Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611
Performing Department
Gulf Coast Research and Education Center
Non Technical Summary
Strawberry is one of the most valuable crops in Florida. In 2019, approximately 49,000 acres were planted with strawberries in the U.S. Florida ranks second and produces about 180 million lbs of strawberries every year, representing 15% of the nation's berries and virtually all those grown in the winter. About 10,000 acres were devoted to strawberry production in Florida in 2019, with an estimated return to the grower of over $300 million (USDA, 2019). Strawberry transplants used in Central Florida are produced in nurseries across the northern U.S., California, and Canada. California alone produces 1.1 billion strawberry transplants valued at $160 million. Transplants from these out-of-state or country nurseries are planted in the field in September/October. Although strawberries flower throughout the winter in Florida, there are typically two peak bloom periods, one in November/December and other in late January/February. Harvest usually begins in late November/early December, with fruit produced during this early period bringing the highest prices. Production increases in February as temperatures rise, and the season typically ends in March due to price declines resulting from the entry of strawberries from California or Mexico into the market. The strawberry crop is affected by several pathogens that can damage the fruit and leaf and cause yield losses as well as root and crown pathogens that kill the plants. The high value of the crop often compels growers to protect their profits by making numerous applications of pesticides on a strict spray schedule. Anthracnose and Botrytis fruit rots, angular leaf spot, powdery mildew, and Pestalotia are among the most important diseases affecting fruit yield, whereas Colletotrichum, Phytophthora and Macrophomina crown rots are the most important causes of plant mortality. Susceptibility to eachdisease differs among strawberrycultivars, but no cultivar has commercially relevant levels of resistance to all diseases. Our goal is to increase the efficacy of control for these diseases with a reduced number of fungicide applications. This will be accomplishedby studying the biology and epidemiology of each of these diseases so that recommendations for control are developed based on i) the need for an application according to weather conditions, ii) the most effective fungicide according to the disease predominant and conditions, as well as knowledge in pathogen resistance. We will also develop and/or improve non-chemical control alternatives to be used in an integrated management approach. For all of these diseases, management strategies involve not only production fields in Florida but also the nurseries that provide transplants since that is how most of the pathogens are introduced into Florida strawberry fields. Developing strategies for fruit and nursery growers to manage diseases while reducing the number offungicide applications helps growers to increase their profits while reducing the risks ofthe pathogensbecoming resistant. Finally, the collaboration with the strawberry breeding program allows the selection of new cultivars with increased levels of disease resistance.Caladium and gerberas are ornamental crops of importance in Florida. The state leads the U.S. in caladium tuber production and supplies 90-95% of the worldwide demand for caladium tubers as propagules, generating nearly $30 millionand supporting local communities in multiple ways. However, newly emerged and existing diseases and pests have taken a huge toll on growers' ability to produce profitable crops.A tuber rot caused by Fusarium and a root rot caused by Pythium are among the most challenging diseases for caladium growers. Our project will screen for the best fungicides to provide growers reasonable disease control and sustained profits, while our long-term project will screen for new cultivars with higher levels of disease resistance.Gerberas are popular ornamental plants that are used for cut flowers as well as for bedding plants in Florida. Powdery mildew, Erysiphe cichoracearum, is a common problem on gerberas and causes serious problems in the production of these ornamentals as well as for the homeowner in gardens. In collaboration with the breeding program, new selections and cultivars will be screened for tolerance to powdery mildew, which could greatly reduce the need for fungicide applications.Blackberry has emerged as an important alternative crop for Florida growers. Citrus growers who have recently been devastated by citrus greening or HLB are particularly interested in growing blackberry. However, many factors need to be researched before the crop can be considered a feasible alternative. Our project will screen and select adapted blackberry varieties for disease resistance and develop and identify effective tools for managing occurring diseases.Industrial hemp, Cannabis sativa, is another crop that is currently being investigated as an alternative crop for Florida growers. The plant has been cultivated for 10,000 years as a fiber and grain crop with modern applications for textiles, building materials, seed oil, and essential oil. As with blackberry or any other new crop to the area, it is important to identify hemp varieties suitable for Florida production, and in the process, identify emerging diseases and develop management practices that are economically viable.
Animal Health Component
60%
Research Effort Categories
Basic
20%
Applied
60%
Developmental
20%
Goals / Objectives
The overall goal of this project is to improve understanding of the biology and epidemiologyof diseases of strawberry, ornamental and alternative crops, in order to develop and improve integrated management strategies.Specific objectives:1. Evaluate chemical and biological products and programs for the control of important strawberry diseases2. Evaluate the occurrence of resistance to fungicides, determine the genetic basis, and develop management strategies to maximize control3. Develop non-chemical alternatives for the management of diseases in strawberry nurseries and production fields4. Diagnosis of important diseases on strawberry and local alternative crops and investigate the disease cycles and develop management strategies5. Evaluate fungicides for control of ornamental diseases and development of cultivar resistance of ornamental crops
Project Methods
Objective 1. Evaluate chemical and biological products and programs for the control of important strawberry diseasesRegistered and experimental fungicides, as well as biological and biorational products, will be evaluated every year for control of anthracnose, gray mold, powdery mildew, angular leaf spot, Phytophthora crown rot and charcoal rot as well as for the new Pestalotia leaf and fruit spot. For each disease, a commercially available cultivar will be selected that is relatively susceptible to the disease to be evaluated. Plots will be established on fumigated beds using four replicate plots of 12-20 plants each. Products will be applied as appropriate for each disease to be tested. Sprays will be applied according to the StAS predictive system in the case of AFR and BFR. However, weekly sprays are sometimes needed for some diseases. Fruit will be harvested twice weekly, graded, and the disease incidence determined. In the case of crown rot diseases, plant mortality will be evaluated weekly. We are currently evaluating the over summer survival of Macrophomina and Neopestalotiopsis after strawberry production and testing the effect of replacement fumigants for methyl bromide on the survival of these pathogens.Objective 2. Evaluate the occurrence of resistance to fungicides, determine the genetic basis, and develop management strategies to maximize control.The occurrence and distribution of isolates of B. cinerea resistant to commonly used fungicides will be determined in strawberry fields in Florida. It is crucial to continue monitoring the efficacy of novel and older SDHI fungicides and the risks for cross-resistance after each season of use in commercial fields. In addition to Botrytis, we will continue monitoring the resistance of Colletotrichum spp. to QoI fungicides, and Phytophthora spp. to mefenoxam.We plan to develop strategies to enhance the use of the most effective fungicides and reduce the risks for developing more resistant populations in the future. We will improve the use of the existing StAS and develop approaches aimed to extend the "product life" of fludioxonil (Switch) and new SDHI fungicides based on a reduced number of fungicide applications and wise and effective rotations.Objective 3. Develop non-chemical alternatives for the management of diseases in strawberry nurseries and production fields Thermal treatment using hot water immersion has been shown to kill or reduce systemic pathogens and pests in propagation material but were insufficient for killing the bacterium causing ALS (Turechek and Peres, 2009). In fact, our research indicates that hot water treatments actually enhance the spread of ALS, because bacteria released from infected plant batches contaminate the bathwater and are spread to non-infected plants, a means by which ALS has become entrenched in the nursery industry. We developed a protocol for the use of aerated steam in a two-step process involving a brief lower-temperature pretreatment, followed by a higher-temperature eradicative treatment. This precision thermotherapy was effective against X. fragariae and reduced the risk of spread between batches without damage to plants. Subsequent work demonstrated the additional benefit of reducing C. acutatum, B. cinerea, Phytophthora spp., P. aphanis, as well as two-spotted spider mites (Wang et al., 2017; Zuniga and Peres 2017; Renkema et al., 2019; Silva et al., 2019). The next step for our research would be to work with strawberry nurseries to scale up the process to commercial levels, which would have an unprecedented impact upon controlling pests and diseases while simultaneously reducing or eliminating pesticide use against a broad range of threats to sustainable production.Prior research indicated that ultraviolet (UV) light is a broad-spectrum and non-chemical means to suppress pathogens and arthropod pests. The discovery that very low nighttime doses of certain wavelengths of UVB and UVC (254 to 283nm) effectively suppressed powdery mildews, as the photolyase-mediated repair of pathogen DNA is inoperative during darkness, has been crucial for the application of this technology in the field. Our research group designed an apparatus and evaluated the use of nighttime application of UV to suppress powdery mildew on commercial strawberry fields. We plan to continue to engineer and improve UV delivery systems and their efficacy against other diseases on strawberry as well as powdery mildews on other crops.Objective 4. Diagnosis of important diseases on strawberry and local alternative crops and investigate the disease cycles and develop management strategies The primary emphasis will be on Pestalotia leaf and fruit spot. Genomic resources for Neopestalotiopsis populations will be collected for comparative genomic analysis. We plan to employ whole-genome sequencing to build primary genomic resources for further investigation. Our preliminary multilocus phylogenetic analysis showed the old and emerging Neopestalotiopsis populations were clonally separated (Baggio et al. 2020). We will develop simple sequence repeat (SSR) markers for genotyping and population genetic analysis of Neopestalotiopsis populations. SSR markers are versatile molecular markers with high genotypic resolution and, therefore, suitable for inferring the routes of microorganism migrations and sources of introductions.We plan to evaluate the effect of temperature and wetness periods on Neopestalotiopsis sp. in in vitro and in planta assays. The effect of wind, water, and manual harvest on the spread of Neopestalotiopsis sp. will be investigated. Survival of Neopestalotiopsis sp. on strawberry debris over summer in Florida will be determined. The effectiveness of thermotherapy for field control of Neopestalotiopsis sp. will be evaluated in a trial where strawberry plants previously infected with Neopestalotiopsis sp. will be treated or not with herbicides applied for crop termination, and the survival of Neopestalotiopsis sp. will be assessed. Identifying potential sources of cultivar resistance against the Neopestalotiopsis sp. affecting strawberry will also be assessed in field trials.In addition, we are currently investigating the etiology of emerging leaf spot diseases on industrial hemp (Cannabis sativa) in Florida, a potentially important crop for the state as well as other crops such as blackberry.Objective 5. Evaluate fungicides for control of ornamental diseases and development of cultivar resistance of ornamental crops Tubers of different selections of caladiums developed by the UF-GCREC ornamental breeder Z. Deng will be inoculated with a technique we developed to inoculate tubers with Fusarium to determine their level of resistance to Fusarium tuber rot. The inoculated tubers will be maintained in a closed box with a moistened paper towel and incubated in a growth chamber and then evaluated for degree of decay. A procedure for screening large numbers of seedlings for Pythium root rot resistance has been developed. The hole on the bottom of each of the 200 cells in a tray provides a convenient entry for pathogen inoculation to the roots of seedlings and cells will be dipped into a zoospore suspension of Pythium. Each tray holds 200-400 plants, and thus this system can potentially allow screening of 30,000 seedlings within 1-2 months. The inoculated seedlings will be maintained in the greenhouse and evaluated for root rot.Results from these trials are used by the ornamental breeding program to guide future crosses and selections, as well as to provide information to growers and extension agents after the release of the cultivars.