Indole-3-acetic Acid-producing bacteria are associated with cranberry stem gall

ABSTRACT Cranberry stem gall is characterized by tumors that girdle stems, thereby killing all distal leaves, flowers, and fruit. Among bacteria isolated from galls, all 11 isolates that were identified as members of the family Enterobacteriaceae caused galls on 50 to 100% of micropropagated cranberry plants that were inoculated. Four of fifteen isolates identified as Pseudomonas spp. caused galls on 10 to 83% of plants inoculated. Twelve of fifteen isolates identified as either Agrobacterium spp. or Rhizobium spp. caused galls on 10 to 50% of plants inoculated, but the galls were smaller than those caused by members of the family Enterobacteriaceae or Pseudomonas spp. There was a positive correlation between the ability of bacteria to produce IAA in vitro and cause galls. In 2002 and 2003, bacteria were isolated from plant and soil samples collected from beds where stem gall had been observed in the past 2 years and beds where stem gall had never been observed. IAA-producing bacteria were common in all samples, although trends were different across years. The results of this study support the hypothesis that IAA-producing bacteria cause cranberry stem gall and suggest that rather than one bacterial species being the cause, multiple strains of bacteria that produce IAA may be responsible for gall formation.