Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 211 - Insects, Mites, and Other Arthropods Affecting Plants | 999 - Citrus, general/other | 1060 - Biology (whole systems) | 100% |
Huanglongbing (HLB) is the main threat the USA citrus industry faces, with no cure available. For this reason, preserving newly planted trees' health is paramount. The risk of becoming infected is exceptionally high for young trees, which flush frequently, attracting more psyllids. Individual protective covers (IPCs) are increasingly being adopted to protect newly planted citrus trees. However, IPCs must be removed after 2-3 years, leaving trees exposed. It would be advantageous to prolong tree health, ensuring several years of high-quality fruit production and increased yield. Brassinosteroids (Brs) are hormones approved for commercial use in Florida citrus. We have demonstrated that Brs delay HLB progression, reduce psyllid colonization and rust mite incidence. Furthermore, Brs advance internal fruit maturation by almost one month in Valencia trees. We propose a combination of IPCs and Brs for enhanced protection against the HLB vector (ACP) and other diseases. We hypothesize that Brs will prolong health of young trees after IPC removal. Objectives: 1) study the effects of IPCs, Brs, and their combination on tree physiology, fruit production, yield and quality, HLB incidence and progression, 2) study the effects of Brs on biology and behavior of the ACP and on reducing incidence and pathogen transmission, 3) assess the effects of IPC+Brs on other pests and diseases, and 4) communicate the project progress and results to stakeholders. This proposal perfectly aligns with priority 2.5: Regional management or eradication of ACP on commercial citrus groves and residential plantings; management strategies should incorporate appropriate resistance management measures.
Our main hypothesis is that Brs will prolong health in trees of producing age after IPC removal. We propose to use a combination of IPCs and foliar applications of commercially available Brs for prolonged protection of citrus trees against HLB and other diseases that limit citrus production in Florida. By doing so, we will provide a ready-to use management tool for growers to increase yield and provide superior quality fruit in an endemic HLB environment.
Experimental approach:Our plots are organized in a complete randomized block design, with 10 replicates consisting of 5 trees each. We will use the 3 middle trees for sampling and rating, leaving the 2 outermost trees as buffer trees.Treatments1) Brs (monthly) in previously IPC-covered trees and in no IPC trees (2 years).2) No Brs in previously IPC- and in no IPC-covered trees (2 years).3) Control (traditional insecticide control).These treatments will be applied to trees primed (already in the field for three years) for the proposed experiment under three scenarios:1) Covered with IPCs for 3 years2) Not covered with IPCs for 3 years3) Control, traditional insecticide control.Because plots and trees are ready for the proposed experiment, research objectives will be attainable within the 2 years of the proposed project. Otherwise, it would require five years to conduct this research.This strategy will allow to determine if Brs treatment a) can prolong health of IPC covered trees once they are uncovered, b) can reduce other pests/diseases, c) has therapeutic effect on disease-affected trees, d) may have some priming effect on protecting trees before they get exposed to psyllids.We will use an automated sprayer for Brs application to fully cover the canopy until runoff (typically 1 minute of spraying in mature bearing trees). Treatments with Brs (186 mL/100 gal. of water) will be performed monthly on sunny days with no wind and always at the same time in the morning.Data collection:Tree growth (root mass density, trunk girth, height, canopy volume, leaf area index), HLB infection rate and incidence of other pests and diseases, fruit yield, quality, and fruit drop rate will be measured.-CLas and psyllid monitoring. CLas will be detected by quantitative real-time polymerase chain reaction (qPCR) quarterly as described in Li et al. (2006). Psyllid infestation will be assessed also quarterly by using the TAP method described by Stansly and Qureshi (2007). In brief, branches will be tapped three times with a 1-ft piece of PVC pipe and insects dislodged on a laminated sheet of letter-sized paper will be counted.-HLB disease assessment. HLB severity will be assessed quarterly on a rating scale of 1 to 5, with 1 = no foliar disease symptoms, 2 = 1- 25% of the canopy with foliar disease symptoms, 3 = 26-50% of the canopy with foliar disease symptoms, 4 = 51-75% of the canopy with foliar disease symptoms, and 5 = 76-100%) of the canopy with foliar disease symptoms.-Tree growth assessment will be performed at the end of spring and fall seasons each year. Tree height will be measured from the soil surface to the top of the tree using a tape measurer (Komelon, Waukesha, WI, USA) and avoiding any erratic shoots. Canopy diameter will be measured parallel and perpendicular to the row, and the canopy volume will be calculated using the formula by Wutscher and Hill (1995):canopy volume = [(diameter parallel to row x diameter perpendicular to row) x height]/4.The leaf area index (LAI) will be determined using a LIA-2200C Plant Canopy Analyzer (LI-COR Biosciences, Lincoln, NE, USA). Scion and rootstock diameters will be measured at 5 cm above and below the graft union respectively, using a Vernier caliper (Fowler high precision, Auburndale, MA, USA). Trunk diameters will be measured in two perpendicular directions and averaged. Root growth/density as a general measure of root health will be measured using 8 soil cores (106-inch deep), 2 per tree quadrant in the wetted/irrigated zone of tree and considered for dry root biomass and used for CLas quantification by qPCR. Fibrous root density per gram of soil will be determined in spring and in fall of every year.-Fruit yield and quality. Fruit drop will be measured weekly, and fruit yield and quality will be determined at the end of each season. Fruit quality will be assessed by determining ?Brix, TTA and ?Brix/acid ratio with conventional methods, and pound solids determined.-Gene expression analysis. Leaf samples will be taken weekly for several months. Gene expression of Chorismate mutase 1 and 2 (ICM1 and 2), Isochorismate synthase (ICS1), chitinase, beta 1, 3-glucanase, NPR1, and PR5 (marker genes) will be studied by real time qRT-PCR.
Target Audience
Professional audience, including extension agents via In Service Trainings and scientists via professional meetings (FSHS and ASHS annual meetings). Stakeholders and growers via trade magazines, field visits to the research sites, and professional venues such as Citrus Expo and Citrus Institute. In different venues, previously, growers and other stakeholders, who routinely now use IPCs were asking what to do with the trees once IPCs are removed. Our experimental sites in this grant show that brassinosteroids can prolongue tree health, so they visit our sites to learn first hand how they can implement this at their groves. Similarly. Extension agent training via UF/IFAS ISTs multiplies our communication effort, because every agent who is attending spreads the information we deliver to their clentele.
Changes / Problems
Nothing Reported
Training & Professional Development
This project has allowed a postdoc and a student to present their accomplishments on this project in FSHS professional meetingduring 2024. It also allowed to continue exposingthem to interact with growers and perform extension activities, including writing informative flyers/bulletins and answer directly questions from them.
Dissemination Streams
We have been delivering presentations at professional meetings (scientific and grower-oriented), and at master gardeners events. Our experimental sites have continued to be known as demonstration sites were growers and other interested audiences (including international: growers and researchers from Brazil, South Africa and Spain) have come to see the results this second year. A direct result from this was that PI Fernando Alferez was invited by Fundecitrus to visit citrus growing region in Brazil and give several taks to growers on the IPC+Brassinosteroid system.
Next Reporting Steps
We will finish the collection of data in our experimental sites as the project will come to an end.Treatments and data collection will follow as in year 2. Publication of results in peer reviewed journals will continue, as we have already published our first manuscripts. EDIS publications will be published, they are in preparation now. Similar extension activities as in year 2 with updated results and recommendations will be performed. A field day is planned for February 2025
Target Audience
Professional audience, including extension agents via In Service Trainings and scientists viaprofessional meetings (FSHSand ASHS annual meetings). Stakeholders and growers via trade magazines, field visits to the research sites,and professional venues such as Citrus Expo and Citrus Institute. In different venues, previously, growers and other stakeholders, who routinely now use IPCs were asking what to do with the trees once IPCs are removed. Our experimental sites in this grant show that brassinosteroids can prolongue tree health, so they visit our sites to learn first hand how they can implement this at their groves. Similarly. Extension agent training via UF/IFAS ISTs multiplies our communication effort, because every agent who is attending spreads the information we deliver to their clentele.
Changes / Problems
Student enrolled late, due to some departmental enrollment timing and deadlines. Also, importantly, right at the beginning of the project, on September 28, 2022 we were impacted by Hurricane Ian. This damaged some of the groves that we were going to use, and part of the experiments had to start a few months later.
Training & Professional Development
This project has allowed a postdoc and a student to present their accomplishments on this project in FSHS and ASHS professional meetings during 2023. It also allowed to expose them to interact with growers and perform extension activities, including writing informative flyers/bulletins and answer directly questions from them.
Dissemination Streams
We have been delivering presentations at professional meetings (scientific and grower-oriented), at master gardeners events, and in service trainings for UF extension agents. Our experimental sites have become demonstration sites were growers and other interested audiences (including international: growers and researchers from Brazil, South Africa and Spain) have come to see the results this first year. One of our experimental sites at SWFREC in Immokalee was a focal point at the SWFREC annual open house, in which our Center opens its doors for surrounding communities. Results have also been communicated to SW FL Master Gardeners associations via invited talks in a couple of occasions.
Next Reporting Steps
Treatments and data collection will follow as in year 1. Publication of results in peer reviewed journals will start, as we are already working in the first manuscripts. EDIS publications will be produced. Similar extension activities as in year 1 with updated results and recommendations will be performed. IP F Alferez has got already an invitation to present at ICRHLB in Riverside, CA in March next year, and in Spain in May next year. Other extension-related invitations in FL are also coming. A field day is planned for spring and another for fall next year <br><br>
<br>What was accomplished under these goals? Year 1. In Fall we performed theIPC removal after 3 years of tree protection. Baseline sampling and measurements were taken. We started monthly treatments of Brs. Monthly monitoring HLB progression, psyllid monitoring quarterly. Tree growth assessment in spring and fall. Yield and quality is being assesed at the end of the season. Expression analysis of genes related to plant immunity weekly after treatment were performed. A manuscript is in preparation and an abstract has been accepted as oral communication at the ICRHLB international meeting in Riverside next March 2024. A workshop has been already delivered at the SWFREC site. In this first year we have been able to demonstratethe efficacy of the combined use of IPCs and Brs on protecting fruit-bearing citrus trees from the HLB vector, CLas infection and other pests and diseases. We have seen that the treatment is more effective in sweet oranges and Tango mandarins than in other varieties like SugarBelle and Early Pride. We have seen a statistically significantincrease in yield and quality inTango mandarins. We see more aboundant and synchronized flushing with the combined IPC+Brassinosteroid treatment and less psyllids per tap sampling. <br><br><b>Publications</b><br>