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Research Project: Improved Strategies for Management of Soilborne Diseases of Horticultural Crops

Location: Horticultural Crops Research

2012 Annual Report

Objective 1: Identify and characterize key pathogens to pinpoint critical pathogen vulnerabilities and develop targeted disease management strategies. Objective 2: Identify plant germplasm and cultivars of small fruits resistant to economically-important soilborne diseases. Objective 3: Expand knowledge of genomic features and regulatory mechanisms in biological control strains of Pseudomonas spp. to develop more consistent and effective tools for biologically-based disease management.

Determine the prevalence and characterize the population diversity of important soilborne pathogens affecting horticultural crops. Results from this research will identify specific pathogen populations that constrain production of horticultural crops. These populations can be targeted in the future to develop more effective, economical, and environmentally-acceptable disease management systems. Evaluate germplasm of black raspberry (Rubus occidentalis) for resistance to Verticillium wilt, caused by V. dahliae, and germplasm of red raspberry (Rubus ideaus) for resistance to the root lesion nematode, P. penetrans. Our research will identify Rubus genotypes and raspberry cultivars that are resistant to these soilborne diseases, and can be deployed in horticultural production systems in the future. Develop improved knowledge of the mechanisms by which the biological control agent Pseudomonas fluorescens Pf-5 suppresses disease. Results from this research will enable pathologists, horticulturists, and growers to develop more effective and reliable biological controls for soilborne diseases of horticultural crops.

Progress Report
This report documents progress for project 5358-12220-004-00D, which began on May 8, 2012 and continues research from Project 5358-12220-003-00D. Objective 1 focuses on the biology of pathogens of horticultural crops. 1) We collected up to 20 isolates of three Pythium species from three forest nurseries to begin an analysis of genetic diversity of the pathogen, which will provide insight into the degree of movement of Pythium species between forest nurseries. Once the extent and impact of pathogen movement is known, disease management strategies that minimize the movement of soilborne pathogens between nurseries can be developed. 2) Twelve populations of the virus-transmitting nematode Xiphinema americanum were collected from across the United States and several regions of the nematode genome were sequenced. Sequences will be compared as a first step towards identifying population level differences linked to the ability of the nematode to transmit virus. This information will be used to develop management practices targeting specific virus-transmitting X. americanum populations. 3) We initiated a study using a combination of multilocus sequence analysis and genome sequencing to evaluate the diversity of Pseudomonas syringae populations that infect blueberry and lilac in the Pacific Northwest. Our second objective is to develop improved plant disease management strategies. 1) Ten genotypes of black raspberry were inoculated with Verticillium dahliae in a greenhouse study. 2) 15 Rubus species were screened against the root lesion nematode Pratylenchus penetrans in a greenhouse study. Additionally, a field trial was established to determine the impact of P. penetrans on the establishment and yield of red raspberry varieties. Information from these greenhouse and field trials will guide breeding programs in the selection of resistant small fruit varieties and growers in the selection of varieties for planting in infested fields. Our third objective focuses on mechanisms of biological control of plant diseases. We completed a direct mRNA sequencing experiment to assess the transcriptome of the biological control bacterium Pseudomonas protegens Pf-5. The goal of this project is to identify factors influencing the expression of genes essential to biological control. We continued to work towards the structural identification of two antifungal natural products detected by genome mining of P. protegens Pf-5. The aim of this work is to identify novel antifungal compounds that contribute to biological control of soilborne fungi causing plant disease.