September 2016 The objectives of this proposal are 1) to determine if a) leaf litter biodegradation treatments reduce Guignardia spp. pseudothecia and improve control afforded by routine fungicide applications; b) if biodegradation is affected by the current fungicide application practices; and c) whether the biodegradation treatments will affect current citrus best management practices (BMP); 2) to determine the seasonal dynamics of leaf litter inoculum load in varying management regime intensities and how environment affects pseudothecia production in the leaf litter; 3) to test if the resistance to black spot in the leaves and fruit in sour orange is correlated and under simple genetic control through laboratory and field testing of progeny of sour orange crosses in both Florida and Australia. In the large field trial, there was a greater amount of G. citricarpa DNA found in 2015 leaf litter so that while there was more G. mangiferae than G. citricarpa, it was less than 10 times. In 2014, there was no pattern in the number of leaves with Guignardia structures over time in any treatment but in 2015, the % leaves with structures increased until the third collection date and the started to decline. There was greater G. citricarpa DNA in the control whereas for G. mangiferae there was more DNA in the soilset treatment. The soilset treatment had the lowest disease incidence in 2015 (1st year trt) and 2016 (2nd year). The third year treatment was applied and will be assessed next spring. The analysis has been more complicated than anticipated so not yet completed. The work was presented in as a poster at the annual conference for APS in 2016. The bagasse field trials confirmed the laboratory experiments that bagasse increased the leaf decomposition rate compared to nothing or urea. Greater soil moisture also accelerate leaf decomposition. The manuscript preparation was accepted with the citation: van Bruggen, A.H.C., Sharma, K., and Shin, K. 2016. Sugar cane processing residue, bagasse, enhances decomposition of citrus leaves and could contribute to citrus black spot management. Crop Protection (accepted). The detached leaf assays for assessment of leaf susceptibility continue. ince it was difficult to coordinate leaf ages between CREC and the USDA, new trees were grafted at the CREC and have just become large enough to harvest leaves for a second repeat of the experiment. Collection of leaf samples from the grove in Immokalee has continued biweekly. Each batch of samples contained 40 samples of 25 leaves collected below 40 trees. Leaves were examined under microscope to check for fructification of Phyllosticta spp. Leaf portions without fructification were discarded and the remainder were immersed in 0.02% tween20 to collect conidia and ascospores. Conidia and ascospores produced in leaf litter were quantified, weather data were collected from FAWN. Data collection is continuing and some of the qPCR data is being processed. In 2014, very little G. citricarpa DNA was found overall while G. mangiferea was high but, substantially more G. citricarpa DNA was detected in the 2015 collections. In general, conidia are always present but ascospores are related to the level of leaf decay. Because there was an increase in pathogen presence in 2015, we have decided to continue sampling since levels were very low in 2014. There appears to be more asexual structure formation in the spring of 2016 than 2015 and greater conidia production. In 2016, fewer ascospores were observed in the spring than in 2015 but in general the overall trends were similar. Summer data has not been fully processed yet. We have been refining the spore DNA extraction and qPCR technique and anticipate getting that data generated in the next quarter. Some of this work was presented as a poster at the annual meeting for APS this year. In Australia, confirmation of the ascospore and conidia production results continues. Sampling of leaf litter in two groves in the Queensland mandarin growing region was completed in April and samples are being processed. In the three years of sampling, the fruitifcation patterns have been different but we are not sure why. Pycnidia are found most of the sampling season but pseudothecia tend to be clustered towards the end of the season. qPCR data are being generated. Inoculations of fruit are complete and preliminary symptoms have been confirmed on susceptible fruit. They have identified several potential candidates for resistance after 2 seasons of inoculations. They repeated the fungicide work to confirm previous results. In 2015, mulch was the best treatment to reduce the amount of leaf litter under trees. The high volume fungicide applications did slightly reduce decomposition of the leaf litter but may not be significant. These results were confirmed in the 2016 trials. The fungicide work was presented at the ICC meeting and will be written up for the proceedings.