Citrus Black Spot Update Nan-Yi Wang, Ke Zhang, Jeffrey Rollins, Megan Dewdney Presenter: Jeffrey Rollins University of Florida 2016 Citrus Expo
Black Spot Background Causal agent: Guignardia citricarpa Asexual name: Phyllosticta citricarpa Hosts: Citrus species and hybrids Symptomatic: Sweet oranges, mandarins and tangerines, lemons, grapefruit Asymptomatic: Sour orange and Tahiti limes Rind spots cause the most economic damage Fresh Market Acceptability Market Access Internal Quality Unaffected Causes premature fruit drop reducing yield
Citrus Black Spot Symptoms Hard Spot Virulent Spot Cracked Spot False Melanose Photo Credit: UF, IFAS, CREC (Photo Credit: T. Schubert, DPI) Photo Credit: UF, IFAS, CREC Photo Credit: UF, IFAS, CREC Hard spot most typical symptom but also virulent spot, cracked spot, and false melanose Photo Credit: UF, IFAS, CREC
Symptoms Occur on Maturing Fruit Unusual to see hard spot more than 2 months before fruit maturity.. but infection occurs months before Symptoms generally occur first on the sunny side of trees Exposure to sunlight increases lesion number Warm temps (~ 81 F; 27 C) also increase disease symptoms
Leaves are Usually Symptomless On oranges, if chemical control used, symptoms extremely rare Does not mean leaves are not infected Certain proportion will harbor the pathogen When symptomatic trees removed, not likely removing disease from grove
Where is Citrus Black Spot? 2013 2006 1920 1980 2010 1929 First record, 1895 1928
Understanding Phyllosticta citricarpa Disease Cycle to Manage Disease & Spread 1 Inoculum 2 Inoculum Disease cycle from Timmer, L. W., and Duncan, L. W. 1999. Citrus Health Management. American Phytopathological Society, St. Paul, MN.
Understanding Phyllosticta citricarpa Disease Cycle to Manage Disease & Spread Two potential forms of inoculum Ascospore (Pazoti et al. 2005) Conidia (Glienke et al. 2011) Wind-borne Move between trees, up to 25 meters (Spósito et al. 2007) Rain splashed <80 cm from the inoculum source (Spósito et al. 2011) Disease cycle from Timmer, L. W., and Duncan, L. W. 1999. Citrus Health Management. American Phytopathological Society, St. Paul, MN.
Genomics-Enabled Approach Established draft genomes of P. citricarpa and P. capitalensis Identified loci for fungicide sensitivity and resistance Identified Mating-type locus Developed markers for P. citricarpa population analysis
Wang, N.-Y.et al. 2016. Phytopathology. doi:10.1094/phyto-12-15-0316-r. What is the Mating Type Structure of P. citricarpa and P. capitalensis? P. capitalensis is homothallic P. citricarpa is heterothallic Consistent with observation that P. capitalensis readily produces ascospores in culture but P. citricarpa does not
One (1) Mating Type in Florida and both (2) in Australia State, Country Florida, US Queens -land Australia Location Total number Number of isolates MAT1 MAT2 Collier 50 0 50 Hendry 62 0 62 Polk 1 0 1 Total 113 0 113 Beerwah 2 0 2 Emerald 1 1 0 Gayndah 4 1 3 Mundubbera 16 8 5 Tiaro 3 2 1 Total 26 12 11 Wang, N.-Y.et al. 2016. Phytopathology. doi:10.1094/phyto-12-15-0316-r.
Wang, N.-Y.et al. 2016. Phytopathology. doi:10.1094/phyto-12-15-0316-r. Florida Results is a Population Lonely Peninsula structure Developed and Analyzed 7 polymorphic SSR loci Compare Australian and Floridian population Only one MLG in Florida
New Report: Both (2) Mating Types in Brazil It is likely that Florida is unique in having only one mating type and therefore only the asexual infection cycle.
Phyllosticta citricarpa Disease Cycle Outside of Florida Disease cycle from Timmer, L. W., and Duncan, L. W. 1999. Citrus Health Management. American Phytopathological Society, St. Paul, MN.
Phyllosticta citricarpa Inoculum Sources in Florida Leaf Drop Overlapping fruit development Dead leaves on orchard floor Fruit & Leaf Symptoms Pycnidium Latent Period Conidia germinate producing appressoria Disease cycle modified from Timmer, L. W., and Duncan, L. W. 1999. Citrus Health Management. American Phytopathological Society, St. Paul, MN.
Despite the presence of the asexual cycle only, the disease continues to spread in Florida 2013
What Does this Mean? Plant debris is the likely means of long distance movement between groves Human activity likely prime means of movement Needs to be minimized to reduce spread Tarping is still necessary All vehicles and equipment Removal of debris Canker decontamination materials (quat) are recommended
Disinfectants do they work? All FDACS recommended quat products contain 6.51% octyl decyl dimethyl ammonium chloride 3.26% didecyl dimethyl ammonium chloride 3.55% dioctyl dimethyl ammonium chloride 8.68% alkyl dimethyl benzyl ammonium chloride Tested C-Quat, Canker Solve RC, Publix bleach Recommended rates for 10 min contact time Quat: 2000 ppm Bleach 200 ppm
Concentration of quaternary ammonium ( g/ml) Inhibition of G. citricarpa by disinfectants 120 100 Bleach 100 n = 5 n = 5 120 Canker Solve % Inhibition of germination 80 60 40 20 80 60 40 20 0 f=100.0308/(1+exp(-(x+0.1964)/0.2264)) -20-3 -2-1 0 1 2 3 Concentration of sodium hypochlorite ( g/ml) 0 f=100.3095/(1+exp(-(x-0.1270)/0.1413)) -1.5-1.0-0.5 0.0 0.5 1.0 1.5 Concentration of quaternary ammonium ( g/ml) 120 % Inhibition of germination 100 80 60 40 20 C-Quat n = 5 0 f=100.3153/(1+exp(-(x-0.1203)/0.1310)) -1.5-1.0-0.5 0.0 0.5 1.0 1.5
Measured EC 50 and EC 90 for 10 min exposure Disinfectant EC50 (ppm) EC90 (ppm) Canker Solve 1.36 a 2.62 a C-Quat 1.26 a 2.53 a Bleach 0.68 b 1.77 b Bleach: >100X efficacy Quat: >300X efficacy
Management Continue fungicide applications at same timings Based on fruit susceptibility Remove any severely declining trees Remove as much dead wood from canopy as possible Avoid overlapping fruit ages as much as possible in bad groves Don t move plant debris out of grove Disinfect vehicles & equipment
Summary There is only asexual reproduction of P. citricarpa occurring in Florida Based on mating type gene evidence; Confirmed by a clonal population * We must remain vigilant in monitoring for introduction of the second P. citricarpa mating type which could mean: Increased rate of spread Genetic recombination Management to date is not recommended to change greatly Manage disease in the grove Minimize movement the pathogen out of and between groves Effort to clean equipment and vehicles between groves is prudent Recommended disinfectants highly effective
Acknowledgement Dr. Megan Dewdney s lab Dr. Jeffrey Rollins Lab Nan-Yi Wang Ke Zhang Dr. Andrew Miles Dr. Tim Schubert
Grower Resources UF/IFAS Citrus Research and Education Center website www.crec.ifas.ufl.edu Annual Florida Citrus Pest Management Guide Citrus Black Spot laminated sheet Citrus Black Spot Management Timing Schedule laminated sheet Packinghouse Citrus Black Spot ID Identification of Early Citrus Black Spot Symptoms Citrus Black Spot Field Identification Pocket Guide