A successful cultivar in any horticultural food crop must meet minimal criteria for numerous traits that are currently or potentially valued in the marketplace. Consumer purchases are stimulated based on “quality” traits innate to the food such as flavor, color, shape, size, degree of damage, and nutrient levels. Janick (2005) stressed that several important quality improvements such as supersweet maize types, Sugarsnap-type peas, seedless watermelon, and “Gold” pineapple caused enhanced demand or new market sectors and are some of the most important genetic breakthroughs in horticultural crop breeding. Consumers may also be attracted to products with greater perceived food safety or environmental sustainability. These characteristics may be conveyed through traceability certification programs or an ecobrand indicating where or how the food was produced. Economic sustainability, furthermore, dictates that suppliers using the cultivar must be able to produce, store, transport, market, and sell a product that appeals to the consumer and produces a profit.
Yield is seldom only about obtaining gross tonnage in horticultural food crops. Most horticultural food crops are tasty, brightly colored, biologically active packages of water. The same nutrients they provide for critical nutrition to humans also make them a marvelous medium for a host of other organisms. Thus, yield is partly about producing tonnage, but also about the proportion of the crop that can be harvested and brought to market in a condition and at a price acceptable to the consumer. Yield traits that a plant breeder must select for include biomass productivity and traditional yield components such as size and number of harvested organs. However, genetically controlled pest, disease, and decay resistances during preharvest and postharvest stages are usually equally important. Superiority for multiple “quality” traits and “yield” traits is essential for economic sustainability in a successful cultivar.
The first challenge for a breeder is to determine which traits are most important. In a subsistence situation, focusing on content of key nutrients that are deficient in a diet that may lack quantity and diversity may be of utmost importance. The challenge in Western countries may be different. Greater nutritional benefit may be gained by substituting a few more servings of appealing, tasty, available, and inexpensive fruits and vegetables of even average nutrient content for foods with more dubious nutrient content. In this case, the breeders' efforts are better directed to traits that would make fruits and vegetables a more desirable and affordable alternative to other less nutritious products.
A related but equally important consideration for the breeder is to focus on those traits most amenable to breeding solutions. Most problems and opportunities faced by the plant breeder can be addressed genetically or horticulturally; application of horticultural solutions, where possible, can free valuable resources for improvement of traits most in need of genetic solutions. The rationale for adding an additional trait to a selection scheme must be strong. Each additional trait will mean that additional lines must be evaluated and resources expended to select for the newly added trait as well as to continue making the same rate of gain for previous traits.
The next issue a breeder encounters is how to assess quality. Ideally, the way it is assessed in the breeding program should reflect the quality that the consumer will encounter. Factors that breeders need to consider include maturity stage, location and season of production, sampling methods, and postharvest handling, storage, and processing parameters. The example of quality components in blackberry fruit examined by Siriwoharn et al. (2004) indicates that this can be complex. They examined the variance contributed to the measurement of several quality parameters (soluble solids, phenolics, total anthocyanin, cyan 3-dioxalylglucoside, and ellagitannins) by experimental design factors, including variation among plots, subsamples within plots, multiple preparations from each subsample, and instrumental variation for multiple measurements of the same preparation. The contribution of each of these factors varied greatly depending on the parameter measured. Variation among plots accounted for almost 40% of the total variance for cyan 3-dioxalylglucoside but was negligible for the other traits. Instrumental variation among measurements accounted for almost 50% of the total variance for total anthocyanin content but was negligible for the other traits. The variation among subsamples was important for all traits, but the contribution to total variance ranged from 25% to nearly 80%. This example illustrates how breeders need to establish the environmental and experimental components that affect quality components before they can effectively hope to alter the genetic component.
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