Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
In recent visits to watermelon fields in Delaware for pollination and fruit set surveys, we found a high number of pollenizer plants in one field that had one or more fasciated stems.
Fasciated stems are ones that are flattened and look like several stems have been fused together. They may be fan shaped in appearance. We also commonly see fasciation in strawberry fruits which develop a “cockscomb” appearance. Fasciation occurs when a growing point changes from a round dome of cells into a crescent shape. Subsequent growth produces a flat stem, flower, or fruit. In some cases fasciation is the result of several embryonic growing points fusing together, with the same flattened or fan-like appearance.
Although the causes of fasciation are not well understood, it is most likely because of a hormonal imbalance. Use of herbicides that are hormone analogs (such as those in the growth regulator or 2,4-D family) can often cause fasciation.
Fasciation can also be due to a random genetic mutation. In some cases, these mutations have been taken advantage of to produce new plants (many ornamentals) that then are propagated vegetatively to keep the fasciated appearance.
Fasciation can also be induced by one or more environmental factors, most commonly cold damage in the spring. Fasciation may also be induced by physical damage to the growing point.
Plant pests may also cause fasciation. Pathogens (bacteria, fungi, virus), insects, and mites, and insects may damage growing points or cause plants to produce excess hormones that will result in fascinated plants.
Go to the Purdue Plant and Pest Diagnostic Laboratory site for a picture of a fascinated sweet potato stem: http://www.ppdl.purdue.edu/PPDL/images/fasciatedsweetpot2.jpg.
