Michelle JOnes - Academia.edu (original) (raw)

Papers by Michelle JOnes

BMC plant biology, Mar 6, 2024

Phytobiomes journal, Apr 5, 2021

Phytobiomes Journal, 2021

Root-associated bacteria play critical roles in shaping plant health for abiotic and biotic stres... more Root-associated bacteria play critical roles in shaping plant health for abiotic and biotic stress tolerance. The Leifsonia genus includes pathogenic and beneficial bacteria but limited research is available comparatively across species regarding their association with plants. We recently identified the plant growth-promoting Leifsonia sp. C5G2 isolated from the rhizosphere of Plectranthus scutellarioides (coleus) that increased stress tolerance and quality of water-stressed greenhouse ornamentals. Using this beneficial strain as a model, we performed comparative genomics with beneficial, commensal, and pathogenic Leifsonia spp. to better understand plant association and growth promotion under abiotic stress. Comparative phylogenetic analyses showed that beneficial and commensal Leifsonia spp. clustered separately from pathogenic Leifsonia xyli subsp. xyli. In addition, the beneficial or commensal strains share biosynthetic gene and orthologous protein clusters that are not shared w...

Frontiers in Plant Science

Developmental petal senescence is a type of programmed cell death (PCD), during which the product... more Developmental petal senescence is a type of programmed cell death (PCD), during which the production of ethylene is induced, the expression of PCD-related genes is upregulated, and nutrients are recycled. Autophagy is an intracellular mechanism involved in PCD modulation and nutrient cycling. As a central component of the autophagy pathway, Autophagy Gene 6 (ATG6) was previously shown as a negative regulator of petal senescence. To better understand the role of autophagy in ethylene biosynthesis and nutrient remobilization during petal senescence, we generated and characterized the knockout (KO) mutants of PhATG6 using CRISPR/Cas9 in Petunia × hybrida ‘Mitchell Diploid.’ PhATG6-KO lines exhibited decreased flower longevity when compared to the flowers of the wild-type or a non-mutated regenerative line (controls), confirming the negative regulatory role of ATG6 in petal senescence. Smaller capsules and fewer seeds per capsule were produced in the KO plants, indicating the crucial fu...

Virus-induced gene silencing (VIGS) is used to down-regulate endogenous plant genes. VIGS efficie... more Virus-induced gene silencing (VIGS) is used to down-regulate endogenous plant genes. VIGS efficiency depends on viral proliferation and systemic movement throughout the plant. Although tobacco rattle virus (TRV)-based VIGS has been successfully used in petunia (Petunia × hybrida), the protocol has not been thoroughly optimized for efficient and uniform gene down-regulation in this species. Therefore, we evaluated six parameters that improved VIGS in petunia. Inoculation of mechanically wounded shoot apical meristems induced the most effective and consistent silencing compared to other methods of inoculation. From an evaluation of ten cultivars, a compact petunia variety, 'Picobella Blue', exhibited a 1.8-fold higher CHS silencing efficiency in corollas. We determined that 20°C day/18°C night temperatures induced stronger gene silencing than 23°C/18°C or 26°C/ 18°C. The development of silencing was more pronounced in plants that were inoculated at 3-4 versus 5 weeks after sowing. While petunias inoculated with pTRV2-NbPDS or pTRV2-PhCHS showed very minimal viral symptoms, plants inoculated with the pTRV2 empty vector (often used as a control) were stunted and developed severe necrosis, which often led to plant death. Viral symptoms were eliminated by developing a control construct containing a fragment of the green fluorescent protein (pTRV2-sGFP). These optimization steps increased the area of chalcone synthase (CHS) silencing by 69 % and phytoene desaturase (PDS) silencing by 28 %. This improved VIGS protocol, including the use of the pTRV2-sGFP control plants, provides stronger down-regulation for high-throughput analyses of gene function in petunia.

HortScience, 2022

Microbial biostimulants can promote ornamental plant growth during production and improve crop pe... more Microbial biostimulants can promote ornamental plant growth during production and improve crop performance under abiotic stresses. Even though biostimulants have shown potential in many agricultural applications, the effectiveness and specificity of many products are not well understood. The objective of this study was to analyze the growth-promoting effects of microbial biostimulants during the greenhouse production of floriculture crops. We evaluated 13 biostimulant products in greenhouse-grown zinnia (Zinnia elegans ‘Magellan Ivory’) and petunia (Petunia ×hybrida ‘Carpet White’) at low fertility (one-third of the optimal fertilizer concentration). Biostimulant products 1 and 2 containing multiple species of beneficial bacteria and fungi, and product 10 containing Bacillus subtilis QST 713, were found to increase various aspects of plant growth, including the growth index, leaf chlorophyll content (SPAD index), and shoot biomass. Both flower biomass and numbers were greater in pet...

Frontiers in Microbiology, 2021

High fertilizer rates are often applied to horticulture crop production systems to produce high q... more High fertilizer rates are often applied to horticulture crop production systems to produce high quality crops with minimal time in production. Much of the nutrients applied in fertilizers are not taken up by the plant and are leached out of the containers during regular irrigation. The application of plant growth promoting rhizobacteria (PGPR) can increase the availability and uptake of essential nutrients by plants, thereby reducing nutrient leaching and environmental contamination. Identification of PGPR can contribute to the formulation of biostimulant products for use in commercial greenhouse production. Here, we have identified Serratia plymuthica MBSA-MJ1 as a PGPR that can promote the growth of containerized horticulture crops grown with low fertilizer inputs. MBSA-MJ1 was applied weekly as a media drench to Petunia×hybrida (petunia), Impatiens walleriana (impatiens), and Viola×wittrockiana (pansy). Plant growth, quality, and tissue nutrient concentration were evaluated 8week...

Frontiers in Microbiology, 2021

Water stress decreases the health and quality of horticulture crops by inhibiting photosynthesis,... more Water stress decreases the health and quality of horticulture crops by inhibiting photosynthesis, transpiration, and nutrient uptake. Application of plant growth promoting rhizobacteria (PGPR) can increase the growth, stress tolerance, and overall quality of field and greenhouse grown crops subjected to water stress. Here, we evaluatedSerratia plymuthicaMBSA-MJ1 for its ability to increase plant growth and quality ofPetunia×hybrida(petunia),Impatiens walleriana(impatiens), andViola×wittrockiana(pansy) plants recovering from severe water stress. Plants were treated weekly with inoculum of MBSA-MJ1, and plant growth and quality were evaluated 2 weeks after recovery from water stress. Application ofS. plymuthicaMBSA-MJ1 increased the visual quality and shoot biomass of petunia and impatiens and increased the flower number of petunia after recovery from water stress. In addition,in vitrocharacterizations showed that MBSA-MJ1 is a motile bacterium with moderate levels of antibiotic resis...

Horticulturae, 2021

The upregulation of endonuclease activities and subsequent decreases in the nucleic acid content ... more The upregulation of endonuclease activities and subsequent decreases in the nucleic acid content of leaves and petals are characteristics of senescence that allow for nutrient remobilization from dying organs. We previously identified a 43-kDa endonuclease activity (PhNUC1) that was upregulated in Petunia × hybrida petals during senescence. PhNUC1 has optimal activity at neutral pH, is enhanced by Co2+, and degrades both DNA and RNA. The peptide sequence of a 43-kDa endonuclease identified from senescing petals by 2-dimensional gel electrophoresis was used to clone the gene (PhENDO1) encoding the senescence-associated protein. PhENDO1 expression was upregulated in petals during the senescence of unpollinated and pollinated flowers and by ethylene treatment. When petunias were grown under nutrient deficient conditions, P-starvation, and to a lesser extent N-starvation, induced expression of PhENDO1. The endogenous expression of PhENDO1 was down regulated using virus induced gene sile...

Frontiers in Plant Science, 2020

Water deficit stress is a major contributor to the loss of ornamental crop value due to its negat... more Water deficit stress is a major contributor to the loss of ornamental crop value due to its negative effects on plant growth and flowering. In addition, post-production water stress can reduce the photosynthetic capacity of plants, negatively impacting crop quality at retail and in the consumer's home and garden. While the application of microbecontaining biostimulant products can increase stress tolerance and crop quality, the success of most commercially available biostimulants in greenhouse production systems is inconsistent. To identify beneficial bacteria with consistent biostimulant activity in greenhouse ornamentals, our study isolated bacteria from the rhizosphere of water stressed greenhouse ornamentals. Five species of popular ornamentals were obtained from 15 different commercial greenhouse facilities and then subjected to three cycles of water stress. Over 1,000 bacterial isolates were collected from the rhizosphere and screened in vitro for osmoadaptability and 1-aminocyclopropane-1carboxylate (ACC) deaminase activity. Eighty selected isolates were evaluated in a high-throughput greenhouse trial for their ability to increase plant size and flower number of water-stressed Petunia × hybrida. Ten bacterial strains selected from the highthroughput trial were then evaluated in a greenhouse validation trial for their ability to increase plant growth and to mitigate the reduction in photosynthetic parameters of water stressed P. hybrida and Pelargonium × hortorum. Application of certain bacteria increased plant size in both species and flower number of P. hybrida after recovery from water stress when compared to untreated water stressed plants. In addition, bacteria application increased the chlorophyll fluorescence parameters including quantum yield and efficiency of photosystem II (PSII) and electron transport rate (ETR), while decreasing the extent of electrolyte leakage during water stress and recovery. Overall, this study identified bacterial strains that can increase tolerance to and recovery from water stress in two commercially important ornamental crop species.

Journal of Natural Resources and Life Sciences Education, 2000

Plant physiology is best explored through participatory activities, where students are closely en... more Plant physiology is best explored through participatory activities, where students are closely engaged in the process of discovery. A two-stage approach to instruction was implemented to enrich the learning in an undergraduate plant physiology laboratory. First, a core of 10 experiments was developed to provide structured, hands-on experience and to teach the principles and skills of modern physiological analyses. During Week 11 of a 15wk semester, students observe a demonstration of a plant response, where the underlying cause of the phenomenon is not evident. Working together in small groups, students hypothesize on the mechanisms that may be involved. They choose among alternative lines of inquiry and decide which variables will be most informative in revealing the underlying nature of the problem. Each research team presents a study plan, and hypotheses and experimental approaches are defended. Results of team experiments are presented during Week 15. To date, inquiry-based projects have focused on the roles of (i) ethylene in seedling development in mouse-ear cress [Arabidopsis thaliana L. (Heynh.)] and tomato (Lycopersicon esculentum Mill.), (ii) glycinebetaine in drought tolerance of maize (Zea mays L.), (iii) catalase in chilling sensitivity of tomato, and (iv) ascorbic acid in oxidative stress in tomato. The Chilling-Injury Problem utilized in 1996 and 1997 is described, and pedagogical advantages as well as challenges to implementation are discussed. The approach appears to foster a capacity for connective, integrative thinking. Students develop competency in judging the reliability and significance of experimental results, and in evaluating whether their conclusions are justified by the data.

Plant Disease, 2020

Botrytis cinerea infects most major greenhouse crops worldwide. With its increasing resistance to... more Botrytis cinerea infects most major greenhouse crops worldwide. With its increasing resistance to conventional fungicides and the movement of the greenhouse industry toward more sustainable production practices, alternative methods of control are needed. The objective of this study was to evaluate a collection of 60 bacterial strains through both a dual-culture assay and greenhouse trials to identify strains with biocontrol activity against B. cinerea. For the dual-culture assay, each bacterial strain was streaked on potato dextrose agar medium with B. cinerea. The B. cinerea growth reduction and the zone of inhibition were measured. Thirty-five strains reduced the growth of B. cinerea. All strains were also tested in an initial greenhouse trial in which Petunia × hybrida ‘Carpet Red Bright’ was sprayed and drenched with the bacteria biweekly for 6 weeks. All open flowers were tagged, and plants were inoculated with B. cinerea (1 × 104 conidia per 1 ml). Disease severity indices cal...

Frontiers in Plant Science, 2020

The sustainability of ornamental crop production is of increasing concern to both producers and c... more The sustainability of ornamental crop production is of increasing concern to both producers and consumers. As resources become more limited, it is important for greenhouse growers to reduce production inputs such as water and chemical fertilizers, without sacrificing crop quality. Plant growth promoting rhizobacteria (PGPR) can stimulate plant growth under resource-limiting conditions by enhancing tolerance to abiotic stress and increasing nutrient availability, uptake, and assimilation. PGPR are beneficial bacteria that colonize the rhizosphere, the narrow zone of soil in the vicinity of the roots that is influenced by root exudates. In this study, in vitro experiments were utilized to screen a collection of 44 Pseudomonas strains for their ability to withstand osmotic stress. A high-throughput greenhouse experiment was then utilized to evaluate selected strains for their ability to stimulate plant growth under resource-limiting conditions when applied to ornamental crop production systems. The development of a highthroughput greenhouse trial identified two pseudomonads, P. poae 29G9 and P. fluorescens 90F12-2, that increased petunia flower number and plant biomass under drought and low-nutrient conditions. These two strains were validated in a productionscale experiment to evaluate the effects on growth promotion of three economically important crops: Petunia × hybrida, Impatiens walleriana, and Viola × wittrockiana. Plants treated with the two bacteria strains had greater shoot biomass than untreated control plants when grown under low-nutrient conditions and after recovery from drought stress. Bacteria treatment resulted in increased flower numbers in drought-stressed P. hybrida and I. walleriana. In addition, bacteria-treated plants grown under low-nutrient conditions had higher leaf nutrient content compared to the untreated plants. Collectively, these results show that the combination of in vitro and greenhouse experiments can efficiently identify beneficial Pseudomonas strains that increase the quality of ornamental crops grown under resource-limiting conditions.

HortScience, 2004

Salinity, drought and temperature frequently limit crop productivity. Transgenic Petunia ×hybrida... more Salinity, drought and temperature frequently limit crop productivity. Transgenic Petunia ×hybrida cv. Mitchell with altered endogenous raffinose family oligosaccharides (RFO) due to over-expression (sense) or under-expression (antisense) of the tomato α-galactosidase gene show that antisense increases in RFO are associated with greater tolerance to freezing stress (Pennycooke et al., 2003). Because vegetative propagules of these antisense lines rooted and established more quickly than their sense counterparts, we hypothesized that antisense lines would also respond to salinity and wilting stress. Salinity treatment plants were exposed to 50-200 mm NaCl graduated 25 mm every 3 days and held at 200 mm for 13 days. Dry-down treatments were watered to pot capacity, then not watered until the onset of wilting. This was repeated in cycles for 26 days. Data were collected on plant growth, root/shoot ratios, and leaf water potential. Fresh and dry weights in four of the six antisense lines ...

HortScience, 2005

Corolla senescence in petunias was accompanied by a decrease in total proteins and a correspondin... more Corolla senescence in petunias was accompanied by a decrease in total proteins and a corresponding increase in proteolytic activity. Transgenic petunias that contain the mutated ethylene receptor (35S:etr1-1) have reduced sensitivity to ethylene and delayed flower senescence. Declines in total protein levels and increases in proteolytic activity were also delayed in etr1-1 flowers and corresponded with corolla wilting. Experiments using class-specific proteinase inhibitors indicated that proteolytic activity in petunia corollas was largely due to cysteine proteinases. Total nitrogen levels within the corollas of both wild type and etr1-1 flowers also decreased during senescence. Nine cDNAs encoding putative cysteine proteinases (CPs) were identified from a petunia EST database developed at the University of Florida. Six of these cysteine proteinases showed increased transcript abundance during corolla senescence (senescence-associated CPs) while three decreased in abundance. Of the ...

HortScience, 2010

Drought stress during the shipping and retailing of floriculture crops can reduce postproduction ... more Drought stress during the shipping and retailing of floriculture crops can reduce postproduction shelf life and marketability. The plant hormone abscisic acid (ABA) mediates drought stress responses by closing stomata and reducing water loss. Applications of exogenous s-ABA effectively reduce water loss and allow a variety of species to survive temporary periods of drought stress. Unfortunately, s-ABA application can also lead to leaf chlorosis, which reduces the overall quality of economically important bedding plant species, including Viola ×wittrockiana (pansy). The goal of this research was to determine how to prevent s-ABA-induced leaf chlorosis in pansy and a closely related species, Viola cornuta (viola). All concentrations of both spray (250 or 500 mg·L−1) and drench (125 or 250 mg·L−1) s-ABA applications induced leaf yellowing. Young plants at the plug stage and 11-cm finished plants with one to two open flowers were further evaluated to determine if the developmental stage...

HortScience, 2014

The family Solanaceae, which includes both important crop and ornamental species, is generally co... more The family Solanaceae, which includes both important crop and ornamental species, is generally considered to have high sensitivity to ethylene. Our objectives were to evaluate ethylene sensitivity between accessions with the family Solanaceae and to determine whether similar sensitivity was observed in seedlings and mature plants. For the seedling evaluations, seeds were germinated and grown in the dark on filter paper saturated with 0 or 100 μM 1-aminocyclopropane-1-carboxylic acid (ACC; the immediate precursor to ethylene). The relative hypocotyl length at 100 μM ACC was compared with untreated control (0 μM) seedlings. Mature plants were treated with 0 or 10 μL·L−1 ethylene in the dark for 24 hours. Ethylene responses including flower abscission, flower senescence, and epinasty were observed and quantified. Seedlings and mature plants were classified as having no response, low, medium, or high ethylene sensitivity based on the severity of the ethylene responses observed. Sensitiv...

HortScience, 2017

Phalaenopsis orchids are an increasingly popular potted house plant in the United States. New cul... more Phalaenopsis orchids are an increasingly popular potted house plant in the United States. New cultivars have a long display life in home environments, but these epiphytes are often overirrigated by consumers. Irrigating potted Phalaenopsis orchids weekly with ice cubes has been recommended as a simple solution to help consumers, but concern has been raised about whether the ice cubes will cause low temperature damage in these tropical plants. The effect of ice cube irrigation on the display life and quality of four cultivars of potted Phalaenopsis orchids was, therefore, evaluated. Irrigation treatments included weekly application of three ice cubes or the equivalent volume of room-temperature tap water. The longevity of individual flowers and the overall display life of the orchid plants were determined. Monthly measurements determined the volume of leachate in the outer decorative pots after irrigation. The quantum yield of photosystem II (ΦPSII) in roots and leaves was evaluated ...

Journal of the American Society for Horticultural Science, 2005

Petunia ×hybrida (Hook) Vilm. cv. Mitchell was transformed with an E. coli gene encoding mannitol... more Petunia ×hybrida (Hook) Vilm. cv. Mitchell was transformed with an E. coli gene encoding mannitol-1-phosphate dehydrogenase (mtlD). Four plant lines that grew on kanamycin and contained the mtlD transgene were identified. Two of these lines contained high levels of mannitol [high-mannitol lines M3 and M8; mean mannitol = 3.39 μmol·g-1 dry weight (DW)] compared to nontransformed wild-type plants (0.86 μmol·g-1 DW), while two lines had mannitol levels similar to wild-type plants (low-mannitol lines M2 and M9; mean mannitol = 1.05 μmol·g-1 DW). Transgenic and control plants were subjected to chilling stress (3 ± 0.5 °C day/0 ± 0.5 °C night, 12-hour photoperiod and 75% relative humidity) to evaluate the role of mannitol in chilling tolerance. Based upon foliage symptoms and membrane leakage after a 3-week chilling treatment, the high-mannitol containing lines, M3 and M8, were more tolerant of chilling stress than the low-mannitol containing transgenic lines, M2 and M9, and wild-type. Un...

BMC plant biology, Mar 6, 2024

Phytobiomes journal, Apr 5, 2021

Phytobiomes Journal, 2021

Root-associated bacteria play critical roles in shaping plant health for abiotic and biotic stres... more Root-associated bacteria play critical roles in shaping plant health for abiotic and biotic stress tolerance. The Leifsonia genus includes pathogenic and beneficial bacteria but limited research is available comparatively across species regarding their association with plants. We recently identified the plant growth-promoting Leifsonia sp. C5G2 isolated from the rhizosphere of Plectranthus scutellarioides (coleus) that increased stress tolerance and quality of water-stressed greenhouse ornamentals. Using this beneficial strain as a model, we performed comparative genomics with beneficial, commensal, and pathogenic Leifsonia spp. to better understand plant association and growth promotion under abiotic stress. Comparative phylogenetic analyses showed that beneficial and commensal Leifsonia spp. clustered separately from pathogenic Leifsonia xyli subsp. xyli. In addition, the beneficial or commensal strains share biosynthetic gene and orthologous protein clusters that are not shared w...

Frontiers in Plant Science

Developmental petal senescence is a type of programmed cell death (PCD), during which the product... more Developmental petal senescence is a type of programmed cell death (PCD), during which the production of ethylene is induced, the expression of PCD-related genes is upregulated, and nutrients are recycled. Autophagy is an intracellular mechanism involved in PCD modulation and nutrient cycling. As a central component of the autophagy pathway, Autophagy Gene 6 (ATG6) was previously shown as a negative regulator of petal senescence. To better understand the role of autophagy in ethylene biosynthesis and nutrient remobilization during petal senescence, we generated and characterized the knockout (KO) mutants of PhATG6 using CRISPR/Cas9 in Petunia × hybrida ‘Mitchell Diploid.’ PhATG6-KO lines exhibited decreased flower longevity when compared to the flowers of the wild-type or a non-mutated regenerative line (controls), confirming the negative regulatory role of ATG6 in petal senescence. Smaller capsules and fewer seeds per capsule were produced in the KO plants, indicating the crucial fu...

Virus-induced gene silencing (VIGS) is used to down-regulate endogenous plant genes. VIGS efficie... more Virus-induced gene silencing (VIGS) is used to down-regulate endogenous plant genes. VIGS efficiency depends on viral proliferation and systemic movement throughout the plant. Although tobacco rattle virus (TRV)-based VIGS has been successfully used in petunia (Petunia × hybrida), the protocol has not been thoroughly optimized for efficient and uniform gene down-regulation in this species. Therefore, we evaluated six parameters that improved VIGS in petunia. Inoculation of mechanically wounded shoot apical meristems induced the most effective and consistent silencing compared to other methods of inoculation. From an evaluation of ten cultivars, a compact petunia variety, 'Picobella Blue', exhibited a 1.8-fold higher CHS silencing efficiency in corollas. We determined that 20°C day/18°C night temperatures induced stronger gene silencing than 23°C/18°C or 26°C/ 18°C. The development of silencing was more pronounced in plants that were inoculated at 3-4 versus 5 weeks after sowing. While petunias inoculated with pTRV2-NbPDS or pTRV2-PhCHS showed very minimal viral symptoms, plants inoculated with the pTRV2 empty vector (often used as a control) were stunted and developed severe necrosis, which often led to plant death. Viral symptoms were eliminated by developing a control construct containing a fragment of the green fluorescent protein (pTRV2-sGFP). These optimization steps increased the area of chalcone synthase (CHS) silencing by 69 % and phytoene desaturase (PDS) silencing by 28 %. This improved VIGS protocol, including the use of the pTRV2-sGFP control plants, provides stronger down-regulation for high-throughput analyses of gene function in petunia.

HortScience, 2022

Microbial biostimulants can promote ornamental plant growth during production and improve crop pe... more Microbial biostimulants can promote ornamental plant growth during production and improve crop performance under abiotic stresses. Even though biostimulants have shown potential in many agricultural applications, the effectiveness and specificity of many products are not well understood. The objective of this study was to analyze the growth-promoting effects of microbial biostimulants during the greenhouse production of floriculture crops. We evaluated 13 biostimulant products in greenhouse-grown zinnia (Zinnia elegans ‘Magellan Ivory’) and petunia (Petunia ×hybrida ‘Carpet White’) at low fertility (one-third of the optimal fertilizer concentration). Biostimulant products 1 and 2 containing multiple species of beneficial bacteria and fungi, and product 10 containing Bacillus subtilis QST 713, were found to increase various aspects of plant growth, including the growth index, leaf chlorophyll content (SPAD index), and shoot biomass. Both flower biomass and numbers were greater in pet...

Frontiers in Microbiology, 2021

High fertilizer rates are often applied to horticulture crop production systems to produce high q... more High fertilizer rates are often applied to horticulture crop production systems to produce high quality crops with minimal time in production. Much of the nutrients applied in fertilizers are not taken up by the plant and are leached out of the containers during regular irrigation. The application of plant growth promoting rhizobacteria (PGPR) can increase the availability and uptake of essential nutrients by plants, thereby reducing nutrient leaching and environmental contamination. Identification of PGPR can contribute to the formulation of biostimulant products for use in commercial greenhouse production. Here, we have identified Serratia plymuthica MBSA-MJ1 as a PGPR that can promote the growth of containerized horticulture crops grown with low fertilizer inputs. MBSA-MJ1 was applied weekly as a media drench to Petunia×hybrida (petunia), Impatiens walleriana (impatiens), and Viola×wittrockiana (pansy). Plant growth, quality, and tissue nutrient concentration were evaluated 8week...

Frontiers in Microbiology, 2021

Water stress decreases the health and quality of horticulture crops by inhibiting photosynthesis,... more Water stress decreases the health and quality of horticulture crops by inhibiting photosynthesis, transpiration, and nutrient uptake. Application of plant growth promoting rhizobacteria (PGPR) can increase the growth, stress tolerance, and overall quality of field and greenhouse grown crops subjected to water stress. Here, we evaluatedSerratia plymuthicaMBSA-MJ1 for its ability to increase plant growth and quality ofPetunia×hybrida(petunia),Impatiens walleriana(impatiens), andViola×wittrockiana(pansy) plants recovering from severe water stress. Plants were treated weekly with inoculum of MBSA-MJ1, and plant growth and quality were evaluated 2 weeks after recovery from water stress. Application ofS. plymuthicaMBSA-MJ1 increased the visual quality and shoot biomass of petunia and impatiens and increased the flower number of petunia after recovery from water stress. In addition,in vitrocharacterizations showed that MBSA-MJ1 is a motile bacterium with moderate levels of antibiotic resis...

Horticulturae, 2021

The upregulation of endonuclease activities and subsequent decreases in the nucleic acid content ... more The upregulation of endonuclease activities and subsequent decreases in the nucleic acid content of leaves and petals are characteristics of senescence that allow for nutrient remobilization from dying organs. We previously identified a 43-kDa endonuclease activity (PhNUC1) that was upregulated in Petunia × hybrida petals during senescence. PhNUC1 has optimal activity at neutral pH, is enhanced by Co2+, and degrades both DNA and RNA. The peptide sequence of a 43-kDa endonuclease identified from senescing petals by 2-dimensional gel electrophoresis was used to clone the gene (PhENDO1) encoding the senescence-associated protein. PhENDO1 expression was upregulated in petals during the senescence of unpollinated and pollinated flowers and by ethylene treatment. When petunias were grown under nutrient deficient conditions, P-starvation, and to a lesser extent N-starvation, induced expression of PhENDO1. The endogenous expression of PhENDO1 was down regulated using virus induced gene sile...

Frontiers in Plant Science, 2020

Water deficit stress is a major contributor to the loss of ornamental crop value due to its negat... more Water deficit stress is a major contributor to the loss of ornamental crop value due to its negative effects on plant growth and flowering. In addition, post-production water stress can reduce the photosynthetic capacity of plants, negatively impacting crop quality at retail and in the consumer's home and garden. While the application of microbecontaining biostimulant products can increase stress tolerance and crop quality, the success of most commercially available biostimulants in greenhouse production systems is inconsistent. To identify beneficial bacteria with consistent biostimulant activity in greenhouse ornamentals, our study isolated bacteria from the rhizosphere of water stressed greenhouse ornamentals. Five species of popular ornamentals were obtained from 15 different commercial greenhouse facilities and then subjected to three cycles of water stress. Over 1,000 bacterial isolates were collected from the rhizosphere and screened in vitro for osmoadaptability and 1-aminocyclopropane-1carboxylate (ACC) deaminase activity. Eighty selected isolates were evaluated in a high-throughput greenhouse trial for their ability to increase plant size and flower number of water-stressed Petunia × hybrida. Ten bacterial strains selected from the highthroughput trial were then evaluated in a greenhouse validation trial for their ability to increase plant growth and to mitigate the reduction in photosynthetic parameters of water stressed P. hybrida and Pelargonium × hortorum. Application of certain bacteria increased plant size in both species and flower number of P. hybrida after recovery from water stress when compared to untreated water stressed plants. In addition, bacteria application increased the chlorophyll fluorescence parameters including quantum yield and efficiency of photosystem II (PSII) and electron transport rate (ETR), while decreasing the extent of electrolyte leakage during water stress and recovery. Overall, this study identified bacterial strains that can increase tolerance to and recovery from water stress in two commercially important ornamental crop species.

Journal of Natural Resources and Life Sciences Education, 2000

Plant physiology is best explored through participatory activities, where students are closely en... more Plant physiology is best explored through participatory activities, where students are closely engaged in the process of discovery. A two-stage approach to instruction was implemented to enrich the learning in an undergraduate plant physiology laboratory. First, a core of 10 experiments was developed to provide structured, hands-on experience and to teach the principles and skills of modern physiological analyses. During Week 11 of a 15wk semester, students observe a demonstration of a plant response, where the underlying cause of the phenomenon is not evident. Working together in small groups, students hypothesize on the mechanisms that may be involved. They choose among alternative lines of inquiry and decide which variables will be most informative in revealing the underlying nature of the problem. Each research team presents a study plan, and hypotheses and experimental approaches are defended. Results of team experiments are presented during Week 15. To date, inquiry-based projects have focused on the roles of (i) ethylene in seedling development in mouse-ear cress [Arabidopsis thaliana L. (Heynh.)] and tomato (Lycopersicon esculentum Mill.), (ii) glycinebetaine in drought tolerance of maize (Zea mays L.), (iii) catalase in chilling sensitivity of tomato, and (iv) ascorbic acid in oxidative stress in tomato. The Chilling-Injury Problem utilized in 1996 and 1997 is described, and pedagogical advantages as well as challenges to implementation are discussed. The approach appears to foster a capacity for connective, integrative thinking. Students develop competency in judging the reliability and significance of experimental results, and in evaluating whether their conclusions are justified by the data.

Plant Disease, 2020

Botrytis cinerea infects most major greenhouse crops worldwide. With its increasing resistance to... more Botrytis cinerea infects most major greenhouse crops worldwide. With its increasing resistance to conventional fungicides and the movement of the greenhouse industry toward more sustainable production practices, alternative methods of control are needed. The objective of this study was to evaluate a collection of 60 bacterial strains through both a dual-culture assay and greenhouse trials to identify strains with biocontrol activity against B. cinerea. For the dual-culture assay, each bacterial strain was streaked on potato dextrose agar medium with B. cinerea. The B. cinerea growth reduction and the zone of inhibition were measured. Thirty-five strains reduced the growth of B. cinerea. All strains were also tested in an initial greenhouse trial in which Petunia × hybrida ‘Carpet Red Bright’ was sprayed and drenched with the bacteria biweekly for 6 weeks. All open flowers were tagged, and plants were inoculated with B. cinerea (1 × 104 conidia per 1 ml). Disease severity indices cal...

Frontiers in Plant Science, 2020

The sustainability of ornamental crop production is of increasing concern to both producers and c... more The sustainability of ornamental crop production is of increasing concern to both producers and consumers. As resources become more limited, it is important for greenhouse growers to reduce production inputs such as water and chemical fertilizers, without sacrificing crop quality. Plant growth promoting rhizobacteria (PGPR) can stimulate plant growth under resource-limiting conditions by enhancing tolerance to abiotic stress and increasing nutrient availability, uptake, and assimilation. PGPR are beneficial bacteria that colonize the rhizosphere, the narrow zone of soil in the vicinity of the roots that is influenced by root exudates. In this study, in vitro experiments were utilized to screen a collection of 44 Pseudomonas strains for their ability to withstand osmotic stress. A high-throughput greenhouse experiment was then utilized to evaluate selected strains for their ability to stimulate plant growth under resource-limiting conditions when applied to ornamental crop production systems. The development of a highthroughput greenhouse trial identified two pseudomonads, P. poae 29G9 and P. fluorescens 90F12-2, that increased petunia flower number and plant biomass under drought and low-nutrient conditions. These two strains were validated in a productionscale experiment to evaluate the effects on growth promotion of three economically important crops: Petunia × hybrida, Impatiens walleriana, and Viola × wittrockiana. Plants treated with the two bacteria strains had greater shoot biomass than untreated control plants when grown under low-nutrient conditions and after recovery from drought stress. Bacteria treatment resulted in increased flower numbers in drought-stressed P. hybrida and I. walleriana. In addition, bacteria-treated plants grown under low-nutrient conditions had higher leaf nutrient content compared to the untreated plants. Collectively, these results show that the combination of in vitro and greenhouse experiments can efficiently identify beneficial Pseudomonas strains that increase the quality of ornamental crops grown under resource-limiting conditions.

HortScience, 2004

Salinity, drought and temperature frequently limit crop productivity. Transgenic Petunia ×hybrida... more Salinity, drought and temperature frequently limit crop productivity. Transgenic Petunia ×hybrida cv. Mitchell with altered endogenous raffinose family oligosaccharides (RFO) due to over-expression (sense) or under-expression (antisense) of the tomato α-galactosidase gene show that antisense increases in RFO are associated with greater tolerance to freezing stress (Pennycooke et al., 2003). Because vegetative propagules of these antisense lines rooted and established more quickly than their sense counterparts, we hypothesized that antisense lines would also respond to salinity and wilting stress. Salinity treatment plants were exposed to 50-200 mm NaCl graduated 25 mm every 3 days and held at 200 mm for 13 days. Dry-down treatments were watered to pot capacity, then not watered until the onset of wilting. This was repeated in cycles for 26 days. Data were collected on plant growth, root/shoot ratios, and leaf water potential. Fresh and dry weights in four of the six antisense lines ...

HortScience, 2005

Corolla senescence in petunias was accompanied by a decrease in total proteins and a correspondin... more Corolla senescence in petunias was accompanied by a decrease in total proteins and a corresponding increase in proteolytic activity. Transgenic petunias that contain the mutated ethylene receptor (35S:etr1-1) have reduced sensitivity to ethylene and delayed flower senescence. Declines in total protein levels and increases in proteolytic activity were also delayed in etr1-1 flowers and corresponded with corolla wilting. Experiments using class-specific proteinase inhibitors indicated that proteolytic activity in petunia corollas was largely due to cysteine proteinases. Total nitrogen levels within the corollas of both wild type and etr1-1 flowers also decreased during senescence. Nine cDNAs encoding putative cysteine proteinases (CPs) were identified from a petunia EST database developed at the University of Florida. Six of these cysteine proteinases showed increased transcript abundance during corolla senescence (senescence-associated CPs) while three decreased in abundance. Of the ...

HortScience, 2010

Drought stress during the shipping and retailing of floriculture crops can reduce postproduction ... more Drought stress during the shipping and retailing of floriculture crops can reduce postproduction shelf life and marketability. The plant hormone abscisic acid (ABA) mediates drought stress responses by closing stomata and reducing water loss. Applications of exogenous s-ABA effectively reduce water loss and allow a variety of species to survive temporary periods of drought stress. Unfortunately, s-ABA application can also lead to leaf chlorosis, which reduces the overall quality of economically important bedding plant species, including Viola ×wittrockiana (pansy). The goal of this research was to determine how to prevent s-ABA-induced leaf chlorosis in pansy and a closely related species, Viola cornuta (viola). All concentrations of both spray (250 or 500 mg·L−1) and drench (125 or 250 mg·L−1) s-ABA applications induced leaf yellowing. Young plants at the plug stage and 11-cm finished plants with one to two open flowers were further evaluated to determine if the developmental stage...

HortScience, 2014

The family Solanaceae, which includes both important crop and ornamental species, is generally co... more The family Solanaceae, which includes both important crop and ornamental species, is generally considered to have high sensitivity to ethylene. Our objectives were to evaluate ethylene sensitivity between accessions with the family Solanaceae and to determine whether similar sensitivity was observed in seedlings and mature plants. For the seedling evaluations, seeds were germinated and grown in the dark on filter paper saturated with 0 or 100 μM 1-aminocyclopropane-1-carboxylic acid (ACC; the immediate precursor to ethylene). The relative hypocotyl length at 100 μM ACC was compared with untreated control (0 μM) seedlings. Mature plants were treated with 0 or 10 μL·L−1 ethylene in the dark for 24 hours. Ethylene responses including flower abscission, flower senescence, and epinasty were observed and quantified. Seedlings and mature plants were classified as having no response, low, medium, or high ethylene sensitivity based on the severity of the ethylene responses observed. Sensitiv...

HortScience, 2017

Phalaenopsis orchids are an increasingly popular potted house plant in the United States. New cul... more Phalaenopsis orchids are an increasingly popular potted house plant in the United States. New cultivars have a long display life in home environments, but these epiphytes are often overirrigated by consumers. Irrigating potted Phalaenopsis orchids weekly with ice cubes has been recommended as a simple solution to help consumers, but concern has been raised about whether the ice cubes will cause low temperature damage in these tropical plants. The effect of ice cube irrigation on the display life and quality of four cultivars of potted Phalaenopsis orchids was, therefore, evaluated. Irrigation treatments included weekly application of three ice cubes or the equivalent volume of room-temperature tap water. The longevity of individual flowers and the overall display life of the orchid plants were determined. Monthly measurements determined the volume of leachate in the outer decorative pots after irrigation. The quantum yield of photosystem II (ΦPSII) in roots and leaves was evaluated ...

Journal of the American Society for Horticultural Science, 2005

Petunia ×hybrida (Hook) Vilm. cv. Mitchell was transformed with an E. coli gene encoding mannitol... more Petunia ×hybrida (Hook) Vilm. cv. Mitchell was transformed with an E. coli gene encoding mannitol-1-phosphate dehydrogenase (mtlD). Four plant lines that grew on kanamycin and contained the mtlD transgene were identified. Two of these lines contained high levels of mannitol [high-mannitol lines M3 and M8; mean mannitol = 3.39 μmol·g-1 dry weight (DW)] compared to nontransformed wild-type plants (0.86 μmol·g-1 DW), while two lines had mannitol levels similar to wild-type plants (low-mannitol lines M2 and M9; mean mannitol = 1.05 μmol·g-1 DW). Transgenic and control plants were subjected to chilling stress (3 ± 0.5 °C day/0 ± 0.5 °C night, 12-hour photoperiod and 75% relative humidity) to evaluate the role of mannitol in chilling tolerance. Based upon foliage symptoms and membrane leakage after a 3-week chilling treatment, the high-mannitol containing lines, M3 and M8, were more tolerant of chilling stress than the low-mannitol containing transgenic lines, M2 and M9, and wild-type. Un...