Performance of newly released grapefruit cultivars and rootstocks in the Indian River Citrus District

Performance of newly released grapefruit cultivars and rootstocks in the Indian River Citrus District

Report Date: 06/14/2022
Project: 18-037C   Year: 2022
Category: Plant Improvement
Author: Ronald Cave
Sponsor: Citrus Research and Development Foundation

     A large-scale trial of HLB-tolerant citrus cultivars addresses the need of Indian River growers to identify the best rootstocks and scions for growing fresh citrus fruit. This project had two objectives: (i) Assess the performance of new grapefruit cultivars with selected rootstocks; and (ii) Evaluate the influence of UFR and other rootstocks on grapefruit scion development in comparison to legacy/standard rootstocks. Trial 1 consisted of 18 grapefruit cultivars on three rootstocks (Sour orange, US-942, and X-639). Trial 2 assessed 31 rootstocks with `Ray Ruby’ grapefruit as the scion. The total number of trees with grapefruit scions is 2,741. Control-release polycoated fertilizer was applied appropriately in May 2022. All trees were treated as needed with appropriate agrochemicals to manage canker, Asian citrus psyllids, mites, and citrus leafminers. No trees died due to the subzero temperatures experienced in February 2022.     Trunk diameter and canopy volume were measured on the three middle trees in each experimental plot in October 2021 to assess tree size. At the time, there were significant differences among scion/rootstock combinations. In Trial 1, `Pummelette UF-5-1-99-2′ grapefruit on US-942 was 6X larger (395.5 ft3) than `US 1-83-179′ grapefruit hybrid on US-942 (70.6 ft3). In Trial 2, grapefruit on UFR-15 was 3X larger (314.3 ft3) than on UFR-17 (123.6 ft3) for trees planted September 2019. Measurements were gathered from trees planted in June 2021 for the first time in May 2022. Phenology data collected monthly recorded flush initiation, flower initiation, full flowering, fruit set, fruit development, fruit color, and fruit maturity per tree. No fruit data were collected because a tree’s first crop is not indicative of future production. Nearly all trees in Trials 1 and 2 have set fruit in May 2022. Fruit data will be collected in January 2023. Long-term evaluation of fruit yield and quality is needed to identify the most promising scions and rootstocks to determine their profitability and capability of meeting grower and market needs.     HLB is widespread in the study grove. Visual blotchy mottle symptoms and twig dieback canopy are present in a few treatments but not widespread. Leaf samples for quantifying CLas titer were collected in May 2022 and sent to Southern Gardens for analysis. Trees that are CLas-free (ct values >38) and CLas-infected and symptomatic (ct values of 26-32) can be found in the same plots, but many symptomatic trees are developing vigorous canopies.      The incidences of Asian citrus psyllid and citrus leafminer were frequent during flush periods. The incidences of aphids, root weevils, and orange dogs were sporadic. Canker damage was noticeable but not uniform; it was especially significant on `Ray Ruby’ grapefruit trees. Tree growth has not been significantly affected by these pests due the timely applications of pesticides.     Results of the study were presented at the annual Florida Citrus Show in January 2022 in Fort Pierce, FL by graduate student Martin Zapien and in his Zapien’s MSc thesis presented to the Graduate School in April 2022. The thesis and data collected to date are available upon request.  


Your browser does not support pdfs, click here to download the file.