Potato virus Y (PVY) is a serious threat to potato production due to effects on tuber yield and quality, in particular, due to induction of potato tuber necrotic ringspot disease (PTNRD), typically associated with recombinant strains of PVY. These recombinant strains have been spreading in the United States for the past several years, although the reasons for this continuing spread remained unclear. To document and assess this spread between 2011 and 2015, strain composition of PVY isolates circulating in the Columbia Basin potato production area was determined from hundreds of seed lots of various cultivars. The proportion of nonrecombinant PVYO isolates circulating in Columbia Basin potato dropped ninefold during this period, from 63% of all PVY-positive plants in 2011 to less than 7% in 2015. This drop in PVYO was concomitant with the rise of the recombinant PVYN-Wi strain incidence, from less than 27% of all PVY-positive plants in 2011 to 53% in 2015. The proportion of the PVYNTN recombinant strain, associated with PTNRD symptoms in susceptible cultivars, increased from 7% in 2011 to approximately 24% in 2015. To further address the shift in strain abundance, screenhouse experiments were conducted and revealed that three of the four most popular potato cultivars grown in the Columbia Basin exhibited strain-specific resistance against PVYO. Reduced levels of systemic movement of PVYO in such cultivars would favor spread of recombinant strains in the field. The negative selection against the nonrecombinant PVYO strain is likely caused by the presence of the Nytbr gene identified in potato cultivars in laboratory experiments. Presence of strain-specific resistance genes in potato cultivars may represent the driving force changing PVY strain composition to predominantly recombinant strains in potato production areas.

Hemp (Cannabis sativa) acreage in Oregon has increased by approximately 240 times in the last five years and a greater number of hemp diseases have been observed. This special report documents pathogens, particularly those causing virus and virus-like diseases, that have been detected from field and greenhouse-grown hemp crops in Oregon, based on plant samples submitted to the Hermiston Agricultural Research and Extension Center Plant Clinic of Oregon State University in 2019 and 2020. Symptoms and signs were used to evaluate disease types and determine diagnostic assays used on each submission. Plants with signs or symptoms of fungal or oomycete infection were cultured to isolate pathogenic organisms and plants with symptoms suspected to be caused by virus infection were assayed for the presence of Beet curly top virus (BCTV), viroids, and phytoplasmas using polymerase chain reaction (PCR), or reverse transcription (RT)-PCR. Diseases with fungal or oomycete, and virus causes accounted for 26.5%, and 42.9% of submissions, respectively; co-infection of viral and fungal or oomycete pathogens were detected from 6.1% of submissions between 2019 and 2020. BCTV, a curtovirus, and hop latent viroid (HLVd) were the predominant pathogens detected from field and indoor grown hemp. Worland-like strains of BCTV represented 93% of all curtovirus detections. Eighty percent of HLVd detections occurred from plants that originated from indoor growing facilities. Based on BCTV vector, beet leafhopper, prevalence, field-grown hemp in western production regions may be affected by curly top and increasing hemp acreage in the landscape may have potential implications on other crops affected by curtoviruses. Virus and virus-like diseases could be a limiting factor for hemp production in some regions of the United States.

Viruses that cause necrotic symptoms in potato tubers can be difficult to distinguish based on symptoms and frequently require multiple molecular tests to identify the pathogen. In this study, a multiplex RT PCR high fidelity PCR protocol was developed using previously validated primers that could accurately detect six important potato viruses and detect multiple viruses in a single sample simultaneously. To test the protocol, 53 tubers previously tested using conventional PCR were retested using this multiplex protocol and blindly evaluated. In every case, the multiplex PCR results were consistent with previous findings. In addition, the multiplex PCR protocol also detected several mixed infections that were previously undetected. The results demonstrate that this technique could be a valuable assay not only for diagnostic laboratories, but also for seed certification and regulatory agency laboratories to diagnose the virus(es) that may be present in tubers with surface or internal necrotic symptoms.Resumen Los virus que causan síntomas necróticos en tubérculos de papa pueden ser difíciles de distinguir con base en los síntomas, y frecuentemente se requiere de múltiples pruebas moleculares para identificar al patógeno. En este estudio, se desarrolló un protocolo múltiple de RT PCR de alta fidelidad de PCR utilizando iniciadores previamente validados que pudieran detectar con precisión seis virus importantes de papa y múltiples virus en una única muestra simultáneamente. Para probar el protocolo, se analizaron nuevamente 53 tubérculos que habían sido probados previamente usando la PCR convencional, utilizando este protocolo múltiple con evaluación ciega. En cada caso, los resultados de PCR múltiple fueron consistentes con lo que se encontró previamente. Además, el protocolo de PCR múltiple también detectó algunas mezclas de infecciones que previamente no se detectaron. Los resultados demuestran que esta técnica pudiera ser un ensayo valioso no solo para laboratorios de diagnóstico, sino también para certificación de semilla y para laboratorios de agencias de regulación para diagnosticar el (los) virus que pudieran estar presentes en tubérculos con síntomas necróticos superficiales o internos.

Tamarillo, or tree tomato (Solanum betaceum), is a perennial small tree or shrub species cultivated in subtropical areas for fresh fruit and juice production. In Ecuador, tamarillo orchards are affected by several viruses, with one previously identified as potato virus Y (PVY); however, the specific strain composition of PVY in tamarillo was not determined. In 2015 and 2016, eight tamarillo plants exhibiting symptoms of leaf drop, mosaic, and mottled fruit were sampled near Tumbaco and Quito, Ecuador. These tamarillo PVY isolates were able to systemically infect tobacco, Nicotiana benthamiana, naranjilla, and tamarillo. Seven of the eight PVY isolates from tamarillo exhibited N-serotype, while one of the PVY isolates studied, Tam15, had no identifiable serotype. One isolate, Tam17, had N-serotype but produced asymptomatic systemic infection in tobacco. In tamarillo, four tamarillo isolates induced mosaic and slight growth retardation and were unable to systemically infect pepper or potato. Tamarillo, on the other hand, was unable to support systemic infection of PVY isolates belonging to the PVYO and PVYEu-N strains. The whole genomes of eight PVY isolates were sequenced from a series of overlapping RT-PCR fragments. Phylogenetically, tamarillo PVY isolates were found to belong to the large PVYN lineage, in a new tamarillo clade. Recombination analysis revealed that these tamarillo PVY isolates represent at least three novel recombinant types not reported before. The combination of the biological and molecular properties found in these eight PVY isolates suggested the existence of a new tamarillo strain of PVY that may have coevolved with S. betaceum.