Project : USDA ARS

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Research Project: Management of Diseases, Pests, and Pollinators of Horticultural Crops

Location: Southern Horticultural Research Unit

2023 Annual Report

Objectives
1. Develop environmentally friendly strategies for the control of small fruit diseases based on chemical, biological, and/or cultural control by conducting basic and applied research on the epidemiology, pathogenesis, and genetics of small fruit pathogens and their hosts. 1.1. Assess the effect of supplemental lights (LED, UV-B) on anthracnose pathogen growth in culture and on infection of greenhouse grown strawberries. 1.2. Assess the use of cover crops to reduce root rot pathogen populations in blueberry fields. 1.3. Develop a protocol to identify anthracnose resistant strawberry seedlings using non-viable culture filtrates of the anthracnose fungi. 2. Expand the scope and efficacy of plant pathogen sanitation technologies at multiple disease management scales involving propagation, general sanitation, and seasonal irrigation water treatment for ornamental production systems. 2.1. Evaluate spatial distribution of bacteria causing bacterial gall of Loropetalum in commercial nurseries and its association with stem cuttings used for propagation. 2.2. Determine rate activity responses for major commercial disinfestants against bacterial, fungal and viral plant pathogens. 2.3. Develop integrated preventive and reactive disease management strategies to control Pseudomonas, Colletotrichum, and Phytophthora in propagation facilities. 2.4. Develop concentration-time (CT) rates with water quality and temperature as covariates for treatment of Phytophthora nicotianae in irrigation water. 2.5. Model the relationship of seasonal dispersal of Phytophthora zoospores in recycled irrigation water with plant disease symptom development and weather conditions. 3. Discover, test, and develop new conventional and organic controls for the Spotted Wing Drosophila (SWD) and develop improved bee-safe practices for their application. 3.1. Discover and test erythritol, its derivates, essential oils, and insect growth regulators (IGRs) for control against SWD and other serious horticultural insect pests. 3.2. Test for additive or synergistic activity from combinations of select compounds from sub-objective 3.1 with biopesticides. 3.3. Test health safety of compounds from sub-objectives 3.1 and 3.2 to honey bees and important native bee crop pollinators. 4. Develop new management and conservation techniques for honey bees and important wild native bee pollinators for small fruit, vegetable and ornamental crop production. 4.1. Collect cocoons from trap-nests for managing orchard bees and chimney bees as fruit pollinators. 4.2. Develop and implement a pollinator release program. 4.3. Assess effects of common and new insecticides on these and other native bee pollinators of horticultural food crops. 4.4. Assess the use of soybean cultivars as bee forage for native and honey bees during the summer dearth along the Gulf Coast.

Approach
Evaluate influence of multiple light spectra, including UV-B light, on strawberry plant growth and as a way to inhibit germination and growth of anthracnose pathogens, thereby reducing disease. Assess effect of rotational cover crops (legume, brassica and grass), fallow and chemical treatments on Phytophthora populations in the soil and on severity of root disease on blueberry in replanted fields. Develop plant screening protocols using non-viable filtrates with presumed toxins of anthracnose pathogens to identify anthracnose resistance in strawberry seedlings. Sample for and analysis for distribution patterns of the bacterial knot pathogen on Loropetalum nursery stock to develop strategies for propagating pathogen-free plants. Identify differences in pathogen sensitivities, substrate demand loads and environmental factors that favor and interfere with disinfestant activity for several disinfestant chemical classes. Evaluate what combination of disease control practices allow for minimum levels of integrated management needed to control several major pathogens in woody plant propagation. Identify water quality and environmental factors that require adjustment in disinfestant concentration exposure to maintain control of Phytophthora in irrigation water. Monitor Phytophthora levels in pond water, the resulting disease progress on woody plants irrigated with the pond water and correlate these with favorable environmental conditions. Investigate how chemical formulation affects the activity of sugar alcohol pesticides, essential oils, and insect growth regulators applied to different stages of the spotted-wing Drosophila (SWD) fly. Identify what combination of chemicals previously tested by this research unit provide maximum mortality of SWD. Evaluate health effects on honey bees, orchard bees, chimney bees, and southeastern blueberry bees exposed to the chemicals evaluated by this research unit for SWD control. Collect orchard bees and chimney bees from across the southern U.S., establish them by commercial blueberry fields in Mississippi, determine their suitability as a pollinator and develop colony rearing practices. Establish orchard bee and chimney bee colonies near cooperating blueberry fields and monitor seasonal dispersal behaviors. Evaluate health effects on bee pollinators exposed to various insecticides, then assay for gene activity, enzyme activity and protein profiles. Evaluate the bloom period of soybean cultivars planted at several dates and monitor the feeding activity and health of native and honey bees.

Progress Report
An Agricultural Research Service plant pathologist at Poplarville, Mississippi, in collaboration with a University researcher at Mississippi State University, also located in Poplarville, reported that various intensities of red and blue light emitting diode (LED) light treatments affect plant vigor, injury, and disease development of strawberries grown in a greenhouse when compared to growth of plants receiving fluorescent supplemental light. Lower light emitting diode intensities had no significant effect due on relative chlorophyll content, plant vigor ratings, or disease severity ratings, but plants in the red and blue light emitting diode treatments had higher injury ratings than those in the fluorescent plus ultraviolet B treatment. The highest intensity red light emitting diode light resulted in the lowest relative chlorophyll content and the greatest injury ratings of plants. Leaves from plants receiving the two higher red light emitting diode intensities received the greatest disease severity ratings following inoculation with the anthracnose pathogen. In the laboratory, exposure of isolates of three species of anthracnose pathogens to high intensity light emitting diode lights for five days had no effect on their growth. Consumer demand for year-long, locally grown, high-quality fruit is increasing which will lead to increased greenhouse production of strawberries in the United States and world-wide. light emitting diode - and lamp-based supplemental lighting will be needed in these greenhouses. These results will assist strawberry growers to make informed decisions on the most appropriate supplemental lighting system and spectra needed for each phase of strawberry production, such as vegetative growth, flowering, pollination, and fruiting. An Agricultural Research Service plant pathologist at Poplarville, Mississippi, in collaboration with university researchers at Mississippi State University, Starkville, Mississippi performed research to characterize the spatial distribution of the bacteria, Pseudomonas amgydali pv. loropetalli, on container grown Loropetalum shrubs in commercial woody plant nurseries. The presence and titer density of the bacteria were measured at three strata within the shrub canopy on symptomatic and non-symptomatic plants throughout commercial blocks of plants. This information will provide development of options to propagate Loropetalum stock free of bacterial gall. We characterized the rate at which commercial disinfestants dry from horticultural production surfaces to evaluate if the products persist long enough on surfaces to eliminate plant pathogens. Multiple experiments were performed to test the influence of fluid dynamics (cohesion and surface tension properties of disinfestants), substrate traits (porous and non-porous material with heat absorbing and reflecting surfaces) and environmental conditions (cool, cloudy to hot, sunny weather) on the evaporative process. We performed a systematic review on the topic of thermotherapy to control plant pathogens in agricultural and horticultural crop production systems. The search was broadly done to obtain all available literature on the application of thermotherapy to eliminate plant pathogens from a range of sources, including soil; organic rooting media; used plant containers; instruments; and post-harvest treatment of produce, plant propagation organs and plant tissues used for vegetative propagation. An Agricultural Research Service plant pathologist and plant geneticist at Poplarville, Mississippi, collaborated with university researchers at Colorado State University, Fort Collins, Colorado to obtain a comparative transcriptomic analysis of Passalora seqouiae, the fungal pathogen the causes Leyland cypress needle blight, with related fungi that cause tree diseases. Agricultural Research Service entomologists in Poplarville, Mississippi, in collaboration with University researchers at the University of Illinois used novel queen monitoring cages (i.e., caged-bee studies) to quantify the effects of toxic phytochemical found in nectar of, yellow jessamine, a native perennial found in the Southeast Area and now found extensively along the Gulf Coast, reported by beekeepers to cause harm to bee hives, namely queen egg-laying and immature development, when in bloom. On going studies are determining the effects of the toxin found in the plant on its overall impact on honeybee queen health. An Agricultural Research Service entomologist in Poplarville, Mississippi, in cooperation with scientists at the University of Hawaii continue testing two natural essential oil-based emulsions that kill 50% - 100% of adult and larval spotted-wing drosophila flies. In the field, three aerial applications of two essential oil compounds, once per week, were as effective as the commercial biopesticide Grandevo, Entrust, and Pyganic. Further research is directed at improving the formulation for greater rain-resistance during the wetter berry harvest months of May and June. Cooperation has expanded to adopt nanotechnology (cotton-based nanofibers) to better deliver these biopesticides to their intended target pests and increase the rain-fastness of active ingredients. An Agricultural Research Service entomologist in Poplarville, Mississippi, has identified 25 active aggregations of wild chimney bees nesting within fallen tree root plates and roadside outcroppings. Females were active from March to June, and thus, will be collected in the fall of 2023, incubated, and released on flowering blueberries in FY2024. Screenhouse repairs, including a new Lumite cover, are underway to house chimney bees for their evaluation as manageable fruit pollinators.

Accomplishments
1. Intensity of supplemental greenhouse lighting affects strawberry plant growth and response to anthracnose infection. As consumer demand for year-long, locally grown, high-quality produce increases in the United States and world-wide, greenhouse production of fruits and vegetables also increases. Supplemental lighting, especially light emitting diode (LED) lighting, is needed for year-round production in greenhouses. ARS researchers in Poplarville, Mississippi, in collaboration with a university researcher at Poplarville, Mississippi, determined that various intensities of red and blue light emitting diode light treatments affected plant vigor, injury, and disease development of strawberries grown in a greenhouse compared to that of plants receiving fluorescent supplemental light. While there was no significant effect on relative chlorophyll content, plant vigor ratings, or disease severity ratings among plants exposed to the lower intensity light emitting diode light treatments; plants exposed to the highest intensity red light emitting diode light treatments had the lowest relative chlorophyll content, the highest injury ratings, and the highest disease severity ratings following inoculation with an anthracnose fungal pathogen. These results will assist producers of greenhouse grown fruits, vegetables, and ornamentals to make informed decisions on the most appropriate supplemental lighting system and spectra needed for each phase of production, such as vegetative growth, flowering, pollination, and fruiting.

2. Sanitizing plant production surfaces of fungal plant pathogens, not so simple. It is a common belief that a disinfestant will kill any and all microorganisms present on a surface. Life would be easier if true, but it is not that simple. The first systematic review and meta-analysis of published literature on disinfestants was done at Thad Cochran Southern Horticultural Laboratory, Poplarville, Mississippi, in collaboration with a researcher at North Carolina State University. This endeavor provides a scientific evaluation of the overall efficacy of disinfestants. Both quaternary ammonium (QAC) and peroxygen (PX) disinfestants were effective against many fungi but also ineffective against some fungi, but not the same fungi, respectively. Both quaternary ammonium and peroxygen compounds were effective when applied to most surfaces. However, quaternary ammoniums were less consistently effective on inorganic surfaces, such as clay pots and gravel, and on some porous surfaces, such as wood. peroxygens were less consistently effective as seed treatments and when applied to crops in production. New generations of quaternary ammoniums have been developed over time. The newer quaternary ammonium generational products were more consistently effective against fungi than the older quaternary ammonium generations. This information provides an applied benefit by helping plant industries select products appropriate for the pathogen and site being targeted for treatment, and as a result, more effectively control fungal plant pathogens and reduce the frequency of costly disease outbreaks. This information provides a scientific benefit by outlining the strengths and weaknesses in our knowledge on effective disinfestant usage.

3. Honeybee cell lines are useful to researchers on many levels. An ARS researcher in Poplarville, Mississippi, demonstrated that a honeybee cell line is a useful tool for the study of cellular responses to active ingredients found in commercial insecticides. AmE-711 honeybee cells showed concentration-dependent reductions in cell viability after exposure to insecticides. The response patterns of AmE-711 cells to the insecticides allowed predictions to be made about the LC50s; LC50s were comparable to those reported at the organismal level. Moreover, AmE-711 cells showed changes in their morphology and gene expression to suggest that insecticide exposure induces cell stress and death, laying the foundation for using the cell line as a model for further toxicological studies in honeybee health and disease.

4. Soybeans…it’s what’s for dinner (at least to a hungry bee). Bee declines are being driven by a combination of factors, and some potential responses we can take include establishment of wildflower habitats among croplands and provision of late-season forage when natural resources are becoming scarce. ARS researchers in Poplarville, Mississippi, monitored pollinators in soybean plots during late summer of 2018 and 2019 in the Gulf Coast region of the United States. Aside from honeybees, native bees such as bumblebees, sweat bees and long-horned bees were abundant. Particularly in years when late-season wild forage is less available, soybeans may provide a valuable source for pollinators.

5. Novel sources of biopesticides for organic agriculture. Americans buy about 11 billion dollars of organic produce each year and this number continues to grow due to the perception of organic food as a healthier and more ethical nutritional option. The costs of growing organic food, however, steadily rises due to there being too few, if any, affordable and effective pesticides on the market. Fortunately, pesticides derived from abundant natural sources such as plants are a common option for insect pest control on organic farms. For southern berry production, neem oil and pyrethrum are the only organic plant-based options. New classes of plant-based pesticides are needed to boost the supply of active ingredients, lower pesticide costs, and thwart insect resistance. Identified were natural insecticides from 5 species of tropical Jatropha (bellyache) bushes. Alcohol was the only solvent needed to extract the active ingredients from powdered root, leaf, and stem tissue. Extracts from south American species, particularly Jatropha clavuligera and Jatropha ribifolia were the most effective, killing 100% of malathion-resistant insects within an hour, a rate much faster than that of a quintessential organic pesticide, neem. In fact, it only takes 300 ppm of the crude Jatropha extract to almost instantly knockdown 50% of tiny insect pests like aphids and bugs. A Canadian/United States startup company has expressed interest in developing Jatropha extracts as a new biopesticide. Talks with ARS researchers in Poplarville, Mississippi, are just getting underway.

U.S. DEPARTMENT OF AGRICULTURE

Southern Horticultural Research Unit: Poplarville, MS