In collaboration with CREC Driector Michael Rogers , we are proceedng with laboratory, greenhouse, and field experiments to determine whether glyphosate can control cirtus greening disease. In the laboratory, we determined the levels of glyphosate that inhibit L. crecesns. Glyphosate inhibits aromatic amino acid synthesis in any organism that produces these compounds. This includes plants and many bacteria, including L. crescens. Liberibacter crescens is also inhbited by glyphosate when the cells are cultured in the presence of aromitc amino acids suggesting that there may be another site of action for glyphosate in addition to the ESPS protein. Based on those experiments, we choose 8 mM and 25 mM concentrations of glyphosate to test for citrus toxicity in the greenhouse. In the greenhouse, 25 mM glyphosate was quite toxic to Valencia citrus. The plants survived 8 mM glyphosate but it delayed growth of flush by two months. We next tested the intervals at which glyphosate can be applied in the greenhouse. Two sprays of 8 mM glyphosate one month apart caused considerable leaf drop two weeks after the second spray. Two sprays of 8 mM glyphosate two months apart hurt the growth of flush but the flush is returning three weeks after the second spray. These interval sprays will continue monthly until the first and last sprays are six months apart. We expect that sprays three months apart will not significant effect citrus growth and yield. The greenhouse experiments above are six weeks ahead of the field trial. Thus, the greenhouse trial will inform us as to the best interval for spraying the field. The field experimental design was done by Michael Rogers. He also did the first spraying of the field trees nearly two months ago. As in the greenhouse, 25 mM glyphosate killed the trees while 8 mM did not. At 8 mM growth was slowed as in the greenhouse experiment. Based on the greenhouse trial, we are going to wait until three month after the first spray to spray again. Pre- and post-spray sampling is being done to assess CLas titer and disease severity. Meanwhile, Zhonglin Mou on our team is working with the citrus transformation facility to make Valencia cis-genic engineered plants that are resistant to glyphosate. This required the construction of an ESPS synthase gene that contains the one base change needed to confer glyphosate resistance. This gene is being inserted into mature and immature citrus. The selection of plants with the mutated gene is simple as it is just a glyphosate screen. These plants should be available early next year if not sooner for both greenhouse and field testing.