Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2005
Publication Date: 7/29/2005
Citation: Abercrombie, J.M., Farnham, M.W., Rushing, J.W. 2005. Genetic combining ability of glucoraphanin level and other horticultural traits of broccoli. Euphytica. 143:145-151. Interpretive Summary: Broccoli is a source of plant compounds called glucosinolates. One of these glucosinolates, glucoraphanin, is known to form a compound called sulforaphane. Research experiments have found that rats fed sulforaphane or broccoli extracts have a lower risk of cancer than rats not fed these materials. Evidence also indicates that sulforaphane protects human cells from cancer-causing agents by inducing those cells to detoxify those harmful agents. Thus, a diet rich in broccoli may protect humans against certain cancers. We are interested in knowing if glucoraphanin levels and the detoxifying activity of broccoli can be altered. If we can increase these factors, this might enhance the capacity of broccoli to protect people against cancer. Most commercial varieties of broccoli are hybrids formed by crossing two inbred parents, but little is known about how glucoraphanin levels in broccoli parents will influence levels in offspring hybrids. Thus, the objective of this research was to cross a group of broccoli parents with known glucoraphanin contentrations and then evaluate the levels in the hybrids resulting from the crosses. Findings of this research indicate that broccoli parents with relatively high glucoraphanin levels tend to produce hybrids that also have high glucoraphanin. On the contrary, parents with low glucoraphanin tend to make hybrids with low levels. Private industry and public broccoli breeders will use this information in their efforts to develop new broccoli hybrids with enhanced healthful attributes of broccoli. Commercialization of such enhanced hybrids could lead to improved health of consumers.
Technical Abstract: Broccoli (Brassica oleracea L., Italica Group) is a source of glucosinolates and their respective isothiocyanate metabolites that are believed to have chemoprotective properties in humans. Glucoraphanin (4-methylsulfinylbutyl glucosinolate) is a predominant glucosinolate of broccoli. Its cognate isothiocyanate, sulforaphane, has proven a potent inducer of phase II detoxification enzymes that protect cells against carcinogens and toxic electrophiles. Little is known about the genetic combining ability for glucosinolate levels or the types of genetic variation (i.e., additive vs. dominance) that influence those levels in broccoli. In this study, a diallel mating design was employed in two field experiments to estimate combining abilities for glucoraphanin content. The diallel population was developed by crossing nine doubled-haploid (inbred) parents in all possible combinations (36), excluding the reciprocals. Horticultural traits of all entries were assessed on a plot basis. In fall 2001, glucoraphanin concentration of broccoli heads ranged from 0.83 to 6.00 µmole/gdw, and in spring 2002, ranged from 0.26 to 7.82 µmole/gdw. In both years, significant general combining ability was observed for glucoraphanin concentration and total head content, days from transplant to harvest, head weight, and stem diameter. Conversely, no significant specific combining ability was observed for any trait in either year. Results indicate that a given inbred will combine with others to make hybrids with relatively predictable levels of head glucoraphanin as well as, other important horticultural traits. This should allow identification of inbreds that typically contribute high glucoraphanin levels when hybridized with others.