Susanne von Bargen

Impact of Piriformospora indica on tomato growth and on interaction with fungal and viral pathogens

Piriformospora indica is a root endophytic fungus with plant-promoting properties in numerous plant species and induces resistance against root and shoot pathogens in barley, wheat, and Arabidopsis. A study over several years showed that the endophyte P. indica colonised the roots of the most consumed vegetable crop tomato. P. indica improved the growth of tomato resulting in increased biomass of leaves by up to 20%. Limitation of disease severity caused by Verticillium dahliae by more than 30% was observed on tomato plants colonised by the endophyte. Further experiments were carried out in hydroponic cultures which are commonly used for the indoor production of tomatoes in central Europe. After adaptation of inoculation techniques (inoculum density, plant stage), it was shown that P. indica influences the concentration of Pepino mosaic virus in tomato shoots. The outcome of the interaction seems to be affected by light intensity. Most importantly, the endophyte increases tomato fruit biomass in hydroponic culture concerning fresh weight (up to 100%) and dry matter content (up to 20%). Hence, P. indica represents a suitable growth promoting endophyte for tomato which can be applied in production systems of this important vegetable plant not only in soil, but also in hydroponic cultures.

A model system for plant-virus interaction—infectivity and seed transmission of Cherry leaf roll virus (CLRV) in Arabidopsis thaliana

The wide natural incidence of Cherry leaf roll virus (CLRV) in deciduous forest trees and nurseries in northern Europe is believed to have occurred, apart from occasional mechanical spread and transmission through grafting, mainly by seed transmission. The mode of the vertical transmission and its role in the epidemiology of the virus has not been investigated, basically due to the inconvenient host-pathogen combinations studied to date. With the aim of obtaining an appropriate system for identification of viral genes and products participating in infection processes and seed transmission of CLRV, we performed infection and seed transmissibility tests with CLRV in Arabidopsis thaliana plants. Two phylogenetically and serologically different CLRV isolates were tested. Both of them were found able to infect A. thaliana plants, exhibited clear symptoms of the infection and spread systemically in the plants. Infection of the seeds and of a remarkable number of seedlings generated from infected seeds was possible for two consecutive generations. These results, for first time, report seed transmission of CLRV in the model plant A. thaliana and allow the assumption to be made of embryo invasion during seed transmission. Furthermore, first indications are given that genetically diverse CLRV isolates exhibit different abilities for vertical transmission in A. thaliana. The CLRV-A. thaliana model system is suitable for investigating viral invasion of developing plant organs and meristematic tissue, a prerequisite for successful virus dissemination via vertical transmission through seed.

High genetic diversity at the inter-/intra-host level of Cherry leaf roll virus population associated with the birch leaf-roll disease in Fennoscandia

ABSTRACT A viral epidemic associated with the Cherry leaf roll virus (CLRV) has emerged in Betula species in Fennoscandia, exhibiting quick and effective spread during the last 15 years. A population genetics approach is chosen in order to characterise the virus diversity and the sources of genetic variation aiming to investigate the epidemiology of the pathogen. In a CLRV population from Rovaniemi urban parks and a population that occurred after infecting young Betula seedlings with scions from the original Finnish trees, the genetic diversity is found to be remarkably high, mixed infections by CLRV variants from different phylogenetic groups are detected in single trees, while recombination is evidenced to occur. The estimated genetic variability is high and the CLRV haplotypes detected exhibit clear clustering and belong to different phylogenetic groups. The structure of the viral population reveals a pathogen with high evolutionary potential assumed to carry on its effective spread.

Emerging Plant Viruses in Urban Green: Detection of the Virome in Birch ( Betula sp.)

Data from next generation sequencing indicate the complexity of the birch virome in the urban landscape of Berlin. It is well known that plant viruses are widespread and contribute to the decline of birch trees. A mixed infection by Cherry leaf roll virus (CLRV), Apple mosaic virus (ApMV) and two newly discovered viruses from the genus Badna- and Carlavirus were investigated in southern Berlin (Steglitz-Zehlendorf) in 2015 and 2016. To gain a more detailed view on epidemiology of this viral complex in birch, the study was enlarged in 2017 including eight districts all over Berlin. Birch trees with symptoms like defoliation and degeneration were selected for determination of viral pathogens by molecular biological methods. Within the complex occurring symptoms in birch trees, new types of symptoms have been identified. Different combinations of plant viruses in single and mixed infection were detected by Reverse Transcription- Polymerase Chain Reaction (RT-PCR.) CLRV and Badnavirus combinations have shown to be distinct and widely distributed. Heterogeneity is also known from the symptomatology of virus containing birch leaves. As the correlation of symptoms and viral infection is not shown yet for the mixed infections, it is unknown if the complexity of the virome is the cause of the variability of symptoms. Epidemiology and pathogenicity of the newly discovered viruses as well as species specificity, life cycle, mode of transmission, host plant range and phylogeny are totally unknown and have to be investigated within the next years.