11 research outputs found
Taming open/closed string duality with a Losev trick
A target space string field theory formulation for open and closed B-model is
provided by giving a Batalin-Vilkovisky quantization of the holomorphic
Chern-Simons theory with off-shell gravity background. The target space
expression for the coefficients of the holomorphic anomaly equation for open
strings are obtained. Furthermore, open/closed string duality is proved from a
judicious integration over the open string fields. In particular, by
restriction to the case of independence on continuous open moduli, the shift
formulas of [7] are reproduced and shown therefore to encode the data of a
closed string dual.Comment: 22 pages, no figures; v.2 Refs. and a comment added
Pest categorisation of Pantoea stewartii subsp. stewartii
Following a request from the European Commission, the EFSA Plant Health Panel performed a pest
categorisation of Pantoea stewartii subsp. stewartii (hereafter P. s. subsp. stewartii). P. s. subsp. stewartii
is a Gram-negative bacterium that causes Stewartâs vascular wilt and leaf blight of sweet corn and maize,
a disease responsible for serious crop losses throughout the world. The bacterium is endemic to the USA
and is now present in Africa, North, Central and South America, Asia and Ukraine. In the EU, it is reported
from Italy with a restricted distribution and under eradication. The bacterium is regulated according to
Council Directive 2000/29/EC (Annex IIAI) as a harmful organism whose introduction and spread in the
EU is banned on seeds of Zea mays. Other reported potential host plants include various species of
the family Poaceae, including weeds, rice (Oryza sativa), oat (Avena sativa) and common wheat
(Triticum aestivum), as well as jackfruit (Artocarpus heterophyllus), the ornamental Dracaena sanderiana
and the palm Bactris gasipaes, but there is uncertainty about whether these are hosts of P. s. subsp.
stewartii or of the other subspecies. The pest could enter the EU via host plants for planting (including
seed) and via insect vectors from neighbouring countries. Host plants are widely distributed and climatic
conditions are conducive in the EU. P. s. subsp. stewartii could spread by movement of host plants for
planting (including seeds) and insect vectors. Impacts could occur on maize and rice. Methods to certify
pest freedom of maize seeds are available. The main knowledge gaps concern the availability of vectors
in the EU, the level of susceptibility of the maize cultivars grown in the EU, the virulence of strains in
recent outbreaks, and the host range of the bacterium. The criteria assessed by the Panel for
consideration as a potential quarantine pest are met
Scientific Opinion on the pest categorisation of <em>Xanthomonas campestris</em> pv. <em>vesicatoria</em> (Doidge) Dye
The European Commission requested the EFSA Panel on Plant Health to perform the pest categorisation for Xanthomonas campestris pv. vesicatoria, which is the causal agent of bacterial spot of tomato and pepper. X. campestris pv. vesicatoria is not a single taxonomic entity, and four separate species have been described:    X. vesicatoria, X. euvesicatoria, X. perforans and X. gardneri. These organisms can be accurately identified based on a range of discriminative methods. Detection methods are available for seeds. Among the four species described within X. campestris pv. vesicatoria, all except X. gardneri were reported to be present in the EU territory. The host plants (tomato and pepper) are cultivated throughout Europe and conditions are conducive to disease development in open fields in southern Europe and in greenhouses. The disease causes a range of symptoms on aerial parts of plants including fruits. Contaminated seeds and transplants are responsible for long-distance dissemination of the pathogen. Control is mainly based on prevention and exclusion. Extraction of seeds from fruit debris using fermentation and acid treatments and thermotherapy treatments were shown to be effective in reducing the bacterial load in seed lots. No methods and chemical control agents are available that effectively control xanthomonads in infected crops. Although no recent data are available on economic losses caused by these pathogens in the EU, the organisms are considered important bacterial pathogens of tomato and pepper. Infections resulting in up to 30 % losses have been reported. Xanthomonads causing bacterial spot of tomato and pepper meet all criteria defined in International Standard for Phytosanitary Measures (ISPM) 21 and they also meet all ISPM 11 criteria, although X. vesicatoria, X. euvesicatoria and X. perforans are present in the EU territory
Scientific Opinion on the risk to plant health posed by <em>Puccinia horiana</em> Hennings for the EU territory, with the identification and evaluation of risk reduction options
The Panel on Plant Health conducted a pest risk assessment for Puccinia horiana Hennings (the causal agent of chrysanthemum white rust) for the EU territory, identified risk management options and evaluated their effectiveness. The assessment was conducted taking into account current EU legislation. The Panel also provided an opinion on the effectiveness of the present EU requirements against this organism, listed in Council Directive 2000/29/EC. Two major pathways for entry were identified: plant material of susceptible hosts for propagation purposes and cut flowers of Chrysanthemum Ă morifolium. The probability of further entry of the pest was considered unlikely, as the existing certification schemes for propagation material should reduce the risk of importing infected cuttings. For cut flowers, pest transfer to susceptible hosts is associated with the potentially incorrect disposal of cut flower waste within the vicinity of places of production, which is considered a rare event. The probability of establishment and further spread were both considered very likely. The current overall impact in the risk assessment area was considered minor, with medium uncertainty, mainly because standard protective actions are taken in most EU production areas. Risk reduction options to reduce the probability of entry and spread and mitigate the impact were analysed. Council Directive 2000/29/EC addresses mainly the sanitary status of the propagation material. The Directive cannot prevent the entry, establishment and spread, or mitigate the impact, of the pathogen. Were the current regulation to be removed, the frequency of introduction would probably increase. This poses a risk because, although the pest is widespread in the risk assessment area, not all Member States are infested and not all pest pathotypes are present. If a statutory certification system, with associated import requirements for propagation material of host plants, were introduced, this would include practically all prescriptions of the present regulation