Bench-Scale Preparation of Mushroom Substrates In Controlled Environments

Conventional composting for mushroom cultivation involves a largely uncontrolled phase in which there are wide variations in temperature and oxygen level, resulting in the production of odor pollutants. The experiments reported in this paper investigated environmental conditions for compost preparation in an attempt to minimize odor production. Substrates for mushroom culture were prepared in flasks under controlled temperature and aeration. The temperature (48 to 72°C), O₂ concentration (0.6 to 8.7 percent v/v) and duration (6 or 20 h) of an initial pasteurization phase were varied before all the substrates were given a standard aerated conditioning period at 47°C. Compost decomposition, initial mineralization rates of ¹⁴C labelled glutamic acid (a measure of microbial activity) and actinomycete and fungal populations all decreased as the pasteurization temperature increased from 48°C to 72°C. The duration and O₂ concentration of the pasteurization treatment did not affect the overall decomposition of the substrate, mineralization of ¹⁴C labelled glutamic acid and subsequent mushroom mycelial extension rate and yield from the substrate. Under the controlled temperature conditions, the optimum pasteurization temperature for mushroom mycelial extension rate and sporophore yield was 60°C but possible benefits of higher temperature zones in a large stack situation were identified: 1) a higher concentration of ammonia which may assist substrate degradation over a prolonged period; 2) the development of high populations of intercellular bacteria following pasteurization at 72°C, 0.6 percent O₂; 3) the recovery of low rates of mineralization of ¹⁴C labelled glutamic acid following the pasteurization of substrate at 72°C to rates above those of the 48°C and 60°C pasteurization treatments.     

Temperature determinants of plant-soil-air mercury relationships

Using the Arrhenius thermodynamic equation, which relates rates of processes to temperature through the quantity E _a , the ‘Heat (or Energy) of Activation’, we have evaluated the thermal relationships for several parameters of Hg cycling. It is shown that release from isolated leaves (shoots) of Hg⁰ is a two-step process with a higher E _a value below 21 °C than above (28 vs 14 kcal mol^?1). Open field air Hg measurements over a mixed stand of grasses and other plants in volcanic soil show strikingly similar behavior to detached organs. Mercury release from volcanic soil was uniform over a wide temperature range, resembling plant and open field emissions above 18 to 21°C with anE _a value of 13 kcal · mol^?1. We conclude that Hg release below 18 to 21 °C is limited by a physiological process, whereas above that range, release is controlled by the physical process of vaporization itself. Plant concentration of total Hg from 5 to 33 °C (air temperature), is a more complex function involving direct accumulation and re-release of Hg⁰ from the atmosphere, release from tissue storage, and root uptake with reduction.     

Study of different climatic conditions to assess the role of solar radiation in reference crop evapotranspiration equations

This study aims to assess radiation-based models versus the FAO Penman–Monteith (FPM) model to determine the best model using linear regression under different weather conditions. The reference evapotranspiration was estimated using 22 radiation-based methods and was compared with the FPM. The results showed that the Stephens method estimates the reference evapotranspiration better than other methods in the most provinces of Iran (nine provinces). However, the values of R² were more than 0.9930 for 24 provinces of Iran. The radiation-based methods estimated the reference evapotranspiration near the Caspian Sea better than other regions. The most precise methods were the Berengena–Gavilan, Modified Priestley–Taylor, and Priestley–Taylor methods for the provinces ES (center of Iran), GI and GO (north of Iran) and the Stephens–Stewart method for IL (west of Iran). Finally, a list of the best performance of each method has been presented to use other regions and next research steps according to the values of mean, maximum, and minimum temperature, relative humidity, solar radiation, elevation, sunshine, and wind speed. The best weather conditions to use radiation-based equations are 23.6–24.6 MJ m^?2 day^?1, 12–20°C, 18–24°C, 5–13°C, and <180 hour month^?1 for solar radiation, mean, maximum, and minimum temperature, and sunshine, respectively.     

Reduction in viability of sclerotia of Macrophomina phaseolina with polyethylene mulching of soil

Mulching of Macrophomina phaseolina-inksted soil (moist or dry) with transparent polyethylene sheets during the hot days of May increased temperature of wet soil at 5 cm from 37°C (unmulched) to 52°C (mulched) and of dry soil from 52°C (unmulched) to 65°C (mulched). At 20 cm mulching increased temperature from 30°C to 41°C (wet) and from 38°C to 42°C (dry). In artificially-infested soil. the sclerotia of M. phaseolina were eradicated at 5 cm by a mulch treatment for 1 week and at 20 cm depth 50% sclerotia lost viability in wet soil but were not affected in dry soil. In a naturally infested soil (5–7 sclerotia g^?1), which gave 20% infection on Vigna, the sclerotia were reduced to such an extent that after 1 week mulching no disease was observed on Vigna.     

Influence of temperature on solvent-pesticide interaction effects towards fungi

The effect of temperature on interactions between combinations of the solvent acetone and the fungicide captan was determined using the fungi Pythium uhimum, Sclerotinia homeocarpa, and Pestalotia sp. Seven concentrations of acetone, ranging from 0.1 to 3.0% (v/v), were interacted with four concentrations of captan, ranging from 1.0 to 10.0 ppm (mg L^?1 ). This procedure was repeated at 15, 20, 25, and 30 °C using potato dextrose agar at pH 5.5. Acetone and captan interacted synergistically towards P. ultimum and S. homeocarpa, and antagonistically towards Pestalotia sp., regardless of the temperature. The exact temperature response was dependent upon both the captan level and culture used. As the temperature increased from 15 to 30 °C, the toxicity of captan decreased by up to 40% with P. ultimum, and from < 10 to 20 with S. homeocarpa and Pestalotia sp. With only a few exceptions, the magnitude of interactions observed generally decreased as the temperature was increased from 15 to 30 °C. This was most pronounced with P. ultimum. Generally, the lowest interaction magnitudes were recorded at 20 °C for P. ultimum, 20 to 25 °C for S. homeocarpa, and 30 °C for Pestalotia sp. The greatest interaction magnitudes were usually obtained at 15 or 30 °C with P. ultimum, 15 °C with S. homeocarpa, and 25 °C with Pestalotia sp.     

Culture,food selection and growth rate in the mycophagous ciliate Grossglockneria acuta Foissner, 1980: First evidence of autochthonous soil ciliates

A culture method with defined medium for the soil ciliate Grossglockneria acuta Foissner, 1980 is described. Food selection studies reveal that it fed exclusively on three out of 11 fungi tested (Mucor mucedo, Mucoraceae and Aspergillus sp.) although all have a chitinous cell wall. The rejected species may synthesize antiprotozoal substances. No growth was obtained with yeast, bacteria, flagellates or the ciliate Colpoda aspera Kahl. Under laboratory conditions generation times ranged from 34.25 h (4.5°C) to 3.86 h (30°C). Correspondingly, population growth rate values ranged between 0.036 h^?1 up to 0.323 h^?1. A significant increase in population growth rate was observed between 5.5° and 21°C, whereas there was no reproduction at 40°C. The most pronounced acceleration in population growth rate occurred between 10° and 21°C. This is near the highest mean monthly temperature of the natural habitat (16.7°C) of our population. Field observations yielded a higher density and frequency of G. acuta in alpine soils than in lowland ones. The experiments suggest that the low annual mean temperature could be responsible for this because highest individual densities develop at 4.5°C. The highly specialized diet and the oral structure—a tentacle which is used in breaking up and sucking out hyphae and spores—are convincing proof that G. acuta is autochthonous to soil. This is emphasized by the fact that we could not find any member of the family Grossglockneridae during the investigation of more than 200 running and stagnant waters.     

Modeling of the fine‐scale temperature response of arylsulfatase activity in soil

Fine‐scale (1.0–2.2 °C) temperature dependence of soil arylsulfatase activity (arylsulfate sulfohydrolase, EC 3.1.6.1) was measured at 0 to 75 °C in a Danish sandy, arable soil. Assays were done with field‐moist soil samples in the absence of toluene as plasmolytic agent – a procedure that primarily measures the extracellular enzymes. The aim was to evaluate the use of temperature models to describe the temperature response of soil arylsulfatase activity. In addition, we searched for increases in activity at high temperatures (e.g., 50–60 °C), which might be associated with unmasking (exposure) of intracellular enzymes. Arylsulfatase activities ranged from 1.1 to 60.3 μg p‐nitrophenol (g dry weight soil)^–1 h^–1, with an optimum temperature at 58.1 °C. The temperature response below 58.1 °C could be described by the Arrhenius equation (r² = 0.978, n = 83) and the simple Ratkowsky equation (r² = 0.977, n = 83). The expanded Ratkowsky equation, which covered the entire temperature range (0–75 °C), was less satisfactory (r² = 0.958, n = 90) because the model underestimated the reaction rates near the optimum temperature. The activation energy (E_a) calculated from the Arrhenius equation was 42.2 kJ mol^–1. This was higher than previously found for other soils (16.5–34.7 kJ mol^–1), possibly due to the use of toluene in these studies. Further analysis of the temperature response showed that no increase in activity occurred due to potential unmasking of intracellular enzymes by disintegration of bacterial cell membranes at high temperatures. Thus, the use of high incubation temperatures did not facilitate the differentiation between intra‐ and extracellular enzyme activity.     

Physiological aspects of N2-fixation by a Spirillum from Digitaria roots

Studies of the physiology of the Spirillum lipoferum recognized as the major organism responsible for N₂-fixation in the roots of Digitaria decumbens cv transvala were performed in order to improve the methods of culture and help to explain the physiology of this N₂-fixing grass bacterial association.Methods for isolation, purification and N₂-fixation assays are described. Acetylene concentrations used for N₂-ase activity measurements should be at least 12%. the Vmax of cultures in the log phase being at a pC₂H₂ of 0.12 atm and the apparent K_m 0.022 atm. Optimal temperatures for N₂-dependent growth are between 32 and 40°C. and little N₂-fixation is observed below 24°C. At 42°C the N₂-ase is inactivated. When cultures grown at 28 or 36°C are transferred to lower temperatures nitrogenase activity declines rapidly. One hour after transfer to 17°C activity is about half that before transfer and is maintained at this level for at least 8 h. After transfer to 10°C activity ceases after 1 h. Growth is very pH dependent, optimal growth on N₂ occurring only between pH 6.8 and 7.8. Nitrogen fixation below pH 5.5 and above 8.0 is less than one-quarter of the optimal. No N₂-fixation occurs in the absence of O₂ and maximal N₂-dependent growth is reached at 1.5% O₂ in the gas mixture bubbled through liquid cultures.In contrast to previous reports, several sugars including glucose can be used by the Spirillum for N₂-fixation, but only when small amounts of starter nitrogen or organic acids are added to the medium. Efficiencies of N₂-fixation on malate and glucose are similar and about 60% of that of cells incorporating NH⁺₄-N. Efficiency of NO^-₃ incorporation is 74% of that of NH⁺₄-N grown cultures. High observed efficiencies (52 mg N₂ fixed g^?1 malate or glucose) are attributed to carbon limited growth at optimum or O₂ limited conditions, both facilitated by slow diffusion rates through the semi-solid agar medium used.     

Fecal coliform and E. coli estimates,tip of the iceberg

Pure cultures of E. coli, Klebsiella and Enterobacter, obtained from hospital patients and from natural waters were tested for their growth patterns by spread plate and membrane filtration procedures at the following temperatures; 35°, 41.5°, 43°, 44.5°, and 35°C for 4 h followed by 18 h at 44.5°C. Results indicated that 44.5°C incubation produces the lowest population estimate and that the application of the membrane filtration technique also reduced the potential population. Three water samples collected during June, August and November were tested for fecal coliform and E. coli populations, with 11 different media (broth and agar) and incubation temperatures of 35°, 41.5°, 43°, 44.5°, and 35°C for 4 h followed by 18 h at 44.5°C. During the study, isolates were collected from all positive MPN tubes at each temperature and from each MF medium-temperature regime, 24 to 50 isolates were collected. From the isolate data corrected coliform (oxidase negative), fecal coliform and E. coli population estimates were made. A sample of feces was diluted in lake water and maintained at 20°C for 56 days. Samples were collected at various times and tested for fecal coliform densities using five media and the same temperature regime as for the lake water samples. Data from these studies indicate that, depending on the age of the population being measured, the temperature of the water sample, and the temperature-media-procedure combination used, fecal coliform and E. coli population estimate techniques measure from 5 to 100% of the potential population.     

Influence of temperature,humidity and inoculation on the degradation of14C-labeled 2-aminobenzimidazole in soil

Degradation of¹⁴C-labeled 2-aminobenzimidazole was measured in sandy loam soils by means of the evolution of¹⁴C into CO₂. The correlation between soil temperature and 2-AB-degradation was investigated utilizing a temperature gradient incubator for temperatures between 1 and 40°C with a water content of 100% of field capacity. Within the temperature interval 1 to 20°C, the evolution of¹⁴C was exponentially related to the inverse of the absolute temperature, in accordance with the Arrhenius' equation. Maximum evolution of¹⁴C was at 22°C while between 25 and 35°C the evolution remained almost constant and at 40°C it was almost nil. The correlation between soil water content and 2-AB-degradation was measured at 25°C in air dry soil and with water contents varying from 5 to 41% (equivalent to 28 to 227% of field capacity (FC)). From 28 to 94% of FC an exponential increase in the evolution of¹⁴C was observed while the evolution was slightly decreasing in soil with water contents above this level. Degradation of 2-AB in soil was greatly enhanced when the soil was inoculated with liquid or with soil aliquots from a soil perfusion apparatus through which 2-AB had been percolating for 6 mo. This indicates the presence of organisms able to decompose 2-AB in the pre-treated soil and in the perfusing water.     

Time-temperature relationships for the inactivation of sclerotia oF Sclerotium oryzae

The viability of sclerotia of Sclerotium oryzae was tested in both wet and dry soil under simulated elevated temperatures in either constant, cyclic or short temperature regimes. In wet soil viability was reduced to zero by a constant temperature of 45°C and above for 1 day or a minimum oven temperature of 55°C for 2 h. Viability of sclerotia were destroyed by either a 10-day constant temperature of 40°C or a 2-h temperature cycle for 3 days at 50°C or 12 days at 45°C. Below 40°C sclerotia were not affected. In dry soil at 60°C, a 3-day constant temperature or a 12 days 2-h temperature cycle eliminated sclerotial viability. Data on time and temperature relationships on loss in viability of sclerotia in soil could thus be used to predict efficacy of soil solarization.     

Landfill Methane Oxidation in Engineered Soil Columns at Low Temperature

Though engineered covers have been suggested for reducing landfill methane emissions via microbial methane oxidation, little is known about the covers' function at low temperature. This study aimed to determine the methane consumption rates of engineered soil columns at low temperature (4–12°C) and to identify soil characteristics that may enhance methane oxidation in the field. Engineered soils (30 cm thick) were mixtures of sewage sludge compost and de-inking waste, amended with sand (SDS soil) or bark chips (SDB soil). At 4–6°C, we achieved rates of 0.09 gCH₄ kgTS^?1d^?1 (0.02 m³ m^?2d^?1) and 0.06 gCH₄ kgTS^?1d^?1 (0.009 m³ m^?2d^?1) with SDS and SDB soils, respectively. With SDS, good movement and exchange of oxygen in porous soil moderated the slowdown of microbial activity so that the rate dropped only by half as temperature declined from 21–23°C to 4–6°C. In SDB, wet bark chips reduced the soil's air-filled porosity and intensified non-methanotrophic microbial activity, thus reducing the methane consumption rate at 4–6°C to one fourth of that at 21–23°C. In conclusion, soil characteristics such as air-filled porosity, water holding capacity, quantity and stabilization of organic amendments that affect the movement and exchange of oxygen are important variables in designing engineered covers for high methane oxidation at low temperature.     

Seasonal effects on photoassimilated carbon-14 in the root system of blue grama and associated soil organic matter

Blue grama (Bouteloua gracilis (H.B.K.) Lag.) was grown at day (14 h) and night temperatures of 25° and 15°C, respectively, in a ¹⁴CO₂-atmosphere during the last 31 of the 55 days from germination to seed set (period 1). An air-tight seal separated the shoot and root spheres. This period was followed by 21 days of a 14°C day (10 h) and 38°C night regime, and 29 days of continuous ?5°C (period 2), and 26 days of the original temperature and light conditions (period 3). Distribution of the assimilated ¹⁴C at the end of period 1 was: roots 33%; root-derived organic matter in the soil 23%; and 22% was released as CO₂. The washed root mass to root-derived soil organic matter ratio of the labelled ¹⁴C was 60 to 40. A root mass decrease of 45% over the cool and frost period changed this ratio to 23 to 77. Polysaccharides and 0.1 n NaOH-extractable organic matter decreased while potential dehydrogenase activity and total organic P increased during this same period, thereby confirming field related observations. Measured dehydrogenase activity overwinter may have two different origins. As total C content of the soil did not increase under the conditions of the experiment, it was postulated that a portion of the observed increase in total C in the field overwinter was of inorganic rather than organic origin.     

Temperature effects on ammonification and nitrification in a tropical soil

Ammonification of soil organic N and nitrification of ammonium-N was studied in Tindall clay loam over a range of temperatures from 20–60 C. Nitrification rates at each temperature were constant throughout the 28 day incubation, whereas most of the ammonification occurred in the first 7 days. The optimum for nitrification was close to 35 C. exhibiting a sharp peak at this temperature at which the potential rate was 4.8 μg N/g day^?1, compared with 0.5 μg N/g day^?1 at 20°C and 0.25 μg N/g day^?1 at 60°C. The optimum temperature for ammonification was approximately 50°C at which the rate was 2.8 μg N/g day^?1 in the first 7 days but only 0.5 μg N/g day^?1 between 14 and 28 days.The temperature responses could be described mathematically with functions of the type log_oN = k × 1/T.The results are discussed in relation to daily patterns of N mineralization in the field where temperatures show diurnal fluctuation.     

Effects of warming, wetting and nitrogen addition on substrate-induced respiration and temperature sensitivity of heterotrophic respiration in a temperate forest soil

Soil heterotrophic respiration and its temperature sensitivity are affected by various climatic and environmental factors.However,little is known about the combined effects of concurrent climatic and environmental changes,such as climatic warming,changing precipitation regimes,and increasing nitrogen(N)deposition.Therefore,in this study,we investigated the individual and combined effects of warming,wetting,and N addition on soil heterotrophic respiration and temperature sensitivity.We incubated soils collected from a temperate forest in South Korea for 60 d at two temperature levels(15 and 20℃,representing the annual mean temperature of the study site and 5℃warming,respectively),three moisture levels(10%,28%,and 50%water-filled pore space(WFPS),representing dry,moist,and wet conditions,respectively),and two N levels(without N and with N addition equivalent to 50 kg N ha^-1year^-1).On day 30,soils were distributed across five different temperatures(10,15,20,25,and 30℃)for 24 h to determine short-term changes in temperature sensitivity(Q₁₀,change in respiration with 10℃increase in temperature)of soil heterotrophic respiration.After completing the incubation on day 60,we measured substrate-induced respiration(SIR)by adding six labile substrates to the three types of treatments.Wetting treatment(increase from 28%to 50%WFPS)reduced SIR by 40.8%(3.77 to 2.23μg CO₂-C g^-1h^-1),but warming(increase from 15 to 20℃)and N addition increased SIR by 47.7%(3.77 to 5.57μg CO₂-C g^-1h^-1)and 42.0%(3.77 to 5.35μg CO₂-C g^-1h^-1),respectively.A combination of any two treatments did not affect SIR,but the combination of three treatments reduced SIR by 42.4%(3.70 to 2.20μg CO₂-C g^-1h^-1).Wetting treatment increased Q₁₀by 25.0%(2.4 to 3.0).However,warming and N addition reduced Q₁₀by 37.5%(2.4 to 1.5)and 16.7%(2.4 to 2.0),respectively.Warming coupled with wetting did not significantly change Q₁₀,while warming coupled with N addition reduced Q₁₀by 33.3%(2.4 to 1.6).The combination of three treatments increased Q₁₀by 12.5%(2.4 to 2.7).Our results demonstrated that among the three factors,soil moisture is the most important one controlling SIR and Q₁₀.The results suggest that the effect of warming on SIR and Q₁₀can be modified significantly by rainfall variability and elevated N availability.Therefore,this study emphasizes that concurrent climatic and environmental changes,such as increasing rainfall variability and N deposition,should be considered when predicting changes induced by warming in soil respiration and its temperature sensitivity.     

Competition between species of Rhizobium for nodulation of Glycine max

Glycine max cv. Malayan is a promiscuously nodulating cultivar which formed nodules with 6 out of 9 strains of Rhizobium spp of diverse origin and all strains of R. japonicum tested. No generalizations can be made as to the probability of strains isolated from a particular host being infective on Malayan as only some isolated from Centrosema pubescens, and Cajanus cajan were able to form nodules. In competition with R. japonicum at 30°C all 20 strains of Rhizobium spp isolated from Malayan grown in Nigeria formed fewer than 50% of the nodules and 14 strains fewer than 25%. Competition was influenced by root temperature. Three strains of Rhizobium spp were poor competitors with R. japonicum between 24° and 33°C but at 36°C they formed more nodules (74–88%) than R. japonicum. Another strain of Rhizobium spp formed the majority of the nodules between 27° and 36°C whereas R. japonicum formed the most at 24°C.     

Polyethylene mulching of soil to reduce viability of sclerotia of Sclerotium oryzae

Mulching of Sclerotium oryzae infested soil (moist or dry) with polyethylene sheets during hot summer days of May and June increased the soil temperature at 5 cm from 36°C (unmulched) to 48°C (wet) and from 44 to 52°C (dry) and at 20cm from 32 to 38°C (wet) and from 35 to 39°C (dry). In artificially-infested soil, the sclerotia were not eradicated but 95–100% loss in viability was observed at 5 cm by a mulch treatment for 1 week and at 20 cm by mulching for 8 weeks. Mulching effects were not influenced by moisture content of soil or by amendments with lucerne or wheat straw. Mulching of naturally-infested soil at a second site did not eradicate S. oryzae but reduced sclerotial viability by 93%.     

Kinetics of glucose uptake by soil microorganisms

The kinetics of glucose uptake by soil microorganisms was investigated. Soil amended with an inorganic nutrient solution containing C glucose at concentrations of 2.5, 5.0, 10.0 or 20.0 mmol 1⁻¹ was maintained at 4, 12 or 25°C for varying times. The soil was analyzed for glucose, soluble ^14C, total organic ¹⁴C and evolved ¹⁴CO₂ to develop a carbon balance for the system and to define Michaelis-Menten kinetic parameters (K_m and V_max) for glucose uptake at each temperature.Glucose uptake rates, as measured by the depletion of glucose or soluble ¹⁴C from solution, were similar in soils maintained at 12 or 25°C. Based on the depletion of soluble ¹⁴C, values for K_m were 2.25 and 2.43 mmol I⁻¹ at 12 and 25°C, respectively, while V_max values were 0.25 and 1.61 h¹⁴', respectively. Glucose depletion at 4°C was faster than at 12C, while soluble ¹⁴C was removed at a significantly slower rate, suggesting soluble-C intermediates were produced in the 4°C system. Based on Chromatographie techniques and GC-MS, a soluble ¹⁴C-compound accumulating in the 4°C system was identified as maltose. The conversion of glucose to maltose resulted in K_m and V_max values of 17.29 mmol I⁻¹ and 0.12h⁻¹, respectively, for soluble ¹⁴C depletion and 4.96mmol1⁻¹ and 0.43 h⁻, respectively, for glucose depletion at 4δC. These results demonstrate the need to differentiate uptake rates for the parent compound as well as for transitory intermediates excreted into the growth medium. Evolution of CO₂ was shown to be a poor indicator of the rapid disappearance of glucose in soils.     

Effect of Varying Soil Temperatures on the Degradation of Methabenzthiazuron,Isocarbamid and Metamitron

The ¹⁴C-labelled herbicidal active ingredients methabenzthiazuron, isocarbamid and metamitron were subjected to decomposition for 10 to 12 weeks in a degraded loess soil at 65% of maximum water holding capacity. To simulate the field situation, the standardised soil temperature of 0, 10 and 20°C were increased several times by 5 or 10°C, either daily or weekly. The rates of ¹⁴CO₂ evolution clearly showed the delay in degradation as a consequence of lowering the temperature or of the retarded microbial activity. For all 3 herbicidal compounds, a strongly reduced degradation was readily observed at 10°C, and at 0°C degradation stopped almost entirely. Daily temperature increases had only a weak stimulating influence. At the standardised temperature of 20°C, however, daily temperature increases, or temperature increases lasting for a longer period, by 5 or 10°C effected a marked increase in the rates of ¹⁴CO₂-evolution. On the other hand, the higher temperatures led to lower extractability of residual herbicide in the soil. In the case of isocarbamid and metamitron, about 90% of the extracted radioactivity still represented the unchanged active ingredient, whilst, in the case of methabenz-thiazuron, this fraction was between 97 and 100%.     

Upper respiratory tract disease (URTD) as a threat to desert tortoise populations: A reevaluation

The relationships between Mycoplasma agassizii, a causative agent of upper respiratory disease (URTD), and desert tortoise (Gopherus agassizii), generally illustrate the complexities of disease dynamics in wild vertebrate populations. In this review, we summarize current understanding of URTD in Mojave desert tortoise populations, we illustrate how inadequate knowledge of tortoise immune systems may obfuscate assessment of disease, and we suggest approaches to future management of URTD in desert tortoise populations. We challenge the view that M. agassizii causes consistent levels of morbidity and/or mortality across the Mojave desert. Instead, URTD may be described more accurately as a context-dependent disease. In addition, new evidence for relatively high levels of natural antibodies to M. agassizii in desert tortoises suggests possible problems in conventional diagnostic tests of disease in tortoises as well as a possible tortoise immune mechanism to protect against M. agassizii. Partly because of the problems in diagnostic testing, we recommend abandoning policies to euthanize tortoises that test positive for an immune response to M. agassizii. Based on this review, we question management strategies aimed solely at reducing Mycoplasma spp. in desert tortoise populations, and advocate a more careful consideration of extrinsic factors as a cause of symptomatic disease.