Impact of individual and combined abiotic and biotic stress on plant performance and bacterial root microbiota of tomato
- Recently crops encounter an increased number of individual and combined abiotic and biotic stress, which severely affect their growth and yield. Plants are associated with a large number of microorganisms including beneficial as well as pathogenic microorganisms. The interaction of plants with beneficial microorganisms can exert a substantial impact on plant growth and health and their potential can be utilized in sustainable plant production systems. Currently, climate change will increase the impact of stress on crops which will more likely be exposed to combined abiotic and biotic stress. At present, knowledge on how abiotic and biotic stress and the combination of both stresses affect the plant performance and the microbiome is limited. Soil-borne pathogens are responsible for relevant economic losses and are difficult to control. The root bacterial endophytes have shown potential in alleviating stress on plants and improving crop yield and quality. This raises the question how individual abiotic stress like salinity (ionic) andRecently crops encounter an increased number of individual and combined abiotic and biotic stress, which severely affect their growth and yield. Plants are associated with a large number of microorganisms including beneficial as well as pathogenic microorganisms. The interaction of plants with beneficial microorganisms can exert a substantial impact on plant growth and health and their potential can be utilized in sustainable plant production systems. Currently, climate change will increase the impact of stress on crops which will more likely be exposed to combined abiotic and biotic stress. At present, knowledge on how abiotic and biotic stress and the combination of both stresses affect the plant performance and the microbiome is limited. Soil-borne pathogens are responsible for relevant economic losses and are difficult to control. The root bacterial endophytes have shown potential in alleviating stress on plants and improving crop yield and quality. This raises the question how individual abiotic stress like salinity (ionic) and drought (osmotic) and the combination with biotic stress (Verticillium dahliae or Fusarium oxysporum) affects the root microbiota and thus the performance of the plant. Therefore, the goal of this thesis was to improve the understanding of the impact of individual and combined biotic and abiotic stress especially the endophytic root microbiota and thus plant performance. The work is focused on the economically important horticultural crop tomato. The bacterial rootendophytes of tomato plants exposed to individual and combined abiotic and biotic stress was studied with culture-independent and culture-dependent methods. Bacterial root endophytes obtained from tomato roots exposed to individual and combined stress were characterized for their traits that are beneficial to plant growth and health in in vitro and in vivo assays. Finally, the efficacy of selected endophytes in alleviating individual and combined abiotic and biotic stress in tomato plants was assessed. Furthermore, stress conditions can alter the composition of root exudates and volatiles, which may in turn affect the root microbiota assembly. Therefore, the volatile profiles of healthy and pathogen (F. oxysporum) infected tomato roots grown in soil was investigated. A soil olfactometer was established to study the impact of root volatiles of healthy and infected tomato on migration of applied beneficial bacteria. The results of tomato characteristics (plant growth, photosynthesis rate) confirmed the negative effect of individual abiotic and biotic stress reported in other studies. However, the response of combined abiotic stress with biotic stress on plant growth varied depending on the type of combined stress.. For instance, a significant higher negative impact on plant growth was observed when tomato plants were cultivated under ionic stress and infected with F. oxysporum. No additional negative effect on plant growth was observed when tomato was infected with V. dahliae. Both culture-dependent and cultureindependent analyses of the root microbiota revealed that individual and combined abiotic and biotic stress alter the root microbiota structure and diversity of tomato. A significantly lower number of cultivable root endophytes was obtained from roots exposed to ionic stress. 16S rRNA amplicon analysis revealed a stronger impact on the diversity of root-associated bacteria in comparison to biotic stress. The endophytes were characterized as member of the phyla Proteobacteria, Actinobacteria and Firmicutes, and members of Bacteriodetes were only detected by culture-independent approach. A total of 683 cultivable bacterial endophytes were characterized using various in vitro and in vivo plant growth-promoting (PGP) assays. As expected, the highest number of root endophytes with tolerance to ionic stress were obtained from tomato roots exposed to ionic stress. Comparably, a high percentage of root endophytes isolated from roots exposed to osmotic were tolerant to osmotic stress showing that the environment affects the selection of microorganisms by the plant. Interestingly, endopyhtes obtained from roots exposed to abiotic stress showed no traits related to plant growth promotion. Based on in vivo and in vitro traits, five selected endophytes were able to alleviate abiotic and biotic stress on plants. These endophytes were obtained from tomato roots infected with V. dahliae. The blend of root emitted volatiles also differed between healthy and F. oxysporum infected tomato plants. The olfactometer setup results highlighted that root volatiles were involved in attraction of bacteria to the plant roots and beneficial bacteria were observed to migrate towards both, diseased and healthy plants in comparable density. It is proposed that root volatiles from healthy and pathogen infected plants not only work as signals but are also used as an energy source for the rhizosphere bacteria. Concluding, the results of this study indicate that abiotic and biotic stress altered the bacterial rootendophytes and thus affects plant performance. The treatment of plants with beneficial microorganisms reduced the negative impact of stress conditions on plant performance. However, more studies using the selected isolates must be performed in the field for drawing inferences on the efficacy of the selected bacterial isolates in ameliorating the effect of abiotic and biotic stress in plants. The extensive isolate collection will serve as a basis for conducting investigations of root-associated bacteria on plant performance. This is important for the development of new plant protection strategies.…
- Nutzpflanzen sind zunehmend mit sowohl individuellem als auch kombiniertem abiotischem und biotischem Stress konfrontiert, die Wachstum und Ertrag stark beeinträchtigen. Pflanzen sind mit einer großen Anzahl an Mikroorganismen assoziiert, die sowohl nützlich als auch pathogen wirken können. Aufgrund der positiven Wirkung von nützlichen Mikroorganismen auf Wachstum und Gesundheit von Pflanzen ist dieses Potenzial in nachhaltigen Pflanzenproduktionssystemen zu nutzen. Kenntnisse darüber, wie individueller und kombinierter Stress die Leistung der Pflanze einschließlich deren Mikrobiom beeinflussen, sind derzeit begrenzt. Es stellt sich daher die Frage, wie abiotische Bedingungen (Salzstress, Trockenheit) insbesondere in Kombination mit biotischem Stress (Verticillium dahliae, Fusarium oxysporum) die Mikrobiota der Wurzel beeinflussen und dies die Leistung der Pflanze. Ziel dieser Arbeit war es, das Verständnis der Auswirkungen von individuellem und kombiniertem biotischem und abiotischem Stress auf die endophytische Mikrobiota der WurzelNutzpflanzen sind zunehmend mit sowohl individuellem als auch kombiniertem abiotischem und biotischem Stress konfrontiert, die Wachstum und Ertrag stark beeinträchtigen. Pflanzen sind mit einer großen Anzahl an Mikroorganismen assoziiert, die sowohl nützlich als auch pathogen wirken können. Aufgrund der positiven Wirkung von nützlichen Mikroorganismen auf Wachstum und Gesundheit von Pflanzen ist dieses Potenzial in nachhaltigen Pflanzenproduktionssystemen zu nutzen. Kenntnisse darüber, wie individueller und kombinierter Stress die Leistung der Pflanze einschließlich deren Mikrobiom beeinflussen, sind derzeit begrenzt. Es stellt sich daher die Frage, wie abiotische Bedingungen (Salzstress, Trockenheit) insbesondere in Kombination mit biotischem Stress (Verticillium dahliae, Fusarium oxysporum) die Mikrobiota der Wurzel beeinflussen und dies die Leistung der Pflanze. Ziel dieser Arbeit war es, das Verständnis der Auswirkungen von individuellem und kombiniertem biotischem und abiotischem Stress auf die endophytische Mikrobiota der Wurzel und die Leistung der Pflanze zu verbessern. Die Untersuchungen erfolgen an der wirtschaftlich bedeutenden gartenbaulichen Kultur Tomate. Die Struktur der bakteriellen endophytischen Mikrobiota der Tomatenwurzel in Abhängigkeit von individuellem und kombiniertem abiotischem und biotischem Stress wurde mit kulturunabhängigen und -abhängigen Methoden analysiert. Die Ergebnisse der Analysen mittels beider Methoden zeigen, dass sowohl abiotische als auch biotische Stressbedingungen signifikant die Struktur der endophytischen Mikrobiota der Wurzel verändern und sich dies auf die Produktivität der Pflanze auswirkt. Insgesamt wurden 683 kultivierbare bakterielle Endophyten hinsichtlich ihrer pflanzenwachstumsfördernden (PGP) Eigenschaften in in vitro und in vivo charakterisiert. Im Ergebnis kulturabhängiger Analysen wurden Endophyten mit wiederholt positiver Wirkung auf das Pflanzenwachstum von Tomate unter individuellem und kombiniertem abiotischen und biotischen Stress selektiert. Die Behandlung von Pflanzen mit diesen nützlichen Mikroorganismen reduzierte den negativen Einfluss von Stress auf das Pflanzenwachstum. Im Weiteren können diese nützlichen Mikroorganismen zu Produkten für die Nutzung in nachhaltigen Pflanzensystemen entwickelt werden. Dazu sind jedoch weitere Untersuchungen insbesondere unter Feldbedingungen notwendig. Zukünftige Arbeiten sollten sich zudem auf die Verbesserung des Verständnisses der Funktionen von Endophyten in der Wurzel konzentrieren. Diese Kenntnisse könnten die Entwicklung neuer Strategien für den Pflanzenschutz unterstützen.…
