Florida citrus breeders recognize the need for an extended grapefruit season. Research has focused on grapefruit and grapefruit-like varieties that can be harvested earlier, without sacrificing aesthetic or eating quality. As with zipper-skin fruit, the selection criteria are rigid. To be successful, a new grapefruit variety must be attractive, productive, have high color, great flavor, and feature a thin peel. Ideally, it would produce fruit roughly comparable in size to existing varieties.
As grapefruit breeding is as difficult as sweet orange, most historic innovations have come from induced mutations or sports discovered in the field. Florida breeders are taking a more systematic approach. This particular article focuses on the efforts of the UF/IFAS Citrus Plant Improvement Team based in Lake Alfred. USDA-Agricultural Research Service (ARS) also includes the extension of Florida’s grapefruit season in its research priorities. The USDA-ARS grapefruit research will be covered separately in a future article to appear here.
Grapefruit development is part of the IFAS triploid citrus breeding program. A primary objective of this research is the extension of Florida’s grapefruit harvesting season (in both directions). Researchers have their eye on the prize: seedless dark-red fleshed grapefruit-like hybrids. In this process, diploid grapefruit and pummelos have been crossed with tetraploid grapefruit to produce seedless offspring. Pummelos are used both for their genetic diversity and their typically lower acid levels. It is hoped these crosses may result in some hybrids with lower acid levels earlier in the season. In the world of grapefruit, lower acid can equate to earlier harvest. The IFAS team also is busy developing new tetraploid grapefruit and pummelo breeding parents for use in future crosses.
Though the breeders are looking for hybrids that most resemble grapefruit in texture, flavor, shape, color, and size, this process also will produce selections that belong in an entirely new category of grapefruit-like fruit. Fruit in the latter category might not slot into traditional grapefruit market channels, but may have value to growers and marketers interested in developing niche markets.
As an added bonus, some of the pummelo parents used by the IFAS team are naturally low in furanocoumarins (compounds associated with drug interaction issues with grapefruit juice). About half of the progeny from crosses made with these pummelo parents also have been found to be low in these compounds. Furthermore, a few of the pummelo parents used have been identified (through preliminary detached leaf assays) as having greater canker tolerance than grapefruit. The jury is still out on canker tolerance, but early results are interesting.