Agrocin-producing pathogenic and nonpathogenic biotype-3 strains ofAgrobacterium tumefaciens active against biotype-3 pathogens

Agrocin-producing pathogenic and nonpathogenic biotype-3 strains ofAgrobacterium tumefaciens were isolated from grapevine gall tissue. In vitro activity of the nonpathogenic agrocin producers was restricted to biotype-3 pathogens used. Pathogenic agrocin producers were active in vitro against biotype-3 agrocin-producing nonpathogens, non-agrocin-producing pathogens, and biotype-1 strains when cultivated on a modified Stonier's medium; on a medium designated AB, two strains stested showed no activity against agrocin-producing nonpathogens, but agrocin of one of these strains was active against other agrocin-producing pathogens. In a greenhouse experiment a marked tendency toward decreased gall formation by biotype-3 pathogens on grapevines was obtained when biotype-3 pathogens and nonpathogenic biotype-3 agrocin producers were applied to wounds simultaneously. In this experiment, agrocin-producting pathogens tended to be more virulent than non-agrocin-producing pathogens.