Introduction:

Fasciations are widespread phenomena reported in more than 100 vascular plant species (Tang and Knap, 1998), affecting dicots and monocots in 39 plant families and 86 genera (Goethals et al., 2001). The term refers to a flattened or ribbon-like appearance. Woody plants, annuals and even cacti are affected. In some plants fasciations occur on woody stems; other plants exhibit this condition in the flower stalk, fruit or flower clusters. Stems, fruits, flowers and roots can become fasciated.

The linear fasciation with a flat, ribbon-shaped appearance is most common. In this instance, the growing point broadens, commonly to two to six inches wide. The fasciated cristate cacti may have a growing ridge which is several feet wide.

Geneve (1990) reports bifurcated fasciations (linear fasciations which split to produce a `Y' shaped double ribbon), multiradiate (stellate) shaped fasciations (the stem splits into three or more short branches) and ring fasciations (the growing point fuses to form a funnel shape) can occur.

Bacteria: Rhodococcus fascians (Tilford) Goodfellow [previously known as Corynebacterium fascians (Tilford) Dows.] is reported to cause fasciations by studying chemical, genetic and the visible properties of the organism produced by the interaction of the bacterium's genetics and the environment, Goodfellow reclassified Cornybacterium fascians as Rhodococcus fascians in 1984. Previous names assigned this bacterium were Phytomonas fascians (Tilford, 1936), and Bacterium fascians (Lacey, 1939).

Crespi (1992) reported fasciation due to bacterial infection was the result of the transmission of a linear plasmid (an extrachromosomal piece of DNA) containing a gene that synthesizes cytokinin.

Within the plant, root meristems are the major sites of cytokinin synthesis, moving through the xylem into the stems. Cytokinin is thought to function as a signal regulating when and where cell proliferation occurs in the plant. Cytokinin appears to have the ability to stimulate the proliferation of a wide spectrum of cell types (Fosket, 1994).

Goethals et al., 2001, report the ability of Rhodococcus fascians to cause fasciations and other plant distortions, while involving a cytokinin-like compound, appears to involve other plant hormones as well. According to these researchers, the exact nature of the signals responsible for the hormonal change in the plant has not yet been identified. For more detail, check out the review by Goethals et al.

Disease Transmission: It is not known if R. fascians is a true soil resident or simply a tranisient. It is known to be seedborne in some hosts and spread by vegetative vegetation and water (Putnam and Miller, 2007).

Plant Genetics: Many annual plants contain a gene responsible for the fasciation of vegetative or flower stems. Gregor Mendel, the father of modern genetics, demonstrated the gene for fasciation was a heritable trait in peas (Gottschalk, 1977). Fasciation was one of the seven characteristics he chose when illustrating the concept of dominant and recessive traits in his cross breeding of peas. These inherited fasciations are meristematic mutations which impart tumor-like properties to the meristem (Tang and Knap, 1998).

The cockscomb celosia (Celosia argentea var cristata) is an excellent example of a plant with inherited fasciation. Other fasciated plants are often identified by the descriptive cultivar names of `torulosa' and `monstora'.

It is not know if the fasciations in most woody plants are inherited. It is known, however, that the tendency toward fasciation is transmissible by budding and grafting once the woody plant develops a fasciation (Geneve, 1990). Growers who cut off fasciated branches often find this condition returns with the development of new branches.

Miscellaneous causes: Herbicides, insects and physical injury to the growing tip are reported to stimulate the occurrence of fasciations (Geneve, 1990). Fasciations also are reported to come about through spontaneous mutations (Gabillard and Pitrat). Conditions favoring rapid growth also favor the development of fasciations.

Photos by C. Swift unless otherwise indicated.

References used:

Crespi, M., Messens, E., Caplan, A.B., Van Montagu, M., & Desomer, J. 1992. Fasciation induction by the phytopathogen Rhodococcus fascians depends upon a linear plasmid encoding a cytokinin synthase gene. EMBO J. 11:795-804.

Fosket, D.K. 1994. Plant Growth and Development: a molecular approach. Academic Press.

Gabillard, D. & Pitrat, M. 1988. A fasciated mutant in Cucumis melo. Rpt. Cucurbit Genet. Coop. 11:37-38.

Geneve, R. August 1990. Fascinated with Fasciations. American Horticulturist. P. 27-31.

Goethals, K., Vereecke, D., Jaziri, M., Van Montague, M., and Holsters, M. 2001. Leafy gall formation by Rhodococcus fascians. Annual. Rev. Phytopathology 39:27-52.

Goldman, I.L. 1998. Inheritance of ffs, a gene conditioning fasciated flower stem in red beet. J. Amer. Soc. Hort. Sci. 123(4):632-634.

Goodfellow, M. 1984. Reclassification of Corynebacterium fascians (Tilford) Dowson in the genus Rhodococcus, as Rhodococcus fascians comb. nov. Syst. Appl. Microbiol. 5:225-29.

Gottschalk, W. 1977. Fasciated peas - Unusual mutants for breeding and research. J. Nucl. Agr. Biol. 6:27-33.

Lacey, M.S. 1939. Studies on a bacterium associated with leafy galls, fasciations and "cauliflower" disease of various plants. Part III. Further isolations, inoculation experiments and cultural studies.Ann. Appl. Biol. 26:262-78.

Murai, N., Skoog, F., Doyle, M.E., & Hanson, R.S. 1980. Relationship between cytokinin production, presence of plasmids, and fasciation caused by strains of Corynebacterium fascians. Proc. Natl. Acad. Sci. USA. 77:619-623.

Putnam, M.L. & MIller, M.L. 2007. Rhodococcus fascians in Herbaceous Perennials. Plant Disease. 91(9):1064-1076.

Tang, Y. & Knap, H.T. 1998. Fasciation mutation enhances meristematic activity and alters pattern formation in soybean. Int. J. Plant Sci. 159 (2):249-260.

Tilford, P.E. 1936. Fasciation of sweet peas caused by Phytomonas fascians n. sp. J. Agric. Res. 53:383-94.