Performing Department
(N/A)
Non Technical Summary
Fire blight, caused by the bacterium Erwinia amylovora, is a devastating disease of apple and pear. It not only reduces yield but also kills trees therefore is a major concern to apple and pear growers. Blossom Protect, a biological control comprised of the yeast Aureobasidium pullulans, is the most effective biocontrol material of fire blight. Organically approved, integrated disease management program centered around Blossom Protect has been developed and successfully used in the Pacific Northwest. However, Blossom Protect can cause fruit russeting, a disorder of the cuticle of developing fruitlets that compromises quality, especially in humid climates. Consequently, in the more humid eastern U.S., the risk of fruit russeting from Blossom Protect has slowed development of effective organic management of fire blight.Therefore, this risk is a critical barrier for organic transition within the region, and development of methods that maintain fruit quality by mitigating russeting risk from Blossom Protect is an important research priority.In this project, we aim to test three russeting management strategies: 1. the "Protection and Clearing" strategy to remove A. pullulans after protection is finished, 2. the "Remedy" strategy to improve fruit finish using plant growth regulators / micronutrients, and 3. the "Adjust" strategy to fine tune the timing / dosage of Blossom Protect.Ultimately, we aim to develop an integrated program that maximize both the fire blight suppression and russeting mitigation. Our extension activities include disseminating knowledge on russeting mitigation to the organic tree fruit community and promoting organic practices in eastern U.S.
Animal Health Component
0%
Research Effort Categories
Basic
20%
Applied
60%
Developmental
20%
Goals / Objectives
Fire blight is one of the most difficult diseases to control in organic apple and pear production due to its devastating damage and the lack of effective control measures. Blossom Protect, a biological control comprised of the yeast-like fungiAureobasidium pullulansas the active ingredient, is the most effective biocontrol control material of fire blight and is now considered 'foundational' for effective fire blight control in organic apple orchards in western United States. Blossom Protect, however, has a drawback in that it is a cause of fruit russeting, a disorder of the cuticle of developing fruitlets that compromises quality, especially in humid climates. Consequently, in the more humid eastern U.S., the risk of fruit russeting from Blossom Protect has slowed the development of effective organic management of fire blight.Therefore, this risk is a critical barrier for organic transition within the region, and the development of methods that maintain fruit quality by mitigating russeting risk from Blossom Protect is an important research priority.In this project, we aim to test three russeting management strategies, with the following specific objectives:Objective. 1.Test the susceptibility ofA. pullulansto different OMRI-listed fungicides.Objective. 2.Determine the russeting mitigation effect of using OMRI-listed fungicides to remove/reduceA. pullulanspopulation at petal fall, when russeting risk increases. The "Protection and Clearing" strategy.Objective. 3.Determine the effect of OMRI-listed plant growth regulators and micronutrients in improving fruit finish.The "Remedy" strategyObjective. 4.Balance fire blight disease suppression and russeting risk by fine-tuning the application dosage, frequency and timing of Blossom Protect. The "Adjust" strategyObjective. 5.Develop an integrated, multi-channel program for fire blight suppression and russeting mitigation.Objective. 6.Disseminate the knowledge on russeting mitigation practices to the organic tree fruit community.The long-term goalis to provide organic growers in the east with effective management tools for fire blight while maintaining the high quality of fruits.
Project Methods
Objective 1: Organic certified fungicides to be tested in this objective include hydrogen peroxide-based contact sterilants, sulfur, lime sulfur, oils, bicarbonates, and copper (Table 2). To test the susceptibility of A. pullulans to these OMRI-listed fungicides, A. pullulans strains DSM14940 and DSM14941 will be isolated from Blossom Protect and cultured on potato dextrose agar (PDA) media. A. pullulans cells will be collected from the PDA surface, resuspended in sterile H2O, adjusted to 106 CFU/ml, before being sprayed to the flowers of 3-year-old potted crabapple trees maintained in a greenhouse. We routinely perform flower induction using both cold induction method or chemical (Perlan) induction method, which yield 50-80 flowers on each tree. 24 hours after inoculation, A. pullulans inoculated crabapple flowers will be sprayed with fungicides to be tested. Water treatment and Captan, a phthalimide fungicide with a known fungicidal effect against A. pullulans, will be included as negative and positive controls. Each fungicide treatment will be applied to 3 trees (approximately 150 flowers). Two days post fungicide treatment, 30 flowers will be collected from each tree to be used for quantification of A. pullulans population. A. pullulans population will be determined using a plating method: each collected flower sample will be placed in a centrifuge tube containing 25 ml of sterile phosphate buffer. The solution will be vortexed for 30 seconds and sonicated for 3 minutes to release yeast cells. After sonication, flower wash solution will be used to prepare 1X, 100X, and 1000X dilutions and all cell suspension will be spread on potato dextrose agar (PDA) amended with streptomycin sulfate (50 µg/liter), chloramphenicol (50 µg/liter), and tetracycline (50 µg/liter) to ensure growth on PDA represent the A. pullulans population. Flowers without A. pullulans inoculation will also be included as a negative control to determine the presence of baseline level of A. pullulans on crab apple flowers. A. pullulans population will be log10-transformed and subjected to the one-way analysis of variance (ANOVA) in the 'stats' package in R. Objective 2: Organically grown apple cultivars "Gala", "Golden Delicious" (representing low and high susceptibility to russeting) and organically grown pear cultivar "Bartlett" will be used in this experiment. Blossom Protect will be tank mixed with Buffer Protect NT and applied at the following rate: 3.17 grams of Blossom Protect and 8.8 grams of Buffer Protect NT per litter of water in concentration, for 0.6 kg of Blossom Protect, and 1.7 kg of Buffer Protect NT per acre. Blossom Protect will be applied to open flowers twice, once at 60% and again at 80% bloom. The three most effective OMRI-listed fungicides selected from Objective 1 will be sprayed on flowers at petal fall approximately 3 days after the last application of Blossom Protect. One group of trees will receive one application of the OMRI-listed fungicides, while another group will receive two applications, with one day apart between applications. Trees without Blossom Protect treatment, trees treated with Blossom Protect but do not receive any fungicides, trees with only the biofungicide treatment, as well as trees treated with Blossom Protect followed by a conventional fungicide (captan) treatment will be included as controls (captan control will not be included in organic orchards as determined by the certification rules). Each treatment will be sprayed to four trees as biological replicates. All treatments will be arranged in a complete randomized block design. Objective 3: Materials to be tested belong to several categories: 1. plant growth regulators such as gibberellic acid GA3, GA4, and GA7, the application of which results in more uniform and smaller epidermal cells and improved fruit finish; 2. boron, a micronutrient that enhances cuticle formation; and 3. kaolin clay, which improves fruit finish by reflecting UV radiation and reducing fruit surface temperatures. Trees to be tested include organically grown apple cultivars "Gala", "Golden Delicious" and pear cultivar "Bartlett". Blossom Protect and Buffer Protect NT will be sprayed on the apple and pear flowers twice (0.6 kg of Blossom Protect per acre), at 60% and at 80% bloom. Objectiver 4: Our preliminary results identified that the labeled rate Blossom Protect and 20% rate of Blossom Protect induced similar levels of host immunity. Therefore, we hypothesize that the labeled rate of Blossom Protect uses an excessive amount of A. pullulans to suppress fire blight. From our preliminary data, we also learned that the A. pullulans amount on apple flowers positively correlates to the russeting severity on fruits at harvest. Therefore, by strategically reducing the application dosage and adjusting the timing, we may reduce russeting severity without compromising the disease suppression efficacy. Objective 5: Blossom Protect and YSY will be applied according to the dosage, frequency, and timing (determined in Objective 4); flowers will be inoculated with E. amylovora at full bloom, the most effective OMRI-listed fungicide in clearing off A. pullulans (determined in Objective 2) will be applied at petal fall to eliminate A. pullulans; the most effective growth regulator/micronutrient that helps to improve fruit finish will be applied at the most appropriate frequency after petal fall (determined in Objective 3). Fire blight disease infection will be evaluated 2 weeks after petal fall, and russeting will be evaluated 1 week before harvest. Three trees will be used in each treatment. Water treatment and streptomycin treatment will be used as negative and positive controls. Data analysis will be performed as described previously.