Location: Horticultural Crops Disease and Pest Management Research Unit
Project Number: 2072-22000-045-013-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2020
End Date: May 31, 2025
Objective:
Objective 1. Identify pathogens and estimate the impact of cranberry fruit rot diseases on yield.
Objective 2. Determine sensitivity of fungal pathogens to site-specific fungicides.
Approach:
Objective 1: Eight cranberry beds on conventional farms and organic farms (if available) will be sampled in the cranberry production areas of the Pacific Northwest (PNW), near Bandon, Oregon and Long Beach, Washington. The location, cultivar, bed age, horticultural practices (e.g. sanding, frost control, harvest methods) and fungicide use will be obtained from the grower. Prior to harvest, cranberries will be collected from three one-meter square quadrants in each bed and total weight of each sample will be measured. Cranberry samples will be sorted based on presence of external rot symptoms verses sound or unblemished cranberries. Symptomatic berries will be sorted by symptoms (e.g. speckle, soft/collapsed berries) and counted. The cranberries will be processed to isolate, store, and identify fungi. Sound cranberries will be counted, weighed, placed in paper bags, and stored at 5°C. Periodically, the stored cranberries will be examined for post-harvest rot symptoms. Symptomatic stored berries will be counted and processed to isolate, store, and identify fungi. In the event that fruit rot is rarely observed in the sampled quadrants in a bed, then additional symptomatic fruit will be collected at 1-meter intervals along transects through the bed, until 100 symptomatic cranberries are collected. Isolates of fungi that have not been previously identified as pathogens of cranberries will be tested for their capacity to cause rot symptoms on wound-inoculated cranberry fruits.
Objective 2: Broad-spectrum, multisite fungicides are routinely used for cranberry fruit rot management. Recently, site-specific fungicides of FRAC groups 3 (the azoles or DMIs) and 11 (strobilurins) were registered for cranberry. It is not known if some of the genera of the cranberry fruit rot pathogens in the PNW are resistant to these groups of site-specific fungicides.
a. Discriminatory dose experiment: Radial growth inhibition assay will be used to test isolates of different genera of the cranberry rot pathogens for sensitivity to different concentrations of FRAC 3 fungicides Proline (Bayer CropScience, a.i. prothioconazole) and Indar (Corteva Agriscience, a.i. fenbuconazole) and Abound (Syngenta, a.i. azoxystrobin), a FRAC 11 fungicide.
b. Screening isolates for resistance: The single discriminatory dose of each fungicide will be used in subsequent screening of isolates to detect FRAC 3 or FRAC 11-resistant fungi in a radial growth inhibition assay. Up to 10 isolates of a genera from a cranberry bed will be screened for resistance to the site-specific fungicides. For some of the fungicide-resistant isolates, the gene that encodes for the protein-target of the fungicide (cyp51A for FRAC 3; cytb for FRAC 11) will be sequenced and common mutations that confer resistance to the fungicide FRAC 3 or 11 group will be sought.
