Introduction
The European Black Poplar Populus nigra or Water Poplar to give it its old English
name, was once one of our most important timber trees, its springy, impact resistant and
low resin content - almost fireproof timber - making it the wood of choice for such
specialist applications as wagons and rifle butts and more generally, only second to oak
as roofing and flooring timbers. With the influx of imported timbers of other species it
has largely fallen out of use and the number of remaining trees is declining fast, with
probably no more than 10,000 individuals left in this country. In contrast the artificial
hybrid between it and the American Cotton Wood Populus deltoides is now planted in
the UK in millions, as the tree of choice for shelter belts and amenity plantings. Poplars
have separate male and female trees, and as a consequence of the vast number of hybrid
males in the countryside, and the relative small number of scattered P. nigra females,
most of the females are pollinated by the foreign hybrids, and very little if any true P.
nigra seed is being produced. (Females are seldom planted because they produce vast
quantities of fluff with their seeds, covering the ground several inches deep in 'cotton
wool'). In addition the Lombardy Poplar, a fastigiate clonal mutant of P. nigra is also
widely planted and is a further source of contaminating pollen. True Populus nigra,
(including italica) usually have spiral galls on their leafstalks due to the aphid Pemphigus
spyrothecae. These never occur on any of the Cotton Wood or Balsam Poplar hybrids.
DNA Fingerprinting
As for all living organisms, Black Poplars have a DNA fingerprint unique to an indi-
vidual. Many trees however, including Black Poplars, are propagated vegetatively, i.e.
through cuttings or layering, and these will therefore share the same genetic fingerprint
as the tree they were taken from.
Preliminary DNA analysis has shown that there is very little remaining genetic variation
between our surviving UK veteran trees. This means that should a virulent pathogenic
virus or fungus appear on our trees from abroad, as has happened with the monoclonal
vegetatively propagated English Elm, unless we can maintain the small amount of genetic
variation we have left in the population, the consequences will be catastrophic. Such a
disease, a lethal fungal infection, Poplar Scab, has already wiped out a large number of
Water Poplars P. nigra in the Manchester area. Fortunately the scab strain involved does
not seem to be able to be able to survive the drier warmer climate of southern England,
but another strain already prevalent in northern Italy could potentially do so.
Aims & Objectives of this DNA Fingerprinting
This project is therefore aimed at sampling the genetic diversity of our trees in Essex, to
find out just how many identical genetic clones we have in the county. Trees propagated
(cloned) vegetatively by cuttings/trunchions will be genetically identical so if you have
Water Poplars on your land and you know how they got there or have propagated them
your self this information would be extremely useful, as we would only need a single
sample from the clone.
Essex Field Club Newsletter No. 58, January 2009 9