Exploiting Somaclonal Variation to Deliver Improved Sweet Orange Cultivars for Processing and the Fresh Market

Sweet orange (Citrus sinensis L. Osbeck) is the most horticulturally important and widely grown Citrus species in Florida and worldwide.  Approximately 90% of Florida orange production and more than 30% of the world crop are used for processing.  Frozen concentrate orange juice has historically been the primary product of the Florida industry, but more recently there has been a strong shift to the more profitable fresh pasteurized not-from-concentrate (NFC) product.  The development of higher quality oranges with expanded maturity dates will facilitate this change and increase the competitive ability of the Florida industry.  Improved clones that are seedless, more attractive and easier to peel have potential to improve the competitiveness of sweet oranges in the fresh market.  No true sweet orange cultivars have been produced by conventional breeding techniques due to its complex biology including large plant size, extended juvenility, and nucellar polyembryony.  Commercial sweet orange cultivars probably originated by the selection of chance seedlings well-adapted to a particular area or from a mutation in a particular cultivar or seedling. Thus, over the past 25 years, we have been exploiting somaclonal variation as a source of useful variation for improving sweet oranges. Selected somaclones are exhibiting improved traits such as earlier maturity, later maturity, better juice quality (color and flavor), higher soluble solids, seedlessness, scion-based tree size control, increased yield, and better stress tolerance.  The first two released sweet orange cultivars from our citrus variety improvement program are SF14W-62 (Valquarius^TM), an early-maturing (midseason) processing Valencia-derived sweet orange that matures 6–8 weeks early than standard Valencia; and  N7-3 (Valenfresh^TM), a late-maturing seedless Valencia sweet orange for fresh market or processing. Both of these clones were regenerated from embryogenic cell culture-derived protoplasts.  These and several other somaclones selected for release, derived from ‘Hamlin’, ‘Valencia’, ‘Rhode Red Valencia’, and OLL (Orie Lee Late) will be described.  Potential contributions of selected somaclones to sustainable sweet orange production in the face of new and severe disease threats will also be discussed.