by BRAD BUCK, UF/IFAS
FORT PIERCE, Fla. — New citrus varieties are now in their fourth year of growth and show
signs of hope for growers in the Indian River District.
University of Florida/IFAS officials and research scientists invite growers to tour the 20-acre
Millennium Block on Nov. 7, 9 a.m. until 2 p.m.
“We are excited about collecting a second year of data for assessing fruit yield and fruit quality,”
said Ronald D. Cave, Director of the UF/IFAS Indian River Research and Education Center
(IRREC) in Fort Pierce, the center of the world’s premier grapefruit production region. “There
certainly are notable visual differences among the numerous scion and rootstock combinations. I
hope growers will come to see those differences and the data from last season’s harvest.”
The grove is a living experiment of more than 5,500 citrus trees representing 142 scion and
rootstock combinations, some of which are tolerating citrus greening better than others. The
grove is situated in the heart of the Indian River citrus production district that is internationally
renowned for its peerless fresh grapefruit. The research is expected to reveal which citrus
varieties and rootstocks will allow growers to stay in business, said Cave.
Research in the Millennium Block (MB) citrus grove began with the first plantings in 2019, Cave
said The Indian River region has seen a steep decline over the last 20 years due initially to the
introduction of citrus canker, followed by the world’s most serious citrus disease, citrus
greening. Breeders have developed new trees, some of which appear more tolerant of the
bacterium that causes citrus greening.
The scion is the above-ground foliage and fruit, while the rootstock is the below ground roots
that are adapted to different soil types and impart resistance to soil-borne diseases but also
influences tree growth and fruit quality.
“Hurricanes Ian and Nicole impacted fruit from the 2022 harvest, so we are eager to evaluate this
season’s production,” said Cave.
Mark Ritenour, a professor of horticulture and postharvest technology, points out more than a
few varieties that show full canopies and decent crop loads. Among the grapefruit and pummelo
hybrids that performed best last year was UF 914, which is a seedless, red-fleshed grapefruit-like
hybrid developed by UF/IFAS breeders at the Citrus Research and Education Center.
This year’s fruit harvest is now underway, Ritenour said.
The research must continue for at least seven years to be robust enough to recommend the best
scions and rootstocks to growers, Ritenour said. However, some of these varieties are already
available for grower testing through a New Varieties Development & Management Corporation
and UF/IFAS “Fast Track” release option (https://nvdmc.org/fast-track/).
“With over 142 new citrus scion-rootstock combinations, we expect that some will rise above the
others and be viable options for the industry.” said Ritenour. “ ‘Star Ruby’ grapefruit, for
example, is one that is not performing well under these Florida conditions.”
Macselynia Hossain, an IRREC agricultural assistant, is involved with the harvest. He said new
data will be available to growers who attend the MB tour .
“I am currently working with data that focuses on brix — or sugar content — acidity, ratio and
yield, and I hope to have it summarized before the tour,” said Hossain. “For this year’s data, we
will have a new baseline to evaluate the grove trees. Data and findings will increase each
year.”
Pete Spyke, a Heritage citrus grower and IRREC Advisory Committee member, said only four
citrus rootstocks were used in the region. “We are looking at about 30 rootstocks in the MB
grove,” Spyke said. “The assumption is that they will replace the three or four rootstocks the
industry has focused on for so long.”
Flavia Zambon began her new position as assistant professor of horticultural production of citrus
and other tree crops last week. Previously, Zambon was a postdoctoral researcher at IRREC
leading the evaluation of grapefruit scion and rootstock combinations planted across 42 blocks
among 16 private growers’ properties.
“The Millennium Block is the pinnacle of local variety trials with several combinations that can
guide us for tailored choices for the future of the Indian River grapefruit region,” said Zambon.
“We will select the most promising combinations before their commercialization. The growers
can make informed decisions based on the data we analyze and provide to them.