Field Day Showcases Efforts to Breed HLB-Tolerant Oranges

By Maegan Beatty

On Oct. 27, Jose Chaparro hosted a citrus breeding research update at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Teaching Orchard in Gainesville. The event included a variety display and field tour.

Chaparro, a UF/IFAS associate professor of horticultural sciences, focused on how he and his team are taking on the significant task of breeding an HLB-tolerant sweet orange.

“If the variety is not HLB tolerant, then it can’t grow here in Florida,” Chaparro said.

POSSIBLE SOLUTIONS
He discussed some possible solutions to HLB. One of those is to modify the orange juice standards to allow the use of HLB-tolerant mandarins and tangors.

There has been a range of tolerance identified in mandarins. Since sweet orange is derived partially from mandarin, he said it is possible to produce fruit with very orange-like characteristics and select for HLB tolerance. Those selections are already being studied. Some will be breeding parents, and others are going into trials and will be moved to processors for testing.

Another possible solution is utilizing CRISPR, which is a non-transgenic way to modify citrus varieties through gene editing to create varieties that are tolerant to HLB. This technology was discussed in detail in the October All In For Citrus podcast episode.

“As a breeder, I am really excited about CRISPR,” Chaparro said.

BREEDING CHALLENGES
Chaparro discussed how oranges come from a single genotype through mutation, meaning all oranges are essentially clones of one another. This also means that all oranges are susceptible to HLB, especially in Florida.

The definition of what is classified as an orange in the juice industry is incredibly restrictive, and this makes breeding even more difficult since nobody has successfully bred an HLB-tolerant sweet orange. Currently, the best sources of HLB resistance have poor fruit quality.

Chaparro identified desirable and undesirable traits of species that are being used to breed an HLB-tolerant sweet orange. The examples below show how unfavorable characteristics can challenge the breeding process.

• Citrus reticulata
  • Pros: Has moderate acidity, seedless, easy to peel, shows HLB tolerance
  • Cons: Low vigor
• Poncirus trifoliata
  • Pros: Cold resistance, citrus tristeza virus resistance, HLB tolerance
  • Cons: High acidity, poor color
• Eremocitrus glauca
  • Pros: Monoembryony, cold resistance, HLB resistance
  • Cons: Poor color, small fruit

Maegan Beatty is an AgNet Media intern.

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