- 2 - 
TO THE LACK OF GOOD GENETIC SYSTEMS FOR THEIR USE IN IDENTIFYING GENES FOR 
VIRULENCE AND CONSTRUCTING STRAINS TO USE IN BIOCHEMICAL STUDIES. 
PLANT PATHOGENIC BACTERIA MAKE EXCELLENT MODEL SYSTEMS FOR BASIC STUDIES ON 
HOST- PARAS I TE„ BECAUSE THE GENETICS OF THE HOST AND PARASITE CAN BE STUDIED 
IN PARALLEL. THE FINDING THAT MEMBERS OF THE GENERA PSEUDOMONAS , ERWINIA, 
AND AGROBACTERIUM NATURALLY EXCHANGE DNA WITH E. COLI AND _P. AERUGINOSA HAS 
GIVEN US THE KEY TO DOING MOLECULAR GENETICS WITH THEM. AS A RESULT, THIS 
IS ONE OF THE MOST ACTIVE AND PROMISING FIELDS OF PLANT PATHOLOGY TODAY. 
BUT EVEN SO THERE ARE ONLY ABOUT A DOZEN LABORATORIES INVOLVED IN THIS 
RESEARCH IN THE UNITED STATES TODAY AND THEIR EFFORTS ARE DIVIDED AMONG A 
NUMBER OF PATHOGENS. BECAUSE MANPOWER IS LIMITED AND BECAUSE WE ARE WORKING 
WITH GENETICALLY UNCHARACTERIZED BACTERIA, IT IS IMPERATIVE THAT WE TAKE 
ADVANTAGE OF THE BEST TECHNOLOGY AVAILABLE TODAY. ALTHOUGH SUCH STUDIES 
COULD POSSIBLY BE DONE BY CLASSICAL GENETICS, THE RECOMBINANT DNA TECHNIQUE 
OFFERS US A USEABLE MEANS OF GENETIC EXCHANGE FOR ORGANISMS IN WHICH GENE 
TRANSFER IS NOT CHARACTERIZED AND IT OFFERS ONE THE ADDED ADVANTAGE OF BEING 
ABLE TO PURIFY GENES FOR VIRULENCE OR HOST SPECIFICITY, STUDY THEIR GENETIC 
ORGANIZATION, AND CHARACTERIZE THEIR GENE PRODUCTS. THE RECOMBINANT DNA 
APPROACH IS FASTER, LESS EQUIVOCAL AND HAS A GREATER CHANCE FOR SUCCESS THAN 
IF THE SAME EXPERIMENTS WERE DONE USING CONJUGATION OR TRANSDUCTION. SIMILAR 
EXPERIMENTS HAVE ALREADY PROVEN VALUEABLE IN THE STUDY OF ANIMAL DISEASES. I 
MIGHT ADD HERE THAT THE PROBLEM OF NODULATION BY NITROGEN FIXING BACTERIA IS 
VERY SIMILAR TO THE PROBLEM OF HOST SPECIFICITY IN PLANT PATHOGENS, AND THAT 
THE SAME RATIONALE APPLIES TO THE FIELD OF NITROGEN FIXATION. IN ADDITION 
STUDIES ON THE GENOMES OF PLANT VIRUSES AND AGROBACTERIUM TUMEFACIENS MAY 
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