Yeasts from Marine and Estuarine Waters with Different Levels of Pollution in the State of Rio de Janeiro, Brazil

Yeast counts were made at 24 marine and estuarine sites in the vicinity of Rio de Janeiro, Brazil. Mean salinities of estuarine sites ranged from 14.2 to 27.4‰, and mean temperatures ranged from 25 to 28°C. Total coliform counts varied from 80% above 100,000 colony-forming units (CFU)/100 ml at heavily polluted sites to 100% below 100 CFU/100 ml at unpolluted sites. Total yeast counts above 100 CFU/100 ml were typical of heavily and moderately polluted water but atypical of lightly polluted and unpolluted water. Mean total yeast counts were 2,880 CFU/100 ml for heavily polluted sites, 202 CFU/100 ml for moderately polluted sites, and 3 CFU/100 ml for lightly polluted and unpolluted sites. Total yeast counts had a positive response to increased pollution levels, and Candida krusei and phenotypically similar yeasts as a group were prevalent in polluted estuarine water but rare in unpolluted seawater. The 549 strains of yeasts and yeast-like organisms isolated were grouped into 67 species, of which the 21 most prevalent made up 86% of the total yeast population. The prevalent genera in the polluted estuary were Candida, Rhodotorula, Torulopsis, Hanseniaspora, Debaryomyces, and Trichosporon.     

Evidence that histidine forms a coordination bond to the A0A and A0B chlorophylls and a second H-bond to the A1A and A1B phylloquinones in M688HPsaA and M668HPsaB variants of Synechocystis sp. PCC 6803

The axial ligands of the acceptor chlorophylls, A_0A and A_0B, in Photosystem I are the Met sulfur atoms of M688_PsaA and M668_PsaB. To determine the role of the Met, His variants were generated in Synechocystis sp. PCC 6803. Molecular dynamics simulations on M688H_PsaA show that there exist low energy conformations with the His coordinated to A_0A and possibly H-bonded to A_1A. Transient EPR studies on M688H_PsaA indicate a more symmetrical electron spin distribution in the A_1A phyllosemiquinone ring consistent with the presence of an H-bond to the C1 carbonyl. Ultrafast optical studies on the variants show that the 150 fs charge separation between P₇₀₀ and A₀ remains unaffected. Studies on the ns timescale show that 57% of the electrons are transferred from A_0A⁻ to A_1A in M688H_PsaA and 48% from A_0B⁻ to A_1B in M668H_PsaB; the remainder recombine with P₇₀₀⁺ with 1/e times of 25 ns and 37 ns, respectively. Those electrons that reach A_1A and A_1B in the branch carrying the mutation are not transferred to F_X, but recombine with P₇₀₀⁺ with 1/e times of ~ 15 μs and ~ 5 μs, respectively. Hence, the His is coordinated to A₀ in all populations, but in a second population, the His may be additionally H-bonded to A₁. Electron transfer from A₀ to A₁ occurs only in the latter, but the higher redox potentials of A₀ and A₁ as a result of the stronger coordination bond to A₀ and the proposed second H-bond to A₁ preclude electron transfer to the Fe/S clusters.     

Genetic consequences of anthropogenic disturbances and population fragmentation in <Emphasis Type="Italic">Acacia senegal</Emphasis>

Acacia senegal is endemic to dry forest and woodland ecosystems of Sub-Saharan Africa and provides both ecological and socio-economic benefits. However, these ecosystems are threatened by escalating human disturbances and fragmentation. To investigate the human impacts on genetic diversity and structure of A. senegal, we studied genetic variability and differentiation of 330 individual trees from 11 natural A. senegal populations, grouped into lightly and heavily disturbed, using 12 polymorphic nuclear microsatellite markers. Gene diversity (H _E ) ranged from H _E = 0.570 to H _E = 0.632. Significant differences (P < 0.05) between the levels of disturbances are reported for mean gene diversity, number of alleles and allelic richness with lightly disturbed populations showing higher values. Overall, the indirect estimates of average outcrossing rates ranged from 0.794 (Kiserian) to 0.999 (Kampi ya Moto) with a mean of 0.997 suggesting a predominantly outcrossing species. There was no significant relationship (P > 0.05) detected between genetic and geographic distances, showing lack of isolation by distance. Analysis of population structure using unweighted pair group method with arithmetic mean and Bayesian model suggests presence of three gene pools as most probable, although most individuals showed mixed ancestry. The diversity and genetic structure reported in this study revealed negative impacts of human disturbance on A. senegal within this ecosystem. We recommend in-situ conservation strategies to safeguard the woodland ecosystem from further deforestation.     

Photosynthetic Light Responses May Explain Vertical Distribution of Hymenophyllaceae Species in a Temperate Rainforest of Southern Chile

Some epiphytic Hymenophyllaceae are restricted to lower parts of the host (<60 cm; 10–100 μmol photons m^-2 s^-1) in a secondary forest of Southern Chile; other species occupy the whole host height (≥10 m; max PPFD >1000 μmol photons m^-2 s^-1). Our aim was to study the photosynthetic light responses of two Hymenophyllaceae species in relation to their contrasting distribution. We determined light tolerance of Hymenoglossum cruentum and Hymenophyllum dentatum by measuring gas exchange, PSI and PSII light energy partitioning, NPQ components, and pigment contents. H. dentatum showed lower maximum photosynthesis rates (A_max) than H. cruentum, but the former species kept its net rates (A_n) near A_max across a wide light range. In contrast, in the latter one, A_n declined at PPFDs >60 μmol photons m^-2 s^-1. H. cruentum, the shadiest plant, showed higher chlorophyll contents than H. dentatum. Differences in energy partitioning at PSI and PSII were consistent with gas exchange results. H. dentatum exhibited a higher light compensation point of the partitioning of absorbed energy between photochemical Y(PSII) and non-photochemical Y(NPQ) processes. Hence, both species allocated energy mainly toward photochemistry instead of heat dissipation at their light saturation points. Above saturation, H. cruentum had higher heat dissipation than H. dentatum. PSI yield (YPSI) remained higher in H. dentatum than H. cruentum in a wider light range. In both species, the main cause of heat dissipation at PSI was a donor side limitation. An early dynamic photo-inhibition of PSII may have caused an over reduction of the Qa⁺ pool decreasing the efficiency of electron donation to PSI. In H. dentatum, a slight increase in heat dissipation due to acceptor side limitation of PSI was observed above 300 μmol photons m^-2s^-1. Differences in photosynthetic responses to light suggest that light tolerance and species plasticity could explain their contrasting vertical distribution.     

Pollution and health risk assessment of heavy metals in urban soil in China

The pollution and potential health risk due to lifetime exposure to heavy metals in urban soil of China were evaluated, based on the urban soil samples collected from published papers from 2005 to 2014. The contamination levels were in the order of Cd > Hg > Cu > Zn > Pb >As > Ni > Cr, and Hg and Cd fell into the category of “moderately contaminated” to “heavily contaminated.” The non-carcinogenic risk for different populations varied greatly, among which children faced high risk, and then the adult female and adult male followed. The hazard index (non-carcinogenic risk) higher than 1.00 occurred in Shanghai, Gansu, Qinghai, Hunan, and Anhui, whereas most of those in northern and western China had low risks. For the carcinogenic risk, Anhui and Ningxia provinces had urban soils exceeding the safe reference (1 × 10^?6–1 × 10^?4). Qinghai and Gansu had high carcinogenic risks since their risk indexes were much closer to the reference, and the others were in low risk.     

长期围封对不同放牧强度下草地植物和AM真菌群落恢复的影响

为探明人为干扰对草地生态系统生态恢复的影响,以不同放牧强度试验草地为研究对象,调查了围封14a后草地植物群落的多样性,并应用第二代高通量测序技术454测序法分析了植物根际土壤中AM真菌的群落结构。研究结果显示,14a围封保育使得不同放牧强度小区与长期封育小区植被盖度及植物多样性指数基本恢复至同一水平。土壤速效磷含量在重度放牧小区最低(1.00 mg/kg),轻度放牧区最高(2.25 mg/kg),其它土壤理化性质指标在不同小区之间没有显著差异。通过分子鉴定发现所有土壤样品中AM真菌共有87个分类单元(VT),隶属于Diversispora、Otospora、Scutellospora、Glomeraceae Glomus、Rhizophagus、Paraglomus和Archaeospora等7个属。对不同放牧强度小区AM真菌进行多样性分析,结果表明长期封育小区AM真菌Shannon多样性指数和Pielou均匀度指数最低,且显著低于中度放牧区,而AM真菌多样性在各放牧小区之间差异不显著。本研究表明长期围封可以有效促进退化草地植物群落的恢复,而AM真菌表现出与植物群落恢复的不同步性。对于草地生态系统退化及恢复过程中植物和土壤功能微生物类群的协同关系还需要进一步系统深入的研究。     

围封对不同退化程度荒漠草原植物群落和土壤的影响

围封是退化草原生态系统恢复的有效措施之一,已在中国北方草原地区实施多年并取得良好的效果。由于不同退化草原生态系统具有完全不同的植被和土壤条件,围封对不同退化草原植物群落和土壤的恢复是否具有一致的影响,目前仍不清楚。对内蒙古地区轻度、中度和重度退化荒漠草原分别设置6年围封后,对植物群落特征和土壤理化性质进行了调查和测定。研究结果发现,围封显著提高了3种退化荒漠草原短花针茅（Stipa breviflora）和无芒隐子草（Cleistogenes songorica）种群以及群落的高度、盖度和地上生物量（P<0.05）,表明围封从多组织层次使退化草原植物群落得到有效的恢复。围封总体提高了轻度和中度退化荒漠草原植物多样性,但降低重度退化荒漠草原的植物多样性。重度退化荒漠草原在围封后群落高度、盖度和地上生物量恢复效率显著高于轻度和中度退化的（P<0.05）,表明围封对重度退化荒漠草原植被恢复更加有效。除轻度退化外,围封显著降低中度和重度退化荒漠草原土壤全碳、全氮、全磷、有效氮和速效磷含量（P<0.05）,但对3种退化荒漠草原的土壤水分含量无显著影响,表明围封对不同退化荒漠草原土壤的影响具有滞后性。研究为荒漠草原围封成效评估提供理论指导和退化荒漠草原生态系统科学合理实施围封政策提供科学依据。     

Lack of Physiological Depth Patterns in Conspecifics of Endemic Antarctic Brown Algae: A Trade-Off between UV Stress Tolerance and Shade Adaptation?

A striking characteristic of endemic Antarctic brown algae is their broad vertical distribution. This feature is largely determined by the shade adaptation in order to cope with the seasonal variation in light availability. However, during spring-summer months, when light penetrates deep in the water column these organisms have to withstand high levels of solar radiation, including UV. In the present study we examine the light use characteristics in parallel to a potential for UV tolerance (measured as content of phenolic compounds, antioxidant activity and maximum quantum yield of fluorescence) in conspecific populations of four Antarctic brown algae (Ascoseira mirabilis, Desmarestia menziesii, D. anceps and Himantothallus grandifolius) distributed over a depth gradient between 5 and 30 m. The main results indicated that a) photosynthetic efficiency was uniform along the depth gradient in all the studied species, and b) short-term (6 h) exposure to UV radiation revealed a high tolerance measured as chlorophyll fluorescence, phlorotannin content and antioxidant capacity. Multivariate analysis of similarity indicated that light requirements for photosynthesis, soluble phlorotannins and antioxidant capacity are the variables determining the responses along the depth gradient in all the studied species. The suite of physiological responses of algae with a shallower distribution (A. mirabilis and D. menziesii) differed from those with deeper vertical range (D. anceps and H. grandifolius). These patterns are consistent with the underwater light penetration that defines two zones: 0–15 m, with influence of UV radiation (1% of UV-B and UV-A at 9 m and 15 m respectively) and a zone below 15 m marked by PAR incidence (1% up to 30 m). These results support the prediction that algae show a UV stress tolerance capacity along a broad depth range according to their marked shade adaptation. The high contents of phlorotannins and antioxidant potential appear to be strongly responsible for the lack of clear depth patterns in light demand characteristics and UV tolerance.     

Interaction of Phytophagous Insects with Salmonella enterica on Plants and Enhanced Persistence of the Pathogen with Macrosteles quadrilineatus Infestation or Frankliniella occidentalis Feeding

Recently, most foodborne illness outbreaks of salmonellosis have been caused by consumption of contaminated fresh produce. Yet, the mechanisms that allow the human pathogen Salmonella enterica to contaminate and grow in plant environments remain poorly described. We examined the effect of feeding by phytophagous insects on survival of S. enterica on lettuce. Larger S. enterica populations were found on leaves infested with Macrosteles quadrilineatus. In contrast, pathogen populations among plants exposed to Frankliniella occidentalis or Myzus persicae were similar to those without insects. However, on plants infested with F. occidentalis, areas of the infested leaf with feeding damage sustained higher S. enterica populations than areas without damage. The spatial distribution of S. enterica cells on leaves infested with F. occidentalis may be altered resulting in higher populations in feeding lesions or survival may be different across a leaf dependent on local damage. Results suggest the possibility of some specificity with select insects and the persistence of S. enterica. Additionally, we demonstrated the potential for phytophagous insects to become contaminated with S. enterica from contaminated plant material. S. enterica was detected in approximately 50% of all M. quadrilineatus, F. occidentalis, and M. persicae after 24 h exposure to contaminated leaves. Particularly, 17% of F. occidentalis, the smallest of the insects tested, harbored more than 10² CFU/F. occidentalis. Our results show that phytophagous insects may influence the population dynamics of S. enterica in agricultural crops. This study provides evidence of a human bacterial pathogen interacting with phytophagous insect during plant infestation.     

A strong conditional mutualism limits and enhances seed dispersal and germination of a tropical palm

Seed predation and seed dispersal can have strong effects on early life history stages of plants. These processes have often been studied as individual effects, but the degree to which their relative importance co-varies with seed predator abundance and how this influences seed germination rates is poorly understood. Therefore, we used a combination of observations and field experiments to determine the degree to which germination rates of the palm Astrocaryum mexicanum varied with abundance of a small mammal seed predator/disperser, Heteromys desmarestianus, in a lowland tropical forest. Patterns of abundance of the two species were strongly related; density of H. desmarestianus was low in sites with low density of A. mexicanum and vice versa. Rates of predation and dispersal of A. mexicanum seeds depended on abundance of H. desmarestianus; sites with high densities of H. desmarestianus had the highest rates of seed predation and lowest rates of seed germination, but a greater total number of seeds were dispersed and there was greater density of seedlings, saplings, and adults of A. mexicanum in these sites. When abundance of H. desmarestianus was experimentally reduced, rates of seed predation decreased, but so did dispersal of A. mexicanum seeds. Critically, rates of germination of dispersed seeds were 5 times greater than undispersed seeds. The results suggest that the relationship between A. mexicanum and H. desmarestianus is a conditional mutualism that results in a strong local effect on the abundance of each species. However, the magnitude and direction of these effects are determined by the relative strength of opposing, but related, mechanisms. A. mexicanum nuts provide H. desmarestianus with a critical food resource, and while seed predation on A. mexicanum nuts by H. desmarestianus is very intense, A. mexicanum ultimately benefits because of the relatively high germination rates of its seeds that are dispersed by H. desmarestianus.     

The intestinal cestode Hymenolepis diminuta as a lead sink for its rat host in the industrial areas of Riyadh,Saudi Arabia

The present study sought to assess the potential of the cestode Hymenolepis diminuta as a bioindicator for lead accumulation in two industrial areas of the city of Riyadh, Saudi Arabia. Rats (Meriones libycus) were collected from two sites (industrial area II and Salbukh) in Riyadh. In the industrial area II, the mean levels of lead concentrations were found to be 1.96, 1.92, 1.4 and 30.72 μg/g in the rats’ liver, kidney and intestine, and in H. diminuta, respectively. In Salbukh, meanwhile, the lead concentrations were 1.63, 1.52, 1.20 and 21.31 μg/g in the rats’ liver, kidney, and intestine, and in H. diminuta, respectively. In addition, in industrial area II, compared with the liver, kidney and intestine of their host, the bioconcentration factors of lead were found to be, respectively, 15.6, 16 and 21.9 times higher in H. diminuta, and were 7.5, 8, and 10.2 times higher in the same organs compared to H. diminuta in Salbukh. The present study, therefore, proved that H. diminuta could be used as a bioindicator for heavy metal contamination in the industrial areas of the city of Riyadh.     

Sterigmatocystin production by nine newly described Aspergillus species in section Versicolores grown on two different media

Nine recently described Aspergillus species and four known species in section Versicolores were tested for their ability to produce sterigmatocystin on two liquid media, Czapek w/20 % Sucrose Broth and Yeast Extract Broth grown in the dark for 1 week at 25 °C. Detection and quantification of ST were performed by reversed-phase liquid chromatography coupled with electrospray ionization ion trap mass spectrometry. Limit of detection was 3 ng/mL and limit of quantification was 10 ng/mL. Nine newly described Aspergillus species from various substrates, A. amoenus, A. creber, A. cvjetkovicii, A. fructus, A. jensenii, A. puulaauensis, A. subversicolor, A. tennesseensis and A. venenatus in section Versicolores were found to produce sterigmatocystin. Production was confirmed in recently collected isolates of A. protuberus and A. versicolor. A. austroafricanus and A. tabacinus did not produce sterigmatocystin.     

Phenotypic responses to light,water, and nutrient conditions in the allopolyploid Arabidopsis suecica and its parent species A. thaliana and A. arenosa: Does the allopolyploid outrange its parents?

Polyploid species possess more than two sets of chromosomes and may show high gene redundancy, hybrid vigor, and masking of deleterious alleles compared to their parent species. Following this, it is hypothesized that this makes them better at adapting to novel environments than their parent species, possibly due to phenotypic plasticity. The allopolyploid Arabidopsis suecica and its parent species A. arenosa and A. thaliana were chosen as a model system to investigate relationships between phenotypic plasticity, fitness, and genetic variation. Particularly, we test if A. suecica is more plastic, show higher genetic diversity, and/or have higher fitness than its parent species. Wild Norwegian populations of each species were analyzed for phenotypic responses to differences in availability of nutrient, water, and light, while genetic diversity was assessed through analysis of AFLP markers. Arabidopsis arenosa showed a higher level of phenotypic plasticity and higher levels of genetic diversity than the two other species, probably related to its outbreeding reproduction strategy. Furthermore, a general positive relationship between genetic diversity and phenotypic plasticity was found. Low genetic diversity was found in the inbreeding A. thaliana. Geographic spacing of populations might explain the clear genetic structure in A. arenosa, while the lack of structure in A. suecica could be due to coherent populations. Fitness measured as allocation of resources to reproduction, pointed toward A. arenosa having lower fitness under poor environmental conditions. Arabidopsis suecica, on the other hand, showed tendencies toward keeping up fitness under different environmental conditions.     

SYNTHETIC HYBRIDS OF HORDEUM BOGDANII WITH ELYMUS CANADENSIS AND SITANION HYSTRIX

Seven viable hybrid seeds were obtained from 48 hand-emasculated Elymus canadensis L., 2n = 28, florets pollinated by Hordeum bogdanii Wilensky, 2n = 14. The hybrids were large, vigorous, and completely sterile plants that bore a closer morphological resemblance to E. canadensis than to H. bogdanii. Chromosome associations in the 21-chromosome hybrids averaged 9.98^I, 5.40^II, and 0.08^III in 264 metaphase-I cells. Chromosome pairing was attributed to allosyndetic pairing between E. canadensis and H. bogdanii chromosomes. The H. bogdanii genome appears to be partially homologous with one of the two E. canadensis genomes. One Sitanion hystrix (Nutt.) J. G. Smith X H. bogdanii hybrid was obtained from a cross involving 37 emasculated S. hystrix florets. This triploid, 2n = 21, hybrid was morphologically intermediate between the parents and totally sterile. Averages of 9.09^I, 5.72^II, and 0.16^III were observed in 106 cells at metaphase I. A modified form of the H. bogdanii genome appears to occur in S. hystrix as well as in E. canadensis. Many allotetraploid Agropyron, Elymus, and Sitanion species apparently contain a genome derived from Hordeum.     

Genetic and morphological contrasts between wild and anthropogenic populations of Agave parryi var. huachucensis in south-eastern Arizona

Background and Aims

At least seven species of Agave, including A. parryi, were cultivated prehistorically in Arizona, serving as important sources of food and fibre. Many relict populations from ancient cultivation remain in the modern landscape, offering a unique opportunity to study pre-Columbian plant manipulation practices. This study examined genetic and morphological variation in six A. p. var. huachucensis populations of unknown origin to compare them with previous work on A. parryi populations of known origin, to infer their cultivation history and to determine whether artificial selection is evident in populations potentially managed by early agriculturalists.

Methods

Six A. p. var. huachucensis and 17 A. parryi populations were sampled, and morphometric, allozyme and microsatellite data were used to compare morphology and genetic structure in purportedly anthropogenic and wild populations, as well as in the two taxa. Analysis of molecular variance and Bayesian clustering were performed to partition variation associated with taxonomic identity and hypothesized evolutionary history, to highlight patterns of similarity among populations and to identify potential wild sources for the planting stock.

Key Results A

p. var. huachucensis and A. parryi populations differed significantly both morphologically and genetically. Like A. parryi, wild A. p. var. huachucensis populations were more genetically diverse than the inferred anthropogenic populations, with greater expected heterozygosity, percentage of polymorphic loci and number of alleles. Inferred anthropogenic populations exhibited many traits indicative of past active cultivation: greater morphological uniformity, fixed heterozygosity for several loci (non-existent in wild populations), fewer multilocus genotypes and strong differentiation among populations.

Conclusions

Where archaeological information is lacking, the genetic signature of many Agave populations in Arizona can be used to infer their evolutionary history and to identify potentially fruitful sites for archaeological investigation of ancient settlements and cultivation practices. The same approach can clearly be adopted for other species in similar situations.     

Plant morphology and grazing history:

Grazing-related, intraspecific, morphological variation was studied in four North American grasses (Bouteloua gracilis, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii) from eight locales in Wind Cave National Park, South Dakota: three locales currently occupied and heavily grazed by prairie dogs (Cynomys ludovicianus), colonized (since settlement) for 2–100 years, where native ungulates concentrate grazing activities; an extinct colony locale from which prairie dogs were removed 30 years previously, moderately to lightly grazed by ungulates; two noncolony locales, moderately to lightly grazed by ungulates; and two locales from within a 50-year-old grazing exclosure, with no known history of grazing by prairie dogs nor any recent grazing by ungulates. Data were collected both in situ and in common environments.Active-colony plants were more frequently and more heavily grazed than those at other grazed locales. In situ, plants from heavily grazed populations were smaller and more prostrate than those from populations with little or no grazing (including the extinct colony) and interpopulation variation corresponded to current grazer use. After several growing seasons in common environments, there were still significant interpopulation differences; however, variation often corresponded with grazing history. Although differences between active-colony and noncolony plants were somewhat reduced (indicating some phenotypic plasticity), active-colony plants were still smaller and more prostrate. However, extinct-colony plants more closely resembled active-colony plants than noncolony plants. Morphological variation among these populations is the result of more than simple grazer use; historical factors and the dynamic nature of the grazing regimes are also contributing factors.Abbreviations A. gerardii Andropogon gerardii - A. smithii Agropyron smithii - BFC Bison Flats colony locale - BFN noncolony locale at Bison Flats - B. gracilis Bouteloua gracilis - EXT Upper Highland extinct-colony locale - GDN common garden - GH greenhouse - NEW new satellite colony locale - PVC Pringle Valley colony locale - PVN noncolony locale in Pringle Valley - S. scoparium Schizachyrium scoparium - WCNP Wind Cave National Park, South Dakota, USA - XFN exclosure locale just inside exclosure fence from BFN - XHQ exclosure locale near headquarters buildings     

褐梗天牛幼虫和成虫空间分布的地统计学研究

褐梗天牛(Arhopalus rusticus Linnaeus)是一种对松、杉、柏等林木危害非常严重的蛀干害虫,主要危害针叶树的衰弱木以及火灾后的枯立木,是继松褐天牛之后携带拟松材线虫能力最强的蛀干害虫。为了更好地控制其危害,深入地研究其种群空间格局,运用地统计学方法分析了3块受害程度不同的油松林内褐梗天牛幼虫和成虫的空间分布特性。结果表明:3种受害程度不同的林分内,褐梗天牛的危害具有显著差异,轻度受害林分内有虫株率为30.8%,中度受害林分内有虫株率为44.3%,而重度受害林分内高达78.3%。根据变异函数曲线图分析得知:轻度受害林、中度受害林和重度受害林内褐梗天牛幼虫种群空间分布最优拟合模型分别为高斯模型、高斯模型和指数模型,成虫的种群空间分布最优拟合模型均为线性模型。在3种林分中褐梗天牛幼虫数量具有明显的空间依赖性,轻度受害林、中度受害林和重度受害林内幼虫数量的空间依赖范围分别是19.10、11.97、61.98m,其空间连续性强度分别是0.646、0.784和0.500;成虫的空间依赖范围分别是43.08、43.23、44.17m,其空间连续性强度分别是0.044、0.021和0.171,但其成虫的数量在空间呈随机分布,没有表现出空间依赖性。根据垂直分布图分析得出:褐梗天牛幼虫和成虫在油松上主要集中聚集在某个高,然后随着高度增加密度降低,随着高度接近地面密度也降低。用Kriging插值法生成的空间分布图显示幼虫在空间分布上具有明显的聚集性,其聚集中心主要集中在林地中心,由林地中心株向整个林地扩散,而成虫则表现为随机分布。     

Prevalence of the Alternaria blight of cumin (Cuminum cyminum L.) in Bangladesh: Morphology,phylogeny and pathogenic variation of Alternaria spp.

Cumin (Cuminum cyminum L.) is an important spice crop worldwide and its production is hampered by the infection of Alternaria blight. Cultivation of cumin in Bangladesh is very limited due to the lack of appropriate germplasm and adequate scientific information regarding the prevalence of Alternaria blight. Field trials were conducted with four advanced lines of cumin viz. CN026, CN028, CN031 and CN038 in five agro-ecological zones (AEZ) to know the adaptation possibility of these lines against the incidence and severity of Alternaria blight of cumin in Bangladesh. Among all lines, CN026 was found as the best in germination capacity and other yield parameters in all locations. The incidence and severity of the disease was observed as high as 98% and 88%, respectively, however, out of the five locations, the incidence and severity of the disease was the lowest in Bogura for the line CN026. In an attempt to identify the causal organism of the Alternaria blight of cumin by using molecular tools, a total of twenty three isolates were collected from the plants showing Alternaria blight symptoms from different AEZ in Bangladesh. Based on the molecular analysis, the isolates were identified as Alternaria alternata, A. burnsii, A. gaisen and A. tenuissima. A. alternata was the most prevalent species followed by A. tenuissima. The isolates of the identified species were found to have genetic, morphological and pathogenic variation. An isolate of A. alternata was observed as the most virulent among the isolates. This is the first report of A. alternata causing Alternaria blight disease of cumin in Bangladesh. The findings of this experiment will help in selecting suitable cumin germplasm and designing proper management strategies against Alternaria blight of cumin in Bangladesh.     

Economic Feasibility of Using Switchgrass Pasture to Produce Beef Cattle Gain and Bioenergy Feedstock

Integration of switchgrass (Panicum virgatum L.) into livestock production systems has potential to improve farm economics and encourage development of a biofuel industry in the Southern Great Plains. The objectives of this study were to determine the economics of seven alternative switchgrass grazing and bioenergy feedstock systems and to determine how sensitive the results are among the systems for a range of cattle and feedstock prices. Data were collected from a completely randomized designed grazing study in south-central Oklahoma in 2008, 2009, and 2010. Stocking density treatments [0, 2.5, 4.9 and 7.4 hd ha^?1] were randomly assigned to 12 0.81-ha switchgrass pastures. Using biological data from the field trial, economic data collected from the marketplace and assumptions about prices of bioenergy feedstock, seven production systems were simulated. The systems included no-graze feedstock only (NG/FS); graze lightly no feedstock (GL/NF); graze moderately no feedstock (GM/NF); graze heavily no feedstock H/NF)]; lightly grazed plus feedstock (GL/F); moderately grazed plus feedstock (GM/F); and heavily grazed plus feedstock (GH/F). Enterprise budgeting was used to compute expected net returns for the seven systems. Random-effects mixed ANOVA models were used to determine the effects of production system on yield, gain, and net return. At a feedstock price $0 Mg^?1, the GM/NF was the most profitable ($45 ha^?1) system. At feedstock prices of $55 and $83 Mg^?1, the GL/F system realized net returns of $232 and $523 ha^?1, respectively, and for feedstock prices >$83 Mg^?1, the NG/FS system was determined to be most economical.     

Release of Lungworm Larvae from Snails in the Environment: Potential for Alternative Transmission Pathways

Background

Gastropod-borne parasites may cause debilitating clinical conditions in animals and humans following the consumption of infected intermediate or paratenic hosts. However, the ingestion of fresh vegetables contaminated by snail mucus and/or water has also been proposed as a source of the infection for some zoonotic metastrongyloids (e.g., Angiostrongylus cantonensis). In the meantime, the feline lungworms Aelurostrongylus abstrusus and Troglostrongylus brevior are increasingly spreading among cat populations, along with their gastropod intermediate hosts. The aim of this study was to assess the potential of alternative transmission pathways for A. abstrusus and T. brevior L3 via the mucus of infected Helix aspersa snails and the water where gastropods died. In addition, the histological examination of snail specimens provided information on the larval localization and inflammatory reactions in the intermediate host.

Methodology/Principal Findings

Twenty-four specimens of H. aspersa received ~500 L1 of A. abstrusus and T. brevior, and were assigned to six study groups. Snails were subjected to different mechanical and chemical stimuli throughout 20 days in order to elicit the production of mucus. At the end of the study, gastropods were submerged in tap water and the sediment was observed for lungworm larvae for three consecutive days. Finally, snails were artificially digested and recovered larvae were counted and morphologically and molecularly identified. The anatomical localization of A. abstrusus and T. brevior larvae within snail tissues was investigated by histology. L3 were detected in the snail mucus (i.e., 37 A. abstrusus and 19 T. brevior) and in the sediment of submerged specimens (172 A. abstrusus and 39 T. brevior). Following the artificial digestion of H. aspersa snails, a mean number of 127.8 A. abstrusus and 60.3 T. brevior larvae were recovered. The number of snail sections positive for A. abstrusus was higher than those for T. brevior.

Conclusions

Results of this study indicate that A. abstrusus and T. brevior infective L3 are shed in the mucus of H. aspersa or in water where infected gastropods had died submerged. Both elimination pathways may represent alternative route(s) of environmental contamination and source of the infection for these nematodes under field conditions and may significantly affect the epidemiology of feline lungworms. Considering that snails may act as intermediate hosts for other metastrongyloid species, the environmental contamination by mucus-released larvae is discussed in a broader context.