BIOLOGICAL-CONTROL OF GRAPE CROWN GALL BY STRAIN F2 5 IS NOT ASSOCIATED WITH AGROCIN PRODUCTION OR COMPETITION FOR ATTACHMENT SITES ON GRAPE CELLS/

Agrocin-minus mutants of nontumorigenic Agrobacterium vitis strain F2/ 5 controlled grape crown gall as well as the wild-type strain, indicat ing that agrocin is not a major factor in the mechanism of biological control. Relative levels of attachment to grape cells by tumorigenic a nd biocontrol strains were also measured. Attachment of tumorigenic st rains (CG49 and K306) and biological control strains (F2/5 and agrocin -minus mutant 1077) was often reduced when mixtures of the strains wer e applied. However, high populations (10(3) to 10(5) CFU/ml) of all st rains attached following mixed inoculations, suggesting that competiti on for attachment sites is also not a factor in the mechanism of biolo gical control. Transfer of T-DNA to grape by CG49 was prevented or gre atly inhibited in the presence of F2/5 or 1077 as measured by expressi on of the GUS reporter gene. The Ti plasmid virulence genes, however, were induced by exudates from grape shoots that had been inoculated wi th F2/5. Sonicated and autoclaved preparations of F2/5 and 1077 did no t control crown gall or inhibit T-DNA transfer. Control by F2/5 is spe cific to grape, since gall formation on tomato, sunflower, and Kalanch oe daigremontiana were not inhibited.