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ABSTRACT
Cranberry stem gall is characterized by tumors that girdle stems, thereby killing all distal leaves, flowers, and fruit. Bacteria that produce high levels of the plant growth hormone indole-3-acetic acid (IAA) are associated with and believed to cause cranberry stem gall. The anatomy of naturally occurring galls on woody cranberry plants and galls caused by inoculation of micropropagated cranberry plants with Pantoea agglomerans strain 4/99 was consistent with elevated levels of IAA in plants. Field galls exhibited hypertrophy and hyperplasia of tissue external to the vascular cambium, resulting in extensive stem swelling and splitting of the periderm. Similarly, galls on micropropagated plants contained enlarged cortical parenchyma cells. The current year's xylem vessels in field galls were narrow and dense compared with xylem vessels of healthy stems. Curved xylem elements apparently developed de novo within field galls and galls on inoculated plants. Cavities and fissures in both types of galls contained dense aggregates of bacteria. Treatment of micropropagated plants with synthetic IAA caused hypertrophy of cortical parenchyma and formation of adventitious roots. The results support the hypothesis that IAA-producing bacteria cause cranberry stem gall.
Additional keywords: plant anatomy, Vaccinium macrocarpon.
The large American cranberry (Vaccinium macrocarpon Ait.) is a woody evergreen vine indigenous to eastern North America. Most commercial plantings of cranberry are established by lightly disking vine cuttings into sand. With adequate moisture, cuttings produce adventitious roots, and in 2 to 3 years, form a dense carpet of prostrate stems, or runners, from which vertically oriented shoots, or uprights, arise. Uprights elongate by about 5 to 10 cm per year, and fruit are produced on the current year's growth. In most regions, fruit are harvested by flooding beds and then dislodging fruit with mechanical reels or rakes. In Wisconsin, beds are flooded again in early winter to form an ice layer to prevent low-temperature injury and desiccation. The flood is withdrawn in early spring, after which frost protection is accomplished either by sprinkler irrigation or reflooding.
Cranberry stem gall is characterized by regions of stem swelling up to several centimeters in length and small galls on woody runners and uprights (9,18). Eventually galls girdle stems, killing all distal leaves, flowers, and fruit. This disorder has been referred to as stem canker or...