Mike Roberts

Highlights of the Progress of the USDA Scion Breeding Program

The 2020 Florida Citrus Show saw many important presentations that highlighted what’s going on in the Florida citrus industry. One such presentation, titled “Progress of the USDA Scion Breeding Program,” presented by USDA-ARS, Ft. Pierce research horticulturist and geneticist Ed Stover, shed light on the development of HLB-tolerant and HLB-resistant citrus scions. Finding citrus varieties that are resistant or tolerant of citrus greening, or HLB, has been the passionate focus of Florida citrus breeders since the devastating disease was discovered in a South Florida citrus grove in 2005. 


Highlights of the Scion Breeding Program’s Progress

The numbers given by Stover in the presentation concerning the amount of scions that have been developed are impressive. There have been more than 26,000 unique hybrids produced in the last 10 years, with 29 cultivars being released.

Stover maintained that the initial thought process was that citrus greening/HLB would kill all forms of citrus, but it was eventually observed in 2009 that some citrus possess a tolerance to citrus greening. In 2010, the first crosses for HLB tolerance were made.

Since then, the majority of hybridizations created by the USDA scion breeding program has focused on creating citrus with HLB resistance or tolerance for varieties like red grapefruit, seedless Mandarins, and “sweet-orangelike” citrus. Other factors breeders have focused on, in addition to HLB tolerance/resistance is fruit quality and emphasizing advanced selections as parents. Stover shared there are over 19,000 new hybrids in the ground and more in greenhouses.

Some of the highlighted scions include:

  • US SunDragon: It’s the first released scion containing Poncirus, or trifoliate orange, for use as fresh fruit. It’s also a breeding parent. It’s described as “like a navel in alligator-hide,” has an apparent tolerance to HLB, and it scored highly in the sweet orange juice trial at USHRL. It’s been used in many crosses, and its hybrids are starting to fruit.
  • FF 1-22-79, irradiated FF 1-42-65: A Fortune x Encore cross, Stover describes this as “Probably our best un-released tangerine.” It has good external and internal color, a slightly pebbly skin that usually comes off in large chunks with little chipping, and a very rich flavor, among other positive features. Additionally, its sibling, 1-42-70, is one of most HLB-tolerant so far in trial, according to Stover’s presentation.
  • Low seeded selections of Irradiated FF-5-51-2: A Clementine x Orlando cross, this is a “good midseason tangerine” that is easy peeling, has a rich flavor, and the segments are dry when separated. Its seedy original hybrid “appears to have useful HLB-tolerance, with no evidence of HLB-affected fruit.”

Florida citrus growers are starting to see the fruits of the USDA’s scion breeding program in the form of HLB-tolerant citrus!

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