In-field solar heat treatment of HLB-infected orange trees for inoculum reduction

In-field solar heat treatment of HLB-infected orange trees for inoculum reduction

Report Date: 10/12/2014
Project: 586   Year: 2014
Category: Horticultural & Management
Author: Reza Ehsani
Sponsor: Citrus Research and Development Foundation

During summer 2014, 9- and 13-month post treatment physiological tests on stomatal conductance, water potential, and leaf anatomy samples were continued. Also, fruit set data, fruit diameter data, average leaf area data, and average leaf area index (LAI) was collected and analyzed. The results of the fruit set analysis show there is a significant difference between the amount of fruit on the trees that were heated to 50’C and 55’C as compared to the sick control trees. The fruit set on the trees heated to 55’C and 50’C are significantly higher compared to untreated trees. The fruit diameter data shows there is a significant difference between the average fruit diameter on the 55’C treated trees as compared to the control trees. There is also a significant difference between the 45’C treated trees and the 55’C treated trees. The fruit on the 55’C trees is also significantly larger than the fruit on the 50’C trees. There was no noticeable difference in the average leaf size for any heat-treated or control trees. However, there were some differences in the average LAI. This measurement was taken to help measure the leaf density of the tree canopy. The trees heated to 55’C and 45’C had a noticeably higher average LAI than the control trees. The trees heated to 55’C had a significantly higher LAI than the trees heated to 50’C. The trees heated to 50’C dropped more leaves than the trees heated to 45’C directly after treatment. Leaf anatomy samples were processed and analyzed. The leaf petioles from 7 days after treatment and 1, 3, and 6 months after treatment were cross-sectioned and stained to measure phloem area. Since the disease is phloem-limited, the phloem was analyzed for any changes due to heat treatment. Ideally, in heat-treated trees that are recovering, the phloem area should increase once the bacterium is no longer present. The results suggest there was an increase in phloem area directly after treatment in all treated trees, and it continued until 1 month after treatment. Then, the phloem area began to decrease again.


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