|WÖHNER, THOMAS - Julius Kuhn Institute|
|RICHTER, KLAUS - Julius Kuhn Institute|
|SUNDIN, GEORGE - Michigan State University|
|ZHAO, YOUFU - University Of Illinois|
|SELLMANN, JÖRG - Julius Kuhn Institute|
|FLACHOWSKY, HENRYK - Julius Kuhn Institute|
|MAGDA-VIOLA, HANKE - Julius Kuhn Institute|
|PEIL, ANDREAS - Julius Kuhn Institute|
Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2017
Publication Date: 12/3/2017
Citation: Wöhner, T., Richter, K., Sundin, G.W., Zhao, Y., Stockwell, V.O., Sellmann, J., Flachowsky, H., Magda-Viola, H., Peil, A. 2017. Inoculation of Malus genotypes with a set of Erwinia amylovora strains indicates a gene-for-gene relationship between the effector gene eop1 and both Malus floribunda 821 and Malus 'Evereste'. Plant Pathology. 67(4):938-947. https://doi.org/10.1111/ppa.12784.
Interpretive Summary: Fire blight, caused by Erwinia amylovora, is the most damaging bacterial disease of pear and apple. In the US, growers spend hundreds of thousands of dollars annually to manage the disease and when regional epidemics occur, losses to growers are in the tens of millions dollars. Developing disease-resistant cultivars of apple and pear could provide effective control of fire blight and decrease economic impacts by reducing management costs required for fighting fire blight and by mitigating epidemics that destroy orchards. Plant breeders in Germany have turned to wild species of apple and crabapple for sources of resistance to fire blight. Previously, they characterized a resistance gene in crabapple that confers immunity to fire blight when moved into apple. Unfortunately, they also discovered that some natural isolates of the fire blight pathogen with a slight change in a virulence protein could overcome the resistance and cause disease on apple carrying the resistance gene from crabapple. Other wild apples have resistance to fire blight, but the question is, will these other novel resistance genes be easily overcome by the pathogen and fail to give sustained disease control? This project involved testing the ability of various natural strains of the fire blight pathogen and a series of virulence gene mutants of one strain to cause disease on wild apple species and progeny of crosses between wild and commercial apples. The project confirmed the importance of virulence genes in pathogenicity of Erwinia amylovora and discovered the ability of some strains of the pathogen to cause disease on apples with newly discovered resistance genes. In some cases, a change in one virulence gene of the pathogen resulted in overcoming new resistance genes in apple. In other cases, it remains a mystery how the pathogen overcame a newly identified resistance in apple. Nonetheless, the study illustrates the importance of using several strains of a pathogen to evaluate the potential efficacy and durability of disease resistant cultivars.
Technical Abstract: The Gram-negative bacterium Erwinia amylovora (Burrill) Winslow. et al., causal agent of fire blight disease in pome fruit trees, encodes a type three secretion system (T3SS) that functions to translocate effector proteins into plant cells that collectively function to suppress host defenses and enable pathogenesis. Until now, there was a lack of knowledge about the interaction of effector proteins and host resistance presented in several wild Malus species. In this study, we tested disease responses in several Malus wild species with a set of effector deletion mutant strains and several highly virulent Erwinia amylovora strains, which are assumed to influence the host resistance response of fire blight-resistant Malus species. Our findings confirm earlier studies that deletion of the T3SS abolished virulence of the pathogen. Furthermore, a new gene-for-gene relationship was established between the effector protein Eop1 and the fire blight resistant ornamental apple 'Evereste' and the wild species M. floribunda 821.