As a result, breeders may observe healthy, undamaged celery lines and select them for commercial release. Unfortunately, workers who harvest high psoralen-producing celery or pack it in grocery stores have, on occasion, developed severe photodermatitis, especially when they are exposed to bright sunlight and the celery is infected with pathogens (Berkley et al., 1986; Birmingham et al., 1961; Finkelstein et al., 1994). There are differences in psoralen content from one variety to another (Beier, 1990; Diawara et al., 1993), but environment seems to have the greatest influence on psoralen production (e.g., Diawara et al., 1995).
Mutations, defined as any change in the base sequence of DNA, can either occur spontaneously or be induced, and both methods have produced new crop varieties. Most mutations are deleterious and therefore useless for breeding purposes. However, a mutation can result in desirable traits and may be selected for breeding. Spontaneous mutations, also called “sports” by horticulturists, are by definition not induced, so breeders wait a long time to see mutants arising from this process, and even longer to see useful ones. Most mutation breeders induce random changes in DNA by using ionizing radiation or mutagenic chemicals, such as ethyl methane sulfonate, to increase the rate and frequency of the mutation process.
In spite of these intrusive methods, induced mutagenesis is considered a conventional breeding technique. Food derived from mutation breeding varieties is widely used and accepted. Organic farming systems permit food from mutated varieties to be sold as organic. In the United States many varieties have been developed using induced mutagenesis, such as lettuce, beans, grapefruit, rice, oats, and wheat. The Food and Agriculture Organization of the United Nations/ International Atomic Energy Agency Mutant Cultivar Database (FAO/IAEA, 2001) lists more than 2,200 varieties of various species worldwide that have been developed using induced mutagenesis agents, including ionizing irradiation and ethyl methane sulfonate. However, the database does not include spontaneous mutations, cell-selected mutants (Rowland et al., 1989), or somaclonal variants (Rowland et al., 2002).
There is no mandated requirement to list new mutant varieties with the database. However, there do not appear to be outstanding examples of mutant varieties with documented unexpected effects beyond what the mutant was selected for, despite the expectation that mutant varieties may possess and generate more unexpected outcomes than ordinary crosses because of the unpredictable and uncontrollable nature of nontargeted mutations. Furthermore, there do not appear to be any examples in which mutant varieties were removed from the market due to unintended or unexpected adverse incidents.