Pathogenicity, Fungicide Resistance, and Genetic Variability ofPhytophthora rubiIsolates from Raspberry (Rubus idaeus) in the Western United States

Abstract

Stewart, J. E., Kroese, D., Tabima, J. F., Larsen, M. M., Fieland, V. J., Press, C. M., Zasada, I. A., and Grünwald, N. J. 2014. Pathogenicity, fungicide resistance, and genetic variability of Phytophthora rubi isolates from raspberry (Rubus idaeus) in the Western United States. Plant Dis. 98:1702-1708.Root rot of raspberry (Rubus idaeus), thought to be primarily caused by Phytophthora rubi, is an economically important disease in the western United States. The objectives of this study were to determine which Phytophthora species are involved in root rot, examine the efficacy of different isolation methods (cane, root, and root/soil baiting with young raspberry plants), and determine if pathogenicity, fungicide resistance, and/or genetic variation exists among P. rubi isolates collected from raspberry fields in Washington, Oregon, and California. Of 275 samples, direct isolation from cane material resulted in a greater number of P. rubi isolates (39%), whereas root/soil baiting yielded the least (11%). Sequencing of the internal transcribed spacer region of 210 of the total 597 collected Phytophthora isolates showed that all but one isolate (identified as P. bisheria) were P. rubi. Results of the pathogenicity and fungicide resistance to mefenoxam comparing 14 total isolates from Washington, Oregon, and California showed that isolates were similarly virulent against red raspberry and the EC 50 frequency distributions showed no significant difference. These results, combined with amplified fragment length polymorphism results show that P. rubi isolates from Washington, Oregon, and California represent one large mixed population. This work provides novel insights into the isolation and biology of P. rubi in western U.S. raspberry production systems.

Canadian Plant Disease Survey 2020 Volume 100: Disease Highlights 2019

“…Pathogenicity of few isolates of Phytophthora rubi was confirmed by inoculating the raspberry variety 'Tulameen' (data not shown). RESULTS AND COMMENTS: Root rot and wilt is a widespread and sporadic disease of red raspberries in British Columbia and other regions of Pacific Northwest (Kempler and Daubeny 2008;Stewart et al 2014). Phytophthora rubi is considered the primary pathogen (Koprivica et al 2009;Stewart et al 2014); however other species of Phytophthora, root lesion nematode (Partylenchus penetrans) and other fungal species, such as Cylindrocarpon, Fusarium, Pythium, and Verticillium are reported to be associated with the wilting and root rot complex of raspberries (Wilcox 1989;Vrain et al 1996;Koprivica et al 2009;Weber and Entrop 2017).…”

Phytophthora urerae sp. nov., a new clade 1c relative of the Irish famine pathogen Phytophthora infestans from South America

“…A Veriti 96‐well thermal cycler (Applied Biosystems) was used to complete these steps. Selective amplification products were prepared as previously described (Stewart et al ., ) and run on a capillary sequencer (ABI 3100 Avant). Electropherograms were analysed via GeneMapper v. 3.7 software (ABI) and visual inspection to extract a matrix of presence and absence of alleles in a range of 50–500 bp.…”

“…AFLP was performed on genomic DNA using the AFLP microbial fingerprinting protocol (Applied Biosystems) with slight modifications as described previously (Gr€ unwald & Hoheisel, 2006;Stewart et al, 2014). Total genomic DNA was obtained from mycelia using the FastDNA SPIN kit (MP Biomedicals LLC).…”

“…DNA (200 ng) was digested and adaptors were ligated for 4 h at 37°C. Preselective amplifications with EcoRI and MseI core primers and the AFLP amplification core mix were performed as previously described (Stewart et al, 2014). Selective PCR was performed with the MseI-AC/EcoRI-AC selective primer combination.…”

Whole genome sequences of the raspberry and strawberry pathogensPhytophthora rubiandP. fragariae

“…These are highly similar in morphology and physiology, but infect different hosts. Sequencing the genomes of these species will advance our understanding of the genomic mechanisms underlying host adaptation and knowledge of molecular mechanisms of plant pathogenicity (5).…”