Foliar phosphate fertilization: a simple, inexpensive, and unregulated approach to control HLB

Foliar phosphate fertilization: a simple, inexpensive, and unregulated approach to control HLB

Report Date: 02/16/2020
Project: 18-024   Year: 2020
Category: Horticultural & Management
Author: Eric Triplett
Sponsor: Citrus Research and Development Foundation

In this quarter, we received permission to continue much our work on this project during the pandemic shutdown. All experiments in the greenhouse and field continue to be maintained.

We also obtained exciting results from our greenhouse experiment where Nabil Killiny graft-inoculated citrus saplings with CLas. We then applied the nutritional treatments to this plants to test the notion that leaf fertilization of potassium phosphate would reduce CLas titer in the leaf midribs compared to root fertilization with calcium phosphate.

Attached with this report are the data. With potassium phosphate fertilization of leaves, the propotion of unfected plants after 3 and 6 months is 80% and 86.7%, respectively. Plants fed calcium phosphate to the roots (analogous to field plants receiving no phosphate fertilizer) had only 40% and 38.5% of unifected plants at 3 and 6 months, respectively. Control plants given neither fertilizer were 26.7% and 38.5% uninfected at 3 and 6 months.

In contrast, after 6 months, 23.1%, 13.3%, and 0% of the highly infected plants were given leaf, root, or no fertilizaiton. Highly infected plants did improve over time with the foliar potassium phosphate fertilization.

So the greenhouse experiments have confirmed our hypothesis, foliar phosphate fertilization prevents and alleviates CLas infection. Treating plants with the equivalent of rock phosphate that is found in Florida citrus groves (calcium phosphate) encourages infection and it gets worse over time.

Now we need the field confirmation of these results. We were in the process of doing qPCR measurements of CLas leaf titer from our two field experiments, when we were ordered to stop data collection and reduce staff in the lab. This happened about the same time as the state-wide stay-at-home orders.

We expect to be able to get back to the qPCR measurements by mid-May.

We are also continuing with our greenhouse experiment on the effects of foliar phosphate treatments on citrate levels in phloem. Again, our efforts on this were curtailed on this with the shutdown. But we will be back at it soon.

All field and greenhouse experiments are on-going. Nothing was lost during the shutdown.

I submitted a preproposal to the USDA to expand our phosphate trials to 20 field experiments over the current two. That preproposal also includes a new disease model. I am eager to share those results with CRDF when the experiments are done.

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