Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 212 - Pathogens and Nematodes Affecting Plants | 910 - Grapefruit | 1040 - Molecular biology | 25% |
| 212 - Pathogens and Nematodes Affecting Plants | 920 - Orange | 1060 - Biology (whole systems) | 25% |
| 212 - Pathogens and Nematodes Affecting Plants | 1114 - Peach | 1040 - Molecular biology | 10% |
| 212 - Pathogens and Nematodes Affecting Plants | 1122 - Strawberry | 1060 - Biology (whole systems) | 10% |
| 212 - Pathogens and Nematodes Affecting Plants | 1429 - Cucurbits, other (includes pumpkin, squash, gourd) | 1040 - Molecular biology | 10% |
| 212 - Pathogens and Nematodes Affecting Plants | 1460 - Tomato | 1060 - Biology (whole systems) | 10% |
| 212 - Pathogens and Nematodes Affecting Plants | 2110 - Ornamental trees and shrubs | 1040 - Molecular biology | 10% |
1. Using the newly-developed super sensitive realtime polymerase chain reaction (PCR) to detect Las bacteria in the germplasms of citrus, and use the two effective chemicals coupled with thermal therapy to treat the budwoods and seeds to obtain real Las-free gerplasms. 2. Using realtime PCR and convential PCR to determine the type(s) of Las bacteria that can survive in Murraya plants and the dynamics of the bacteria in the plants, as well as their possibility to be transmitted to citrus by the asian citrus psyllids. 3. Optimizing the growth factors and conditions for improving the growth rate of Las bacterium in vitro, and knocking out and complementing some of the putative effector genes of Las. 4. Using the chemicals and thermotherapy device, we will apply and modify the application system for practical and cost effective control of citrus HLB.
This research relates to inhouse project objective: 1. Characterize ecology, biology, epidemiology, molecular genetics, and vector and host (crop and weed) interactions of domestic, exotic, newly emerging, and re- emerging pathogens. Continue application of new chemical and thermal therapies to eliminate Las: A. Optimization of chemical treatments - We are exploring different delivery system for the chemical control, these trials are conducted both in greenhouse and fields. One penetration system has been developed for better delivery of the selected chemicals into citrus plants. B. Testing of application methodology - Thermotherapy treatment greenhouse trials. Using a temperature-controlled growth chamber, we evaluated the duration and temperature required to eliminate or suppress the Las bacterium in citrus, using three temperature treatments (40�C, 42�C and 45�C) for time periods ranging from 2 to 10 days. Results of qPCR after treatment illustrate significant decreases in the Las bacterial titer, reaching an undetectable level, combined with healthy vigorous growth on all surviving trees. Repeated qPCR testing confirmed that previously infected, heat-treated plants showed no detectable levels of Las, while untreated control plants remained highly infected. Continuous thermal exposure to 40-42�C for a minimum of 48 hours was sufficient to significantly reduce titer or eliminate Las bacteria entirely in HLB-affected citrus seedlings. Thermotherapy/chemotherapy of citrus trees at USDA Pico�s Farm: Previously, over 50 Valencia trees were treated with thermotherapy at Pico�s Farm using portable greenhouses and solarization. Treatment durations are weather dependent and trees are exposed to at least 25 hours of >40�C before tent is removed. Due to systemic infection of Las, trees are also being treated with various chemicals such as penicillin and streptomycin to reduce Las titer in the roots. Additional chemicals, compounds, and biocontrol agents are also being added to the treatment regime. Thermotherapy treatment commercial groves: We continue to extensively collaborate with one commercial grove in Fort Pierce, FL. A one year sampling was completed on the block of trees heated in the previous spring. Although most display HLB symptoms, many continue to flush, produce fruit, and appear healthier than before treatment. The grower believes the trees have significantly recovered and look similar to neighboring trees that have not shown any decline. Statistically, this block of trees that underwent thermotherapy for 3 days did show a significant decrease in Las titer after 22 months (two-tailed t-test of t31 = 2.77; two-sided p=0.0093). Due to the improved appearance of the treated trees, the grower built his own version of the portable greenhouse and began treating another group of trees with thermotherapy. We have added another block of trees into our study and will continue to work with this cooperator and monitor both set of trees. Thermotherapy of dooryard citrus: As a continuation of the thermal treatment project, 26 HLB infected dooryard citrus were placed under commercially available portable greenhouses for 7 to 10 days and 6 trees were left untreated for controls. The year and a half post treatment data is statistically significant (two-tailed t-test of t25 = 7.99; two-sided p