Millennium Block

Millennium Block Research Shows Promising Results

Daniel CooperGrapefruit, Indian River, Research

Millennium Block
The Millennium Block was planted in 2019.
Photo courtesy of UF/IFAS

A recent update of Millennium Block research at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center in Fort Pierce indicates the 5,500 trees in the project are yielding promising results.

The four trials within the Millennium Block aim to unlock the genetic potential of new scion and rootstock hybrids never tested in field conditions. They focus on finding grapefruit scion/rootstock combinations that are HLB tolerant. The outcomes from UF/IFAS and U.S. Department of Agriculture breeding programs have been instrumental in this endeavor. Several new scion and rootstock varieties were planted in 2019.

Flavia Zambon, UF/IFAS assistant professor, leads the research.

“It took time, but we are finally seeing highly different results from the 30-plus rootstock materials at the Millennium Block,” Zambon said recently. “These differences are crucial for grower decision-making, as rootstocks influence canopy size, plant height and yield.”

Results from last season’s trials are particularly noteworthy. They include:

  • Among all the rootstocks tested, Ray Ruby grapefruit grafted onto UFR-15 produced the highest yield, reaching an average of 90 boxes per acre (227 trees/acre) and Brix between 6.5 and 7. UFR-15 has been available to growers since 2015. Higher juice quality was achieved in Ray Ruby grafted onto 2247 x 6070-02-2, a tetrazyg rootstock that produces small trees with very high soluble solids.
  • The dwarf 2247 x 6070-02-2 performed the best for Glenn Navel juice quality, followed by Willis and US-897, with Brix between 7 and 8.
  • The grapefruit scion/rootstock combination trial of 18 scions grafted onto three different rootstocks also shows impressive results. A fortuitous label mistake led to the planting of a historical golden grapefruit named Triumph. A sister of the Jackson grapefruit, this seedy grapefruit-orange hybrid is packed with juice and has the highest yield of the trial, averaging over 200 boxes per acre in a 227 trees/acre setting. It shows little to no HLB symptoms. Grafted onto X-639, the tree has a dense canopy and dark green leaves. The fruit breaks color very early in the season, and its harvest occurs in late November. Although setting early, the harvest window is considerable, with fruit still on the tree in mid-March and almost no fruit drop.
  • Following Triumph is its sister, Jackson, grafted onto US-942 and UF-914. UF-914 is a pummelo hybrid with a deep red color and low in furocoumarins. That’s a desirable trait for people who can’t eat grapefruit due to the interaction of the component to several medicines. This variety was also among the highest in Brix when grafted onto sour orange and US-942, reaching between 8 and 9 degrees Brix.
  • Other combinations also had high Brix values but were not yielding well in this specific field setting.

Source: Indian River Citrus League

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