Short answers, pulled from the story.
Dutch elm disease is caused by a microfungus transmitted by two species of Scolytus bark beetles. The first, less aggressive strain, Ophiostoma ulmi, arrived in Europe from Asia in 1910 and was accidentally introduced to North America in 1928. A second, far more virulent strain, Ophiostoma novo-ulmi, appeared in the United States in the 1940s and first reached Britain in the early 1970s via a cargo of Canadian rock elm.
An American white elm in Boston, Massachusetts served as the Liberty Tree, the site of the first colonial resistance meetings against British taxation from 1765 onward. When British forces felled it in 1775 to destroy this symbol of rebellion, Americans responded by planting Liberty Elms widely and sewing elm symbols onto their revolutionary flags.
Elm wood's interlocking grain and resistance to splitting made it the material of choice for wagon-wheel hubs, ship keels, chair seats, and coffins. Hollowed elm trunks were used as water pipes throughout medieval Europe, and elm timbers were sunk as piers in the original London Bridge. The first written references to elm in construction appear in Linear B lists from Knossos in the Mycenaean period, which record elm chariots and wheels.
In Greek mythology, the nymph Ptelea, whose name means elm, was one of the eight hamadryads, daughters of Oxylos and Hamadryas. In the Iliad, mountain nymphs plant elms on the tomb of Eetion after Achilles kills him, and the elms planted on the tomb of Protesilaus, the first Greek to fall at Troy, were said to wither whenever they caught sight of the ruins of Troy.
Elms that are sterile, such as English elm Ulmus minor 'Atinia', are reproduced by vegetative methods including the winter transplanting of root suckers, hardwood cuttings, softwood cuttings, grafting, ground and air layering, and micropropagation. Transplanting root suckers remains the easiest and most common method for European field elm and its hybrids. Mutant weeping cultivars such as 'Camperdown' and 'Horizontalis' are grafted at two to three metres height.
Breeding programmes began in the Netherlands in 1928, followed by North America in 1937, Italy in 1978, and Spain in 1986. Notable results include the cultivars 'Valley Forge' and 'Jefferson' in the United States, and transgenic American elms that showed reduced disease symptoms in trials reported in 2007 by researchers at the State University of New York. The National Elm Trial in North America, begun in 2005, is assessing the nineteen leading cultivars over a ten-year period.