A risk infection simulation model for fusarium head blight of wheat

Fusarium Head Blight (FHB) is a disease of great concern in wheat (Triticum aestivum). Due to its relatively narrow susceptible phase and environmental dependence, the pathosystem is suitable for modeling. In the present work, a mechanistic model for estimating an infection index of FHB was developed. The model is process-based driven by rates, rules and coefficients for estimating the dynamics of flowering, airborne inoculum density and infection frequency. The latter is a function of temperature during an infection event (IE), which is defined based on a combination of daily records of precipitation and mean relative humidity. The daily infection index is the product of the daily proportion of susceptible tissue available, infection frequency and spore cloud density. The model was evaluated with an independent dataset of epidemics recorded in experimental plots (five years and three planting dates) at Passo Fundo, Brazil. Four models that use different factors were tested, and results showed all were able to explain variation for disease incidence and severity. A model that uses a correction factor for extending host susceptibility and daily spore cloud density to account for post-flowering infections was the most accurate explaining 93% of the variation in disease severity and 69% of disease incidence according to regression analysis.

Etiology and epidemiology of Pythium root rot in hydroponic crops: current knowledge and perspectives

The etiology and epidemiology of Pythium root rot in hydroponically-grown crops are reviewed with emphasis on knowledge and concepts considered important for managing the disease in commercial greenhouses. Pythium root rot continually threatens the productivity of numerous kinds of crops in hydroponic systems around the world including cucumber, tomato, sweet pepper, spinach, lettuce, nasturtium, arugula, rose, and chrysanthemum. Principal causal agents include Pythium aphanidermatum, Pythium dissotocum, members of Pythium group F, and Pythium ultimum var. ultimum. Perspectives are given of sources of initial inoculum of Pythium spp. in hydroponic systems, of infection and colonization of roots by the pathogens, symptom development and inoculum production in host roots, and inoculum dispersal in nutrient solutions. Recent findings that a specific elicitor produced by P. aphanidermatum may trigger necrosis (browning) of the roots and the transition from biotrophic to necrotrophic infection are considered. Effects on root rot epidemics of host factors (disease susceptibility, phenological growth stage, root exudates and phenolic substances), the root environment (rooting media, concentrations of dissolved oxygen and phenolic substances in the nutrient solution, microbial communities and temperature) and human interferences (cropping practices and control measures) are reviewed. Recent findings on predisposition of roots to Pythium attack by environmental stress factors are highlighted. The commonly minor impact on epidemics of measures to disinfest nutrient solution as it recirculates outside the crop is contrasted with the impact of treatments that suppress Pythium in the roots and root zone of the crop. New discoveries that infection of roots by P. aphanidermatum markedly slows the increase in leaf area and whole-plant carbon gain without significant effect on the efficiency of photosynthesis per unit area of leaf are noted. The platform of knowledge and understanding of the etiology and epidemiology of root rot, and its effects on the physiology of the whole plant, are discussed in relation to new research directions and development of better practices to manage the disease in hydroponic crops. Focus is on methods and technologies for tracking Pythium and root rot, and on developing, integrating, and optimizing treatments to suppress the pathogen in the root zone and progress of root rot.

Genetic variability of Puccinia triticina Eriks. in Brazil

Studies on the genetic variability of Puccinia triticina in inoculum collected in Brazil started in 1941 with Vallega (20). The pioneering work in Brazil dates from 1949 (16) at "Instituto Agronômico do Sul", Ministry of Agriculture (MA), in Pelotas, Rio Grande do Sul State (RS), and continued after 1975 at Embrapa Wheat in Passo Fundo, RS. In 2002, analyses for the identification of P. triticina races continued at OR Seed breeding, simultaneously to Embrapa's program, both in Passo Fundo. The investigators involved in the identification of races in Brazil were Ady Raul da Silva in Pelotas (MA), Eliza Coelho in Pelotas (MA) and in Passo Fundo (Embrapa), Amarilis Labes Barcellos in Pelotas (MA) and in Passo Fundo (Embrapa and OR), Camila Turra in Passo Fundo (OR) and Marcia Chaves in Passo Fundo (Embrapa). From 1979 to 2010 growing season, 59 races were determined, according to the differentiation based on the expression of each Lr resistance gene. On average, one to three new races are detected per year. Research has focused on the use of vertical resistance; however, lately some institutes have searched more durable resistance, of the adult-plant type (horizontal, less race-specific). The uninterrupted monitoring of the wheat rust pathogenic population in Brazil during so many decades allowed the understanding of the evolution and virulence of races. The use of international nomenclature adopted by some programs has allowed the comparison of the fungus variability in Brazil with that in other countries, especially where frontiers are not barriers for spore transportation, confirmed by the occurrence of the same races all over one region.

Adjuvant concentrations and uredospore densities on Phakopsora pachyrhizi infection efficiency in soybean

Experiments were carried out in a growth chamber to evaluate the effect of spreader and uredospore concentrations on the efficiency of infection by Phakopsora pachyrhizi, the causal agent of Asian soybean rust. CD 214 RR soybean cultivar was inoculated with the following polyoxyethylene sorbitane monolaurate concentrations: 0, 30, 60, 120, 240, 480 and 960 µL.L-1 water, as well as a fixed uredospore concentration of 2 x 10(4) spores.mL-1. In a second phase, the inoculum concentrations of 0, 5 x 10³, 1 x 10(4), 2 x 10(4), 4 x 10(4), 8 x 10(4) and 16 x 10(4) uredospores.mL-1 were evaluated, and the spreader concentration of 240 µL.L-1, selected in the previous experiment, was fixed. The spreader concentration of 240 µL.L-1 can be used in artificial inoculation studies, as well as up to 4 x 10(4) uredospores.mL-1. In this work, there was a correlation between uredia and lesion density. Thus, the use of lesion density is recommended to assess disease intensity for its accuracy and less time consuming. There was also a positive correlation between uredia and lesion density.

Limitations in controlling white mold on common beans with Trichoderma spp. at the fall-winter season

We studied the effectiveness of application of Trichoderma spp. in controlling white mold on common beans at the fall-winter crop in the Zona da Mata region of the State of Minas Gerais, Brazil. There was no effect of the antagonist in reducing the disease severity, which could be explained by the low temperatures and the high inoculum pressure in the field. We concluded that Trichoderma applications are not recommended for control of white mold on common beans at the fall-winter season in regions with average temperature bellow 20 °C, since this condition favor more the pathogen than the antagonist.

Influence of substrates, light, filter paper and pH on the sporulation of Cercospora sojina

Fungi require special substrates for their isolation, vegetative growth and sporulation. In experiments conducted in the laboratory, the influence of substrates, light, filter paper and pH on the sporulation of Cercospora sojina conidia, the causal agent of soybean frogeye leaf spot, was assessed. The media potato sucrose agar, V-8 agar, tomato extract agar, soybean leaf extract agar, soybean seed extract agar, soybean meal agar, soybean flour agar and wheat flour agar were tested, added on the surface, with and without filter paper and under two light regimes, with 12 h light at 25°± 2°C and in the dark. A triple factorial 8x2x2 (substrates x light/dark x with/without filter paper) design with four replicates was used. V-8 agar medium was employed and the pH was adjusted with HCl 0.1N or NaOH 0.1N before autoclaving to the values: 3, 4, 5, 6, 7 and 8, and the pH of V-8 agar medium is 6.7. The evaluation was done on the seventh day of incubation. Data underwent regression analysis. Sporulation was maximized on the agar media V-8, seed extract, oat flour, tomato extract, and potato sucrose in the presence of filter paper and 12h light. On V-8 medium, maximal sporulation was obtained with pH 6.7.

Macrophomina phaseolina: density and longevity of microsclerotia in soybean root tissues and free on the soil, and competitive saprophytic ability

In field experiments, the density of Macrophomina phaseolina microsclerotia in root tissues of naturally colonized soybean cultivars was quantified. The density of free sclerotia on the soil was determined for plots of crop rotation (soybean-corn) and soybean monoculture soon after soybean harvest. M. phaseolina natural infection was also determined for the roots of weeds grown in the experimental area. To verify the ability of M. phaseolina to colonize dead substrates, senesced stem segments from the main plant species representing the agricultural system of southern Brazil were exposed on naturally infested soil for 30 and 60 days. To quantify the sclerotia, the methodology of Cloud and Rupe (1991) and Mengistu et al. (2007) was employed. Sclerotium density, assessed based on colony forming units (CFU), ranged from 156 to 1,108/g root tissue. Sclerotium longevity, also assessed according to CFU, was 157 days for the rotation and 163 days for the monoculture system. M. phaseolina did not colonize saprophytically any dead stem segment of Avena strigosa,Avena sativa,Hordeum vulgare,Brassica napus,Gossypium hirsutum,Secale cereale,Helianthus annus,Triticosecalerimpaui, and Triticum aestivum. Mp was isolated from infected root tissues of Amaranthus viridis,Bidens pilosa,Cardiospermum halicacabum,Euphorbia heterophylla,Ipomoea sp., and Richardia brasiliensis. The survival mechanisms of M. phaseolina studied in this paper met the microsclerotium longevity in soybean root tissues, free on the soil, as well as asymptomatic colonization of weeds.

Semi-selective culture medium for Exserohilum turcicum isolation from corn seeds

Northern corn leaf blight, caused by Exserohilum turcicum (Et), is a disease of widespread occurrence in regions where corn, sweetcorn and popcorn are grown. This disease has great potential to cause damage and has been studied for years, but the association of its causal agent with seeds remains unconfirmed. Thus, the availability of a sensitive method to detect and quantify the inoculum in seeds, even at low incidence, is essential. The aim of this study was to develop a method to detect and quantify the presence of the fungus infecting and infesting corn and popcorn seeds. Artificially and naturally infected seeds were employed to develop the medium. The semi-selective medium was composed of carbendazim (active ingredient) (60 mg/L), captan (30 mg/L), streptomycin sulfate (500 mg/L) and neomycin sulfate (600 mg/L) aggregated to the medium lactose casein hydrolysate agar medium. By using this, Et was detected in naturally infected corn seeds, showing 0.124% incidence, in four out of ten analyzed samples. In addition, 1.04 conidia were detected per infested seed. By means of isolation, pathogenicity test, morphological characterization and comparison with descriptions of the species in the literature, the fungus isolated from the seeds was confirmed to be Et. Both infection and infestation were considered low; thus, for studies of Et detection in corn seeds, the use of semi-selective medium and more than 1,200 seeds/sample is suggested.

Key factors to inoculate Botrytis cinerea in tomato plants

Studies addressing the biological control of Botrytis cinerea have been unsuccessful because of fails in inoculating tomato plants with the pathogen. With the aim of establishing a methodology for inoculation into stems, experiments were designed to assess: i. the aggressiveness of pathogen isolates; ii. the age at which tomato plants should be inoculated; iii. the susceptibility of tissues at different stem heights; iv. the need for a moist chamber after inoculation; and v. the effectiveness of gelatin regarding inoculum adhesion. Infection with an isolate from tomato plants that was previously inoculated into petioles and then re-isolated was successful. An isolate from strawberry plants was also aggressive, although less than that from tomato plants. Tomato plants close to flowering, at 65 days after sowing, and younger, middle and apical stem portions were more susceptible. There was positive correlation between lesion length and sporulation and between lesion length and broken stems. Lesion length and the percentage of sporulation sites were reduced by using a moist chamber and were not affected by adding gelatin to the inoculum suspension. This methodology has been adopted in studies of B. cinerea in tomato plants showing reproducible results. The obtained results may assist researchers who study the gray mold.

The role of arbuscular mycorrhizal fungi on the early-stage restoration of seasonally dry tropical forest in Chamela, Mexico

It was evaluated the effect of two different sources of local inocula from two contrasting sites (mature forest, pasture) of arbuscular mycorrhizae fungi (AMF) and a non-mycorrhizal control on the plant growth of six woody species differing in functional characteristics (slow-, intermediate- and fast-growth), when introduced in a seasonally tropical dry forest (STDF) converted into abandoned pasture. Six plots (12 X 12m) were set as AMF inoculum source. Six replicates of six different species arranged in a Latin Square design were set in each plot. Plant height, cover area and the number of leaves produced by individual plant was measured monthly during the first growing season in each treatment. Species differed in their ability to benefit from AMF and the largest responsiveness in plant height and leaf production was exhibited by the slow-growing species Swietenia humilis, Hintonia latiflora and Cordia alliodora. At the end of the growing season (November), the plant height of the fast growing species Tabebuia donnel-smithii, Ceiba pentandra and Guazuma ulmifolia were not influenced by AMF. However, inocula of AMF increased leaf production of all plant species regardless the functional characteristics of the species, suggesting a better exploitation of above-ground space and generating a light limited environment under the canopy, which contributed to pasture suppression. Inoculation of seedlings planted in abandoned pasture areas is recommended for ecological restoration due to the high responsiveness of seedling growth in most of species. Use of forest inoculum with its higher diversity of AMF could accelerate the ecological restoration of the above and below-ground comunities.

Establishment of anammox process in sludge samples collected from swine wastewater treatment system

The high load of nitrogen present in swine wastewater is one of the biggest management challenges of the activity. The Anammox process emerges as a good alternative for biological removal of nitrogen. This study aims to acclimate sludge collected from swine effluent treatment systems to establish the Anammox process. Two sludge samples were collected at Embrapa Swine and Poultry, Concordia - SC, Brazil, one from the bottom of an inactive anaerobic pond (inoculum A) and another from an aeration tank (inoculum B). Both were acclimated until the depletion of NO3-N, being subsequently inoculated in two reactors (Reactor A - Inoculum A and Reactor B - Inoculum B). The Reactor A showed activity after 110 days of operation, while the Reactor B needed 170 days. The difference in the start-up time could be explained by the different environmental conditions to which each sludge was submitted. FISH and PCR analyses confirmed the presence of microorganisms with Anammox activity, demonstrating that the sludge of swine wastewater treatment systems is a good source of inoculum for the development of the Anammox process.

Effect of cycle time and airflow in biological nitrogen removal from poultry slaughterhouse wastewater using sequencing batch reactor

This study aimed to evaluate the influence of airflow (0.25, 0.50 and 0.75 L.L-1.min-1) and cycle time (10.45 h, 14.25 h and 17.35 h) on a sequencing batch reactor (SBR) performance in promoting nitrification and denitrification of poultry slaughterhouse wastewater. The operational stages included feeding, aerobic and anoxic reactions, sedimentation and discharge. SBR was operated in a laboratory scale with a working volume of 4 L, keeping 25% of biomass retained inside the reactor as inoculum for the next batch. In the anoxic stage, C: N ratio was maintained between 5 and 6 by adding cassava starch wastewater. A factorial design (22) with five repetitions was designed at the central point to evaluate the influence of cycle time and airflow on total inorganic nitrogen removal (N-NH4++N-NO2-+N-NO3-) and in the whole process (nitrification and denitrification). The highest total inorganic nitrogen removal (93.3%) was observed for airflow of 0.25 L.L-1.min‑1 and a cycle time of 14.25 h. At the end of the experiment, the sludge inside the reactor was characterized by fluorescent in situ hybridization (FISH), indicating the presence of ammonia and nitrite oxidizing bacteria.

Infection of sparrows (Passer domesticus) and different mice strains with Lawsonia intracellularis

The susceptibility of sparrows (Passer domesticus) and strains of mice (Swiss, BALB/c, C-57 and DB-A) to Lawsonia intracellularis infection was studied. Thirty-two sparrows were inoculated with pure culture of L. intracellularis and eleven received sham inoculum. Feces were collected on -1, 7, 14 and 21 days post infection (dpi) for detection of L. intracellularis by PCR. After 21 days, all sparrows were euthanized and the tissues processed for histology and immunohistochemistry (IHC). One hundred sixty mice of four different strains (n=40, per strain) were used. For each mouse strain, 16 animals received mucosa homogenate from a pig infected with L. intracellularis, 16 received pure culture of L. intracellularis and eight animals received sham inoculum. Two control and four inoculated mice from each group were euthanized on 7, 14, 21 and 28 dpi. Sections of intestine were collected for histologic analysis and IHC and pooled feces were collected for L. intracellularis PCR. None of the sparrows had any histologic lesions characteristic of proliferative enteropathy or antigen labeling by IHC. All sparrow fecal samples were negative by PCR. All mice strains studied had histopathological lesions typical of PE and IHC labeling consistent with L. intracellularis infection, especially those animals inoculated with pure culture. The most severe lesions were observed in DB-A and Swiss mice. Fecal shedding was detected in all mice strains, with peak at 14 dpi. We conclude that sparrows do not seem to be relevant in the epidemiology of L. intracellularis. The results showed variations in the lesions among the four mice strains used.

Ascophyllum nodosum in the diet of tilapia (Oreochromis niloticus) and its effect after inoculation of Aeromonas hydrophila

The objective of this study was to evaluate the effect of Ascophyllum nodosum brown seaweed meal (FAM) on the health of Nile tilapia submitted to inoculation with Aeromonas hydrophila. The experiment was conducted for a period of 40 days using 120 Nile tilapia fingerlings, with age of 40 days, distributed in 20 tanks. A diet including Ascophyllum nodosum seaweed meal at 20g.kg-1 and a control diet (without FAM) were provided which constituted the treatments. Thirty days after beginning the experiment, A. hydrophila was inoculated by bacterial inoculum diluted in sterile saline solution at a concentration of 10(6) CFU ml-1. Except for the width, which was greater for the treatment with the provision of FAM (P<0.05), there was no influence on the performance parameters of the fingerlings, but the occurrence of lesions in animals inoculated with A. hydrophila and fed with FAM was lower and they also exhibited a decline in the lesions in a shorter period of time than the control group. FAM prevents hepatopancreatic congestion in infected animals. Ascophyllum nodosum brown seaweed meal reduced the number of lesions in fish in a shorter time when compared to the control group.

Pasteurella multocida type A as the primary agent of pneumonia and septicaemia in pigs

Abstract: In order to understand better the pathological aspects and spread of Pasteurella multocida type A as the primary cause of pneumonia in pigs, was made an experiment with intranasal inoculation of different concentrations of inocula [Group (G1): 108 Colony Forming Units (CFU)/ml; G2: 107 CFU/ml; G3: 106 CFU/ml and G4: 105 CFU/ml], using two pigs per group. The pigs were obtained from a high health status herd. Pigs were monitored clinically for 4 days and subsequently necropsied. All pigs had clinical signs and lesions associated with respiratory disease. Dyspnoea and hyperthermia were the main clinical signs observed. Suppurative cranioventral bronchopneumonia, in some cases associated with necrosuppurative pleuropneumonia, fibrinous pericarditis and pleuritic, were the most frequent types of lesion found. The disease evolved with septicaemia, characterized by septic infarctions in the liver and spleen, with the detection of P. multocida type A. In this study, P. multocida type A strain #11246 was the primary agent of fibrinous pleuritis and suppurative cranioventral bronchopneumonia, pericarditis and septicaemia in the pigs. All concentrations of inoculum used (105-108 CFU/ml) were able to produce clinical and pathological changes of pneumonia, pleuritis, pericarditis and septicemia in challenged animals.