ABSTRACT
Raspberry (Rubus idaeus L.) is an economically important fruit crop in Canada and about 80% of red raspberries are cultivated in British Columbia. In 2018, foliar symptoms associated with root rot and wilting complex disease were observed in raspberry field of Fraser Valley areas of British Columbia. Plants were stunted with reduced numbers of primocanes. Chlorosis and necrosis on leaves and partial wilting of branches were observed. When plants were uprooted, necrosis and browning on roots were observed. Two isolates of oomycetes pathogen were isolated using baiting with rhododendron leaves and pear fruit as described in Sapkota et al. 2022. Using FastDNA Spin kit (MP Biomedical, Burlingame, CA), genomic DNA of pathogen isolates was extracted from mycelia cultured on 20% clarified V8 agar medium amended with 10 mg pimaricin, 250 mg ampicillin, 10 mg rifampicin (V8PAR) per liter following the manufacturer's standard protocol. Pathogens were identified using colony morphology on 20% clarified V8 PAR as well as internal transcribed spacer (ITS) sequencing with ITS1 primers (White et al. 1990) and multiplex targeted-sequencing with degenerate primers of three nuclear genes: heat shock protein90 (HSP90), elongation factor 1 alpha (EF1α) and beta tubulin (ßtub). BLAST searches of ITS sequences of isolates of this study (accession nos. OP180065, OP180066) in NCBI GenBank showed 98.5 to 99.6% identity with the ITS sequence of P. gonapodyides (accession nos. MN513238.1, MG753496.1). Multiplex targeted sequencing also identified both isolates as a P. gonapodyides (accession nos. SRR20227809, SRR20227807) when mapped with the reference sequences (accession nos. HSP90: KX251233.1, EF1α: KX251231.1, ß-tub: KX639710.1). Pathogenicity was confirmed by inoculating mycelial suspension of one isolate of P. gonapodyides on root of intact plants and mycelial plugs of two isolates on detached stems of the raspberry plants, 'Chemainus' in the greenhouse using methods described in Sapkota et al. 2022. Two experiments were conducted with three replicates in each test. Experiments were arranged using completely randomized design. In detached stem assays, distinct dark-lesion symptom appeared at 7 to 9 days after inoculation while uninoculated control stems remained asymptomatic. Intact plants showed wilting and foliar symptoms 15 days after inoculation and progressed higher at 4 to 5 weeks after inoculation. Root infection with dark brown to black color was observed when roots were assessed at 5 weeks after inoculation. The diseased root and crown tissues tested positive for Phytophthora in Agdia ImmunoStrip and P. gonapodyides was re-isolated and confirmed with multiplex-targeted sequencing. Phytophthora gonapodyides was previously reported from raspberry in Chile (Wilcox and Latorre 2002). To our best knowledge, this is the first report of P. gonapodyides infecting red raspberry in British Columbia, Canada. The detection of new Phytophthora species on raspberry may become a new potential problem to growers in addition to P. rubi, which is already a major cause of raspberry decline in the region.
ABSTRACT
Bacterial spot caused by Xanthomonas spp. is the second most important bacterial disease after bacterial wilt of tomato and pepper in Taiwan. To determine the species composition of the Xanthomonas population over 27 years (1989 to 2016) across the country, a large collections of strains from tomato (n = 292) and pepper (n = 198) were examined. In the 1989 to 1999 population, all strains (n = 147) from pepper and 95% strains (n = 198) from tomato were Xanthomonas euvesicatoria. The remaining 5% of strains from tomato were X. vesicatoria. In a 2000 to 2009 population from tomato (n = 36), 22% of the strains were X. perforans and the remaining 78% strains were X. euvesicatoria. In the 2010 to 2016 population, 92% of the strains (n = 50) from pepper were still X. euvesicatoria and the remaining 8% of the strains were X. perforans; however, 99% (n = 58) of the strains from tomato were X. perforans. All of the evaluated (n = 25) strains of X. euvesicatoria collected during 1990 to 2006 were tomato race T1. Four pepper races (P1, P2, P7, and P8) were identified in the X. euvesicatoria population. The strains of X. vesicatoria collected during 1989 to 1999 (n = 8) were tomato race T2 and strains of X. perforans from tomato collected during 2010 to 2016 (n = 12) were race T4 (83%) and race T3 (17%). Four strains of X. perforans from pepper were race T4. All of the strains of X. vesicatoria and X. perforans caused a hypersensitive response in all pepper differentials. Biochemical characterization of representative strains (n = 48) showed that strains of X. euvesicatoria were negative on and amylolytic test and positive on lipase and oxidative-fermentative (OF) tests. The strains of X. vesicatoria were positive on amylolytic and OF tests and were negative on the lipase test. All X. perforans strains showed positive reactions on three tests. Evaluation of the same 48 strains for the sensitivity to copper sulfate (50, 100, 200, 300, and 400 mg liter-1) revealed that the majority of X. euvesicatoria (86%) and X. perforans (94%) strains in the 2010 to 2016 population were tolerant to copper sulfate. The findings suggest that management strategies and breeding programs should consider the new X. perforans species and their new races. The increased number of copper-sulfate-tolerant strains in the 2010 to 2016 population further shows the need for alternative options to copper for managing bacterial spot of tomato and pepper.
