[NHCOLL-L:1685] Does gamma irradiation damage herbarium specimens?

[Bronwyn.Collins at csiro.au]

Does gamma irradiation damage herbarium specimens so they are unsuitable for
future DNA research (such as comparing taxa to establish relatedness)? Is
anyone able to give us advice on this, or refer us to someone who could?

Our institution is constantly exporting and importing herbarium specimens,
both as loans and as gifts/exchanges. Our specimens consist mainly of
pressed and dried plant specimens mounted by means of glue or tape onto
card. The specimens we deal with come from all over the world.
 
Routinely, incoming specimens are cold treated for 7 days at -18 degrees C.
This does not damage the specimens. 

However, any prohibited specimens, such as weeds or specimens containing
soil or bark, must be treated more savagely, if they are to be removed from
a quarantine approved facility (for example, to be incorporated into our
collections), and these treatments may damage the herbarium specimens. (The
aim is to devitalise weed seeds, so that they cannot grow if they somehow
get out into the environment, and to kill all types of pathogens including
fungal, bacterial, viral etc that might be in soil or bark, for the same
reason.)
 
The usual treatment we have applied is gamma irradiation at 25 kGray (2.5 M
rad). This does not damage the specimens morphologically, but we have
assumed that the irradiation makes the specimens useless for any future DNA
work. (We only have this treatment applied to specimens which are being
incorporated into our own collections. Prohibited material on loan from
other institutions is worked on in a quarantine approved area prior to
re-export, to ensure that the other institution's material is not damaged in
any way by quarantine treatments.)
 
The other treatments that are available (heat treatments, ethylene oxide)
would damage the specimens morphologically, and damage the mounting card,
labels and glue or tape.

If you would like to see the details of treatments open to us, you can find
our current quarantine rules at 
 
http://www.aqis.gov.au/icon/asp/ex_casecontent.asp?intNodeId=358&intCommodit
yId=923&Types=none&WhichQuery=Go+to+full+text

Bronwyn Collins
Loans Officer
Australian National Herbarium
GPO Box 1600
Canberra ACT 2615
AUSTRALIA