Browsing by Author "Flinn, Barry"

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    Growth promotion and colonization of switchgrass (Panicum virgatum) cv. Alamo by bacterial endophyte Burkholderia phytofirmans strain PsJN
    Kim, Seonhwa; Lowman, James Scott; Hou, Guichuan; Nowak, Jerzy; Flinn, Barry; Mei, Chuansheng (2012-05-30)
    Background Switchgrass is one of the most promising bioenergy crop candidates for the US. It gives relatively high biomass yield and can grow on marginal lands. However, its yields vary from year to year and from location to location. Thus it is imperative to develop a low input and sustainable switchgrass feedstock production system. One of the most feasible ways to increase biomass yields is to harness benefits of microbial endophytes. Results We demonstrate that one of the most studied plant growth promoting bacterial endophytes, Burkholderia phytofirmans strain PsJN, is able to colonize and significantly promote growth of switchgrass cv. Alamo under in vitro, growth chamber, and greenhouse conditions. In several in vitro experiments, the average fresh weight of PsJN-inoculated plants was approximately 50% higher than non-inoculated plants. When one-month-old seedlings were grown in a growth chamber for 30 days, the PsJN-inoculated Alamo plants had significantly higher shoot and root biomass compared to controls. Biomass yield (dry weight) averaged from five experiments was 54.1% higher in the inoculated treatment compared to non-inoculated control. Similar results were obtained in greenhouse experiments with transplants grown in 4-gallon pots for two months. The inoculated plants exhibited more early tillers and persistent growth vigor with 48.6% higher biomass than controls. We also found that PsJN could significantly promote growth of switchgrass cv. Alamo under sub-optimal conditions. However, PsJN-mediated growth promotion in switchgrass is genotype specific. Conclusions Our results show B. phytofirmans strain PsJN significantly promotes growth of switchgrass cv. Alamo under different conditions, especially in the early growth stages leading to enhanced production of tillers. This phenomenon may benefit switchgrass establishment in the first year. Moreover, PsJN significantly stimulated growth of switchgrass cv. Alamo under sub-optimal conditions, indicating that the use of the beneficial bacterial endophytes may boost switchgrass growth on marginal lands and significantly contribute to the development of a low input and sustainable feedstock production system.
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    Utilizing Beneficial Bacterial Endophytes to Promote Switchgrass Growth in Low- input Agricultural Production Systems
    Lowman, James Scott (Virginia Tech, 2014-02-20)
    The US Department of Energy has focused research efforts on developing switchgrass into a bioenergy feedstock, helping to offset the use of non-renewable fossil fuels and make the US more energy independent. Bacterial endophytes, which reside inside plant tissues, are proven to increase yield and stress resistance in a number of plants. The primary objective of this dissertation was to explore the use of endophytes to improve biomass yields of switchgrass on lands not suitable for food crops and better understand the underlying mechanisms of the plant-endophyte interaction. Integration of this research into K-12 STEM education to increase interest in plant sciences and create the next generation of scientists with the motivation to help solve the challenges facing society in the twenty first century was the objective of the outreach component of this project. Chapter one demonstrates the ability of Burkholderia phytofirmans strain PsJN to colonize switchgrass and promote plant growth under in vitro (approximately 50% higher), and growth chamber and greenhouse (48.6% higher biomass yields) conditions. The objectives of Chapter two were to determine stand establishment in the field with different nutrient levels. PsJN bacterization positively benefited growth and development of switchgrass seedlings in the field with both low and high nutrient content. Highly significant (p<0.001) stimulation of root and shoot growth, lateral root formation and number of tillers was recorded on soil with low fertility. PsJN bacterization also enhanced biomass accumulation during the two seasons of growth on both poor (p<0.001) and rich (p<0.05) soil, indicating the potential for the use of PsJN in a low-input switchgrass feedstock production system. Chapter three outlines differences in gene expression patterns upon bacterization, between the responsive cv. Alamo, and a non-responsive cv. Cave-in-Rock. Using EST microarrays and quantitative PCR up- and down-regulated genes were identified in both cultivars. One of the key genes identified was a member of the tau class, glutathione S-transferase (GST). GST enzymes are known to be involved in plants responses to stress. Using overexpression and knockout/knockdown techniques we demonstrated that GST is likely involved in the bacterization induced early plant growth promotion in switchgrass. Chapter four describes the potential for the utilization of beneficial bacterial endophytes capable of fixing atmospheric nitrogen in a free-living state in the development of low-input switchgrass feedstock production systems. Sphingomonas sp. strain NSL isolated from switchgrass tissue was able to grow on nitrogen free medium and stimulated growth of switchgrass cv. Alamo under nitrogen deficient conditions. The ability to fix atmospheric nitrogen was also moved to Burkholderia phytofirmans strain PsJN via horizontal gene transfer from the legume nodulating Burkholderia phymatum. The transformed PsJN was able to fix nitrogen and promote plant growth under nitrogen limited conditions. At every step of the research described in this dissertation efforts were made to include its elements into K-12 education. Chapter five describes four case studies aiming at the enhancement of youth interest in plant sciences in the socieoeconomically depressed areas of Southside Virginia.