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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Research Project #432612

Research Project: Field Evaluation of the Selected Variants of Ruby Red Grapefruit Volunteer Seedlings for Greater Huanglongbing (HLB) Resistance/Tolerance

Location: Subtropical Plant Pathology Research

Project Number: 6034-22000-042-17-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Apr 1, 2017
End Date: Mar 31, 2020

Objective:
To sustain the Florida citrus industry, the success of new plantings is key. Although resistant commercial varieties are not currently available, we have proved the selection concept for natural huanglongbing (HLB) resistance/tolerance, which has allowed us to obtain several variant citrus plants with much greater HLB resistance/tolerance. Exploitation of the natural resistance of these variants may provide the framework for the survival of the citrus industry in Florida since it would allow growers to overcome the loss of existing trees that have succumb to HLB with new, more resistant plantings that can survive/thrive in the presence of HLB. Therefore, the objectives of this proposal are: 1) conduct a field trial using the selected grapefruit seedlings to ensure the productivity of the trees in Florida where HLB is endemic; and 2) evaluate the quality of the fruit produced. Achievement of these goals will produce a more resistant/tolerant variety that could be available in the near future since its use would not require the regulatory approval that transgenic trees and/or chemical compounds are subject to.

Approach:
1) Field trial of selected trees for huanglongbing (HLB) resistance: The field trial will be set up using a randomized complete block design with a factorial combination of the top two lines deemed resistant/tolerant in the greenhouse screened on two different rootstocks (Commercial Sour Orange and Karun Jamir Sour Orange, which has shown greater resistance/tolerance in our greenhouse test for the past several years) at both Picos Farm and Scott’s Grove in Fort Pierce, FL. Picos Farm will represent groves under high psyllid pressure using horticulture practices that maintain tree health but are not optimized for fruit growth, whereas, Scott’s Grove will represent groves with lower disease pressure, more frequent insecticide sprays, and horticulture practices that are optimized for maximum fruit yield. Ten replicates of six trees will be planted and the Best Management Practices for each individual location will be used to care for the trees. 2) Evaluation of fruit quality of selected trees: Fruit quality will be evaluated for the selected Volunteer Grapefruit (VG) seedlings, as well as control using the following sensory evaluation and chemical analysis. For sensory evaluation, a trained panel will perform a descriptive analysis where basic taste (sweetness, sourness and bitterness) as well as flavor are rated on a 0-15 point scale after panelists were trained using reference standards. If fruit from the control are available, difference-from-reference tests might be preferred, where panelists compare the test samples against the labelled control. These tests will be repeated for each rootstock and location. Further, if any selection appears promising, acceptance tests will be performed using staff from the USHRL. Fifty-five untrained panelists will participate and indicate how much they like or dislike any particular sample using a 9-point hedonic scale. Taste panels will take place in isolated booths under red lighting, with each booth containing a computer and Compusense® Five software for data recording and analysis.