Biology and epidemics of Candidatus Liberibacter species,psyllid‐transmitted plant‐pathogenic bacteria

Candidatus Liberibacter species are Gram‐negative bacteria that live as phloem‐limited obligate parasites in plants, and are associated with several plant diseases. These bacteria are transmitted by insects called psyllids, or jumping plant lice, which feed on plant phloem sap. Citrus huanglongbing (yellow shoot) or citrus greening disease is associated with three different species of Ca. Liberibacter – Ca. L. asiaticus, Ca. L. africanus and Ca. L. americanus – all originally found on different continents. Ca. L. asiaticus is the most severe pathogen, spread by Asian citrus psyllid Diaphorina citri and causing devastating epidemics in several countries. Ca. L. africanus occurs in Africa where it is spread by the African citrus psyllid Trioza erytreae. Ca. Liberibacter solanacearum is associated with diseases in several solanaceous plants, and transmitted by potato psyllid Bactericera cockerelli. Zebra chip disease is causing large damage in potato crops in North America. In Europe Ca. Liberibacter solanacearum is associated with diseases of the Apiaceae family of plants, carrot and celery, and transmitted by psyllids Trioza apicalis and Bactericera trigonica. When Ca. Liberibacter is suspected as the disease agent, the diagnosis is confirmed by DNA‐based detection methods. Ca. Liberibacter‐associated plant diseases can be controlled by using healthy plant propagation material, eradicating symptomatic plants, and by controlling the psyllid populations spreading the disease.     

Spatially Explicit Assessment of Sandhill Crane Exposure to Potential Transmission Line Collision Risk

Infrastructure development can affect avian populations through direct collision mortality. Estimating the exposure of local bird populations to the risk of direct mortality from infrastructure development requires site- and species-specific data, which managers may find difficult to obtain at the scale over which management decisions are made. We quantify the potential exposure of sandhill cranes (Antigone canadensis) to collision with horizontal structures (e.g., transmission lines) within vital wintering grounds of the Middle Rio Grande Valley (MRGV), New Mexico, USA, 2014–2020. Limited maneuverability and visual acuity make sandhill cranes vulnerable to collisions with infrastructure bisecting their flight paths. We used data from 81 global positioning system (GPS)-tagged cranes to estimate the spatially explicit flight height distribution along the MRGV, the passage rate across hypothetical transmission lines, and the resulting exposure rate (exposed passes/crane/day). The exposure rate ranged from 0–0.28 exposed passes/crane/day (median = 0.015) assuming an exposure zone of 7–60 m above ground level, and identified hotspots of potential exposure within the MRGV. Mapped exposure rates can assist in the siting of proposed high-voltage transmission lines, or other infrastructure, to limit effects on sandhill cranes and other avian species at risk of collision. Our approach can be replicated and applied in similar situations where birds are exposed to possible collision with power lines. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

硬粒小麦 长穗偃麦草2E和4E附加系及E染色体传递

为探讨长穗偃麦草E染色体在硬粒小麦背景中的传递特点,利用染色体特异分子标记、基因组原位杂交(GISH)、非变性荧光原位杂交(ND FISH)等方法,对小偃麦8801(AABBEE)与硬粒小麦(AABB)杂交后代中选育的株系Du_No.2和Du_No.4进行了分析。结果表明：(1)分子标记检测株系Du_No.2及Du_No.4分别能扩增出长穗偃麦草2E、4E染色体特异条带。(2)GISH和ND FISH分析显示,株系Du_No.2和Du_No.4分别附加了1条2E和4E染色体,表明株系Du_No.2 和Du_No.4分别为硬粒小麦 长穗偃麦草2E和4E单体附加系。(3)2个株系的减数分裂过程观察发现,后期Ⅰ、Ⅱ和末期Ⅱ都有E染色体分离异常现象,且株系Du_No.2和 Du_No.4的异常率分别为22.24%和36.18%。(4)2个株系分别与硬粒小麦进行正反杂交的后代PCR分析表明, 2E和4E染色体经雄配子的传递率分别为4.41%和2.17%,而通过雌配子的传递率都为零,表明2E和4E染色体在硬粒小麦背景中能通过雄配子传递,但不通过雌配子的传递。该研究为创建全套硬粒小麦 长穗偃麦草双体附加系及代换系提供基础。     

Transmission routes of Salmonella Typhimurium DT 104 between 14 cattle and pig herds in Denmark demonstrated by molecular fingerprinting

AIMS: Salmonella Typhimurium DT 104 is generally assumed to be spread by contact between live animals, e.g. by trading. The aim of the present study was to assess the importance of other routes of transmission in the dissemination of this bacterium. METHODS AND RESULTS: An outbreak among 14 cattle and pig herds located in a geographically narrow area in Denmark was investigated. Epidemiological information and disease history of the herds was obtained through interviews. Based on this, the hypothesis for horizontal spread was proposed, and these were confirmed by comparison of the pulsed field gel electrophoresis (PFGE) and the plasmid profiles of isolates obtained by continuous sampling over a period of almost 3 years. CONCLUSIONS: The study indicated that other routes might play an important role, than the trading of live animals, in the spread of S. Typhimurium DT 104 among livestock. SIGNIFICANCE AND IMPACT OF THE STUDY: Salmonella Typhimurium DT 104 infected herd might pose a significant risk to herds located within the same geographic area. In advising on how to avoid the spread of this bacterium, factors like person contacts, sharing of equipment and contaminated slurry should be focussed on in addition to infected animals.     

Contrasting scales of oviposition and parasitism in praying mantids

We report on spatial patterns of parasitism of oothecae (egg cases) of praying mantises (Stagmomantis limbata) by torymid wasps, Podagrion spp. Using collections of mapped mantid oothecae from Riparian sites in the Sonoran desert and Grassland sites in the Chiricahua Mountains (both in Arizona, USA), we characterized the spatial distributions of oothecae and parasitism. The likelihood of an egg case suffering some parasitism was higher at Grassland sites, which had high oothecal densities, than at low-density Riparian sites. However, experimental isolation of Grassland oothecae to densities comparable to Riparian sites reduced parasitism rates. At Riparian sites, parasitized oothecae exhibited on average the same extent of parasitism as parasitized oothecae at high densities but with much greater variation. Indeed, large fractions of Riparian oothecae suffered both severe (>50%) and light (<20%) parasitism, whereas most parasitized Grassland oothecae suffered intermediate levels of parasitism. Analysis of first nearest neighbor distances indicated that the parasite load of an ootheca did not depend on its immediate isolation. However, extending the analysis to include subsequent nearest neighbors (using a technique from spatial statistics called the R(K) function), we found that even though oothecae of S. limbata were spatially clustered, some oothecae in a (statistically defined) cluster escaped parasitism when overall oothecal densities were low. This pattern suggests that when oothecae are sparsely distributed, Podagrion wasps exploit only a fraction of the oothecae available locally, even though the oothecae are strongly aggregated relative to their overall density. We suggest this lack of congruency in the scales of oothecal deposition and parasitism at low densities (which is absent when oothecae are at high densities) may be explained in part by behavioral aspects of the parasite's reproduction, including increased host fidelity by relatively sedentary female parasites. Received: June 13, 2000 / Accepted: October 16, 2000     

High levels of congenital transmission of Toxoplasma gondii in a commercial sheep flock

Our current understanding of congenital transmission of Toxoplasma gondii from ewe to lamb dictates that infection frequently results in abortion and the death of the developing foetus, that the birth of live infected lambs occurs rarely and that the cat is the predominant source of infection in ewes. Using direct polymerase chain reaction detection of T. gondii, we report high levels of congenital transmission occurring in a commercially managed sheep flock. We sampled foetal-derived placental tissue and tissues from aborted lambs and showed that congenital transmission was detected in these tissues from 61% of all pregnancies. Where pregnancies resulted in the death of one or more lambs, T. gondii was detected in the lamb tissue for all but one of 18 (94%) pregnancies. Of the successful pregnancies resulting in the birth of live lambs we were able to detect T. gondii in foetal-derived placental tissue from 37 of 70 (42%) pregnancies. These results show that congenital transmission is occurring in a high percentage of lambings including normal healthy lambings, at this farm, suggesting that this route of transmission from generation to generation may be much more significant than that reported previously. These results may have implications for sheep husbandry and future epidemiological studies of T. gondii.     

Investigation of a preferentially transmitted Aegilops sharonensis chromosome in wheat

Summary An attempt to produce a set of addition lines of Aegilops sharonensis to the wheat variety Chinese Spring produced only one addition line. This was due to preferential transmission of one chromosome from Ae. sharonensis. This chromosome was studied in detail by established cytological methods of chromosome observation and by the newer techniques of C-banding and in situ hybridization of a cloned DNA sequence. The chromosome was found to be partially homologous to an Ae. sharonensis chromosome of similar behaviour in another wheat addition line. The incomplete homology of the two Ae. sharonensis chromosomes was due to the presence of a translocated segment of a wheat chromosome. — Substitution lines of the Ae. sharonensis chromosome for wheat homoeologous group 4 were produced and the Ae. sharonensis chromosome thereby designated 4 S ^l .