Embryo rescue of cucumber (Cucumis sativus), muskmelon (C. melo) and some wild Cucumis species (C. anguria, C. zeyheri, and C. metuliferus)

Cucumis sativus is one of the most economically important crops of the Cucurbitaceae. Recent cucumber cultivars are susceptible to some serious diseases and pests, including downy mildew, powdery mildew, nematodes, and spider mites. Sources of resistance to these pathogens and pests were identified in some accessions of wild Cucumis species. One possible way of introducing these resistances into cucumber germplasm is interspecific hybridization. However, C. sativus is sexually incompatible with nearly all other Cucumis species, because of substantially different chromosome numbers, n = 7 in C. sativus versus n = 12 in C. melo and most wild Cucumis species. Overcoming this obstacle can be accomplished through the use of embryo rescue and/or ovule culture. Results of experiments using these methods, especially of embryo rescue of cucumber and selected wild Cucumis species after intra- and interspecific hybridization, are summarized in this paper. Various culture media and selected genotypes were tested in our experiments. Successful regeneration of mature embryos of some Cucumis spp. was observed on all types of media, and callus or sporadic plant formation from immature embryos and seeds occurred on media with coconut water and gibberellic acid

A set of Cucurbitaceae taxa for differentiation of Pseudoperonospora cubensis pathotypes

Cucurbit downy mildew (Pseudoperonospora cubensis) is characterized by large variation in pathogenicity, specificity and host-parasite interactions. This report reviews the current state of understanding regarding interactions between P. cubensis and Cucurbitaceae, the genetic control of host reactions, and overall variation within the pathogen. A well-characterized set of differential Cucurbitaceae taxa and genotypes for the identification ofP. cubensis pathotypes or races has not yet been designated. A preliminary set designated by Thomas et al. (1987) was, in certain cases, deficient in taxonomic description, determination of membership at the level of accession, uniformity of differential response, and international availability. An improved differential set of cucurbit accessions for characterization of pathogenic variability of P. cubensis isolates is proposed in this paper. The proposed set includes 12 taxa from six genera (Benincasa, Citrullus, Cucumis, Cucurbita, Lagenaria and Luffa). These differentials are natural host plants of P. cubensis, and basic information on their host-parasite specificity and variability is available. The members of this new set are taxonomically well characterized and available as genebank accessions. The data about host genera and pathogen variation summarized here fully support previous reports about the existence of distinct physiological forms (pathotypes and races) of P. cubensis, and a tetrade coding system is offered to designate P. cubensis pathotypes. This paper presents evidence that such forms may be delimited based on host genus, species and intraspecific specificities. This proposed differential set of Cucurbitaceae should serve as an appropriate baseline for more detailed research about P. cubensis isolate variation and population structure at the pathotype level. Steps to foster international collaboration on this topic are suggested and discussed

Factors affecting protoplast isolation and cultivation of Cucumis spp.

Protoplasts of Cucumis anguria, Cucumis melo (3 accessions), Cucumis metuliferus and Cucumis sativus were isolated from leaves, growing apices, hypocotyls and calluses. Plants were cultured on 2 concentrations of sucrose. The effect of plant culture medium, explant age and explant type on protoplast viability were investigated. The protoplasts were cultured in 3 types of culture medium and at two temperatures. Optimal age range for protoplast isolation was 1-5 weeks depending on explant type and genotype. Viabilities ranging between 50 % and 80 % were obtained from all explants and genotypes. Increased concentration of sucrose had negative impact on viability of protoplasts. The highest level of regeneration achieved was callus, regenerated from leaf protoplasts of C. melo cv. ‘Charentais’ and C. melo ‘MR-1’. The lowest regeneration capability was observed in hypocotyls. Liquid LCM medium (B5 macro and microelements (1 g · l-1 CaCl2), B5 vitamins with 1g· l-1 myo-inositol, 2 mg· l-1 ascorbic acid, 0.8 mg· l-1 glycine, 20 mg· l-1 glutamine, 100 mg · l-1 casein hydrolysate, 70 g · l-1 mannitol, 10 g · l-1 sucrose, 5 g · l-1 glucose, 585 mg · l-1 MES, 5.37 μmol· l-1 NAA, 2.26 μmol· l-1 2,4-D, 2.22 μmol · l-1 BA) was optimal for protoplast regeneration. Agarose-solidified medium caused a decrease in the number of cell divisions (used in C. melo ‘PI 124112’). Cultivation at 25ºC resulted in a higher frequency of cell divisions (tested in C. metuliferus)

Spatially uniform calibration of a liquid xenon detector at low energies using 83m-Kr

A difficult task with many particle detectors focusing on interactions below ~100 keV is to perform a calibration in the appropriate energy range that adequately probes all regions of the detector. Because detector response can vary greatly in various locations within the device, a spatially uniform calibration is important. We present a new method for calibration of liquid xenon (LXe) detectors, using the short-lived 83m-Kr. This source has transitions at 9.4 and 32.1 keV, and as a noble gas like Xe, it disperses uniformly in all regions of the detector. Even for low source activities, the existence of the two transitions provides a method of identifying the decays that is free of background. We find that at decreasing energies, the LXe light yield increases, while the amount of electric field quenching is diminished. Additionally, we show that if any long-lived radioactive backgrounds are introduced by this method, they will present less than 67E-6 events/kg/day in the next generation of LXe dark matter direct detection searchesComment: 9 pages, 9 figures. Accepted to Review of Scientific Instrument

Oidium neolycopersici: Intra-specific variability inferred from AFLP analysis and relationship with closely related powdery mildew fungi infecting various plant species

Previous works indicated a considerable variation in the pathogenicity, virulence, and host range of Oidium neolycopersici isolates causing tomato powdery mildew epidemics in many parts of the world. In this study, rDNA internal transcribed spacer (ITS) sequences, and amplified fragment length polymorphism (AFLP) patterns were analyzed in 17 O. neolycopersici samples collected in Europe, North America, and Japan, including those which overcame some of the tomato major resistance genes. The ITS sequences were identical in all 10 samples tested and were also identical to ITS sequences of eight previously studied O. neolycopersici specimens. The AFLP analysis revealed a high genetic diversity in O. neolycopersici and indicated that all 17 samples represented different genotypes. This might suggest the existence of either a yet unrevealed sexual reproduction or other genetic mechanisms that maintain a high genetic variability in O. neolycopersici. No clear correlation was found between the virulence and the AFLP patterns of the O. neolycopersici isolates studied. The relationship between O. neolycopersici and powdery mildew anamorphs infecting Aquilegia vulgaris, Chelidonium majus, Passiflora caerulea, and Sedum alboroseum was also investigated. These anamorphs are morphologically indistinguishable from and phylogenetically closely related to O. neolycopersici. The cross-inoculation tests and the analyses of ITS sequences and AFLP patterns jointly indicated that the powdery mildew anamorphs collected from the above mentioned plant species all represent distinct, but closely related species according to the phylogenetic species recognition. All these species were pathogenic only to their original host plant species, except O. neolycopersici which infected S. alboroseum, tobacco, petunia, and Arabidopsis thaliana, in addition to tomato, in cross-inoculation tests. This is the first genome-wide study that investigates the relationships among powdery mildews that are closely related based on ITS sequences and morphology. The results indicate that morphologically indistinguishable powdery mildews that differed in only one to five single nucleotide positions in their ITS region are to be considered as different taxa with distinct host ranges

The Nature of Incomes of Small Entrepreneurship and the Theoretical Bases of Their Taxation

The article is aimed at studying the essence and nature of incomes of natural persons of entrepreneurship in the structure of factor incomes. The main identification attributes and features of such incomes are analyzed. The views of the leading scholars on the theoretical bases of taxation of incomes from small business are characterized alongside with influence of taxation on performance of the basic public functions of entrepreneurship on the part of natural persons. It is proved that connection of entrepreneurial incomes with peculiarities of their taxation is manifested in two aspects. First, in terms of distribution of the tax burden between different types of factorial incomes, secondly, distribution of the tax burden between economic entities which have chosen different models of economic behavior. Prospect for further researches in this direction is evaluation of influence of taxation on the economic activity of entrepreneurs, structure of production, and distribution of incomes of taxes

Positronic lithium, an electronically stable Li-e+^+ ground state

Calculations of the positron-Li system were performed using the Stochastic Variational Method and yielded a minimum energy of -7.53208 Hartree for the L=0 ground state. Unlike previous calculations of this system, the system was found to be stable against dissociation into the Ps + Li$^+$ channel with a binding energy of 0.00217 Hartree and is therefore electronically stable. This is the first instance of a rigorous calculation predicting that it is possible to combine a positron with a neutral atom and form an electronically stable bound state.Comment: 11 pages, 2 tables. To be published in Phys.Rev.Let

From Multiview Image Curves to 3D Drawings

Reconstructing 3D scenes from multiple views has made impressive strides in recent years, chiefly by correlating isolated feature points, intensity patterns, or curvilinear structures. In the general setting - without controlled acquisition, abundant texture, curves and surfaces following specific models or limiting scene complexity - most methods produce unorganized point clouds, meshes, or voxel representations, with some exceptions producing unorganized clouds of 3D curve fragments. Ideally, many applications require structured representations of curves, surfaces and their spatial relationships. This paper presents a step in this direction by formulating an approach that combines 2D image curves into a collection of 3D curves, with topological connectivity between them represented as a 3D graph. This results in a 3D drawing, which is complementary to surface representations in the same sense as a 3D scaffold complements a tent taut over it. We evaluate our results against truth on synthetic and real datasets.Comment: Expanded ECCV 2016 version with tweaked figures and including an overview of the supplementary material available at multiview-3d-drawing.sourceforge.ne