Nutritional Changes in a Vegetable over Time Related to the Improvement of Important Horticultural Traits Using Broccoli As an Example

For many decades, plant breeders have worked to improve fruit and vegetable crops for numerous economically important traits, such as host plant resistance to disease, yield, and fruit or vegetable quality. Most improvements have been made with little knowledge as to how, or if, nutritional or phytonutrient concentrations might also be indirectly altered in the process. There has been some speculation that concentrations of nutrients in fruits and vegetables may have actually been reduced as crops have undergone improvements. However, for most horticultural crops, any current evidence indicating changes in mineral concentration is circumstantial at best. To effectively determine whether or not changes may have occurred over time with the development and release of new cultivars replacing older ones, appropriate field studies must be conducted wherein concentrations in harvested fruits and vegetables from “old” versus “new” crop cultivars are compared directly. Few such studies have been conducted with fruit or vegetable crops. Using broccoli as a test crop, we have conducted field studies to compare mineral concentrations in broccoli heads harvested from cultivars released over several decades. The oldest broccoli cultivars tested in these studies had relatively high concentrations of most minerals assayed, but they produced inferior quality heads that are not saleable in the current marketplace. More importantly, with cultivars released and grown from the 1970s to the present, we found no evidence that mineral concentrations of harvested heads that meet modern quality standards have declined or increased. This is an interesting outcome because there is no indication that breeders have been monitoring mineral concentrations of broccoli during this period in which hybrids became the predominant cultivar type and numerous horticultural quality attributes were enhanced. In some specific cases, breeding efforts have sought to enhance particular phytonutrients with known health promoting effects. Specific examples of this are found in efforts to increase levels of aliphatic glucosinolates in broccoli or work to increase carotenoid levels in carrots. In general, horticultural crop breeders in both the public and private sectors now consider nutritional content of fruits and vegetables as additional quality attributes with similar importance as other traits. Maintaining high nutritional content of new horticultural cultivars will be important in future crop improvement efforts; however, these efforts must balance the ever present demand for increased resistance to existing and emerging diseases, tolerance to different abiotic stresses, improved quality attributes, and also adequate crop yield.