in the soil profile was confirmed by a nondestructive nuclear magnetic resonance method. Survival data were fitted to a modified logistic model, and estimated survival times were compared. In the second set of experiments, pathogen-inoculated farmyard manure or slurry was applied to soil columns with 1-month-old lettuce plants. More pathogen cells percolated to greater depths after slurry than after manure application. Survival of E. coli O157:H7 was significantly longer in soil with slurry than in that with manure, while survival of Salmonella serovar Typhimurium was equally high with manure and slurry. The densities of the pathogens were not different in the rhizosphere compared to the bulk soil with manure, while the densities were higher by 0.88 ± 0.11 and 0.71 ± 0.23 log CFU per g (dry weight), respectively, in the rhizosphere than in bulk soil after slurry application. Our results suggest that surface application of manure may decrease the risk of contamination of groundwater and lettuce roots compared to injection of slurry.
Survival of the green fluorescent protein-transformed human pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium was studied in a laboratory-simulated lettuce production ...chain. Dairy cows were fed three different roughage types: high-digestible grass silage plus maize silage (6:4), low-digestible grass silage, and straw. Each was adjusted with supplemental concentrates to high and low crude protein levels. The pathogens were added to manure, which was subsequently mixed (after 56 and 28 days for E. coli O157:H7 and Salmonella serovar Typhimurium, respectively) with two pairs of organically and conventionally managed loamy and sandy soil. After another 14 days, iceberg lettuce seedlings were planted and then checked for pathogens after 21 days of growth. Survival data were fitted to a logistic decline function (exponential for E. coli O157:H7 in soil). Roughage type significantly influenced the rate of decline of E. coli O157:H7 in manure, with the fastest decline in manure from the pure straw diet and the slowest in manure from the diet of grass silage plus maize silage. Roughage type showed no effect on the rate of decline of Salmonella serovar Typhimurium, although decline was significantly faster in the manure derived from straw than in the manure from the diet of grass silage plus maize silage. The pH and fiber content of the manure were significant explanatory factors and were positively correlated with the rate of decline. With E. coli O157:H7 there was a trend of faster decline in organic than in conventional soils. No pathogens were detected in the edible lettuce parts. The results indicate that cattle diet and soil management are important factors with respect to the survival of human pathogens in the environment.
The herbicide glyphosate, N-(phosphonomethyl) glycine, has been used extensively in the past 40years, under the assumption that side effects were minimal. However, in recent years, concerns have ...increased worldwide about the potential wide ranging direct and indirect health effects of the large scale use of glyphosate. In 2015, the World Health Organization reclassified glyphosate as probably carcinogenic to humans. A detailed overview is given of the scientific literature on the movement and residues of glyphosate and its breakdown product aminomethyl phosphonic acid (AMPA) in soil and water, their toxicity to macro- and microorganisms, their effects on microbial compositions and potential indirect effects on plant, animal and human health. Although the acute toxic effects of glyphosate and AMPA on mammals are low, there are animal data raising the possibility of health effects associated with chronic, ultra-low doses related to accumulation of these compounds in the environment. Intensive glyphosate use has led to the selection of glyphosate-resistant weeds and microorganisms. Shifts in microbial compositions due to selective pressure by glyphosate may have contributed to the proliferation of plant and animal pathogens. Research on a link between glyphosate and antibiotic resistance is still scarce but we hypothesize that the selection pressure for glyphosate-resistance in bacteria could lead to shifts in microbiome composition and increases in antibiotic resistance to clinically important antimicrobial agents. We recommend interdisciplinary research on the associations between low level chronic glyphosate exposure, distortions in microbial communities, expansion of antibiotic resistance and the emergence of animal, human and plant diseases. Independent research is needed to revisit the tolerance thresholds for glyphosate residues in water, food and animal feed taking all possible health risks into account.
Sources:
Antibiotic resistance papers: Cantas et al., 2013
Glyphosate use (relative area sprayed): USDA NASS, 2014. Display omitted
•Glyphosate and its degradation product AMPA have accumulated in the environment.•Chronic low dose effects on animals and humans have been documented recently.•Shifts in microbial community composition in soil, plants and animal guts resulted.•Glyphosate and antibiotic resistance have arisen in fungi and bacteria in parallel.•Glyphosate may serve as one of the drivers for antibiotic resistance.
The One Health concept proposes that there is a connection between human, animal and environmental health. Plants and their health are not explicitly included. In this review, we broaden the One ...Health concept to include soil, plant, animal and ecosystem health. We argue that the health conditions of all organisms in an ecosystem are interconnected through the cycling of subsets of microbial communities from the environment (in particular the soil) to plants, animals and humans, and back into the environment. After an introduction on health concepts, we present examples of community stability and resilience, diversity and interconnectedness as affected by pollutants, and integrity of nutrient cycles and energy flows. Next, we explain our concept of microbial cycling in relation to ecosystem health, and end with examples of plant and animal disease outbreaks in relation to microbial community composition and diversity. We conclude that we need a better understanding of the role of interconnected microbiomes in promoting plant and animal health and possible ways to stimulate a healthy, diverse microbiome throughout human-dominated ecosystems. We suggest that it is essential to maintain ecosystem and soil health through diversification of plant communities and oligotrophication of managed ecosystems.
Display omitted
•The health conditions of all organisms in an ecosystem are interconnected.•Subsets of microbial communities cycle through successive habitats via food webs•Ecosystem management determines the quality of cycling microbiomes and eco-health.•Oligotrophication and pesticide reduction promote microbiome quality and eco-health.
The citrus disease huanglongbing (HLB), associated with an uncultured bacterial pathogen, is threatening the citrus industry worldwide. A mathematical model of the transmission of HLB between its ...psyllid vector and citrus host has been developed to characterize the dynamics of the vector and disease development, focusing on the spread of the pathogen from flush to flush (a newly developing cluster of very young leaves on the expanding terminal end of a shoot) within a tree. This approach differs from that of prior models for vector-transmitted plant diseases where the entire plant is the unit of analysis. Dynamics of vector and host populations are simulated realistically as the flush population approaches complete infection. Model analysis indicates that vector activity is essential for initial infection but is not necessary for continued infection because infection can occur from flush to flush through internal movement in the tree. Flush production, within-tree spread, and latent period are the most important parameters influencing HLB development. The model shows that the effect of spraying of psyllids depends on time of initial spraying, frequency, and efficacy of the insecticides. Similarly, effects of removal of symptomatic flush depend on the frequency of removal and the time of initiation of this practice since the start of the epidemic. Within-tree resistance to spread, possibly affected by inherent or induced resistance, is a major factor affecting epidemic development, supporting the notion that alternate routes of transmission besides that by the vector can be important for epidemic development.
Plant disease management in organic farming systems van Bruggen, Ariena HC; Gamliel, Abraham; Finckh, Maria R
Pest management science,
2016, 2016-01, January 2016, 2016-Jan, 2016-01-00, 20160101, Letnik:
72, Številka:
1
Journal Article
Two approaches to correlative species distribution models (MaxEnt and Multi-Model Framework) were used to predict global and local potential distribution of huanglongbing (HLB) caused by
Candidatus
...Liberibacter asiaticus (
C
Las) and its vector the Asian citrus psyllid (ACP,
Diaphorina citri
Kuwayama). Long-term climate data were sourced from the Worldclim website. The global distribution of
C
Las and ACP was gathered from online databases, literature review and communication with specialists. Data on
C
las and ACP distribution in the USA were not used in model calibration to allow model validation for independent locations. Both models successfully predicted Florida and coastal areas in the Gulf Coast states as highly suitable for
C
las and ACP. The models also predicted that coastal areas in California were climatologically favorable for ACP and
C
las, but less so than in Florida. When current USA presence data were included in the models, the suitable areas for ACP establishment expanded to the Central Valley, CA, while this area remained less conducive for
C
Las. Climate suitability was primarily related to rainfall and secondarily to temperature. Globally, both models predicted that climates in large areas of Africa, Latin America and North Australia were highly suitable for ACP and
C
Las, while the climate in the Mediterranean area was moderately suitable for ACP but less suitable for
C
Las, except for that in southern Portugal and Spain.
C
las predictions from our models could be informative for countries like Australia, New Zealand, citrus-producing European countries and much of Africa, where
C
Las and
D. citri
have not been reported.
The effects of four average temperatures (7, 16, 23 and 33°C) and daily oscillations with three amplitudes (0, ±4, ±7°C) on the survival of the enteropathogens Escherichia coli O157:H7 and Salmonella ...serovar Typhimurium were investigated in small microcosms. Manure was inoculated with a green fluorescent protein transformed strain of either pathogen at 10⁷ cells g⁻¹ dry weight. Samples were collected immediately after inoculation, and 1 and 2 weeks after inoculation for E. coli O157:H7, and immediately and after 2 and 3 weeks for Salmonella serovar Typhimurium. Population densities were determined by dilution plating and direct counting. In addition, total bacterial CFUs were determined. Growth and survival data were fitted to a modified logistic model. Analysis of the estimated parameter values showed that E. coli O157:H7 survived for shorter periods of time and was more sensitive to competition by the native microbial community than Salmonella serovar Typhimurium. Survival of both pathogens significantly declined with increasing mean temperatures and with increasing amplitude in daily temperature oscillations. The results indicated that responses of enteropathogens to fluctuating temperatures cannot be deduced from temperature relationships determined under constant temperatures.
Several Salmonella enterica outbreaks have been traced back to contaminated tomatoes. In this study, the internalization of S. enterica Typhimurium via tomato leaves was investigated as affected by ...surfactants and bacterial rdar morphotype, which was reported to be important for the environmental persistence and attachment of Salmonella to plants. Surfactants, especially Silwet L-77, promoted ingress and survival of S. enterica Typhimurium in tomato leaves. In each of two experiments, 84 tomato plants were inoculated two to four times before fruiting with GFP-labeled S. enterica Typhimurium strain MAE110 (with rdar morphotype) or MAE119 (without rdar). For each inoculation, single leaflets were dipped in 10(9) CFU/ml Salmonella suspension with Silwet L-77. Inoculated and adjacent leaflets were tested for Salmonella survival for 3 weeks after each inoculation. The surface and pulp of ripe fruits produced on these plants were also examined for Salmonella. Populations of both Salmonella strains in inoculated leaflets decreased during 2 weeks after inoculation but remained unchanged (at about 10(4) CFU/g) in week 3. Populations of MAE110 were significantly higher (P<0.05) than those of MAE119 from day 3 after inoculation. In the first year, nine fruits collected from one of the 42 MAE119 inoculated plants were positive for S. enterica Typhimurium. In the second year, Salmonella was detected in adjacent non-inoculated leaves of eight tomato plants (five inoculated with strain MAE110). The pulp of 12 fruits from two plants inoculated with MAE110 was Salmonella positive (about 10(6) CFU/g). Internalization was confirmed by fluorescence and confocal laser microscopy. For the first time, convincing evidence is presented that S. enterica can move inside tomato plants grown in natural field soil and colonize fruits at high levels without inducing any symptoms, except for a slight reduction in plant growth.
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