Location: Subtropical Insects and Horticulture Research
Project Number: 6034-21000-018-018-A
Project Type: Cooperative Agreement
Start Date: Nov 1, 2018
End Date: Mar 31, 2021
Objective:
The objective is to determine if application of Fe2+ and an organic acid will cure, substantially reduce HLB titer, rejuvenate citrus trees infected with huanglongbing (HLB). The Cooperator will conduct the field tests and ARS will conduct the greenhouse and laboratory tests.
Approach:
ARS will conduct the greenhouse and laboratory components of the research.
Laboratory experiments -
The effect of the ratio and concentration of Fe2+ + organic acid on hydroxyl radical production and hydroxyl radical stability will be determined using a 2-component mixture-amount experimental design. The experiment will include include 5 replications as well as points to determine lack-of-fit, and sufficient points to model quadratic curvature. This will determine the main and interaction effects of proportion and amount, and will determine if proportion interacts with amount. Hydroxyl radical production will be determined by measuring the amount of light emitted, using a luminometer, from the reaction of hydroxyl radicals with luminol. The stability of the hydroxyl radicals will be measured that same way but chlorogenic acid, a hydroxy radical scavenger, will be included in the reaction mix.
Greenhouse studies -
1) Determine the phytotoxic levels of Fe2+ + organic acid solutions on citrus. A 2-component mixture-amount experimental design that include 5 replications as well as points to determine lack-of-fit, and sufficient points to model quadratic curvature will be used. This will determine the main and interaction effects of proportion and amount, and will determine if proportion interacts with amount. Solutions will be applied weekly for four weeks and phytotoxity assessed via leaf discoloration and burning. Healthy citron plants will be used.
2) Determine the effect of Fe2+ + organic acid solutions on huanglongbing (HLB) titer using a rapid greenhouse, HLB-infected citron, rooted shoot bud assay. An Fe2+ + citric acid solution will be applied weekly for 4 months to HLB-infected citron plants. A completely randomized design with 12 replicates will be used. HLB and horticultural health status will be measured by PCR and growth assessements, respectively, at the beginning and the end.
3) Determine the effect of Fe2+ + organic acid solutions on protecting healthy citrus from becoming infected by HLB+ psyllids. An Fe2+ + citric acid solution will be applied weekly for 4 weeks to healthy citron plants, then HLB+ psyllids will feed on these plants for 1 week. Plants will then be grown for 2 months and data collected on HLB status and horticultural health. A completely randomized design with 24 replicates will be used.
4) Determine the main and interactive effects of supplemental iron (Fe2+), manganese, boron, zinc, and copper using a rapid greenhouse, HLB-infected citron, rooted shoot bud assay. Treatment solutions will be applied weekly for 4 months to HLB-infected citron plants. A resolution V irregular fractional factorial with blocks and 12 replicates will be used to determine main and 2-factor interaction effects. HLB and horticultural health status will be measured by PCR and growth assessements, respectively, at the beginning and the end.
