Dr. Donald S. Fredrickson 
2 
December 27, 1979 
B. There is not a single documented case where a serious bacterial plant 
pathogen (some under State quarantine) have escaped from a laboratory. 
Furthermore geographic, climatic and natural barriers restrict a given 
plant pathogen to a given area. For example, Xanthomonas oryzae , 
a serious pathogen of rice, does not exist in California because of 
relatively dry climatic conditions even though thousands of acres of 
susceptible rice varieties are grown here. These natural barriers 
also limit where the host plant must be cultivated. We had discussed 
portions of this well known limiting factor of plant pathogens at the 
Workshop on Risk Assessment of Agricultural Pathogens held on March 
20-21, 1978. Everyone seemed to have agreed on this fundamental 
fact and yet the prohibition on plant pathogens remains in the 
Guidelines! 
C. Because of the complexity of pathogenesis, it is extremely difficult 
to perceive the "creation" of a new plant pathogen by recombinant 
DNA technologies. In order to create such a pathogen one cannot 
simply draw upon the existing gene pool to do so. Otherwise we 
simply would construct a pathogen no more serious than the one that 
exists in the wild habitat. Even so, suppose we do construct a 
"new" plant pathogen, a number of critical criteria must be met 
before it can compete effectively in nature. 
2. Appendix A. Sublist A (page 69232) 
There are seven genera and two species of two other genera of the 
Enterobacteriaceae in Sublist A [a total of 9 of 12 genera (acc. Bergey's 
Manual of Determinative Bacteriology, eighth edition)]. 
I specifically focus your attention to the listing of Erwinia amylovora . 
I suggest the listing be modified and list the genus Erwinia instead 
of a single species. Erwinia species comprise plant pathogens and 
epiphytes. Like the other Enterobacteria listed, they readily exchange 
genetic material by natural means with _E. coli (Federal Register Part IV, 
July 28, 1978, page 33177). EL coli and other genera display about 20% 
DNA* DNA homologies with Erwinia species. Such homologies also exist 
between EL coli and the other genera in Sublist A. (See enclosed reprint 
of the genetic homology experiments as one of several examples) . 
The genetic inter-relationship between these Sublist A genera and 
Erwinia (also a bona fide member of the Enterobacteriaceae) indicates a 
genetic continuum within this family of bacteria. I find it difficult 
to see the rationale of restricting the exemption to a single species 
feuch as Erwinia amylovora ) within this family. Particularly Erwinia 
species because of their inoffensive feature relative to other genera 
in Sublist A that comprise species that are opportunistic pathogens of 
man. 
I hope that RAC will ponder these recommendations and hopefully 
incorporate them as revisions in the new Guidelines. 
Yours sincerely 
CIK:rl 
^xcf^Dr. William Gartland 
"Clarence I. Kado 
Professor 
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