January 2021The objectives for this proposal are 1) Conduct field trials of new products and fungicide programs for PFD management as well as validation trials for the Citrus Advisory System (CAS); 2) Investigate the reasons for the movement of Postbloom fruit drop (PFD) to new areas and recent major outbreaks; 3) Evaluate methods for initial inoculum reduction on leaves so that early fungicide applications could be more effective and identify the constituents of the flower extracts using omics techniques. The two validation trials for CAS have been laid out in the Fort Mead area and a small amount of disease has been observed on early bloom in at least one site. We hope for at least one positive site. The fungicide trial is in the planning stages and will be laid out in the next few weeks. The majority of analysis for the leaf wetness models is now completed and manuscript preparation is underway. We compared the output of leaf wetness sensors to combinations of predictive models for accuracy and sensitivity. As will all models, reliability was heavily influenced by the quality of the weather station data. Reasonable accuracy was found for one, three, or four models in combination but with just two models, the predictive capacity was poor. We are in discussions for how this information could be used to improve CAS predictions. We are working on evaluating PFD risks via an analysis for prediction accuracy. When we extracted leaf compounds from citrus to evaluate them for stimulation of appresoria and conidia production, we were greatly surprised to find they stimulated germination and conidia production as much as the floral extracts. The mature citrus leaves from Valencia tree were extracted by sonication with water at room temperature for three hours. The extract was filtered and concentrated under reduced pressure to yield a dried sample. The concentrated extract was then chromatographed over silica gel (3.5 × 30 cm; 40-63 µm particle size) and eluted with gradient mixtures of n-hexane/acetone/MeOH (10:1:0 . 0:0:1, each 2 L) to afford seven sub-fractions (F17). Seven fractions were analyzed by UHPLC to analyze their polarity. The UHPLC system was following: 0 -5 min, 8% B; 5-16 min, 8-90% B; 16-17 min, 90-100% B; 17-24 min, 100% B. The mobile phase included 0.1 % formic acid aqueous solution (A) and 0.1 % formic acid containing acetonitrile (B). According to their polarity, seven subfractions were combined into two fractions. One fraction contains highly polar compounds and the other one possesses medium polar compounds. The high-polarity extract greatly induceds conidia germination in 12 hours, even more than floral extracts. This is counter our hypothesis that sugars were responsible for the stimulation as the extracts that contain most sugars did not stimulate germination to the same extent. We are in conversation with the USDA to recommence work in their wind tunnel to conduct the experiment with conidia on flowers for the final comparison. However, it is not clear when the USDA will reopen their facilities. We hope it will be soon.