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<\/p>\nActivities of the Georgia Envirotron facility include interdisciplinary researches in Environmental Science, Food Safety, Crop and Soil Sciences, Entomology, Plant Pathology, Urban Agriculture etc. Research summaries of leading scientists, graduate, undergraduate and Young Scholars Internship students are presented below.<\/p>\n
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Understanding Drought Tolerance for\u00a0Breeding Warm-Season Grasses<\/strong><\/p>\n David Jespersen, Assistant Professor, Crop and Soil Sciences<\/em><\/p>\n Drought stress is a major environmental stress which\u00a0damages and limits the growth of warm-season grasses.\u00a0A collaborative project among several universities in the\u00a0southern United States, including the University of Georgia,\u00a0was formed to evaluate the drought performance of several\u00a0warm-season grasses including bermudagrass, zoysia, St.\u00a0Augustine grass, and seashore paspalum. In addition to\u00a0characterizing drought tolerance of a wide selection of\u00a0experimental varieties, important physiological responses\u00a0to drought were further detailed in select varieties of\u00a0bermudagrass and seashore paspalum to better understand\u00a0potential mechanisms for drought tolerance. This project\u00a0will ultimately advance the ability of turf breeders to\u00a0develop improved varieties which can withstand severe levels\u00a0of drought.<\/p>\n <\/p>\n Soil Microbial Respiration Measurement Deploying Non-Steady-State Chambers Integrated Into Conviron Growth Chambers<\/strong><\/p>\n Nosir Shukurov (Fulbright Visiting Scientist from Institute of Geology and Geophysics, Uzbekistan),\u00a0<\/em>Viktor Tishchenko (Griffin, Univeristy of Gerogia)\u00a0<\/em><\/p>\n Soil basal respiration measurement is widely used in studies of soil C cycling, net crop photosynthesis estimations, overall soil biological\u00a0activity estimations, heterotrophic microbiological activity studies etc. Chamber technique can be adapted to a wide range of experimental objectives and commonly used approach in soil respiration estimations. In order to efficiently and economically measure soil respiration in large number of samples over extended incubation period, we chose non-steady-state chamber design (static system) that allowed us to integrate Vaisala GMP 222 carbon dioxide probe (widely used in Conviron chambers) into small-volume soil respiration chamber and perform real-time CO2<\/sub> measurement under controlled environment conditions (PGW36 Conviron chamber). Time-dependent CO2 <\/sub>diffusion error was reduced by adding ventilation inside the respiration chamber (resembling flow-through chamber type), taking measurements at constant chamber deployment intervals, and increasing soil sample surface area. Based on continuous CO2<\/sub> concentration measurements (18 second interval), the rate of CO2<\/sub> accumulation (\u0394C\/\u0394T) was estimated from the slope of the linear regression line. Experimental trial in the Calcisol soil sample showed initial two-fold increase in the respiration rate during the first 3-4 days of incubation and then gradually decreased for 3 weeks.<\/p>\n Testing irrigation and fertilization rates for young peach plants in controlled environment<\/strong><\/p>\n Bruno Casamali, Marc W. van Iersel, and Dario J. Chavez (Department of Horticulture, University of Georgia)<\/em><\/p>\n Accurate irrigation and fertilization management for agricultural crops has become a subject of\u00a0interest, due largely to widespread problems with drought and fertilizer runoff. Irrigation\u00a0and\u00a0fertilization guidelines are needed for peach growers in the southeastern U.S. to avoid plant\u00a0stresses and improve production. Although studies in controlled environment cannot be easily\u00a0translated to field situations, they can provide a better understanding the trees\u2019 physiological\u00a0responses to different irrigation and fertilization conditions. Greenhouse experiments were\u00a0conducted: one to test different irrigation rates and another to test different fertilization rates,\u00a0with both experiments testing two scions (\u2018Flavorich\u2019 and \u2018Julyprince\u2019) and two rootstocks\u00a0(\u2018MP-29\u2019 and \u2018Guardian\u2019). For the irrigation experiment, flower bud break percentage was\u00a0affected by the scion and rootstock treatments. Plants receiving the highest irrigation level\u00a0(volumetric water content (VWC) of 45%) were ~35% taller than the treatments with a VWC of\u00a015 and 35%. Plants growing with a VWC of 45% or those grafted onto \u2018Guardian\u2019 displayed the\u00a0greatest trunk cross-sectional area increase (TCSAI). In general, plants receiving the lowest\u00a0irrigation level (VWC of 15%) had the lowest stem water potential in comparison to those\u00a0receiving more water. For the fertilizer experiment, \u2018Flavorich\u2019 scion reached peak bloom faster\u00a0and had more abundant bloom than \u2018Julyprince\u2019. Photosynthetic activity was affected by the\u00a0interactions between the fertilizer vs. scion and fertilizer vs. rootstock treatments. Plants\u00a0receiving greater amounts of fertilizer (18, 13.5, and 9 g of N per plant) had ~2x the TCSAI than\u00a0the plants receiving the lower amounts of fertilizer (4.5 and 2.3 g of N per plant). Higher doses\u00a0of irrigation and fertilization tend to increase plant height and TCSAI. However, the\u00a0photosynthetic activity appeared to be less dependent of the irrigation and fertilization rates,\u00a0similar to the bud break progression, which was found to be more dependent on the scion and\u00a0rootstock cultivars.<\/p>\n Development of\u00a0 sorghum root system phenotyping and screening\u00a0methods for phosphorus efficiency<\/strong><\/p>\n Viktor Tishchenko (Univestity of Georgia), Ming Li Wang (USDA – PGRCU), Daniel Sabo (Georgia Institute of Technology)<\/em><\/p>\n Phenotyping for Gummy Stem Blight Resistance in Watermelon<\/strong><\/p>\n Winnie Gimode and Cecilia McGregor, University of Georgia<\/em><\/p>\n Institute of Plant Breeding, Genetics and Genomics, University of Georgia.<\/p>\n Gummy stem blight (GSB) is a major fungal disease of field-grown watermelons in southeastern US, caused by Stagonosporopsis<\/em> pathogen. This pathogen thrives in warm and humid conditions that is conducive for germination of the spores. Infection is optimum at temperatures between 21\u00b0C-26\u00b0C, and high moisture levels (above 90% relative humidity), accompanied by leaf wetness. The impact of GSB on watermelon production can be severe, resulting in huge yield losses.<\/p>\n Resistance to fungicides poses a major challenge in management of GSB. In addition, the repeated use of fungicides may have a negative impact on the environment, particularly if residues persist in the soil. Using cultivars resistant to GSB would be a cheaper, more environmentally sustainable option for disease management. Currently, no commercial watermelon cultivars are resistant to GSB.<\/p>\n This study therefore aims to identify quantitative trait loci (QTL) associated with gummy stem blight resistance in watermelon and further introgress the loci into watermelon cultivars. In order to achieve this, we are utilizing the growth chambers for phenotyping purposes, since the temperature, light and humidity settings can be controlled. Phenotyping for GSB involves screening watermelon seedlings by inoculating them with the fungus (Stagonosporopsis citrulli<\/em>) through spraying. Due to the high humidity and consistent temperature levels required for development of this disease, the growth chambers have been ideal for these purposes, and we are getting relatively consistent results!<\/p>\n Heat\/cold tolerance studies of cotton genotypes differing in the degree of fatty acid saturation.<\/strong> Dr. John L. Snider. and Viktor Tishchenko (University of Georgia)<\/em><\/p>\n Heat or cold tolerance can be influenced by fatty acid saturation levels, where plants having cellular membranes with a greater degree of fatty acid saturation have lower membrane fluidity at cool temperatures, which makes them more prone to chilling injury and likely limits seedling vigor under cool conditions. The study currently being conducted at the Envirotron facility assesses seedling vigor and cold tolerance for cotton genotypes differing in the degree of fatty acid saturation. We will be measuring seedling growth characteristics (nodal development, leaf area development, fresh weight, dry weight) and photosynthetic efficiency under contrasting temperature regimes.<\/p>\n <\/p>\n Application of root demand irrigation approach on turfgrass (Seashore Paspalum).<\/strong><\/p>\n Dr. Paul L. Raymer (University of Georgia), Dr. Viktor Tishchenko (University of Georgia)<\/em><\/p>\n <\/p>\n Eschericha coli<\/em>\u00a0O157:H7 pre-harvest contamination of ready-to-eat produce<\/strong>.\u00a0 Over the past six years, growth chambers at the Envirotron have been in use by Dr. Marilyn Erickson from the Center for Food Safety to explore a number of issues associated with pre-harvest contamination of ready-to-eat produce.\u00a0 As a source of contamination of enteric pathogens (Escherichia coli<\/em>\u00a0O157:H7,\u00a0Salmonella<\/em>, and\u00a0Listeria monocytogenes<\/em>), animal manure-based soil amendments are of concern for their potential to introduce and contaminate fields and crops grown in those fields. \u00a0Aerobic composting of animal manures is one process that may be used to reduce pathogen levels; however, insufficient heat generated at the surface of compost heaps may arise leading to pathogen survival.\u00a0 Although turning of compost piles is advocated to facilitate exposure of all material to heat generated from microbial breakdown of compost materials, Dr. Erickson’s lab has also been investigating nonthermal parameters that affect pathogen inactivation at surface sites of composting piles by holding compost mixtures in small trays or containers within the growth chambers under defined temperature, humidity, and light conditions.\u00a0 Results from several of these studies are highlighted below:<\/p>\n Another focus of research that has required our use of controlled and contained conditions in growth chambers is to ascertain whether lettuce-infesting insects could influence the fate of either surface or internalized populations of\u00a0E. coli<\/em>\u00a0O157:H7.\u00a0 Brief exposure (~18 h) of lettuce leaves to insects (5 cabbage loopers, 10 thrips, or 10 aphids) prior to inoculation of plants with\u00a0E. coli<\/em>\u00a0O157:H7 resulted in significantly reduced internalized populations of the pathogens within these leaves after approximately 2 weeks, as compared with leaves not exposed to insects. \u00a0These results suggest that internalization of\u00a0E. coli<\/em>\u00a0O157:H7 may be minimized by plant defenses that are induced in response to intrusive insect activities.<\/p>\n A third area of research employing leafy green plants cultivated in growth chambers has been to examine the potential for internalization of enteric pathogens through roots or leaf stomata.\u00a0\u00a0E. coli<\/em>\u00a0O157:H7 in contaminated water was applied by application to the soil or by spraying the leaves of the plants.\u00a0 Uptake of pathogen into roots occurred when soil contained 7 log CFU\/g.\u00a0 Greater internalization of\u00a0E. coli<\/em>\u00a0O157:H7 occurred in lettuce and parsley roots surrounded by saturated soil compared to moist soil.\u00a0 Uptake into roots occurred later for parsley than lettuce or spinach under saturated conditions.\u00a0 Exposure of the leaf surface to 7 log CFU\/ml spray led to internalization of the pathogen into leaves of mature lettuce and spinach plants.\u00a0 When sprayed at this concentration, no differences in the degree of internalization occurred for virulent and non-virulent surrogate strains of\u00a0E. coli<\/em>\u00a0O157:H7.\u00a0 Internalized populations of\u00a0E. coli<\/em>\u00a0O157:H7 were greater in spinach compared to lettuce one week after the spray event implying differences in the level of defenses activated by these leafy greens.<\/p>\n Currently, growth chambers are being used to explore the short-term survival of\u00a0E. coli<\/em>O157:H7 sprayed on five different cultivars of mature cabbage plants.\u00a0 Pathogen survival on these cultivars will be compared to the plant’s expression of several plant defense protein genes and to the plant’s constitutive levels of total phenols and antioxidant capacity.\u00a0 In addition, chemical treatments that have previously been shown to alter phytochemical levels in leafy greens will be applied to one cultivar one week prior to pathogen exposure.\u00a0 Subsequently, treated and untreated plants will be applied to determine if pathogen survival has been impacted.<\/p>\n Interspecific Arachis Breeding Project. The growth chambers are being utilized to grow four wild Arachis species which are being used as female parents for interspecific crosses. The males Arachis species are being grown in our greenhouse facility. The use of the growth chambers allow us to synchronize pollinations by controlling light and temperature so that the male flowers can be collected and immediately used to pollinate the females. In the greenhouse, male flowers are collected in the morning and then used in the evening to pollinate the female plants. Each day flowers from the male plants are harvested and transported to the growth chamber to apply pollen to the stigma. This process is repeated each day flowers are available to help increase the success of obtaining a true hybrid since Arachis species are vigorous self pollinating plants. The resulting hybrid F1\u2019s will be used to create synthetic allotetraploids by treatment with colchine which doubles the chromosomes producing a tetraploid from a diploid. (The majority of Arachis species are diploid whereas cultivated peanuts are tetraploid). The resulting synthetic allotetraploids will be crossed with cultivated peanuts to create mapping populations and introgress disease resistance traits into cultivated peanuts.<\/p>\n Morphological Characterizations of Subterranean Clover for Determination of Genetic Redundancy. Genetic redundancy is of prime concern for curation of crop species. The USDA, ARS, PGRCU Trifolium subterranean collection is suspect of having genetic redundant accessions. Our goal was to determine whether or not genetic redundant accessions do in fact exist within the U.S. subterranean clover collection. Subclover seed were planted in potting soil within each of five4″ plastic pots. A sub-sample of 90 subclover accessions were tested. Soon after seed germination, each pot utilized in the test were moved to growth chambers at the Georgia Envirotron. Plants were grown in a 16 hour photoperiod regime with a 27\u00b0C \/ 17 \u00b0C day\/night temperature setting. Successful morphological characterizations were recorded for leaf marking, flower color, and stipule color.<\/p>\n Combined Effects of Elevated Carbon Dioxide Levels and Temperature on the Biology of the Mealybug Phenacoccus madeirensis Green (Homoptera: Pseudococcidae) The combined effects of elevated CO2 levels (400 and 700 \u00b5L\/L) and temperatures (20, 25 and 30 0C) on the development, survival and reproduction of two generations of the mealybug Phenacoccus madeirensis were investigated. Mealybugs were reared on chrysanthemums grown in growth chambers set at a specific CO2 level and temperature. The duration to egg hatching and to adulthood of the mealybugs was recorded by examining the mealybug cohorts daily. Hatching rates of eggs and survival rate to adulthood were determined by recording the number of individuals that successfully molted into the next developmental stage. The proportion of females in the population was determined by fractioning the number of females over the total number of adults at the end of the experiment. Adult females were isolated in leaf cages and their eggs were collected daily to determine fecundity. The nutritional status (carbon concentration, nitrogen concentration, and the relative water content of leaves) of chrysanthemum were also studied to interpret the performance of mealybugs at elevated CO2 level and temperature. The development of mealybug is temperature-dependent. Duration of development did not differ among different CO2 level treatments and generations. A female completed its development in about 20 days at 30 0C, 28 days at 25 0C, and 47 days at 20 0C. Males have longer duration of development than females. Survival rates, proportion of females, fecundity, duration of reproduction, and the parameters of host plant nutritional status did not differ significantly among temperature and CO2 level treatments and between generations.<\/p>\n Fate of\u00a0Eschericha col<\/em>i O157:H7 in Manure Compost Applied to Soil to Grow Vegetables in an Envirotron Growth Chamber. Animal waste in the form of raw manure or composted manure is routinely applied to the land as a crop fertilizer and\/or soil amendment. A potential risk arising from the disposal of animal waste of fecal origin is the spread of enteric pathogens. Many outbreaks or cases of\u00a0E. coli<\/em>O157:H7 infection have been associated with water or food directly or indirectly contaminated with animal manure. Cross-contamination of produce from manure or improperly composted manure used on the farm can be a source of pathogen contamination during preharvest. Although competition with soil microorganisms and adverse environmental conditions can reduce pathogens, there is little information regarding the ability of\u00a0E. coli<\/em>O157:H7 to survive in manure-amended soils. In this study, our objective was to determine the fate of\u00a0E. coli<\/em>\u00a0O157:H7 in soil and on vegetables in a controlled and contained plant growth chamber environment.<\/p>\n A five-strain mixture of green fluorescent protein (GFP)-expressing i O157:H7 was prepared and inoculated at 107 CFU\/g into the compost. The inoculated compost was mixed with Tifton clay soil at a ratio of 1: 100. Twenty horticultural pots for each of baby carrot and green onion plants were filled with inoculated and fertilized soil (ca.5000 g). Three healthy transplants of each plant were planted into each pot 100 mm apart from each other, and then irrigated with city tap water. The pots were placed in the Envirotron with control of light, temperature, and CO2 levels. Special air filters was installed to prevent pathogens from spreading to the environment. Plants were irrigated every other day, and fertilized with soluble fertilizer (Sam’s Choice Deep Feeding All purpose Food) every two weeks. Soil samples from around the plant (Soil), plant leaves and stem samples (Plant), and soil samples just under the roots (S\/p) in triplicate were analyzed for\u00a0E. coli\u00a0<\/em>O157:H7 at approximately weekly intervals for the first four weeks, and every 2 weeks for the rest of plant growth cycle (up to 3 months). Soil moisture content and pH were also determined. Over a period of 64 days in onion, the population of GFP-expressing\u00a0E. coli<\/em>\u00a0O157:H7 in soil and soil under roots samples was steadily reduced by 3 log , whereas in plant samples was reduced by 2. With carrot, it took 84 days to achieve a reduction of 2.3 log in soil. Seventy days were needed to get a reduction of 1.7 log in carrot plant.<\/p>\n Image analysis for non-destructive and non-invasive quantification of root growth and soil water content in rhizotrons. Studies aiming at quantification of roots growing in soil are often constrained by the lack of suitable methods for continuous, nondestructive measurements. A system is presented in which maize (Zea mays<\/em>\u00a0L.) seedlings were grown in acrylic containers \u2013 rhizotrons \u2013 in a soil layer 6-mm thick. These thin-layer soil rhizotrons facilitate homogeneous soil preparation and nondestructive observation of root growth. Rhizotrons with plants were placed in an Envirotron CG72 growth chamber, on a rack slanted to a 45o angle to promote growth of roots along the transparent acrylic sheet. At 2- to 3-day intervals, rhizotrons were placed on a flatbed scanner to collect digital images from which root length and root diameters were measured using RMS software. Images taken during the course of the experiment were also analyzed with QUACOS software that measures average pixel color values. Color readings obtained were converted to soil water content using images of reference soils of known soil water contents.<\/p>\n To verify that roots observed at the surface of the rhizotrons were representative of the total root system in the rhizotrons, they were compared with destructive samples of roots that were carefully washed from soil and analyzed for total root length and root diameter. A significant positive relation was found between visible and washed out roots. However, the influence of soil water content and soil bulk density was reflected on seminal roots rather than first order laterals that are responsible for more than 80% of the total root length.<\/p>\n Changes in soil water content during plant growth could be quantified in the range of 0.04 to .26 cm3 cm\u20133 if image areas of 500 x 500 pixel were analyzed and averaged. With spatial resolution of 12 x 12 pixel, however, soil water contents could only be discriminated below 0.09 cm3 cm-3 due to the spatial variation of color readings.<\/p>\n Results show that this thin-layer soil rhizotron system allows researchers to observe and quantify simultaneously the time courses of seedling root development and soil water content without disturbance to the soil or roots.<\/p>\n <\/p>\n Snider, J.L., N. Thangthong, C. Pilon, G. Virk, V. Tishchenko. 2018. OJIP fluorescence\u00a0parameters as rapid indicators of cotton (Gossypium hirsutum L.) seedling vigor under\u00a0contrasting growth temperature regimes. Plant Physiology and Biochemistry.<\/p>\n Hu, W., J.L. Snider, D.R. Chastain, and V. Tishchenko. 2018. Sub-optimal growth\u00a0temperature decreases photosynthetic thermotolerance by differentially affecting the heat\u00a0sensitivity of thylakoid component processes in cotton seedlings. Environmental and\u00a0Experimental Botany.<\/p>\n Tishchenko V.\u00a0
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Phenotype screening and selection for tolerance to low-phosphorus stress conditions was developed at the Georgia Envirotron. Methodology that uses P-loaded alumina as a phosphorus buffer in the quarts sand culture was used to perform efficient, economical, high throughput sorghum screening for P-efficiency under controlled nutrition conditions. Solid-phase sand-alumina culture system provided stable, diffusion-limited, slow-release conditions with varying P availability to plants. This technique provided better media conditions control and reproducibility compared to complex soil systems and, at the same time, better mimicked natural conditions compared to hydroponic cultures. Sorghum was selected due to its wide range adaptability to abiotic stress (such as drought and barren soil). Significant genetic variation in tolerance to abiotic stress exists in sorghum germplasm and cultivars. \u00a0In situ<\/em> electrical capacitance tomography (ETC) method was used for monitoring root development with greater accuracy due to media and plants consistency. The identified materials may be used in plant breeding programs for development of cultivars with high phosphorus use efficiency.<\/p>\n
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Root Demand Irrigation (RDI) \u2013 innovative, low-pressure, energy-efficient, plant-driven subsurface irrigation. Porous subsurface tubes are used which serve as water reservoir releasing water in response to plant exudates when it\u2019s needed. RDI is claiming to improve water-use efficiency by delivering water – and potentially nutrients – directly to the root zone. It uses low-pressure (about 2 psi or less) that requires less energy and allows to use natural flow (without pumping) from collected and stored water in uplifted containers. RDI requires minimal filtration and can use ground water, ponds, and canals as well as recycled or treated water without expensive treatment because water doesn\u2019t reach the surface. Here, turfgrass subsoil irrigation is tested and optimized on the example of Cecil soils of the Piedmont plateau. RDI tubes installed at 12, 18, and 24 in. intervals and 6 and 12 in. depths (see the graph). Soil moisture is measured with Decagon soil moisture sensors (GS1) installed between lines at the depth of 3 in. together with water flow meter, solenoid valves and sensors are connected to a timer (Toro) and a data logger (Campbell Scientific, CR1000) to continuously track water use and plant response. Different subsurface irrigation timing and pressure modes together with installation spacing and depths are compared to conventional sprinkle irrigation.<\/p>\n
\n<\/strong>Dr. Marilyn Erickson. Center for Food Safety, University of Georgia.<\/em><\/p>\n\n
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\n<\/em><\/strong>Noelle Barkley, Roy Pittman, Angie Lewis. USDA<\/em><\/p>\n
\n<\/strong>Brad Morris. Plant Genetics Resources Conservation Unit.<\/em><\/p>\n
\nJuang-Horng Chong1, Marc W. Van Iersel2, and Ron D. Oetting2
\n1 Department of Horticulture, Sunchon National University, South Korea, 2 Department of Horticulture<\/p>\n
\n<\/strong>Mahbub Islam1, Jennie Morgan1, Michael P. Doyle1 and Xuiping Jiang2.
\n1Center for Food Safety, 2University of Clemson.<\/em><\/p>\n
\n<\/strong>Rolf O. Kuchenbuch1 and Keith T. Ingram2.
\n1Center for Agricultural Landscape and Land Use Research, Muncheberg, Germany, 2Department of Crop and Soil Sciences.<\/em><\/p>\n
\nRefereed Publications,\u00a0Conference\u00a0or Professional Meeting Presentations<\/h3>\n