New genetic tools to improve citrus fruit quality and drive consumer demand

Consumers are attracted to citrus fruit first by color and appearance, and later by aroma, flavor and inherent health-promoting benefits. Each of these attributes represents a complex trait under polygenic control. Citrus peel and flesh color is determined primarily by accumulations of various carotenoid compounds. Flavor and aroma, likewise, are a composite of a multitude of primary and secondary metabolites in different combinations and concentrations that interact with human sensory receptors to result in the perception of flavor and aroma. Flavor, aroma and health-promoting benefits of citrus are tied together through metabolic pathway interconnections, as well; therefore, genetic improvement of these consumer-critical characteristics is a daunting task, made all the more challenging by limitations imposed on breeding woody perennial fruit tree species. Historically, improvement in these traits for citrus has been a happenstance process of selection from populations of trees, of which the majority are usually unacceptable. Chemical and genomic dissection of important components underlying fruit quality has led toward the development of new tools to make the creation and selection of citrus cultivars improved in quality attributes more targeted and efficient. The use of single nucleotide polymorphism (SNP) platforms and other technologies have resulted in high-density linkage maps and the identification of critical quantitative trait locus (QTL) regions controlling fruit quality. Availability of several citrus genome sequences enables identification of candidate genes underlying QTLs, which can be used to develop precise markers for selection. The development of these tools will be described, as well as their applications in genetic improvement of citrus fruit quality.