Breeding vegetables adapted to high temperatures: A case study with broccoli

Authors: Farnham, Mark; BJORKMAN, T - Cornell University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2011
Publication Date: 8/1/2011
Citation: Farnham, M.W., Bjorkman, T. 2011. Breeding vegetables adapted to high temperatures: A case study with broccoli. HortScience. 46:1093-1097.

Interpretive Summary: An environmental stress, like higher than optimum temperatures or drought conditions, can be damaging to vegetable production. Some such stress conditions directly reduce growth, while others affect development in a way that reduces or eliminates the crop’s value. An example of the latter is high temperature stress in broccoli. Breeding for tolerance to this stress has great potential for meeting increased demand in a larger production region like the eastern seaboard. Thus, the broccoli improvement program at the U.S. Vegetable Laboratory (USVL) in Charleston, South Carolina has conducted a breeding effort for over a decade to select broccoli more adapted to the high temperature conditions that occur during Southeastern summers. General experiences from this successful broccoli breeding effort are presented as a case study for other programs that intend to focus new efforts on breeding vegetable crops for adaptation to an environmental stress. Stress tolerance is a complex trait and progress is expected to be incremental. However, this broccoli example well illustrates that progress can be consistent by setting a clear target, by keenly observing plant response in order to select the more casual expression of tolerance, and by providing the most selective environment. Public and private breeding programs that focus some effort on breeding for environmental stress tolerance will find useful insights in the information and suggested approaches presented in this discussion.

Technical Abstract: Breeding a vegetable crop for adaptation to a temperature regime that is higher than the recognized optimum for the species in question is an example of breeding for abiotic stress tolerance. Before embarking on a project to breed for such stress tolerance, we propose that several critical considerations or questions must be addressed. These considerations include the following: 1) What is the effect of the abiotic stress on the crop to be improved; 2) What will be the conditions of the selection environment; 3) What germplasm is available that contains the necessary genetic variation to initiate improvement; 4) What breeding scheme will be employed to facilitate improvement; and 5) What will be the specific goals of the breeding effort. Herein we use a case study with broccoli to breed for adaptation to high temperature environments to provide examples of how each of the above considerations might be addressed in developing an improvement effort. Based on documented success with this case study wherein broccoli quality and performance in high temperature summer environments has been improved, insights are provided that should be useful to future attempts to breed vegetables more tolerant of an abiotic stress.