John Bailey Special threats posed by the Japanese Knotweed by ruq19861



                                                             John Bailey

                  Special threats posed by the Japanese Knotweed invasion
             Le particolari minacce causate dalla diffusione del poligono giapponese

     Fallopia japonica var. japonica is nowadays viewed                    F. japonica var. japonica. Currently all seed produced is
as a persistant and noxious weed (Beerling et al., 1994)                   hybridogenous, but some of the hermaphrodite 8x F. ×
but it was originally introduced to Europe in the 1840’s                   bohemica plants are perfectly fertile and inter crossable
as an expensive and highly valued garden plant via the                     with F. japonica var. japonica. Spread of such plants
commercial nursery of Philipp Franz von Siebold in                         and the possibility of a few generations of back-crossing
Leiden. Historical research indicated that only male-                      recreating the missing hermaphrodite F. japonica var.
sterile (female) plants of this gynodioecious taxon were                   japonica are two outcomes best avoided.
introduced (Bailey & Conolly, 2000). Molecular stud-                           The occurrence of thousands of hectares of male ster-
ies at Leicester con¿rmed that all the material tested                     ile Àowers of F. japonica var. japonica around the world,
from a survey of the United Kingdom belonged to a                          without access to congeneric pollen has proved to be a
single clone (Hollingsworth & Bailey, 2000). The small                     vast unintended breeding experiment – since any member
number of individuals tested from outside the UK also                      of the Polygonaceae capable of pollinating it has done so.
belonged to this clone. Lack of genetic diversity has had                  Most notably the ubiquitous hybrid between F. japonica
little effect on this plant and due to its strong powers of                and F. baldschuanica (Bailey, 2001; Bailey & Spencer,
vegetative reproduction it has managed to spread exten-                    2003) which brings together two taxa that no one would
sively throughout northern & western Europe and North                      have previously regarded as even remotely close enough
America, and to a lesser extent in southern Europe and                     to hybridise, but is this just the tip of the iceberg? This
Australasia. Within 20 years of the introduction of F.                     hybrid was only uncovered by a careful cytological study
japonica, the arrival of hermaphrodite individuals of its                  of open-pollinated Fallopia seed, not something that
congener F. sachalinensis (again with limited genetic di-                  has been done outside the UK the Czech Republic and
versity: Pashley et al., 2007) allowed seed to be formed                   Belgium. An important and relevant question to pose is -
via hybridisation to give the hybrid F. × bohemica, which                  how many more such ‘hopeful monsters’ await discovery
has since turned out to be a more persistent pest than ei-                 around the world and what further consequences could
ther of its parents, and is rapidly spreading through Eu-                  they have?
rope and North America (Bailey & Wisskirchen, 2006;                            In the UK we have a very interesting legislative situ-
Bailey et al., 1996; Bímová et al., 2001). By crossing                     ation regarding Japanese Knotweed. Section 14 of the
with F. sachalinensis the plants have regained much of                     farsighted 1981 Wildlife and Countryside Act made it an
the genetic diversity that they lacked in their founder                    offence for any person who “… plants or otherwise causes
populations. Another important feature of these plants is                  to grow in the wild ...” Japanese Knotweed or Giant Hog-
polyploidy, ranging from diploid to decaploid and with                     weed (Heracleum mantegazzianum). Here the situation
all points in between. Even the hybrid F. × bohemica                       rested for many years and no convictions were ever made
is commonly found at three different ploidy levels 4x,                     under the act for Japanese Knotweed. However move-
6x and 8x, with different proportions of the japonica                      ment of soil contaminated with Japanese Knotweed rhi-
and sachalinensis genomes and important differences                        zome during construction work remained a major cause
in fertility. Polyploidy in perennials with strong vegeta-                 of spread of the plant. In the 1990 Environment Protection
tive reproduction mechanisms is in some measure a rec-                     Act such soil contaminated with Japanese Knotweed was
ipe for evolution. Such high polyploids are shielded by                    classi¿ed as controlled waste and its disposal was strictly
their multiple genomes from the effects of aneuploidy,                     regulated. This has focussed much attention on Japanese
are able to undergo wide hybridisations and the result-                    Knotweed and placed a monetary value on the remedia-
ant perennial offspring can maintain themselves almost                     tion of Knotweed infested redevelopment sites; Wembley
inde¿nitely until a rare event such as allopolyploidy or                   Stadium and the London Olympic sites being two high
the chance meeting of two balanced stable gametes from                     pro¿le examples. This in turn has led to a proliferation of
infertile parents, brings a return to fertility. Seed collect-             ¿rms specialising in J      oval and intense interest in de-
ed from open pollinated F. × bohemica plants can vary                      veloping more cost effective methods of dealing with
enormously in chromosome number, yet most plants are                       infestation. These vary from removal of all infested soil
perfectly viable and indistinguishable from normal eu-                     (and a wide safety margin of non-infested soil) from the
ploid hybrids in everything but chromosome number.                         site in special covered vehicles, and deposition in regis-
Given that the two parents of F. × bohemica have differ-                   tered deep land-¿ll sites, to excavation and on site burial
ent native distribution ranges (F. sachalinensis occurring                 of material secured by geotextile membranes. It should be
much further north and F. japonica much further south)                     noted that it is not in the ¿nancial interests of such com-
it seems highly likely that the genome rearrangements                      panies to quash exaggerated media claims of the dangers
caused by such hybridisations could easily lead to the                     caused by this plant.
production of individuals much better suited to the par-                       Outside of the building industry UK control efforts
ticular adventive climate that they happen to ¿nd them-                    are fairly fragmented and often driven forward by partic-
selves in. In addition to these sorts of rearrangement is                  ular highly motivated individuals operating at a regional
the question of the restoration of sexual reproduction to                  level, such as the Cornish Knotweed Forum founded in

1997. Even the biological control program has depended                    Bailey J. P. & Conolly A. P., 2000 – Prize-Winners to Pa-
on the determination of a single individual to both forge                    riahs, a History of Japanese Knotweed s.l. (Polygo-
the alliance of funding bodies and to superintend the re-                    naceae) in the British Isles. Watsonia, 23: 93-110.
search program. Funding for the latter has come from                      Bailey J. P. & Spencer M., 2003 – New records for Fal-
such disparate bodies as Network Rail, Cornwall County                       lopia × conollyana: is it truly such a rarity? Watsonia,
Council and the Welsh Assembly. In October 2008 CABI                         24: 452-453.
Bioscience announced that it had ¿nished the demanding                    Bailey J. P. & Wisskirchen R., 2006 – The distribution
testing program on potential biocontrol agents imported                      and origins of Fallopia × bohemica (Polygonaceae) in
from Japan and were seeking government approval for                          Europe. Nordic Journal of Botany, 24: 173-200.
the release of the Japanese Psyllid Aphalara itadori. It is               Beerling D. J., Bailey J. P. & Conolly A. P., 1994 – Bi-
estimated that a decision will not be made before 2010                       ological Flora of the British Isles No.183 Fallopia
and even then there is no certainty that permission will                     japonica. Journal of Ecology, 82 (4): 959-979.
be granted. Even if the release is permitted it will not                  Bímová K., Mandák B. & Pyšek P., 2001 – Experimen-
act as a magic bullet, it will still require public educa-                   tal control of Reynoutria congeners: a comparative
tion and conventional eradication programs to continue                       study of a hybrid and its parents. In: Plant invasions:
if we are ever to halt the relentless onward march of this                   Species ecology and ecosystem management. Brundu
plant.                                                                       G., Brock J., Camarda I., Child L. & Wade M. (eds.).
                                                                             Backhuys Publisher, Leiden: 283-290.
                                                                          Hollingsworth M. L. & Bailey J. P., 2000 – Evidence for
                       References                                            massive clonal growth in the invasive weed Fallopia
                                                                             japonica (Japanese Knotweed). Botanical Journal of
Bailey J. P., 2001 – Fallopia × conollyana The Railway-                      the Linnaean Society, 133: 463-472.
   yard Knotweed. Watsonia, 23: 539-541.                                  Pashley C. H., Bailey J. P. & Ferris C., 2007 – Clonal
Bailey J. P., Child L. E. & Conolly A. P., 1996 – A sur-                     diversity in British populations of the alien invasive
   vey of the distribution of Fallopia × bohemica (Chrtek                    Giant Knotweed, Fallopia sachalinensis (F. Schmidt)
   & Chrtkova) J. Bailey (Polygonaceae) in the British                       Ronse Decraene, in the context of European and Japa-
   Isles. Watsonia, 21: 187-198.                                             nese plants. Watsonia, 26: 359-371.

                                                              John Bailey
                            Biology Department, University of Leicester, Leicester LE1 7RH, United Kingdom

                                   Le specie alloctone in Italia: censimenti, invasività e piani di azione
                     Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano
                                                        Volume XXXVI – Fascicolo I

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