We continue to work with Michael Rogers on glyphosate as a treatment for citrus greening disease.
Over a period of five months in the greenhouse, we determined the optimal concentration of glyphosate that citrus Valencia saplings could tolerate as well as the frequency with which it could be applied. We learned that citrus can tolerate an 8 mM spray of glyphosate every three months. The plents would lose a few leaves at first but after three months, flush would appear and the plants appeared to recover.
The sprays were applied at monthly intervals. We learned that monthly and semi-monthly sprays were too frequent. We also learned that 25 mM sprays were lethal. Thus, those were discontinued. The source of glyphosate was RoundUp as pure glyphosate was too expensive. RoundUp would be the source that growers would use in any case.
A field experiment was then started six weeks after the greenhouse experiment. The plots were set up at Lake Alfred by Michael Rogers. Prior to the first spray, the trees were sampled to determine CLas titer. Disease severity of the trees also determined.
As we now know from the greenhouse experiment that a three-month interval allows for tree survival and continued growth, the field plot is scheduled to be sprayed again in early August. The trees will be sampled and assessed for disease severity before and after the three-month spray.
Qualitatively, the results from the field are encouraging and mimic the results from the greenhouse. Those plants sprayed with 8 mM glyphosate are recovering and have new flush. The untreated control plants have no new flush. The plants sprayed with 25 mM glyphosate were nearly killed. We are not treating those trees again. We will let them recover.
We are eager to continue this experiment over the next few months and hope to learn the effect of glyphosate on CLas titer over the next three months.
Meanwhile, the transformation of citrus to generate RoundUp ready plants in a cis-genic manner is in progress at Lake Alfred. We believe that using cis-genic plants will be the long-term solution.