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Student Three Minute Thesis Competition

2022 UF Plant Science Council Symposium Poster Competition 

Jose Suazo, University of Florida

Poster Title: Evaluation of St. Augustinegrass Fertilization Regimens

Abstract: St. Augustinegrass (Stenotaphrum secundatum) is adapted to warm subtropical regions and is the most widely produced and utilized species for sod and lawns in Florida. Fertilization is an important component of lawn management; however, there are environmental concerns associated with the application of fertilizers. Several ordinances exist throughout Florida dictating the timing of fertilization. Knowledge regarding the timing of applications, amounts and the responses of differing cultivars is critical for obtaining adequate turf quality with minimal application of fertilizers. The objective of this study was to evaluate the effects of four fertilization regimens (UF-IFAS recommendations, summer blackout, national retail product recommendations, and no added fertility) and two mowing heights (5.0 and 8.75 cm) on three St. Augustinegrass cultivars (‘CitraBlue’, ‘Floratam’, and ‘Palmetto’). The experimental design was a RCBD with a strip-split plot design and three replications with cultivars as main plots, mowing heights as strips and fertility treatments as sub-sub-plots. Chlorophyll levels (SPAD units) of leaves and visual turfgrass quality, color, and density ratings were measured monthly from Sep 2018 to Dec 2020 and seasonal averages calculated (spring = Jan to Apr; summer = May to Aug; fall = Sep to Dec). There were significant differences in turfgrass quality, color, density, and SPAD units between cultivars and fertilizer treatments for each season but no significant interactions. No added fertility showed lower performance; differences between the three regimens were minimal. CitraBlue generally showed superior turfgrasss quality ratings across seasons.

Alex Rodriguez, University of Florida

Poster Title: Preemergence and postemergence weed control in sweet corn on organic soils

Abstract: Atrazine and cultivation have been the foundation of weed management programs for sweet corn production on organic soils in southern Florida. However, due to a shift to mainly grass weed species and reduced efficacy of atrazine there is a need for alternative weed management programs for sweet corn. Therefore, field experiments were conducted on organic soil in Belle Glade, FL, in 2020 to evaluate preemergence and postemergence weed management programs for sweet corn using novel broad-spectrum herbicides and cultivation. Preemergence herbicides included pyroxasulfone, pyroxasulfone + atrazine + fluthiacet-methyl, S-metolachlor, S-metolachlor + atrazine, and atrazine. Postemergence herbicides included tembotrione, mesotrione, mesotrione + atrazine, topramezone, topramezone + atrazine, topramezone + bentazon, and mechanical cultivation between the V4 and V8 stages of sweet corn. In the preemergence study, fall panicum control was >85% at 56 days after treatment (DAT) for all treatments that included pyroxasulfone. S-metolachlor + atrazine and all treatments that included pyroxasulfone provided >86% control of broadleaf weeds at 56 DAT. In the postemergence study, all treatments that included topramezone provided 71 to 94% fall panicum control at 42 DAT. All postemergence herbicides provided 89 to 100% broadleaf weeds control at 42 DAT with the exception of 70 and 75% common purslane control with mesotrione alone and tembotrione, respectively. Overall, the results suggest that pyroxasulfone can provide efficacious residual control of problematic weeds on organic soils. In addition, topramezone alone or in combination with atrazine or bentazon can be used for effective weed control in sweet corn on organic soils.

Rebecca Arias, University of Florida

Poster Title: Sterilization of turf bermudagrass line FB1628 (Cyondon. spp) to induce calli for Agrobacterium-mediated transformation

Abstract: Turf bermudagrass (Cyondon spp.) is of significant economic importance in Florida and the southern United States. It is the most widely used warm-season turfgrass species on golf courses and sports fields, world-wide. Bermudagrass is susceptible to caterpillar species, including the tropical sod webworm (TSW) (Herpetogramma phaeopteralis) which is a major pest causing damage to bermudagrass and significant economic impact to the turfgrass industry. This damage extends to golf courses, parks, sports fields, and other areas that require a general-purpose turf. Therefore, the objective of this research is to develop repeatable callus induction methods for ‘FB1628’. The long-term goal is to utilize plant transformation for insertion of the Bt gene cry1Ac to confer resistance to TSW. Sterilization of plant material is a critical step to regenerate healthy calli susceptible to Agrobacterium-mediated transformation. This research focused on a reliable sterilization protocol that would result in a higher success rate of callus induction while also lowering rates of contamination. The multi-step process involved: collection of plant media in an aseptic manner, treatment in 70% ethanol, treatment in 1.2% NaOH, and a final treatment in 0.1% PPM. Facilitation of these techniques will lead to increased callus growth, which will be applied in the next step of the project and continue research into a TSW-resistant turf bermudagrass.

David May, University of Florida

Poster Title: Targeted multi-allelic mutagenesis in polyploid, apomictic bahiagrass (Paspalum notatum Flugge) using the CRISPR/Cas9 system

Abstract: Bahiagrass (Paspalum notatum Flugge) is a subtropical perennial grass species widely cultivated in the southeastern United States and Central and South America both as forage and turf. The clustered regularly interspaced short palindromic repeats /CRISPR-associated protein 9 (CRISPR/Cas9) system has been applied in functional studies and genetic modification of many economically important plant species. This technology holds special importance for improvement of the numerous polyploid and apomictic or clonally propagated species found in the Plant kingdom as it is capable of generating desired multicopy mutations in a single generation without the need for crossing.
Here, we provide a preliminary report of CRISPR/Cas-mediated genome editing applied in the apomictic tetraploid bahiagrass cultivar ‘Argentine,’ targeting the chlorophyll biosynthesis gene Magnesium-protoporphyrin IX chelatase (Mg-chelatase). This target was chosen to generate a rapidly scorable phenotype to facilitate optimizations in the genome editing protocol and reduce the effort associated with molecular analysis. To generate the edited low-chlorophyll bahiagrass plants, a pair of guide RNAs (gRNA) targeting a conserved region of the third exons of the multiple P. notatum Mg-chelatase copies were cloned into an expression vector containing Cas9 and the NPTII selectable marker, which was introduced into mature seed-derived callus cultures by biolistics. A uniform callus line displaying a yellow phenotype has emerged in the regeneration phase of tissue culture, and an initial set of Sanger reads have confirmed multi-allelic editing. The Mg-chelatase visual marker system described here will allow for further optimization of genome editing tools or their delivery in bahiagrass, enabling precision breeding of this species.

Jordan McBreen, University of Florida

Poster Title: Predicting grain yield and related traits in wheat under heat-related stress environments using UAV-based hyperspectral imaging and functional regression.

Abstract: Developing improved wheat (Triticum aestivum) varieties that are adapted to a wide range of environmental conditions in a timely manner is key to successful wheat breeding and post-anthesis heat stress is a common yield-limiting factor in the US wheat growing areas. The annual occurrence of moderate heat stress, accompanied by periodic extreme heat stress events, prevents wheat from reaching its full yield potential. Quantifying certain physiological traits under heat-stress is crucial for maximizing genetic gain for wheat yield and yield related components. In-season estimation of yield and certain physiological traits related to heat stress tolerance can lead to the speeding up of the breeding process by allowing for early genotype selection decisions to be made in a process known as genomic selection (GS). In cases where there are fewer plots to collect data from and a narrow range of phenotypic values, traditional methods of yield-prediction modeling become less robust. To handle this, we consider the agreement between observed and predicted trait values for a number of GS models and also employ function on function regression with signal compression that addresses limitations of previous regression techniques to create a model for predicting grain yield in wheat under heat stress environmental conditions, and when data availability is constrained, by the processing of high-dimensionality spectral data derived from the canopy reflectance of wheat plants collected via unmanned aerial vehicle (UAV-based) remote sensing high throughput phenotyping.

Andrew Egesa, University of Florida

Poster Title:Effect of heat stress on reproductive development in Zea mays L.

Abstract: Heat stress is one of the major limiting factors for crop productivity, resulting annually in significant yield losses especially in cereals, such as maize (Zea mays), rice (Oryza sativa), and wheat (Triticum aestivum). This is due to the substantial impact that heat stress has on the reproductive development of the cereals. As such, we investigated the effect of heat stress on the tricellular stage of pollen development in Z. mays. B73 Maize plants at the early tricellular stage of pollen development were subjected to moderate heat stress (35oC/25oC, day/night), for two days, while a parallel set of plants were maintained at 25oC/21oC, the control conditions. Heat stress hastened the development of maize anthers resulting in improper maturation and reduction in pollen dehiscence. Apart from the downregulation of the late pollen gene (ZmMADS2), known to aid anther dehiscence, we observed altered synthesis of flavanols and anthocyanins in anthers of the heat exposed maize plants. Evidence from other crops suggests that anther indehiscence due to heat stress is caused by impaired moisture flow and sugar metabolism, a similar scenario may be true in maize anthers. However, our findings indicate that secondary metabolism may also have a critical role in this process. Therefore, these findings point out the need to investigate the role of secondary metabolism in anther dehiscence as well as the necessity to evaluate other maize genotypes to understand how they respond to heat stress to select for and to breed maize plants tolerant to heat stress.

Taehoon Kim, University of Florida

Poster Title: Genome-wide identification and expression analysis of light-responsive Hsf and Hsp genes in Lactuca sativa

Abstract: Heat shock factors (Hsfs) and Heat shock proteins (Hsps) belong to an essential group of molecular regulators involved in controlling cellular processes under normal and stress conditions. The role of Hsfs and Hsps is well known in model plant species under diverse stress conditions. However, in lettuce (Lactuca sativa), a highly consumed vegetable crop grown in the field and in hydroponic systems, the role of these gene families in response to artificial light is not well characterized. Using a genome-wide analysis approach, we identified 32 Hsfs and 22 small heat shock proteins (LsHsps) in lettuce, some of which do not have orthologous in Arabidopsis, poplar, and rice. LsHsp60s, LsHsp90s, and LsHsp100s are highly conserved among dicot and monocot species. Surprisingly, LsHsp70s have three times more members than Arabidopsis and two times more than rice. Genome triplication might have contributed to the increased number of LsHsp70s genes. Chromosomal distribution analysis shows larger tandem repeats of LsHsp70s genes in Chr1, Chr7, Chr8, and Chr9. At the transcriptional level, some genes of the LsHsfs, LsHsps, LsHsp60s, and LsHsp70s families were highly responsive to UV and high light stress, in contrast of LsHsp90s and LsHsp100s which did not respond to a light stimulus. Our genome-wide analysis provides a detail identification of Hsfs and Hsps in lettuce. Chromosomal location and syntenic region analysis together with our transcriptional analysis under different light conditions provide candidate genes for breeding programs aiming to produce lettuce varieties able to grow healthy under hydroponic systems that use artificial light.

Blair Kleiman, Florida International University

Poster Title: How do weeds affect insects in mango cultivation of Homestead, Fl?

Abstract: Using weeds- wild, unwanted plants-as insectary plants to support beneficial insects is an emerging topic of agricultural research. Weeds use in tropical fruit production reliant on pollination could increase fruit yield, and biodiversity of beneficial insects in mango farms of South Florida. Weeds are a cost-effective insectary plant, useful to parasitoids, predators, and pollinators, expanding their range into farms, and possibly increasing crop protection from pests and biotic pollination. The objective of this study is to determine the effects of weeds as refuge resource plants to enhance the abundance and diversity of beneficial insect species, which will benefit mango (Mangifera indica) crop production. More biodiverse farms, hosting varied plants and insects, are more resilient and less vulnerable to environmental stressors. Using native weeds, which have the potential to act as insectary plants when growing companion plants isn’t possible and increasingly likely in changing climates, to add to the variety of diets for beneficial insects increases the conservation of plants and their plant-pollinator networks. Weeds can provide resources to maintain balanced predator-prey dynamics, and allow for less chemical use of pesticides and herbicides, and more environmentally sound agriculture across South Florida. This study questions 1. How do the number and diversity of insects differ on mango in the presence or absence of weeds? 2. What is the impact on mango fruit yield in the presence of weeds? Increasing the diversity of pollinators through weeds can buffer against lapses in pollination by agricultural bees, Apis mellifera, and increase crop production.

Kiara Taibi-Briz, Florida International University

Poster Title: Studies on cellulolytic activity, ethanol tolerance and silver compound sensitivity of Raffaelea lauricola

Abstract: Laurel wilt is caused by Raffaelea lauricola, a fungal pathogen transmitted by the invasive ambrosia beetle Xyleborus glabratus. The female ambrosia beetle bore into the trunk of a healthy or stressed tree and inoculate the galleries with ambrosia fungus (R. lauricola) on which the brood feeds. The fungus flourishes in the galleries of sapwood which clogs up the flow of water and nutrients in the tree. The fungus attacks the vascular system of trees in the Lauraceae family, and it has killed millions of trees since it was first found in the southeastern United States in 2004. Laurel wilt has been a devastating disease for avocados groves in Southern Florida and now has become a potential threat to the California avocado industry. The infected avocado trees can be saved by injecting them with a fungicide. But it is expensive and time-consuming and must be repeated every two or three year. Understanding of the biology of the pathogen may provide new insight into the control of the disease.
Although Raffaelea lauricola inside the galleries is known to consume and grow on wood, a clear demonstration of its cellulolytic ability has not been reported. In some ambrosia beetle-fungus relationship it has been reported that the beetle prefers stressed or dying trees, which have more ethanol in their tissue. This reliance on ethanol for host tree colonization promotes the growth of their ethanol tolerant fungal symbiont while inhibiting the growth of ethanol susceptible microbial competitors. Interestingly, R. lauricola is known to produce ethanol under laboratory conditions, but ethanol tolerance of R. lauricola has not been studied. Silver ions and silver based compounds have strong antimicrobial properties with multiple mode of action. Therefore, use of silver-based compounds may expand treatment options for the management of laurel wilt.

Anju Biswas, University of Florida

Poster Title: Application of spatial analysis to improve the heritability and selection accuracy in Alfalfa (Medicago sativa L.) breeding

Abstract: Field trials are associated to intrinsic and extrinsic distinctions, which can add some form of spatial variation between experimental units. Local control such as blocking, and randomization cannot account for all the spatial variation effectively. Spatial variation is common in complex and large experimental designs in plant breeding programs. A better way to control these variations is to utilize spatial analysis which can detect the variation patterns. Plots close to each other are expected to be more correlated than those are far apart. The objectives of our study were: i) fit a base model without accounting for spatial variation and a spatial model to check the significant effect of rows and columns; and ii) estimate genetic parameters [narrow-sense heritability h2 and selection accuracy] using both models. The experiment was established in November 2017 and the experimental design was row column with augmented representation of three controls. The alfalfa breeding population was composed of 145 full-sib and 36 half-sib families. Herbage accumulation (HA) was collected four times between 2018 and 2019. We found that the autocorrelation of row and column were significant when fitting a spatial analysis. Higher h2 and selection accuracy were obtained when accounting for spatial variation on each harvest. The spatial model showed better fit than the base model to reduce the error and improve the estimation of genetic parameters in our alfalfa breeding program.

Hannah Rusch, University of Florida

Poster Title: Leaf Area Index as an Indicator of Forage Production Potential 

Abstract: Bahiagrass (Paspalum notatum Flugge) pastures produce abundant, low-quality forage. Nitrogen inputs improve bahiagrass nutritive value and the inclusion of legumes like rhizoma peanut (Arachis glabrata Benth) can help to achieve this. Grazing management influences the quantity and quality of forage available. Indicators are needed to optimize grazing practices to maximize forage supply and nutritive value. The objectives of this study were 1) to evaluate the effect of rhizoma peanut inclusion and defoliation on forage production, and 2) to determine whether leaf area index (LAI) might serve as an indicator to optimize grazing. A randomized complete block design with a split plot arrangement was implemented near Gainesville, Florida, USA in summer 2020. Whole plots consisted of sole bahiagrass and mixed bahiagrass + rhizoma peanut pastures. Treatments were applied at the split plot level and included: defoliated, defoliated + manure, and undefoliated. Monthly defoliation was applied to quantify biomass production. Weekly LAI measurements were collected to monitor canopy growth between defoliation events. Inclusion of rhizoma peanut increased forage production relative to sole bahiagrass. Similarly, defoliation increased forage production relative to the undefoliated treatment. A clear relationship was observed among treatments in relation to mean and maximum LAI. Our results suggest LAI may be a key management indicator to optimize forage productivity. Further research is necessary to determine whether LAI can be used to manipulate grazing intensity and frequency. The relationship between LAI and forage quality must be included when considering the animal performance aspect of a grazing system.

Kevin Lewin, Florida International University

Poster Title: Ethnomedicinal Properties of Mountain Soursop (Annona montana)

Abstract: Annona muricata, also called soursop, graviola, and guanabana, is the most tropical member of the Annonaceae family growing in tropical and subtropical regions of the world. Best growth is achieved in deep, rich, well-drained, semi-dry soil, but the soursop tree can be and is commonly grown in acid and sandy soil, and in the porous, oolite limestone of South Florida and the Bahama Islands. All the parts, fruits, seeds, leaves and roots, of the plant have been known to be used in many products. Annona muricata has shown to have anticancer, anticonvulsant, anti-arthritic, antiparasitic, antimalarial, hepatoprotective and antidiabetic activities. Annona montana tree somewhat resembles that of the soursop but has a more spreading crown and very glossy leaves. It is slightly hardier and bears continuously. A lot of research has gone into Annona muricata, soursop, and its ethnomedicinal uses, but not a lot is known of the A. montana, also known as Mountain Soursop in South Florida. The objectives of this study is to identify the pharmaceutical compounds in leaves, pulp, and seeds of the A. montana. Glycosides, alkaloids, flavonoids, glycoside saponin assay on the leaves, pulp, and seeds of the A. montana will be conducted. The highest concentration of compounds that are found were alkaloid compounds called acetogenins. This is the main compound that is thought to be the reason for the medicinal qualities that the tree possesses.

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