Horticultural & Management


Large-scale testing of the endophytic bacterium Frateuria defendens, a potential biocontrol agent of HLB

Report Date: 07/12/2021   Project: 19-027C   Year: 2021

Large-scale testing of the endophytic bacterium Frateuria defendens, a potential biocontrol agent of HLB

Report Date: 07/12/2021
Project: 19-027C   Year: 2021
Percentage Completion: 0.75
Category: Horticultural & Management
Author: Ute Albrecht
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them: The overall goal of the proposed research is to test the effectiveness of Frateuria defendens (Frd) in reducing HLB damage in FL citrus. The original proposal was revised for a 1-year feasibility study. Objective 1. Determine the optimal application method of Frd to citrus trees.We continued with the spray experiment that was initiated in Dec 2020 and data (horticultural and plant health assesment; CLas and Frd titer determination) are being collected bimonthly. The last dataset collected (April) suggested a positive but weak effect of weekly foliar sprays of Frd on the number of leaves and internodes and a slight reduction of CLas titers compared to the plants sprayed biweekly and non-sprayed controls.  We are continuuing our experimentation regarding viability/survival of Frd in citrus tissues. Our studies indicate that an organisms or compound that is associated with CLas (but not CLas itself) inhibits Frd growth in CLas infected leaves.  Because of the growth promoting effects of Frd observed in the first experiment, a follow-up experiment was initiated to test the hypothesis that Frd influences the hormonal balance in citrus plants. For this experiment  Frd is applied by leaf infiltration. Plant growth is evaluated on a bimonthly basis.  We have also initiated an experiment to assess Frd efficacy against CLas when delivered by stem injection. For this experiment Frd is compared against oxytetracycline.  Objective 2. Determine if Frd pre-treatment can prevent trees from getting infected with Candidatus Liberibacter asiaticus (CLas).So far, efficacy of Frd applications (foliar or injected) in restoring health of HLB affected plants was not found to be strong enough to justify initiation of this experiment.  2. Please state what work is anticipated for next quarter: We will continue with the foliar spray, leaf infiltration, and stem injection experiments, collection of horticultural information, and CLas and Frd titer determination.    3. Please state budget status (underspend or overspend, and why): Approximately 85% of funds have been spent which, as expected, is slightly overspent because funds were less than what is needed to fund a postdoc for one full year.



Evaluating sustainability of yield and fruit quality of sweet oranges with use of controlled release fertilizer and micronutrients

Report Date: 06/29/2021   Project: 18-061C   Year: 2021

Evaluating sustainability of yield and fruit quality of sweet oranges with use of controlled release fertilizer and micronutrients

Report Date: 06/29/2021
Project: 18-061C   Year: 2021
Percentage Completion: 0.85
Category: Horticultural & Management
Author: Tript Vashisth
Sponsor: Citrus Research and Development Foundation

This project is an continuation of an objective of existing CRDF funded project (# 00124558 ; ended in March 2019, final report submited to CRDF) with some added treatments to be evaluated in comparison to control (dry conventional fertilizer with foliar micronutrients).  Objective 1 which is the continuation of # 00124558 included 10 treatments.Altogether currently there are 25 treatments of citrus nutrition that are being compared to control. Within this quarter we have successfully harvested the trial. The Mn and B treatment is still the best performing treatment across all the treatments in Fort Meade. Where treatment with CRF and tiger micronutrients (6-6-3-1) is consitent good performer at both the sites. Altogether our data so far suggests that use CRF and soil applied micronutirents with slightly acidic pH is beneficial for the trees. No significant differences have been oberserved in new added treatments, it is speculated that two two years is not long enough duration to statitiscally impact the yield. We anticipate that we whould be able to see effect of treatments in upcoming year.Unfortunately, due to Covid-19 related restriction we could not perform sensory analysis, however we collected juice for flavor analysis in order to asses the effect of nutritional treatments on sensory aspect of juice. Currently, we are in process of data organization and analysis of field data and flavor analysis of juice samples.Within this quater the we successfully collected data on tree health, leaf and soil nutrition. We continue to analyze the data. 



Understanding the role of systemic acquired resistance (SAR) in enhancing tolerance to HLB in the Parson Brown sweet orange

Report Date: 06/28/2021   Project: 20-014   Year: 2021

Understanding the role of systemic acquired resistance (SAR) in enhancing tolerance to HLB in the Parson Brown sweet orange

Report Date: 06/28/2021
Project: 20-014   Year: 2021
Percentage Completion: 0.5
Category: Horticultural & Management
Author: Manjul Dutt
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them:Project objectives:Objective 1: Determine the effect of systemic acquired resistance (SAR) in enhanced tolerance to HLB  Objective 2: Monitor tree health and HLB levels Objective 3: Conduct Juice analysis and evaluate quality parameters from selected Parson Brown trees.  We have identified and collected leaf samples in the spring from 8 Parson Brown groves. Groves are spread all around the major citrus growing regions. We have evaluated the samples collected from the first quarter. All trees are HLB positive with Parson Brown Ct values comparable to the Hamlins. Parson Brown trees in most samples had elevated PR1 and PR2 . DNA and RNA analysis in this quarter will allow us to see if the trend continues through the summer.  2. Please state what work is anticipated for next quarter:In the next quarter, we will again sample the same groves and collect similar leaf samples. HLB levels will be evaluated using qPCR and we will evaluate the genetic differences between the samples. We will also collect data on some physiological parameters.   3. Please state budget status (underspend or overspend, and why):We are on target with the spending for this project.    



Using a Multipronged Approach to Engineer Citrus for Canker Resistance

Report Date: 06/24/2021   Project: 18-013   Year: 2021

Using a Multipronged Approach to Engineer Citrus for Canker Resistance

Report Date: 06/24/2021
Project: 18-013   Year: 2021
Percentage Completion: 0.65
Category: Horticultural & Management
Author: Jeffrey Jones
Sponsor: Citrus Research and Development Foundation

This project is a continuation of previously funded CRDF grants to TWO BLADES focused on utilizing multiple strategies to produce canker-resistant citrus plants plus the addition of a new strategy using gene editing. The project has focused on transforming Duncan grapefruit with genes that express EFR or a gene construct designated ProBs314EBE:avrGf2 that is activated by citrus canker bacteria virulence factors. We also are in the process of testing citrus that has been transformed to modify the bs5 gene to enhance resistance to the citrus canker bacterium. Objective 1. To determine if Bs3-generated transgenic grapefruit plants are resistant to diverse strains of the citrus canker bacterium  in greenhouse experiments and to the citrus canker bacterium in field experiments in Fort Pierce.  We are in the process of characterizing if different TAL effector variants activate the transgene in order to determine if variants of TAL effectors are effectively targeted.  In order to do this TAL variants we are in the process of inoculating into leaves of the transgenic plant, JJ5, and 5′-RACE will be used to identify transcription starts.  We will be able to determine if several unique TAL effectors are able to activate transcription. As for developing a different transgenic with  ProBs314EBE:avrGf2, we have placed our constuct in a different vector that is acceptable for future transgenic purposes. The previous constructs contain an additional selectable marker that allowed for identifying putative transgenics with a higher success rate. Given that there was concern about the additional marker, the new construct contains only NPT as a selectable marker. However, there were issues with the construct.  Therefore a new construct was made. This construct was recently sent to Vladimir Orbovic, who is in the process of creating additional transformants.   Objective 2. To determine if EFR-generated transgenic grapefruit plants are resistant to the citrus canker bacterium in field experiments in Fort Pierce. We have grafted our two most promising EFR transgenic plants (based on ROS activity) onto two rootstocks (812 and Sour Orange) and planted them in the field at Fort Pierce in collaboration Dr. Ed Stover. We will rate these in the next few weeks. We will be conducting futher greenhouse assays on ROS activity to determine if other EFR transgenics may have more potential for resistance to citrus canker than the two currently in the field. Objective 3. To determine if bs5-generated transgenic Carrizo plants are resistant to X. citri and to generate transgenic grapefruit carrying the pepper bs5. We have recently received budwood from UC Berkeley. The budwood was from two transgenic events and a third was from a tree that was run through the transformation process, but that was negative for the gene. The latter was to serve as the negative control as it had undergone the transformation process. We have grafted the buds and several have developed into branches.  We are currently growing these.  In the past few months neither of the branches that were created by crispr were actively growing. Recently both of the branches for the transgenic trees have begun growing and we plan on conducting further population experiments in order to confirm previous results on the the level of resistance.  



Cover crops and nematicides: comprehensive nematode IPM across the grove landscape

Report Date: 06/24/2021   Project: 18-036C   Year: 2021

Cover crops and nematicides: comprehensive nematode IPM across the grove landscape

Report Date: 06/24/2021
Project: 18-036C   Year: 2021
Percentage Completion: 0.83
Category: Horticultural & Management
Author: Larry Duncan
Sponsor: Citrus Research and Development Foundation

Nematicide treatments for the final spring season were applied.  Sting nematode populations were monitored monthly in row middle treatments of cover crop or native vegetation. Results to date were reported at the Florida Citrus Show in May and in the June issue of Citrus Industry.     



Cover crops and nematicides: comprehensive nematode IPM across the grove landscape

Report Date: 06/24/2021   Project: 18-036C   Year: 2021

Cover crops and nematicides: comprehensive nematode IPM across the grove landscape

Report Date: 06/24/2021
Project: 18-036C   Year: 2021
Percentage Completion: 0.83
Category: Horticultural & Management
Author: Larry Duncan
Sponsor: Citrus Research and Development Foundation

Nematicide treatments for the final spring season were applied.  Sting nematode populations were monitored monthly in row middle treatments of cover crop or native vegetation. Results to date were reported at the Florida Citrus Show in May and in the June issue of Citrus Industry. The primary information conveyed to both outlets is that 1) during two years, perennial peanut reduced the number of sting nematodes in row middles by more than 90%, which may be beneficial as the trees grow and root systems expand, 2) to the extent that the different nematicides reduced sting nematode numbers, the trees responded with increased vegetative (fibrous roots and trunks) growth, 3) during the first two years of production, tree growth rate was inversely related to number of fruit, 4) preliminary observation of tree growth in groves heavily damaged by sting nematode indicates that tolerance of sting nematode herbivory is likely conferred by blocking HLB occurrance via use of individual protective covers.     



Phloem specific responses to CLas for the identification of novel HLB resistance genes

Report Date: 06/15/2021   Project: 18-019   Year: 2021

Phloem specific responses to CLas for the identification of novel HLB resistance genes

Report Date: 06/15/2021
Project: 18-019   Year: 2021
Percentage Completion: 0.55
Category: Horticultural & Management
Author: Elizabeth Rogers
Sponsor: Citrus Research and Development Foundation

Our project is examining phloem gene expression changes in response to CLas infection in HLB-susceptible sweet orange and HLB-resistant Poncirus and Carrizo (a sweet orange – Poncirus cross). We are using a recently developed methodology for woody crops that allows gene expression profiling of phloem tissues. The method leverages a translating ribosome affinity purification strategy (called TRAP) to isolate and characterize translating mRNAs from phloem specific tissues. Our approach is unlike other gene expression profiling methods in that it only samples gene transcripts that are actively being transcribed into proteins and is thus a better representation of active cellular processes than total cellular mRNA. Sweet orange, and HLB-resistant Poncirus and Carrizo (sweet orange x Poncirus) will be transformed to express the tagged ribosomal proteins under the control of characterized phloem-specific promoters; tagged ribosomal proteins under control of the nearly ubiquitous CaMV 35S promoter will be used as a control. Transgenic plants will be exposed to CLas+ or CLas- ACP and leaves sampled 1, 2, 4, 8, and 12 weeks later. Ribosome-associated mRNA will be sequenced and analyzed to identify differentially regulated genes at each time point and between each citrus cultivar. Comparisons of susceptible and resistant phloem cell responses to CLas will identify those genes that are differentially regulated during these host responses. Identified genes will represent unique phloem specific targets for CRISPR knockout or overexpression, permitting the generation of HLB-resistant variants of major citrus cultivars.During the 2nd quarter of the third year of our grant, the Stover lab has completed production of the transgenics needed for this project. Many lines have been sent to the Rogers lab and the last few are growing well in the greenhouse and will be large enough to sent soon. The Rogers lab has continued small-scale no-choice psyllid inoculation experiments. ARS  facilities are still at a maximum of 25% occupancy due to the COVID-19 pandemic; we are teleworking the remaining time. This continues to slow down progress on grant milestones. We are very much hoping to be allowed to move to the next phases of reopening soon, which will allow for much more rapid progress. In addition, the grant-funded post-doc, Dr. Tamara Collum has accepted a permanent position; her last day will be July 2, 2021. We wish her well and are glad she isn’t going far and will be available to answer questions while we hire another post-doc to continue most of the day-to-day work of this project.     



Whole tree vs. rootstock or scion tolerance to HLB

Report Date: 05/25/2021   Project: 19-009   Year: 2021

Whole tree vs. rootstock or scion tolerance to HLB

Report Date: 05/25/2021
Project: 19-009   Year: 2021
Percentage Completion: 0.5
Category: Horticultural & Management
Author: Evan Johnson
Sponsor: Citrus Research and Development Foundation

In the last quarter, CLas inoculations of experimental trees occured and 2 and 7 week samples have been taken for RNAseq and metabolomics by the postdoc in Dr. Johnson’s and Dr. Wang’s labs respectively.  Soil samples were also collected from around the sampled roots for metabolomic analysis of root leachate.  These samples are currently being stored at -80 degrees celsius.  The second sampling was taken at 7 weeks instead of 6 weeks to allow enough root growth for sampling as a root flush was actively occuring.  Biweekly samples have been taken to assess CLas infection of the roots.  Once positive trees are confirmed metabolomic and RNAseq analysis of the appropriate collected samples will begin.            



Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

Report Date: 05/25/2021   Project: 19-010   Year: 2021

Determining new cost-benefit guided Phytophthora propagule treatment thresholds for HLB-affected citrus

Report Date: 05/25/2021
Project: 19-010   Year: 2021
Percentage Completion: 0.45
Category: Horticultural & Management
Author: Evan Johnson
Sponsor: Citrus Research and Development Foundation

HLB is known to make citrus roots more susceptible to Phytophthora root rot.  It also reduces the efficacy of chemical management of Phytophthora root rot, creating a difficult management scenario.  Current Phytophthora management recommendations are based on pre-HLB work done in the 1980s.  These three conditions raise the question of whether yield improvement from Phytophthora management is enough to pay for the management costs themselves.  The goal of this project is to develop new soil propagule density managment thresholds and recommendations for chemical management of Phytophthora root rot based on ecomonic analysis of yield responses in different soil conditions. Yield was collected on the Valencia plots in the last quarter.  Irrigations systems for chemigation treatments has been installed and the spring treatment has been put out.  In all but one treatment the first treatment of the year is phosphite. We have begun HLB inoculations of Phytophthora postive rootstocks for a greenhouse experiment to determine if the newly labeled chemistries have the same limitation on HLB-affected plants as fosetyl-Al and mefanoxam have shown.  Many of the new chemistries are directly effective against Phytophthora in the soil rather than acting after uptake by the roots, so this is likely to reduce the limitations of Phytophthora management in HLB-affected groves and test the hypothesis.           



Evaluation of the control effect of bactericides against citrus Huanglongbing via trunk injection

Report Date: 05/07/2021   Project: 18-064   Year: 2021

Evaluation of the control effect of bactericides against citrus Huanglongbing via trunk injection

Report Date: 05/07/2021
Project: 18-064   Year: 2021
Percentage Completion: 0.75
Category: Horticultural & Management
Author: Nian Wang
Sponsor: Citrus Research and Development Foundation

Objective 1. To illustrate whether application of bactericides via trunk injection could efficiently manage citrus HLB and how bactericides via trunk injection affects Las and HLB diseased trees. 1.1.          Determination of the in planta minimum bactericidal concentrations (MBCs) of bactericides against LasThis has been completed for both streptomycin and oxytetracycline against Las.  A manuscript entitled: “Residue dynamics of streptomycin in citrus delivered by foliar spray and trunk injection and effect on Candidatus Liberibacter asiaticus titer” was accepted for publication by Phytopathology.1.2.          Effect of bactericides via trunk injection on citrus HLB disease progression, tree health, yield and fruit quality in different aged trees with a different disease severityThe field experiments were performed at four different groves on different aged trees with a different disease severity. They are one located in Avon Park, FL,  3-year old Valencia trees; one in Bartow, FL, 2-year old W. Murrcot trees; and one in  Auburndale, FL, 7-year old Hamlin  trees (planted in 02/2012). The last one is in CREC-, Lake Alfred, FL, 20-year old Hamlin trees. The HLB disease severity and tree size (canopy volume and trunk diameter) in the four groves were estimated immediately prior to treatment application. For the field tests, the experiment design is a randomized complete block design (RCBD) for 9 treatments, including 6 injection treatments (3 different doses for OTC or STR), 2 spray treatments (OTC or STR spraying), and one No treatment as a negative control. Each injection treatment consisted of 9 or 15 trees divided into 3 blocks of 3 or 5 trees each. Each spray treatment consisted of 30 trees divided into 3 blocks of 10 trees each. For all the four field trials, the injection treatment applications were completed by the end of April 2019. The 1st application of spray treatments were completed during spring flushing in February or March 2019, the 2nd applications were conducted in late June to early July 2019, and the 3rd applications were conducted in early to middle October 2019. Leaf samples have been collected from the treated trees at the following time points: 0 (pre- injection), 7, 14, 28 days, 2, 4, 6, 8, 10 and 12 months after treatment (MPT). The estimation of Las titers in these leaf samples are ongoing with qPCR assays. The first estimation of HLB disease severity and growth performance (height, trunk diameter, and canopy volume) of immature trees after treatment were performed in May 2019 (three months after the injection) and continued in a 3-months interval. Fruit yield and quality data were collected for the Bartow trial (W. Murrcot), Auburndale trial (Hamlin), and CREC trial (Hamlin) in January 2021. We investigated the effect of10 adjuvants on oxytetracycline absorption via foliar spray.  Four adjuvants including Flame slightly increased the antimicrobial effect of OTC on Las.Objective 2. To examine the dynamics and residues of bactericide injected into citrus and systemic movement within the vascular system of trees and characterize the degradation metabolites of bactericides in citrus. Leaf and root samples have been collected from OTC or STR treated trees in the Avon Park grove at the following time points:0 (pre- injection), 2, 4, 7, 14, 28 days, 2, 4, 6,  8, 10, and 12 months after injection. The samples have been processed for OTC or STR extraction, and the concentrations of OTC and STR in these samples were determined by HPLC assays. Fruit samples were collected for the Bartow trial (W. Murrcot), Auburndale trial (Hamlin), and CREC trial (Hamlin) during harvest in January 2020, and for the Avon Park trial (Valencia) in April 2020. The samples were processed for OTC or STR extraction, and the concentrations of OTC and STR in these samples were determined by HPLC assays. We have collected data for 60 and 360 days post treatment. We have analyzed the residues of OTC and STR for fruit samples harvested in January 2021. Objective 3. To determine whether trunk injection of bactericides could decrease Las acquisition by Asian citrus psyllids (ACP)Twenty 1.5-year old citrus (Valencia sweet orange) plants were graft-inoculated by Las carrying buds in February 2020. These plants are being tested for Las infection and 4 plants were confirmed with Las infection (Ct values are between 34.0 and 35.0) at 4 months after grafting. They will be subjected to OTC or STR treatment by trunk injection and ACP acquisition access for 7 to 14 days. We have determined the time points to test OTC and STR treatment on ACP acquisition of Las. Objective 4. To monitor resistance development in Las against bactericides and evaluate potential side effects of trunk injection of bactericides Monitoring resistance development in Las against bactericides. Leaf samples for this test have been collected from 5 trees injected with OTC and 5 trees injected with STR at the highest doses in each of the three groves at 6 and 9 months after the injection, respectively. PCR-sequencing analysis on Las 16SrRNA gene showed there was no mutation compared with the reported sequence. We are further confirming the results. Evaluation of potential side effects of trunk injection of bactericides have been completed. We have collected another set of samples to monitor Las resistance against OTC and STR. The samples were sent out for sequencing to monitor the mutations of OTC and STR resistance related genes.        



Right Leaf Sampling-The first and most critical step to good nutrition program

Report Date: 04/26/2021   Project: 20-011   Year: 2021

Right Leaf Sampling-The first and most critical step to good nutrition program

Report Date: 04/26/2021
Project: 20-011   Year: 2021
Percentage Completion: 0.05
Category: Horticultural & Management
Author: Tripti Vashisth
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them:1. To determine how many leaf nutrient sampling per year are required to effectively capture the tree nutritional statusand adjust fertilizer accordingly.2. To establish the relationship of leaf nutrient concentration with yield, fruit drop, and canopy density3. To determine how the leaf nutrient (all 14 nutrient) levels change in the tree throughout the year.4. To evaluate how the leaf age affects the leaf nutrient status.The project started this quarter. The main goal for this quarter was to identify sites, mark trees, and collect baseline data.We surveyed 10+ sites to finalize the 4 sites for this trial, two sites are on Ridge and 2 are in southwest.. Ine ach site morethan 100 trees were manually screed for canopy density and disease index rating to identify trees as Mild and Severe. Thefinal data trees were tagged and tree health data such as canopy volume, leaf area index, leaf chlorophyll, leaf size andweight, root density been collected. Leaf samples for starch quantification and leaf, root and soil for nutrient analysis hasbeen collected are being processed. The spring flush has been tagged on the trees.  2. Please state what work is anticipated for next quarter:1. Data analysis and interpretation2. Processing samples for starch3. Tagging summer flush4. Collecting samples for nutrient analysis5. Applying fertilizer treatments based on leaf results   3. Please state budget status (underspend or overspend, and why): Currently, the project is still in the set up phase.The budget is spent as per the plan where major funds have been used for nutrient anlaysis. We have found dedicatedpersonnels to work on this project starting this quarter.       



Right Leaf Sampling-The first and most critical step to good nutrition program

Report Date: 04/26/2021   Project: 20-011   Year: 2021

Right Leaf Sampling-The first and most critical step to good nutrition program

Report Date: 04/26/2021
Project: 20-011   Year: 2021
Percentage Completion: 0.05
Category: Horticultural & Management
Author: Tripti Vashisth
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them:1. To determine how many leaf nutrient sampling per year are required to effectively capture the tree nutritional statusand adjust fertilizer accordingly.2. To establish the relationship of leaf nutrient concentration with yield, fruit drop, and canopy density3. To determine how the leaf nutrient (all 14 nutrient) levels change in the tree throughout the year.4. To evaluate how the leaf age affects the leaf nutrient status.The project started this quarter. The main goal for this quarter was to identify sites, mark trees, and collect baseline data.We surveyed 10+ sites to finalize the 4 sites for this trial, two sites are on Ridge and 2 are in southwest.. Ine ach site morethan 100 trees were manually screed for canopy density and disease index rating to identify trees as Mild and Severe. Thefinal data trees were tagged and tree health data such as canopy volume, leaf area index, leaf chlorophyll, leaf size andweight, root density been collected. Leaf samples for starch quantification and leaf, root and soil for nutrient analysis hasbeen collected are being processed. The spring flush has been tagged on the trees.  2. Please state what work is anticipated for next quarter:1. Data analysis and interpretation2. Processing samples for starch3. Tagging summer flush4. Collecting samples for nutrient analysis5. Applying fertilizer treatments based on leaf results   3. Please state budget status (underspend or overspend, and why): Currently, the project is still in the set up phase.The budget is spent as per the plan where major funds have been used for nutrient anlaysis. We have found dedicatedpersonnels to work on this project starting this quarter.       



The effect of the ionization state of iron and citric acid on the health of HLB-infected trees.

Report Date: 04/23/2021   Project: 18-050C   Year: 2021

The effect of the ionization state of iron and citric acid on the health of HLB-infected trees.

Report Date: 04/23/2021
Project: 18-050C   Year: 2021
Percentage Completion: 1
Category: Horticultural & Management
Author: Randall Niedz
Sponsor: Citrus Research and Development Foundation

Objective 1  – Determine the effect of the ratio and concentration of Fe2+ + organic acid on hydroxyl radical production and stability. Objective complete. Objective 2  – Determine the phytotoxic levels of Fe2+ + organic acid solutions on citrus. Objective complete.  Objective 3  – Determine the effect of Fe2+ + organic acid solutions on HLB titer using a rapid greenhouse, HLB-infected citron, rooted shoot bud assay. Continuing work to develop a rapid greenhouse screening system.  Current systems are not yet ready for screening methods to cure or manage HLB. No CRDF funds being used for this research. Objective 4  – Requires screening system – see objective 3 discussion.Objective 5  – Requires screening system – see objective 3 discussion. Objectives 6 and 8 (Note: there is no 7)    – These are the field tests for the various ferrous iron (Fe2+) and citric acid treatments on HLB status and horticultural measures for both mature (HLB symptomatic) and nonbearing (non-symptomatic) trees. Throughout this quarter (Jan 1 – Mar 31) as well as the project timeline, conventional pesticide spray applications for non-bearing grapefruit trees were applied to all the treatments in the trial and were based on scouting and were in accordance with IFAS guidelines.  Similarly, irrigation events were made based on tree and field conditions as determined by soil feel and appearance, tensiometer readings, water table observation well measurements and visual assessment of tree canopy.   Fertilizer applications were made via fertigation and were `spoon fed’ with frequent small applications bi-weekly.  No dry fertilizer was used. All 7 experimental treatments were applied to the trial block as per the protocol.   There was one cold front that impacted the trial location in Indian River County on 02/04/2021 with a low temperature documented at 35.97 . F.  Only very minor leaf drop occurred 5 days after the cold weather.  Rainfall over this quarter was 5.79 in. with on 0.33 in. recorded in March 2021 requiring frequent irrigation events.  Visual assessments of tree condition were made on 01/14/21 using a numerical rating of 1-4 for each tree quadrant and were averaged for each tree.  Other field measurements included fruit counts (01/28/2021) and trunk caliper measurements (03/31/2021).  Leaf sampling for PCR analysis was performed on 01/27/2021.   As in prior quarters, a ground application of herbicide was made, and plant material was removed in preparation for a 03/06/2021 UAV flight to collect aerial imagery for canopy area determinations.   Aerial images were taken with a UAV equipped with a 20 MP digital camera on 3/6/2021.  A set of overlapping images were taken at two altitudes  – 75 and 150 feet.  Images taken at 75 feet are for photo-documentation (0.27 inch/pixel) of the experiment and will be made available at the completion of the project.  Images taken at 150 feet (0.53 inch/pixel) were processed by segmenting the image into trees and background using machine learning image analysis.  Once the trees were segmented (identified and separated from the background), various measures were made/calculated including canopy area, density, perimeter, convex hull area and perimeter, and minimum and maximum caliper diameters.  These measures, as well as the ground measures, will be correlated (statistical analysis) with the iron treatments to determine their effects. 



The effect of the ionization state of iron and citric acid on the health of HLB-infected trees.

Report Date: 04/23/2021   Project: 18-050C   Year: 2021

The effect of the ionization state of iron and citric acid on the health of HLB-infected trees.

Report Date: 04/23/2021
Project: 18-050C   Year: 2021
Percentage Completion: 1
Category: Horticultural & Management
Author: Randall Niedz
Sponsor: Citrus Research and Development Foundation

Objective 1  – Determine the effect of the ratio and concentration of Fe2+ + organic acid on hydroxyl radical production and stability. Objective complete. Objective 2  – Determine the phytotoxic levels of Fe2+ + organic acid solutions on citrus. Objective complete.  Objective 3  – Determine the effect of Fe2+ + organic acid solutions on HLB titer using a rapid greenhouse, HLB-infected citron, rooted shoot bud assay. Continuing work to develop a rapid greenhouse screening system.  Current systems are not yet ready for screening methods to cure or manage HLB. No CRDF funds being used for this research. Objective 4  – Requires screening system – see objective 3 discussion.Objective 5  – Requires screening system – see objective 3 discussion. Objectives 6 and 8 (Note: there is no 7)    – These are the field tests for the various ferrous iron (Fe2+) and citric acid treatments on HLB status and horticultural measures for both mature (HLB symptomatic) and nonbearing (non-symptomatic) trees. Throughout this quarter (Jan 1 – Mar 31) as well as the project timeline, conventional pesticide spray applications for non-bearing grapefruit trees were applied to all the treatments in the trial and were based on scouting and were in accordance with IFAS guidelines.  Similarly, irrigation events were made based on tree and field conditions as determined by soil feel and appearance, tensiometer readings, water table observation well measurements and visual assessment of tree canopy.   Fertilizer applications were made via fertigation and were `spoon fed’ with frequent small applications bi-weekly.  No dry fertilizer was used. All 7 experimental treatments were applied to the trial block as per the protocol.   There was one cold front that impacted the trial location in Indian River County on 02/04/2021 with a low temperature documented at 35.97 . F.  Only very minor leaf drop occurred 5 days after the cold weather.  Rainfall over this quarter was 5.79 in. with on 0.33 in. recorded in March 2021 requiring frequent irrigation events.  Visual assessments of tree condition were made on 01/14/21 using a numerical rating of 1-4 for each tree quadrant and were averaged for each tree.  Other field measurements included fruit counts (01/28/2021) and trunk caliper measurements (03/31/2021).  Leaf sampling for PCR analysis was performed on 01/27/2021.   As in prior quarters, a ground application of herbicide was made, and plant material was removed in preparation for a 03/06/2021 UAV flight to collect aerial imagery for canopy area determinations.   Aerial images were taken with a UAV equipped with a 20 MP digital camera on 3/6/2021.  A set of overlapping images were taken at two altitudes  – 75 and 150 feet.  Images taken at 75 feet are for photo-documentation (0.27 inch/pixel) of the experiment and will be made available at the completion of the project.  Images taken at 150 feet (0.53 inch/pixel) were processed by segmenting the image into trees and background using machine learning image analysis.  Once the trees were segmented (identified and separated from the background), various measures were made/calculated including canopy area, density, perimeter, convex hull area and perimeter, and minimum and maximum caliper diameters.  These measures, as well as the ground measures, will be correlated (statistical analysis) with the iron treatments to determine their effects. 



Organic acids compared to conventional acidification for improved nutrient uptake and root physiology

Report Date: 04/16/2021   Project: 20-004   Year: 2021

Organic acids compared to conventional acidification for improved nutrient uptake and root physiology

Report Date: 04/16/2021
Project: 20-004   Year: 2021
Percentage Completion: 0.1
Category: Horticultural & Management
Author: Evan Johnson
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them: Objective 1: Determine effects of lowered soil pH on CLas populations and root physiology including internal root apoplast and vascular tissue pH.We are preparing plant material for CLas inoculation to initiate these experiments  Objective 2: Field test multiple acidification materials including organic acids for tree response CLas suppression, nutrient uptake, and root and vascular pH changes  We have identified multiple candidate field sites and are currently working on assessing soil characteristics to make sure they fit within the desired starting conditions, especially pH, for the trial.    2. Please state what work is anticipated for next quarter: In the next quarter we anticipate inoculating greenhouse trees with CLas for objective 1.  In the next quarter we anticipate finalizing field site selection, layout of plots, preliminary plot data collection, and initiation of treatments for objective 2   3. Please state budget status (underspend or overspend, and why):  The budget is in underspend because we need final field site selection before determining the injection equipment and amount of chemical for application based on row length.