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NOTICES 
lated viruses with small (<10‘ daltons) 
single-stranded DNA genomes. These 
viruses are not known to integrate into 
host chromosomes or to incorporate 
cellular genes into their genomes. 
CaMV is spread in nature by aphids, in 
which it survives for a few hours. 
Spontaneous mutants of CaMV which 
lack a factor essential for aphid trans- 
mission arise frequently. BGMV is 
spread in nature by whiteflies. and 
certain other single-stranded DNA 
plant viruses are transmitted by leaf- 
hoppers. These single-stranded plant 
viruses persist for days or weeks in 
their Insect vectors, but are thought 
not to replicate there. 
The DNA plant viruses have narrow 
host ranges and are relatively difficult 
to transmit mechanically to plants. 
For this reason, they are most unlike- 
ly to be accidentally transmitted from 
spillage of purified virus preparations. 
When these viruses are used as vec- 
tors in intact plants, or propagative 
plant parts, the plants should be 
grown under PI conditions— that is, in 
either a limited access greenhouse or 
plant growth cabinet which is insect- 
proof. preferably with positive air 
pressure, and in which an insect fumi- 
gation regime is maintained. Soil, 
plant pots, and unwanted infected 
plant materials should be removed 
from the greenhouse or cabinet in 
sealed insect-proof containers and 
sterilized. It is not necessary to steril- 
ize run-off water from the infected 
plants, as this is not a plausible route 
for secondary infection. When the vir- 
uses are used as vectors in tissue cul- 
tures or in small plants in axenic cul- 
tures. no special containment is recom- 
mended Infected plant materials 
which have to be removed from the 
greenhouse or cabinet for further re- 
search. should be maintained under 
insect-proof conditions. These meas- 
ures provide an entirely adequate 
degree of containment. They are simi- 
lar to those required in many coun- 
tries for licensed handling a l exotic" 
plant viruses. 
The CaMV strain used as a elorUng 
vector should bo a matant that lards 
the aphid ' nrnmnstro f act or . 
The viruses or thotr DMA may aloe 
be useful as vectors to uuroAsoe genes 
into plant protoplasts. The fsagiMty of 
plant pro top lasts oentbuted with the 
properties of the viruooo menuooe d 
above provide adequate safety. Since 
no nsk le the environment from the 
use of the DMA plant virus protoplast 
system is envisaged, no special con- 
tainment is recommended, except as 
described in the following paragraph. 
Experiments Involving the use of 
plant virus genomes Is propagate DMA 
sequences from eukaryotic viruses will 
be evaluated an a caw-by-case 
basis( 4i) and will hr c a n dusted under 
the recommended eontauuneiM condi- 
tions. 
FEDUAl RECISTH. VOL 43. NO 144 — HMD AY, ART M. 1«Tt 
