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Alan H Gibson - One of the best experts on this subject based on the ideXlab platform.
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diversity and genetic structure of a natural population of rhizobium leguminosarum bv trifolii isolated from trifolium subterraneum l
Molecular Ecology, 1995Co-Authors: David H Demezas, Terry Reardon, Steven R Strain, John M Watson, Alan H GibsonAbstract:A collection of 121 isolates of Rhizobium leguminosarum biovar (bv.) trifolii was obtained from root nodules of Trifolium subterraneum L. (subclover) plants growing in an established pasture. The collection consisted of a single isolate from each of 18 plants sampled from seven microplots. The following year, a further 28 and 27 isolates were collected from the first and seventh sampling points, respectively. Analysis of restriction fragment length polymorphisms (RFLPs) of both chromosomal and Sym (symbiotic) plasmid DNA and multilocus enzyme electrophoresis (MLEE) were used to assess the diversity, genetic relationships and structure of this population. Symbiotic effectiveness tests were used to examine the symbiotic phenotype of each isolate collected in the first year. Analysis of RFLPs of the first year isolates revealed 13 chromosomal types and 25 Sym plasmid types. Similar Sym plasmid types were grouped into 14 families containing 1–6 members. No new chromosomal types and six new Sym plasmid types were detected in the second year. The symbiotic effectiveness of the first year isolates of the same Sym plasmid type was similar. Significant differences in symbiotic effectiveness were detected between different Sym plasmid types in the same plasmid family. Representative isolates of each chromosomal type Sym plasmid type identified in the first year were analysed using multilocus enzyme electrophoresis. Mean genetic diversity per locus was high (0.559). Enzyme electrophoresis revealed 17 electrophoretic types (ETs). Ouster analysis of the enzyme data revealed large genetic diversity amongst the ETs. Strong linkage disequilibrium was observed for the population as a whole, i.e. clonal population structure, but significantly less disequilibrium was observed among a cluster of ETs suggesting that recombination occurred between ETs within the cluster. Our results revealed that a population of naturally occurring isolates of Rhizobium leguminosarum bv. trifolii can be genetically diverse and support the possibility that recombination plays a role in generating new genotypes.
Boaz Tsaban - One of the best experts on this subject based on the ideXlab platform.
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The Hurewicz covering property and slaloms in the Baire space, Fundamenta Mathematicae 181
2012Co-Authors: Boaz TsabanAbstract:Abstract. According to a result of Kočinac and Scheepers, the Hurewicz covering property is equivalent to a somewhat simpler selection property: For each sequence of large open covers of the space one can choose finitely many elements from each cover to obtain a groupable cover of the space. We simplify the characterization further by omitting the need to consider sequences of covers: A set of reals X satisfies the Hurewicz property if, and only if, each large open cover of X contains a groupable Subcover. The proof uses a rigorously justified abuse of notation and a “structure ” counterpart of a combinatorial characterization, in terms of slaloms, of the minimal cardinality b of an unbounded family of functions in the Baire space. In particular, we obtain a new characterization of b. 1
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The Hurewicz covering property and slaloms in the Baire space, submitted
2012Co-Authors: Boaz TsabanAbstract:Abstract. According to a result of Kočinac and Scheepers, the Hurewicz covering property is equivalent to a somewhat simpler selection property: For each sequence of large open covers of the space one can choose finitely many elements from each cover to obtain a groupable cover of the space. We simplify the characterization further by omitting the need to consider sequences of covers: A set of reals X has the Hurewicz property if, and only if, each large open cover of X contains a groupable Subcover. This solves in the affirmative a problem of Scheepers. The proof uses a rigorously justified abuse of notation and a “structure ” counterpart of a combinatorial characterization, in terms of slaloms, of the minimal cardinality b of an unbounded family of functions in the Baire space. In particular, we obtain a new characterization of b. 1
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THE HUREWICZ COVERING PROPERTY AND SLALOMS IN THE BAIRE SPACE
2004Co-Authors: Boaz TsabanAbstract:Abstract. According to a result of Kočinac and Scheepers, the Hurewicz covering property is equivalent to a somewhat simpler selection property: For each sequence of large open covers of the space one can choose finitely many elements from each cover to obtain a groupable cover of the space. We simplify the characterization further by omitting the need to consider sequences of covers: A set of reals X satisfies the Hurewicz property if, and only if, each large open cover of X contains a groupable Subcover. This solves in the affirmative a problem of Scheepers. The proof uses a rigorously justified abuse of notation and a “structure ” counterpart of a combinatorial characterization, in terms of slaloms, of the minimal cardinality b of an unbounded family of functions in the Baire space. In particular, we obtain a new characterization of b. 1
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THE HUREWICZ COVERING PROPERTY AND SLALOMS IN THE BAIRE SPACE
2003Co-Authors: Boaz TsabanAbstract:Abstract. According to a result of Kočinac and Scheepers, the Hurewicz covering property is equivalent to a somewhat simpler selection property: For each sequence of large open covers of the space one can choose finitely many elements from each cover to obtain a groupable cover of the space. We simplify the characterization further by omitting the need to consider sequences of covers: A set of reals X satisfies the Hurewicz property if, and only if, each large open cover of X contains a groupable Subcover. The proof uses a “structure ” counterpart of a combinatorial characterization, in terms of slaloms, of the minimal cardinality b of an unbounded family of functions in the Baire space. In particular, we obtain a new characterization of b. 1
Peter J Bottomley - One of the best experts on this subject based on the ideXlab platform.
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AN ABSTRACT OF THE THESIS OF Blanca Valdivia de Cap ' for the degree of Master of Science in Microbiology presented on January 19. 1987. Title: Indigenous Rhizobium trifolii Isolated From Nodules of Red Clover Grown in Subclovet Pasture Soils. Abstract ap
2016Co-Authors: Peter J BottomleyAbstract:A series of identification methods were used to determine the composition of Rhizobium trifolii populations in nodules recovered from uninoculated red clover (Trifolium pratense L) cv. 'florie ' grown in two acidic Oregon soils. Both soils, Abiqua and Whobrey had been in subclover subterraneum L.) pasture for thirty to forty years. The red clover isolates, 24 from Abiqua and 30 from Whobrey soils, were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to elucidate their protein profile patterns. Serological assays performed with antisera raised to two representative isolates from each soil type, revealed that 30 and 47 % of the Whobrey isolates were clustered into two serogroups, WR 26 and WR 27, respectively. A third serogroup, AR 21, made up 50 % of the Abiqua isolates. Each set of isolates was also challenged to antisera raised to major serogroups previously recovered and identified from subclover grown in the respective soils. Gel-immune-diffusion studies indicated that none of the Whobrey isolates were antigenically identical to serogroups WS 1-01 or WS 2-01, previously discovered in this soil. A similar analysis of the Abiqua isolates revealed that only 2 isolates were antigenically identical to any of the
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serological and ecological characteristics of a nodule dominant serotype from an indigenous soil population of rhizobium leguminosarum bv trifolii
Applied and Environmental Microbiology, 1994Co-Authors: Kamtin Leung, Kathryn Yap, Narjes Dashti, Peter J BottomleyAbstract:Although at least 13 antigenically distinct serotypes of Rhizobium leguminosarum bv. trifolii exist in an Abiqua silty clay loam soil, one serotype, AS6, occupies ≥50% of the root nodules formed on field-grown subclover and between 33 and 78% of the nodules formed on five annual clover species grown in the same soil under laboratory conditions. The dominance of subclover nodules by serotype AS6 was reproducible over a 4-year sampling period and throughout the entire 200- by 100-m pasture examined. Serotype AS6 was composed of three antigenically distinct subtypes (AS6-a, AS6-b, and AS6-c). Each subtype contributed about one-third of the AS6 isolates recovered from nodules of field-grown subclover plants and maintained similar population densities in nonrhizosphere and rhizosphere soil. Rhizobia with the AS6 antigenic signature accounted for from 20 to 100% of the soil populations of R. leguminosarum in arable and pasture soils under legumes throughout the state of Oregon. Over a 12-month period, the population densities of the serotype AS6 complex and three minor nodule-occupying serotypes (AG4, AP17, and AS21) were measured in the rhizospheres of field-grown subclover and orchard grass and in nonrhizosphere Abiqua soil. Regardless of season or serotype, the orchard grass rhizosphere effect was minimal, with the ratio between rhizosphere and nonrhizosphere serotype population densities ranging between 2.5 (midsummer) and 10.5 (spring). In contrast, the magnitude of the subclover rhizosphere effect varied seasonally and among serotypes. Between October and December the ratios for all serotypes were similar (12.5 to 25.5). However, in the spring (April and May), the magnitude of the rhizosphere effect varied among the indigenous serotypes (ratios, 10.5 to 442) and for minor nodule-occupying serotypes AS21 (ratio, 442) and AP17 (ratio, 47) was as great as, or even greater than, the magnitude of the rhizosphere effect observed with the AS6 complex (ratio, 65.5).
Arnold W Miller - One of the best experts on this subject based on the ideXlab platform.
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A Nonhereditary Borel-cover γ-set
2015Co-Authors: Arnold W MillerAbstract:In this paper we prove that if there is a Borel-cover γ-set of car-dinality the continuum, then there is one which is not hereditary. In this paper we answer some of the questions raised by Bartoszyński and Tsaban [1] concerning hereditary properties of sets defined by certain Borel covering properties. Define. An ω-cover of a set X is a family of sets such that every finite subset of X is included in an element of the cover but X itself is not in the family. Define. A γ-cover of a set X is an infinite family of sets such that every element of X is in all but finitely many elements of the family. Define. A set X is called a Borel-cover γ-set iff every countable ω-cover of X by Borel sets contains a γ-cover. These concepts were introduced by Gerlits and Nagy [5] for open covers. Being a Borel-cover γ-set is equivalent to saying that for any ω-sequence of countable Borel ω-covers of X we can choose one element from each and get a γ-cover of X – this is denoted S1(BΩ,BΓ). The equivalence was proved by Gerlitz and Nagy [5] for open covers but the proof works also for Borel covers as was noted in Scheepers and Tsaban [8]: Let Bn be Borel ω-covers of X. Since {U ∩ V: U ∈ U, V ∈ V} is an ω-cover if U and V are, we may assume that Bn+1 refines Bn. Let xn for n < ω be distinct elements of X and let B = {A \ {xn} : n < ω,A ∈ Bn} It is easy to check that B is an ω-cover of X. Now let C be a γ-Subcover of B. Note that for any fixed n at most finitely many of the elements of C ca
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a nonhereditary borel cover gamma set
Real analysis exchange, 2004Co-Authors: Arnold W MillerAbstract:In this paper we prove that if there is a Borel-cover γ-set of cardinality the continuum, then there is one which is not hereditary. In this paper we answer some of the questions raised by Bartoszynski and Tsaban [1] concerning hereditary properties of sets defined by certain Borel covering properties. Define. An ω-cover of a set X is a family of sets such that every finite subset of X is included in an element of the cover but X itself is not in the family. Define. A γ-cover of a set X is an infinite family of sets such that every element of X is in all but finitely many elements of the family. Define. A set X is called a Borel-cover γ-set iff every countable ω-cover of X by Borel sets contains a γ-cover. These concepts were introduced by Gerlits and Nagy [5] for open covers. Being a Borel-cover γ-set is equivalent to saying that for any ω-sequence of countable Borel ω-covers of X we can choose one element from each and get a γ-cover of X – this is denoted S1(BΩ,BΓ). The equivalence was proved by Gerlitz and Nagy [5] for open covers but the proof works also for Borel covers as was noted in Scheepers and Tsaban [8]: Let Bn be Borel ω-covers of X. Since {U ∩ V : U ∈ U , V ∈ V} is an ω-cover if U and V are, we may assume that Bn+1 refines Bn. Let xn for n < ω be distinct elements of X and let B = {A \ {xn} : n < ω,A ∈ Bn} It is easy to check that B is an ω-cover of X. Now let C be a γ-Subcover of B. Note that for any fixed n at most finitely many of the elements of C can Thanks to the Fields Institute for Research in Mathematical Sciences at the University of Toronto for their support during the time this paper was written and to Juris Steprāns who directed the special program in set theory and analysis. Mathematics Subject Classification 2000: 03E50; 03E17
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The cardinal characteristic for relative γ-sets
2004Co-Authors: Arnold W MillerAbstract:Abstract: For X a separable metric space define p(X) to be the smallest cardinality of a subset Z of X which is not a relative γ-set in X, i.e., there exists an ω-cover of X with no γ-Subcover of Z. We give a characterization of p(2 ω) and p(ω ω) in terms of definable free filters on ω which is related to the psuedointersection number p. We show that for every uncountable standard analytic space X that either p(X) = p(2 ω) or p(X) = p(ω ω). We show that both of following statements are each relatively consistent with ZFC: (a) p = p(ω ω) < p(2 ω) and (b) p < p(ω ω) = p(2 ω) First we define γ-set. An open cover U of a topological space X is an ω-cover iff for every finite F ⊆ X there exists U ∈ U with F ⊆ U. The space X is a γ-set iff for every ω-cover of X there exists a sequence (Un ∈ U: n < ω) such that for every x ∈ X for all but finitely many n we have x ∈ Un, equivalently X = ⋃ ⋂ Un or ∀x ∈ X ∀ ∞ n ∈ ω x ∈ Un. m<ω n>m We refer to the sequence (Un: n < ω) as a γ-cover of X, although technically we are supposed to assume that the Un are distinct. In this paper all our spaces are separable metric spaces, so we may assume that all ω-covers are countable. This is because we can replace an arbitrary ω-cover with a refinement consisting of finite unions of basic open sets. The γ-sets were first considered by Gerlits and Nagy [5]. One of the things that they showed was the following. The psuedointersection number p is defined as follows: p = min{|F | : F ⊆ [ω] ω has the FIP and ¬∃X ∈ [ω] ω ∀Y ∈ F X ⊆ ∗ Y
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Infinite Combinatorics and Definability
1996Co-Authors: Arnold W MillerAbstract:The topic of this paper is Borel versions of infinite combina-torial theorems. For example it is shown that there cannot be a Borel subset of [!] which is a maximal independent family. A Borel version of the delta systems lemma is proved. We prove a parameterized version of the Galvin-Prikry Theorem. We show that it is consistent that any! 2 cover of reals by Borel sets has an! 1 Subcover. We show that if V=L then there ar
I V Castro - One of the best experts on this subject based on the ideXlab platform.
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nodulation and growth of subterranean clover trifolium subterraneum l in soils previously treated with sewage sludge
Soil Biology & Biochemistry, 1995Co-Authors: Eric M Ferreira, I V CastroAbstract:Abstract A 2-year pot experiment testing the use of sewage sludges as fertilizers for subclover plants was carried out under greenhouse conditions. Two limed soil samples (leptosol and Luvisol) and two anaerobically digested sewage sludges (Evora and Belmonte) were used at the rates of 5, 10, 20 and 60 t ha −1 , together with a standard mineral fertilizer-treated (PK) sample and an untreated control. Half the pots with the Leptosol received sludge from Evora and the other half sludge from Belmonte. The soils in all pots were inoculated with a mixture of two indigenous selected Rhizobium leguminosarum bv. trifolii strains. The Luvisol was amended with the sludge from Evora, soil in half of the pots being inoculated with the Rhizobium inoculum. In the first year, the number of nodules and dry weight of shoots increased with lower rates of sludge amendments but decreased with the highest rate (60 t ha −1 ), except dry weights on the Luvisol. With the standard mineral fertilization, the number of nodules and dry weight of shoots were always significantly superior to the other treatments. On the Luvisol, the number of nodules and the dry weight of shoots of the inoculated pots of all treatments were significantly superior to the uninoculated pots. In the second year, the number of nodules and dry weight of shoots increased with all rates of sludge amendments. The harmful effects of the highest rates of sludges disappeared at 60 t ha −1 and the number of nodules and dry weight of shoots were superior to the standard mineral fertilization. The effect of rhizobial inoculation still remained, but to a smaller extent, probably due to an increase of the rhizobial population and breakdown of soil organic matter. Both sludges can be used as organic fertilizers. The sludge from Evora however, was superior to that from Belmonte, probably as a result of larger amounts of nutrients associated with a higher pH value.
