Browsing by Author "Kathryn L. Kingsley"

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Exploring endophytic communities of plants: Methods for assessing diversity, effects on host development and potential biotechnological applications
(Springer International Publishing, 2019) Satish K. Verma; Ravindra N. Kharwar; Surendra K. Gond; Kathryn L. Kingsley; James Francis White
Endophytic microbes colonize plants growing in diverse habitats and play important roles in modulating development and improving fitness of host plants. Endophytes may be major components of undiscovered microbial diversity. Further, endophytes may have applications in growth promotion of crop plants and protectors of plants from biotic and abiotic stresses. Endophytes have been a source of bioactive molecules of pharmaceutical importance. Major focus areas in the investigation of endophytes include (1) assessment of endophyte diversity, (2) determining the roles played by endophytes in modulation of host plant development and (3) assessing the biotechnological potentials of endophytes. The study of endophytes is particularly challenging because endophytic microbes often go unobserved in plants, many endophytes cannot be isolated, and plants free of endophytes sometimes cannot be obtained, making it difficult to conduct experiments. In this chapter we discuss some of the methodologies that are being used to overcome challenges to the study of endophytic microbes. © Springer Nature Switzerland AG 2019.
Fungal disease prevention in seedlings of rice (Oryza sativa) and other grasses by growth-promoting seed-associated endophytic bacteria from invasive phragmites australis
(MDPI AG, 2018) Satish K. Verma; Kathryn L. Kingsley; Marshall S. Bergen; Kurt P. Kowalski; James F. White
Non-cultivated plants carry microbial endophytes that may be used to enhance development and disease resistance of crop species where growth-promoting and protective microbes may have been lost. During seedling establishment, seedlings may be infected by several fungal pathogens that are seed or soil borne. Several species of Fusarium, Pythium and other water moulds cause seed rots during germination. Fusarium blights of seedlings are also very common and significantly affect seedling development. In the present study we screened nine endophytic bacteria isolated from the seeds of invasive Phragmites australis by inoculating onto rice, Bermuda grass (Cynodon dactylon), or annual bluegrass (Poa annua) seeds to evaluate plant growth promotion and protection from disease caused by Fusarium oxysporum. We found that three bacteria belonging to genus Pseudomonas spp. (SLB4-P. fluorescens, SLB6-Pseudomonas sp. and SY1-Pseudomonas sp.) promoted seedling development, including enhancement of root and shoot growth, and stimulation of root hair formation. These bacteria were also found to increase phosphate solubilization in in vitro experiments. Pseudomonas sp. (SY1) significantly protected grass seedlings from Fusarium infection. In co-culture experiments, strain SY1 strongly inhibited fungal pathogens with 85.71% growth inhibition of F. oxysporum, 86.33% growth inhibition of Curvularia sp. and 82.14% growth inhibition of Alternaria sp. Seedlings previously treated with bacteria were found much less infected by F. oxysporum in comparison to non-treated controls. On microscopic observation we found that bacteria appeared to degrade fungal mycelia actively. Metabolite products of strain SY1 in agar were also found to inhibit fungal growth on nutrient media. Pseudomonas sp. (SY1) was found to produce antifungal volatiles. Polymerase chain reaction (PCR) amplification using specific primers for pyrrolnitirin synthesis and HCN (hydrogen cyanide) production suggested presence of genes for both compounds in the genome of SY1. HCN was detected in cultures of SY1. We conclude that microbes from non-cultivated plants may provide disease protection and promote growth of crop plants. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
Pantoea spp. Associated with smooth crabgrass (Digitaria ischaemum) seed inhibit competitor plant species
(MDPI AG, 2019) Matthew T. Elmore; James F. White; Kathryn L. Kingsley; Katherine H. Diehl; Satish K. Verma
Digitaria ischaemum (Schreb.) Schreb. ex Muhl. and Poa annua L. are competitive, early successional species which are usually considered weeds in agricultural and turfgrass systems. Bacteria and fungi associated with D. ischaemum and P. annua seed may contribute to their competitiveness by antagonizing competitor forbs, and were studied in axenic culture. Pantoea spp. were the most common bacterial isolate of D. ischaemum seed, while Epicoccum and Curvularia spp. were common fungal isolates. A variety of species were collected from non-surface sterilized P. annua. Certain Pantoea spp. isolates were antagonistic to competitor forbs Taraxacum officinale, Trifolium repens. All bacterial isolates that affected T. officinale mortality were isolated from D. ischaemum seed while none of the P. annua isolates affected mortality. Two selected bacterial isolates identified as Pantoea ananatis were evaluated further on D. ischaemum, T. repens (a competitor forb) and P. annua (a competitor grass) alone and in combination with a Curvularia sp. fungus. These bacteria alone caused >65% T. repens seedling mortality but did not affect P. annua seedling mortality. These experiments demonstrate that Pantoea ananatis associated with D. ischaemum seeds is antagonistic to competitor forbs in axenic culture. The weedy character of D. ischaemum could at least in part stem from the possession of bacteria that are antagonistic to competitor species. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
Rhizophagy cycle: An oxidative process in plants for nutrient extraction from symbiotic microbes
(MDPI AG, 2018) James F. White; Kathryn L. Kingsley; Satish K. Verma; Kurt P. Kowalski
In this paper, we describe a mechanism for the transfer of nutrients from symbiotic microbes (bacteria and fungi) to host plant roots that we term the ‘rhizophagy cycle.’ In the rhizophagy cycle, microbes alternate between a root intracellular endophytic phase and a free-living soil phase. Microbes acquire soil nutrients in the free-living soil phase; nutrients are extracted through exposure to host-produced reactive oxygen in the intracellular endophytic phase. We conducted experiments on several seed-vectored microbes in several host species. We found that initially the symbiotic microbes grow on the rhizoplane in the exudate zone adjacent the root meristem. Microbes enter root tip meristem cells—locating within the periplasmic spaces between cell wall and plasma membrane. In the periplasmic spaces of root cells, microbes convert to wall-less protoplast forms. As root cells mature, microbes continue to be subjected to reactive oxygen (superoxide) produced by NADPH oxidases (NOX) on the root cell plasma membranes. Reactive oxygen degrades some of the intracellular microbes, also likely inducing electrolyte leakage from microbes—effectively extracting nutrients from microbes. Surviving bacteria in root epidermal cells trigger root hair elongation and as hairs elongate bacteria exit at the hair tips, reforming cell walls and cell shapes as microbes emerge into the rhizosphere where they may obtain additional nutrients. Precisely what nutrients are transferred through rhizophagy or how important this process is for nutrient acquisition is still unknown. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
Seed-vectored microbes: Their roles in improving seedling fitness and competitor plant suppression
(Springer International Publishing, 2019) James Francis White; Kathryn L. Kingsley; Susan Butterworth; Lara Brindisi; Judy W. Gatei; Matthew T. Elmore; Satish Kumar Verma; Xiang Yao; Kurt P. Kowalski
This chapter discusses the roles of seed-vectored microbes in modulating seedling development and increasing fitness of plants in terms of increased biotic and abiotic stress tolerance. Particular emphasis is placed on microbes that function in the rhizophagy cycle. These microbes have been shown to enter into root cells and stimulate root growth. In some cases microbe entry into root cells results in root growth repression. The term 'endobiome interference' has been applied to the phenomenon of plant growth repression due to intracellular microbes. The potential application of endobiome interference to produce bioherbicides that selectively enhance growth of target crops but inhibit competitor weeds is discussed. © Springer Nature Switzerland AG 2019.