DNA Fingerprinting of all Veteran European Black Poplar trees in Essex by Dr Ken Adams, BSBI

Introduction

The European Black Poplar (Populus nigra) or   Water Poplar to give it its old English name, as 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 riffle buts 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 leaf stalks 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 individual. 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.