33174 
NOTtCfS 
DNA sequences will b« evaluated by 
:he Recombinant DNA Molecule Pro* 
gram Advisory Committee on a case- 
by-case basis and win be conducted 
under physical containment conditions 
recommended by the committee. Ex- 
periments should be done In estab- 
lished Invertebrate cell lines and 
should follow, where appropriate, cri- 
teria recommended for vertebrate viral 
DNA vectors (Sec. J.a(a-c)]. 
c. Plant host-vector system*.— The 
DNA plant viruses which could cur- 
rently serve as vectors for cloning 
genes In plants and plant cell proto- 
plasts are Cauliflower Mosaic Virus 
(CaMV) and Its dose relatives, which 
have relaxed circular double stranded 
DNA genomes with a molecular weight 
of 4.8x10*. and Bean Oolden Mosaic 
Virus (BO MV) and related viruses 
with small ( < 10* dal to ns) slngled- 
§ trended DNA genomes. These viruses 
are not known to Integrate Into host 
chromosomes, or to Incorporate cellu- 
lar genes Into their genomes. CaMV Is 
spread In nature by aphids. In which it 
survives for a few hours. Spontaneous 
mutants of CaMV that are not trans- 
mitted by aphids arlss frequently; 
these mutants fail to make a transmis- 
sion factor essential for aphid trans- 
mission. BO MV Is spread In nature by 
white flies. In which It survives for ssv- 
eral days to three weeks; certain other 
■ingle-stranded DNA plant viruses are 
transmitted by leafhoppera, in which 
the viruses persist for days or weeks. 
Single-stranded DNA plant viruses are 
thought not to replicate In their Insect 
vector. 
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 preparations of the 
virus. 
When these viruses are used as vec- 
tors with Intact plants, the plants 
should be grows tn either a limited 
access ptsilMs* or plant growth 
cabinet wtflefc la insect-proof, prefer- 
ably with pustUws air pressure, and In 
which an Insect fumigation regime Is 
maintained. Sod. plant pots and un- 
wanted Infected plant materials 
should be removed from the green- 
house ok cabinet In sealed Insect proof 
containers and sterilised. It Is not nec- 
essary to sterilize run-off water from 
the Infected plants as thM is not s 
plausible route for secondary Infec- 
tion. Infected plant materials to be 
used for further research, which have 
to be removed from the greenhouse or 
cabinet, should be maintained under 
Insect proof conditions. These meas- 
ures provide an entirely adequate 
degree at oonteinment and are similar 
to those required in many countries 
for licensed handling of "exotic" plant 
vlrisss * 
The viruses or their DNA may also 
be useful ss a vector to Introduce 
genes Into plant protoplasts. The fra- 
gility of plant protoplasts combined 
with the properties of the viruses men- 
tioned above provide adequate safety. 
Since no risk to the environment from 
the use of the DNA plant vlrua/proto- 
plast system Is envisaged, no special 
containment is recommended. 
Experiments Involving the use of 
plant virus genomes to propagate DNA 
sequences from eukaryotic viruses will 
be evaluated by the Recombinant 
DNA Molecule Program Advisory 
Committee on a case-by-case basis and 
will be conducted under containment 
conditions recommended by that com- 
mittee. 
Arrxwotx O.— Retort or a Workshop 
or Risk Assessment or Agricultural 
Pathooers 
Conducted by. Recombinant DNA 
Molecule Program Advisory Commit- 
tee. 
Sponsored by; UA Department of 
Agriculture. National Science Founda- 
tion. and National Institutes of 
Health. March 30-31. 1078. 
Contents 
Introduction. 
Hazard classification of plant pathogens 
Table 1.— Survival data of plant protoplasts 
Table 3 -Available evidence for exchange 
among bacterial plant pathogens and 
symbionts 
References 
Participants 
Liaison representatives 
IHTRODUCTIOK 
An assessment of risk Involved In re- 
combinant DNA research on plant and 
Insect pathogens necessarily entails 
consideration of different concerns 
than those applied to risk assessment 
of research with pathogens of man 
and animals This fundamental differ- 
ence provided the basis on which the 
recommendations of our committee 
were formulated. 
There was a consensus amongst the 
committee members that working with 
plant pathogens and baculovlruses In 
recombinant DNA studies presents no 
more hazard than that which exists In 
current laboratory studies with the 
pathogens themselves. It la significant 
that to the best of our knowledge 
there have been no cases recorded In 
which laboratory studies with cultures 
of plant pathogens have resulted In Ill- 
ness in man or animals exposed to 
these organisms. Neither Is there s do- 
cumented case In which laboratory 
studies with cultures have resulted In 
an escape resulting In an outbreak of 
disease In plants growing under natu- 
ral conditions. 
We believe that any potential risk 
that might arise from studies Involv- 
ing plant pathogens Is now adequately 
covered by existing federal and state 
quarantine regulations. These have 
evolved to enable government to deal 
with the practicalities of plant disease 
control (Oram, E., 1960. Chapter 9. pp. 
314-356 In "Plant Pathology, An Ad- 
vanced Treatise", J. O. Horsfall and A. 
E. Dlmond, eds.. vol. 3. Acad. Press., 
New York). They take precedence over 
any other regulations since they deter- 
mine whether or not an Investigator 
has access to a particular pathogen. 
With plants, resistance to disease Is 
the rule, susceptibility Is the excep- 
tion. Thus, the common occurrence of 
resistance poses an Important barrier 
to the successful establishment of po- 
tential pathogens. There Is no patho- 
gen that Is highly virulent on all plant 
species. Rather, the majority of patho- 
gens are restricted to a relatively small 
number of host plants and within 
these specific susceptible hosts vari- 
etal variation In resistance Is usually 
present. Breeding for disease resis- 
tance has provided a means for effect- 
ing relatively rapid changes In varie- 
ties. In the United States today, ap- 
proximately 95 percent of the acreage 
In crops of economic Importance Is 
planted to varieties that carry resis- 
tance to one or more major diseases. 
This Is one of the key factors In the 
productivity of American agriculture. 
Even when a particularly destructive 
new race or strain of a plant pathogen 
arises. It Is possible to change the 
available varieties and to reduce or 
minimize the threat within the space 
of two or three years. This was the 
case when a virulent strain of the 
pathogen that causes Helminthospor- 
ium leaf blight spread throughout the 
com growing area of the United States 
In 1970 and It was necessary to discon- 
tinue the growing of those hybrids 
that carried the factor for male steril- 
ity which also conferred susceptibility 
to the disease (Ullstrup, A. J., 1972, 
Ann. Rev. Phytopath. 10:37-50). 
Virulent plant pathogens commonly 
are contained In nature because for 
their very survival and dissemination 
within a region, or for an epidemic to 
develop, they require specific environ- 
mental factors (Colhoun. J., 1973, 
Ann. Rev. Phytopath. 11:343-364). For 
example, bacterial wilt caused by 
Pseudomonas solanaoearum rarely 
occurs north of the Mason-Dlxon line. 
The causal bacterium Is sensitive to 
low temperatures and has a relatively 
high optimum temperature for 
growth. Even when Introduced Inad- 
vertently Into Northern states it does 
not overwinter In the soil or affect sus- 
ceptible crops the following year 
(Kelman, A.. 1963, N. Carolina Agr. 
Exp. Sta. Bull. 99, 194p). 
In considering hypothetical risks of 
recombinant DNA research on plant 
pathogenic organisms our committee 
considered the following questions; 
ffDfkAl MOtlTH, VOL «>, NO. 14*— IVIDAV, MT N. 1*7» 
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