Mike Roberts

Rootstock Improvement in the HLB Era

Citrus greening, or HLB, has put the Florida citrus industry in serious jeopardy, and much of the research coming out of institutions like The University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) is focused on finding some way to beat the disease. For plant cell genetics professor Dr. Jude Grosser, that focus has been put on developing rootstocks that are resistant or tolerant of citrus greening. He and others presented an “Update on rootstock improvement in the HLB era” at the 2020 Florida Citrus Show on those rootstocks that may just be Florida citrus’s future in the era of citrus greening.

Rootstocks for a Citrus Greening Era

Grosser is part of the UF/CREC Citrus Improvement Team, which he maintained was tasked with establishing “a common sense, delicate balance between providing viable/profitable rootstock options for the short-medium term, and developing the homerun rootstock(s) that will be the answer to HLB for the future, regardless of the scion,” in the presentation. Since the Florida citrus industry is currently dealing with citrus greening by spraying to control the Asian citrus psyllid (the vector that spreads citrus greening), perfect nutrition and irrigation, and replacing citrus trees that are falling below profitable production levels due to citrus greening, it’s important for Grosser’s team to develop rootstock options for both the present and the future.

Some highlights on rootstocks from presentation include:

  • New Rootstocks being considered for commercial release: Cleo+Carrizo; Blue 1, Orange 1804 (Argentina), Orange 16, Orange 14 & Amb+HBJL-2B.
  • Valencia/UFR-17 is emerging as a good HLB-tolerant rootstock for higher-density plantings. Resets of UFR-17 have been growing in Orie Lee Alligator Grove for the past six years with no psyllid control. The trees are healthy and produced 2.5 boxes per tree in 2019.
  • Hybridizing the rootstock, Gauntlet, which is “exceptionally tolerant of HLB,” but “does not make a good rootstock itself due to slow growth and excessive zygotic seed production” has corrected the problem with vigor.

The presentation maintained that rootstock improvements with an eye towards HLB tolerance and/or resistance are likely to come in stages. The first is developing rootstocks that “reduce the frequency of HLB infection, and reduce the severity of the disease once infected.” The presentation maintained this has already been shown to work with mid- and late-season oranges that have received optimized nutrition. The second stage is developing rootstocks that can protect the entire tree, no matter the scion grafted to it. The presentation shared that research is underway concerning rootstocks that mitigate the disease.

The work coming out of UF/IFAS and affiliated organizations, like UF/CREC, has made the continuation of the Florida citrus industry a reality, and their efforts will pay off in the future with HLB tolerant and resistant rootstocks!

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