Sanitation practices to exclude Phytophthora and canker Citrus Nurserymen s meeting May 16, 2012 Jim Graham UF/CREC
Recent outbreaks of Phytophthora in citrus nurseries and mefenoxam fungicide resistance in citrus resets *Poorly performing nursery trees in propagation and tree losses to Phytophthora root rot on citrus resets *Recovery of high populations from trees in nurseries (liners and budded trees) with symptoms of yellowvein chlorosis and severe root loss in containers *Young trees in groves collapsing despite frequent applications of mefenoxam from which mefenoxam resistant Phytophthora are recovered
Fungicides are being use in place of proper management to prevent introduction and spread of Phytophthora
*Do not enter greenhouses after visiting citrus groves to minimize the risk of introducing Diaprepes, Phytophthora, Canker, Alternaria, etc *To prevent transmission of Phytophthora or other soil-borne diseases from the ground to the potted plants on the bench tops, hose nozzles should never contact the ground *After each use, the nozzle end of the hose should be hung on a hook. If the nozzle end touches the ground, immediately disinfest the nozzle with 10% bleach solution *Potted trees or seedling trays should never be placed on the floor and then returned to the bench top *Pots that fall on the ground should never be placed back on the bench and substrate that spills should never be placed back into the pot
*Media should be stored on a concrete pad that is periodically treated with a disinfectant *The pile should be kept covered with a tarp to minimize exposure to wind-blown soil/debris *Restrict access to the substrate storage area *Station a copper footbath and dedicated pair of boots at the entrance to the storage area *Prior to each entry into the storage area disinfect the soles of boots with copper *Tractor tires, scoops, shovels used to move the substrate should be disinfected with 10% bleach solution or copper, as appropriate
* After each use, the filling area and conveyor belts should be thoroughly cleaned with water and/or blower to remove leftover substrate and allowed to dry completely before next use * After each use, sweep up substrate and debris from the floor and mop with a disinfecting floor cleaner * Tools used for the potting process should be disinfected with 10% bleach solution before and after each use * If the tool comes in contact with floor, immediately disinfest with 10% bleach solution
*Head house area - sweep up substrate and debris from the floor and periodically mop the traffic areas with a disinfecting floor cleaner solution *Greenhouse walkways periodically sweep off substrate and treat with copper
*Shovels used for moving substrate should be disinfected with 10% bleach solution before and after use *Avoid contact of the shovel blade with the floor *Buckets and tubs should only be filled with "clean" substrate to use for planting *Buckets or tubs filled with "clean" substrate sitting on the floor should not be stacked on top of each other *Debris sticking to the bottom may contaminate the soil when stacked
*In pot filling area, pots should be staged off the floor on a pallet or shelf *Used pots should be soaked and washed with detergent to remove all substrate and debris *Pots should be disinfected by soaking in 10% bleach solution for 10 minutes *After disinfection, pots should be stored in a clean dry place away from substrate and debris to prevent recontamination
Assay of citrus seed for viable X. citri pv. citri (Xcc) after extraction from canker fruit Jim Graham UF/CREC Mike Irey US Sugar Corp. Chuck Reed Reed Brothers Citrus
Canker risk for seed blocks in citrus nurseries *Unprotected from infections by: - aerial pathogens (e.g. fungi, bacteria) - soil-borne pathogens (e.g. Phytophthora) - vector-transmitted diseases (e.g. HLB) *To manage risks, seed are treated with hot water (125 F), disinfectants (bleach), and fungicides (e.g. 8-hydroxyquinoline sulfate) *Bactericidal activity of these procedures against Xcc seed infestation has not been tested
Thunderstorm in July introduced Xcc into seed block trees from south to north Canker-affected Swingle fruit in the tops of trees in late August
Objective Confirm that citrus seed extraction and disinfection process for treating seed against fungi utilizing hot water, fungicide and bleach treatments is effective for eliminating Xcc from seed extracted with cankerinfected fruit peel
Canker infected Carrizo fruit before seed extraction Fruit had moderate to severe canker symptoms i.e., worst case
Seed extraction *Seeds were extracted by hand and placed in a plastic container with the symptomatic fruit peel *Fruit peel and seeds were then stirred to insure that seeds came in contact with Xcc
Extracted seed treatment Seeds were allowed to remain in the extracted juice for 8 hr
Seed treatment steps *Then seeds incubated in pectin and baking soda for 12 hrs, before the seeds were washed *After washing, seeds were hot water treated at 125 F for 10 minutes in water containing 10 % household bleach (6 % sodium hypochlorite) *8-hydroxyquinoline sulfate (1 tablespoon per 5 gal water) was applied and seeds were air-dried
Three treatments were evaluated after the seed extraction process *Seeds extracted, air-dried, and then infested with Xcc *Full treatment as described without Xcc infestation *Full treatment except no bleach
Validation of bacterial recovery *Seed were soaked in Xcc inoculum at 10 4 cfu per ml *Seed were washed with phosphate-buffer saline and a surfactant *Wash solution was infiltrated into grapefruit leaves for detection of viable Xcc *Canker lesions in the grapefruit confirmed that recovery and bioassay methods were effective for detection of viable Xcc in seed washes
Detection of Xcc from seed extracted from canker-affected fruit without and with artificial inoculation (positive check) Treatment Total lesions per leaf (Expt. 1) Total lesions per leaf (Expt. 2) 1- Seed soaked in Xcc inoculum 2- Hot water + bleach 3- Hot water w/out bleach 7.3* 15.2 0.0 0.0 0.0 0.0 *Values are the means of 2 replicate samples in treatment 1 or 5 replicate samples in treatments 2 and 3
Conclusion *Treatments of seed extracted from canker-infected fruit with hot water at 125 F for 10 minutes and 8- hydroxyquinoline sulfate, with or without 10% bleach in the wash step nullified recovery of Xcc *Although seed treatment is effective, given canker outbreaks in nurseries due to infested seed, the best management practice is use only non-infected fruit for seed extraction