664 PB 104 AGROBACTERIUM INFECTION OF WHITE ASH (FRAXINUS AMERICANA L.)
Both greenhouse-grown white ash plants derived from tissue culture and rooted microshoots in high humidity trays were inoculated with 11 tumor-inducing Agrobacterium strains. Eight strains stimulated mutative gall formation. Plants inoculated with strain A281 exhibited a higher frequency of callus formation (greenhouse-22.2%; microshoots-18.8%) than other strains at the site of the wound. Therefore, strain A281 was used to inoculate seed and seedling explants in vitro. Explants were placed on MS medium containiner no plant growth regulators and inoculated at 0, 3, 5, 7, or 10 days after initiation. Plants inoculated at 10 days showed a higher frequency of callus formation (16.4%) than with earlier inoculations. Also, rewounding of the explant at inoculation resulted in a higher frequency of callus formation (11.3%) compared to not rewounding the explant (3.9%).