Generative propagation of Robinia x ambigua POIR. – Pink locust

The genus Robinia is a small group of about 10 species of trees and shrubs indigenous only to NorthAmerica. Two species are endemicto Mexico, one being confined to south-western part of the country, while the rest are endemic to the south-eastern part of USA. Of the mostimportant species and varieties of genus Robinia, Robinia x ambigua Poir.(Robinia viscosa x R. pseudo-acacia)-pink locust can be considered asthe most significant one for bee-forage and decorative planting. In this paper a generative propagation method is presented for pink locust

Generative propagation of Robinia x ambigua POIR. – Pink locust

The genus Robinia is a small group of about 10 species of trees and shrubs indigenous only to NorthAmerica. Two species are endemic to Mexico, one being confined to south-western part of the country, while the rest are endemic to the south-eastern part of USA. Of the most important species and varieties of genus Robinia, Robinia x ambigua Poir.(Robinia viscosa x R. pseudo-acacia)-pink locust can be considered as the most significant one for bee-forage and decorative planting. In this paper a generative propagation method is presented for pink locust

Clonal selection of black locust (Robinia pseudoacacia L.) in Hungary: a review

Black locust (Robinia pseudoacacia L.) is the most important fast growing stand-forming tree species in Hungary. Its importance is increasing in many other countries, too. As a result of a new selection programme 13 black locust clones have been improved for setting up clones trials and seed orchard. In 2003 five of them (R.p. `Bácska', `Homoki', 'Szálas', `Oszlopos' and `Vacsi') were registered as cultivar­candidates. Tissue culture method has proved as a suitable mean of propagating superior individuals. The micropropagated plants have been growing successfully in the clone trials

Clonal selection of black locust (Robinia pseudoacacia L.) in Hungary: a review

Black locust (Robinia pseudoacacia L.) is the most important fast growing stand-forming tree species in Hungary. Its importance is increasing in many other countries, too. As a result of a new selection programme 13 black locust clones have been improved for setting up clones trials and seed orchard. In 2003 five of them (R.p. `Bácska', `Homoki', 'Szálas', `Oszlopos' and `Vacsi') were registered as cultivar­candidates. Tissue culture method has proved as a suitable mean of propagating superior individuals. The micropropagated plants have been growing successfully in the clone trials

Equality of domination and transversal numbers in hypergraphs

A subset <i>S</i> of the vertex set of a hypergraph ℋ is called a dominating set of ℋ if for every vertex <i>v</i> not in <i>S</i> there exists <i>u ∈ S</i> such that <i>u</i> and <i>v</i> are contained in an edge in ℋ. The minimum cardinality of a dominating set in ℋ is called the domination number of ℋ and is denoted by γ(ℋ). A transversal of a hypergraph ℋ is defined to be a subset <i>T</i> of the vertex set such that <i>T ⋂ E ≠ Ø</i> for every edge <i>E</i> of ℋ. The transversal number of ℋ, denoted by <i>t</i>.(ℋ), is the minimum number of vertices in a transversal. A hypergraph is of rank <i>k</i> if each of its edges contains at most <i>k</i> vertices. The inequality <i>t</i>(ℋ) = γ(ℋ) is valid for every hypergraph ℋ without isolated vertices. In this paper, we investigate the hypergraphs satisfying <i>t</i>(ℋ) = γ(ℋ), and prove that their recognition problem is NP-hard already on the class of linear hypergraphs of rank 3, while on unrestricted problem instances it lies inside the complexity class ϴ ^p₂. Structurally we focus our attention on hypergraphs in which each subhypergraph ℋ¹ without isolated vertices fulfills the equality <i>t</i>(ℋ¹) = (ℋ¹). We show that if each induced subhypergraph satisfies the equality then it holds for the non-induced ones as well. Moreover, we prove that for every positive integer <i>k</i>, there are only a finite number of forbidden subhypergraphs of rank <i>k</i>, and each of them has domination number at most <i>k</i>