Members of the Ralstonia solanacearum (Rs) species complex have recently been reported to cause bacterial wilt on southern highbush (SHB) blueberries in Florida (Norman et al. 2018), a disease first reported on blueberry (northern highbush; Vaccinium corymbosum) in New Jersey (Patel et al. 2013). SHB blueberries are widely grown in the southern United States, and SHB cultivars represent the majority of the blueberry acreage in Georgia - the U.S. state with the largest blueberry acreage (NASS 2022). In Fall 2020, three-year old SHB plants (cv. 'Indigocrisp') showing leaf bronzing, wilting, and dieback were collected from two field sites in Clinch County, GA. At these locations, numerous plants were rapidly dying, with symptoms appearing to have spread down rows. Plant material tested positive using the ImmunoStrip® for Rs (Agdia, Inc., Elkhart, IN). From one location, the remaining sample was submitted to USDA-APHIS Select Agent Services who determined that Rs was present but a select agent (Rs Race 3, Biovar 2) was not. Following this, six adjacent, symptomatic SHB plants were collected from the same field location. These plants tested positive using the ImmunoStrip® for Rs, and red-pigmented mucoid colonies typical of Rs formed within 48 h at 28°C on triphenyltetrazolium chloroide (TZC) isolation medium (Kelman 1954). DNA was extracted from pure Rs cultures using the cetyltrimethylammonium bromide (CTAB) method (Doyle and Doyle 1987) and tested using polymerase chain reaction (PCR). Primers pairs AMB013/AMB014 (Fegan and Prior 2005) and ENDO-F/ENDO-R (Ji et al. 2007) were used to amplify 558 nt and 843 nt portions of the 16S rRNA region and Rs endoglucanase gene, respectively. Resulting amplicons were purified using an E.Z.N.A.® Cycle Pure Kit (Omega Bio-Tek, Norcross, GA), Sanger sequenced in both directions (Eurofins Genomics, Louisville, KY), and compared to publicly available Rs sequences in Genbank. The 16 rRNA sequence from all obtained isolates (accession ON938207) had 100% identity to Rs strain CFBP2957 (FP885897), while the endoglucase sequence (ON938206) had 100% identity to phylotype IIa, sequevar 5 Rs strain CIP-426 (MF461810) and phylotype IIa, sequevar 39 Rs strain 19-058 (MT314067), among others. To fulfill Koch's postulates, an isolate ('Ral21-1') was grown on TZC medium for 48 h at 28°C and suspended in 8.5 g/L NaCl at 1 x 108 CFU/ml. Five young, tissue cultured SHB plants (cv. 'Kestrel') in 25 cm pots were drenched with 50 ml of Rs suspension. For six weeks, plants were maintained in the greenhouse at 21-32°C. Typical bacterial wilt symptoms (leaf bronzing/scorching) developed in all inoculated plants, and infections were confirmed using Immunostrip®. Rs was reisolated and confirmed via PCR and sequencing as previously described. While Ralstonia has been known to cause disease on numerous crops in Georgia, this represents a first report of bacterial wilt in Georgia blueberries. Relative to rabbiteye blueberries (V. virgatum), recent reports suggest that SHB are much more susceptible to bacterial wilt (Conner et al. 2022). Accordingly, given the transition from rabbiteye to SHB within Georgia's blueberry production region over the past two decades and the ability of Rs to spread easily in water, soil, or via infected plant material, the presence of this disease within the state represents a significant threat to blueberry production. Additional characterization of Ralstonia isolates from Georgia may help assess the risk of future outbreaks.

Citrus tristeza virus (CTV) [genus Closterovirus; family Closteroviridae] is one of the most important, economically devastating viruses of citrus worldwide. On citrus trees grafted onto sour orange rootstock, typical CTV symptoms include dieback and defoliation, stunting, curling and chlorotic leaves, stem-pitting, and pinholes below the bud union on the inner face of the bark (Moreno et al. 2008). This single-stranded, positive-sense RNA virus is most efficiently transmitted by the brown citrus aphid (Toxoptera citricida), but it can also be transmitted by other aphid species and through grafting of infected plant material onto healthy plants (Moreno et al 2008; Herron et al. 2006). In Fall 2020, leaf material for virus testing was collected from 13 navel orange trees (Citrus × sinensis) grafted onto Poncirus trifoliata rootstocks (including 'Flying Dragon') located in a citrus research orchard in Tifton, GA. Trees ranged in age from 2 to 10 years, with the younger trees having been grafted from cuttings taken from the older trees. The oldest of these trees was derived from cuttings taken in 2009 from an orange tree growing locally in a residential yard in Tifton; this parent tree was more than 15 years old when these cuttings were obtained and was no longer available for sampling as of 2020. Symptoms or other visible signs of disease had not been noted on any of the tested trees, and trees were chosen for testing prior to the further dissemination of this plant material. The presence of CTV was verified via molecular and serological testing. CTV infection was initially confirmed in 8 of 13 tested samples using the ImmunoStrip® for CTV assay (Agdia® Inc., Elkhart, IN, cat no: ISK 78900/0025) according to the manufacturer's instructions. RNA was extracted from leaf material collected from the 13 sampled trees using the RNeasy Plant Mini Kit (Qiagen, Valencia, CA). Following cDNA synthesis, samples were tested for the presence of CTV by reverse-transcription PCR using primer pair AR18F (5'-ATGTCAGGCAGCTTGGGAAATT-3') and AR18R (5'-TTCGTGTCTAAGTCRCGCTAAACA-3') which produces a 511 bp amplicon (Roy et al., 2005). PCR reactions confirmed the presence of CTV, with the same eight samples that had previously tested positive via Immunostrip® producing PCR fragments of the expected size. Amplified products from two of these samples were then sequenced using Sanger sequencing (Retrogen Inc, San Diego, CA, USA) and subjected to BLAST analysis (https://blast.ncbi.nlm.nih.gov/Blast.cgi) for further identification. Sequence analysis revealed that the obtained partial sequences (MW540805) from the p18 gene of both isolates were 100% identical to one another and shared 100% identity to corresponding sequences from CTV strain N4 (MK779711.1). To the best of our knowledge, this is the first report of CTV infecting citrus plants in Georgia. CTV could pose an imminent threat to the emerging citrus industry in Georgia if it were to become established in commercial citrus plantings either via the dissemination of infected plant material or via vector transfer of the virus under field conditions. While the brown citrus aphid is not known to be widespread in Georgia at this time, other CTV vectors are prevalent including the cotton aphid (Aphis gossypii) and the black citrus aphid (T. aurantia). Georgia citrus growers and plant propagators should be aware of this virus and take appropriate control measures to prevent the spread of this viral diseas.

HomePlant DiseaseVol. 104, No. 6First Report of Bacterial Leaf Scorch Disease of American Elm Caused by Xylella fastidiosa in Georgia, U.S.A. PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Bacterial Leaf Scorch Disease of American Elm Caused by Xylella fastidiosa in Georgia, U.S.A.M. E. Ali, O. Hudson, S. Waliullah, P. Ji, J. L. Williams-Woodward, and J. E. OliverM. E. Ali†Corresponding author: M. E. Ali; E-mail Address: ma49268@uga.eduhttp://orcid.org/0000-0002-5871-5055Department of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, O. HudsonDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, S. WaliullahDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, P. JiDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, J. L. Williams-WoodwardDepartment of Plant Pathology, University of Georgia, Athens, GA 30602Search for more papers by this author, and J. E. Oliverhttp://orcid.org/0000-0003-2692-5055Department of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this authorAffiliationsAuthors and Affiliations M. E. Ali1 † O. Hudson1 S. Waliullah1 P. Ji1 J. L. Williams-Woodward2 J. E. Oliver1 1Department of Plant Pathology, University of Georgia, Tifton, GA 31793 2Department of Plant Pathology, University of Georgia, Athens, GA 30602 Published Online:7 Apr 2020https://doi.org/10.1094/PDIS-11-19-2367-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat The American elm (Ulmus americana) is a highly desirable deciduous shade tree with moderately dense foliage and a symmetrical broad or upright vase-shaped crown. This plant is susceptible to various diseases because of rapid terminal growth when new springwood vessels are fully functional. The American elm, along with many other shade tree species, can be affected by Xylella fastidiosa (Hearon et al. 1980), and X. fastidiosa has been previously confirmed on American elm in Ontario (Goodwin and Zhang 1997), Washington, D.C. (Harris and Balci 2015), Oklahoma (Olson et al. 2006), and Alabama (Parker et al. 2012). X. fastidiosa colonizes the xylem vessels of plant hosts and can cause bacterial leaf scorch disease (Pearson et al. 1998). On elm, X. fastidiosa causes leaf discoloration and browning, marginal scorching, and dieback. In the summer of 2019, chlorosis and marginal leaf scorch symptoms consistent with those of bacterial leaf scorch disease were observed on an American elm tree in a nursery in Pulaski County, Georgia. This elm tree was propagated from cuttings taken from a mature tree in Houston County, Georgia. Initial identification of the disease was performed by assessing characteristic symptoms of infection like leaf scorch, dieback signs, and so on, as described in Hernandez-Martinez et al. (2006). X. fastidiosa was verified via molecular and serological methods. Genomic DNA was extracted from the petioles and midribs of symptomatic leaves using the DNeasy Plant Kit (Qiagen, Valencia, CA), and real-time PCR was performed in a Cepheid smart cycler II (Sunnyvale, CA) using iQ SYBR Green Supermix (BioRad Laboratories, Hercules, CA). A 25-µl reaction was prepared according to the manufacturer’s protocol with primers XF-F/XF-R, which target the 16s rRNA processing protein (Harper et al. 2010). Real-time PCR results confirmed the presence of X. fastidiosa in all symptomatic leaves. The recombinase-polymerase-amplification technology-based AmplifyRP Acceler8 end-point detection assay (Agdia, Elkhart, IN) was carried out on symptomatic tissue using according to the manufacturer’s instructions, and this assay also confirmed the presence of X. fastidiosa in all symptomatic leaves (Waliullah et al. 2019). For further confirmation, the remaining petiole tissue was tested for X. fastidiosa using the DAS-ELISA Reagent Set for X. fastidiosa (Agdia) with minor modifications to the manufacturer’s protocol. In addition to tests of the symptomatic plant, testing of leaves from five additional young elm trees from the same nursery was also carried out according to the same procedures. These five visually healthy young elms tested negative for X. fastidiosa based upon all three testing methods. In total, three independent tests confirmed the presence of X. fastidiosa in symptomatic elm tissues, whereas asymptomatic elm trees from the same nursery tested negative. Attempts to isolate the bacteria from symptomatic leaf tissue on periwinkle wilt media (Davis et al. 1981) were not successful; however, the strong association of symptoms with the thrice-confirmed presence of X. fastidiosa in symptomatic tissue clearly indicates the role of X. fastidiosa in the observed symptoms. Although X. fastidiosa is most commonly transmitted by xylem-feeding insects, cuttings taken from infected hosts can produce infected plants; however, the mature tree used for propagation in this case could not be located for testing. To the best of our knowledge, this is the first report of X. fastidiosa associated with the American elm in Georgia. The presence of X. fastidiosa in American elm has the potential to impact homeowners, landscapers, and nursery producers within Georgia, and our findings suggest that Georgia tree nursery growers should monitor their nursery stock for bacterial leaf scorch disease.The author(s) declare no conflict of interest.References:Davis, M. J., et al. 1981. Curr. Microbiol. 6:309. https://doi.org/10.1007/BF01566883 Crossref, ISI, Google ScholarGoodwin, P. H., and Zhang, S. 1997. Can. J. Plant Pathol. 19:13. https://doi.org/10.1080/07060669709500564 Crossref, ISI, Google ScholarHarper, S. J., et al. 2010. Phytopathology 100:1282. https://doi.org/10.1094/PHYTO-06-10-0168 Link, ISI, Google ScholarHarris, J. L., and Balci, Y. 2015. PLoS One 10:e012129. Google ScholarHearon, S. S., et al. 1980. Can. J. Bot. 58:1986. https://doi.org/10.1139/b80-228 Crossref, ISI, Google ScholarHernandez-Martinez, R., et al. 2006. Plant Dis. 90:1143. https://doi.org/10.1094/PD-90-1143 Link, ISI, Google ScholarOlson, B. R., et al. 2006. Plant Dis. 90:108. https://doi.org/10.1094/PD-90-0108B Link, ISI, Google ScholarParker, J. K., et al. 2012. Appl. Environ. Microbiol. 78:1385. https://doi.org/10.1128/AEM.06679-11 Crossref, ISI, Google ScholarPearson, R. C., et al. 1998. Compendium of Grape Diseases. American Phytopathological Society, St. Paul, MN. Google ScholarWaliullah, S., et al. 2019. PLoS One 14:e0221903. https://doi.org/10.1371/journal.pone.0221903 Crossref, ISI, Google ScholarThe author(s) declare no conflict of interest.DetailsFiguresLiterature CitedRelated Vol. 104, No. 6 June 2020SubscribeISSN:0191-2917e-ISSN:1943-7692 DownloadCaptionSymptoms of citrus yellow mottle-associated virus on a leaf of Washington navel orange (J. X. Wu et al.). Photo credit: M. J. Cao. Effect of pydiflumetofen + difenoconazole on the severity of Cercospora leaf spot caused by Cercospora beticola in a small plot (S. J. Pethybridge et al.). Photo credit: S. J. Pethybridge. Metrics Article History Issue Date: 8 Jun 2020Published: 7 Apr 2020First Look: 28 Jan 2020Accepted: 27 Jan 2020 Page: 1853 Information© 2020 The American Phytopathological SocietyKeywordsAmerican elmXylella fastidiosaleaf scorchshade treeThe author(s) declare no conflict of interest.Cited byXylella fastidiosa (Pierce's disease of grapevines)CABI Compendium, Vol. CABI CompendiumRecent advancement in plant disease management

In recent years, citrus production has rapidly increased within the state of Georgia (USA), and there are now citrus plantings within at least 32 counties in residential, production, and nursery settings. Among the pathogens capable of infecting citrus are viroids, the smallest plant pathogens. Viroids are comprised of circular, single-stranded RNA ranging from 246-463 nucleotides in length (Ito et al., 2002). Hop stunt viroid (HSVd) is one of several viroids known to infect citrus. This viroid has been previously reported within Arizona, California, Florida, Texas, and Washington in the United States and in other locations throughout the world (Hadidi, 2017). HSVd is often spread mechanically on contaminated tools or through grafting. With a wide host range that includes the families Moraceae, Rosaceae, and Rutaceae (citrus), this viroid can easily move throughout a nursery and spread to other plants (Hadidi, 2017). Symptoms of HSVd include a discoloration and gumming of phloem tissues, stem pitting, bark splitting, and chlorotic and stunted growth in susceptible citrus varieties including tangerines and their hybrids (Hadidi, 2017). There are not typically symptoms on leaves or fruits; however, lime plants have shown some yellowing on leaves (Hadidi, 2017). In May and June of 2020, leaf samples were collected from 12 different citrus plants in nursery settings in Berrien and Mitchell counties in Georgia. The cultivars sampled from Citrus reticulata 'Dekopon'. The sampled trees looked relatively healthy with little or no signs of damage, but were selected for testing to ensure that they were viroid free. Reverse transcription-polymerase chain reaction (RT-PCR) was initially used to verify infection with HSVd. Genomic RNA was extracted from the leaf tissue of twelve plants using the TRIzol reagent (Thermofisher, Waltham, MA). Following cDNA synthesis, samples were tested for the presence of HSVd using the primer pair HSVd-F (5'-GGCAACTCTTCTCAGAATCCAGC-3') and HSVd-R (5'-CCGGGGCTCCTTTCTCAGGTAAGT-3') which produces a 302 bp amplicon (Sano et al., 1988). The PCR reactions for nine of the tested samples did not result in the production of any bands, however the other three samples, all Citrus reticulata 'Dekopon', produced the expected amplicon for HSVd. The amplified products were sequenced using Sanger sequencing (Retrogen Inc, San Diego, CA, USA) and the identity of the fragment sequences was confirmed using BLAST analysis (https://blast.ncbi.nlm.nih.gov/Blast.cgi). Partial sequences from these amplicons (deposited as accession number MT632007) shared 99% identity to corresponding HSVd sequences in Genbank (accession number MG779542). In addition to RT-PCR and sequencing, the recombinase-polymerase-amplification (RPA) technology based AmplifyRP® Acceler8™ end-point detection assay (Agdia® Inc., Elkhart, IN) was performed on previously confirmed tissue according to the manufacturer's instructions. This assay also confirmed the presence of HSVd viroid in the three samples that had been previously confirmed via RT-PCR. To the best of our knowledge, this is the first report of HSVd infecting Citrus reticulata 'Dekopon' in Georgia. If this viroid were to spread within the growing Georgia citrus industry, it could pose a significant threat to citrus plantings that contain susceptible varieties. Nursery stock infected with this viroid should be destroyed, and Georgia nursery producers and citrus growers should take appropriate precautions to prevent the spread of this viroid disease, including properly sanitizing tools used for citrus grafting and pruning. Further research is needed to determine the distribution of HSVd and its potential to impact commercial citrus production in Georgia.

HomePlant DiseaseVol. 104, No. 3First Report of Downy Mildew on Blackberry Caused by Peronospora sparsa in Georgia, U.S.A. PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Downy Mildew on Blackberry Caused by Peronospora sparsa in Georgia, U.S.A.M. E. Ali, O. Hudson, S. Waliullah, J. Brock, B. Hayes, J. L. Williams-Woodward, and J. E. OliverM. E. Ali†Corresponding author: M. E. Ali; E-mail Address: ma49268@uga.eduhttp://orcid.org/0000-0002-5871-5055Department of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, O. HudsonDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, S. WaliullahDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, J. BrockDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author, B. HayesUniversity of Georgia Cooperative Extension, Mitchell County, Camilla, GA 31730Search for more papers by this author, J. L. Williams-WoodwardDepartment of Plant Pathology, University of Georgia, Athens, GA 30602Search for more papers by this author, and J. E. OliverDepartment of Plant Pathology, University of Georgia, Tifton, GA 31793Search for more papers by this author AffiliationsAuthors and Affiliations M. E. Ali1 † O. Hudson1 S. Waliullah1 J. Brock1 B. Hayes2 J. L. Williams-Woodward3 J. E. Oliver1 1Department of Plant Pathology, University of Georgia, Tifton, GA 31793 2University of Georgia Cooperative Extension, Mitchell County, Camilla, GA 31730 3Department of Plant Pathology, University of Georgia, Athens, GA 30602 Published Online:30 Dec 2019https://doi.org/10.1094/PDIS-09-19-1962-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Blackberries (Rubus L. subgenus Rubus) are small, round, aggregate berries comprising a cluster of tiny fruits called drupelets that grow on flowering shrubs or trailing vines (Clark et al. 2007). The acreage of blackberry production in Georgia has increased 10-fold in the last 15 years to 880 acres (NASS 2017). Downy mildew of blackberry, caused by the oomycete pathogen Peronospora sparsa, is a systemic disease that impacts blackberry production in many regions worldwide. Symptoms of downy mildew on blackberry include yellowing on the upper leaf surface and reddish-brown angular lesions with necrotic centers and chlorotic margins. In May 2019, leaf symptoms typical of blackberry downy mildew were observed on blackberry cultivar ‘Ouachita’ plantlets at a nursery in Mitchell County, Georgia. Initial identification was done based on the morphological characteristics of the sporangia and sporangiophores. Round or slightly ovoid sporangia were observed that were colorless to yellowish-brown, consistent with Peronospora sp. (Gubler and Rebollar-Alviter 2017). The identification of P. sparsa was further confirmed using nucleic acid-based molecular methods directly on infected plant tissue. Genomic DNA was extracted from symptomatic leaf tissue and tested for the presence of P. sparsa by targeting the P. sparsa-specific rDNA-ITS region using “P” primer pair P1 (5′-CACGTGAACCGTATCAACC-3′) and P2 (5′-GATAGGGCTTGCCCAGTAG-3′) with an amplicon size of 94 bp (Hukkanen et al. 2006). PCR reactions produced the expected sizes of the fragments for P. sparsa. The amplified products were then sequenced and subjected to BLAST analysis (https://blast.ncbi.nlm.nih.gov/Blast.cgi) for further identification. Sequence analysis revealed that the obtained partial sequence of P. sparsa-specific rDNA-ITS (GenBank submission no. MN477916) shared 100% identity to corresponding sequences from P. sparsa (accession no. Y15816). Samples were also tested for the presence of P. sparsa by real-time PCR using the same set of “P” primers. For real-time PCR, plant internal control primer pair R1 (5′-CAAACGACTCTCGGCAAC-3′) and R2 (5′-CCTCGGCCTAATGGCTT-3′) was used to target the highly conserved region of 5.8S plant ribosomal DNA (Hukkanen et al. 2006). The real-time PCR assay was performed in a Cepheid smart cycler II (Sunnyvale, CA) using iQ SYBR Green Supermix (BioRad Laboratories, Hercules, CA) in a 25-µl reaction according to the manufacturer’s protocol (Harper et al. 2010). All four samples extracted from symptomatic leaves were positive based on the real-time PCR assay. In addition, Koch’s postulates were fulfilled to verify the pathogenicity of the P. sparsa. Leaves from four uninfected blackberry plants (also cv. Ouachita) were surface sterilized, laid under sporulating leaf tissue, and incubated at 17°C with a 12-h photoperiod in a moist chamber. After 16 days, on the previously uninfected leaves, sporangiophores and sporangia consistent with P. sparsa developed. As a control, additional leaves from the same four plants were surface sterilized, placed in a moist chamber, incubated at 17°C with a 12-h photoperiod, and examined 16 days later. No lesions or sporulation developed on the uninoculated controls. To the best of our knowledge, this is the first report of P. sparsa causing downy mildew on blackberry in Georgia. Our findings suggest that Georgia blackberry growers should be aware of this disease and accordingly establish management measures for P. sparsa.The author(s) declare no conflict of interest.References:Clark, J. R., et al. 2007. Page 19 in: Plant Breeding Reviews. Wiley, Hoboken, NJ. https://doi.org/10.1002/9780470168035.ch2 Crossref, Google ScholarGubler, W. D., and Rebollar-Alviter, A. 2017. Page 25 in: Compendium of Raspberry and Blackberry Diseases and Pests, 2nd Ed. APS Press, St. Paul, MN. Google ScholarHarper, S. J., et al. 2010. Phytopathology 100:1282. https://doi.org/10.1094/PHYTO-06-10-0168 Link, ISI, Google ScholarHukkanen, A., et al. 2006. Eur. J. Plant Pathol. 116:225. https://doi.org/10.1007/s10658-006-9054-z Crossref, ISI, Google ScholarNational Agricultural Statistics Service (NASS). 2017. 2017 Census of Agriculture. Retrieved September 19, 2019, from https://www.nass.usda.gov/​Publications/AgCensus/​2017/Full_Report/​Volume_1,_Chapter_2_​US_State_Level/​st99_2_0033_0033.pdf. Google ScholarThe author(s) declare no conflict of interest.DetailsFiguresLiterature CitedRelated Vol. 104, No. 3 March 2020SubscribeISSN:0191-2917e-ISSN:1943-7692 DownloadCaptionPathogenicity of Lasiodiploidia pseudotheobromae in a coffee plant 3 days after inoculation (R. L. Freitas-Lopes et al.). Photo credit: U. P. Lopes. Seedling blight of soybean caused by soilborne pathogens (J. R. Lamichhane et al.). Photo credit: M. I. Chilvers. Metrics Downloaded 3,002 times Article History Issue Date: 3 Mar 2020Published: 30 Dec 2019First Look: 11 Nov 2019Accepted: 2 Nov 2019 Page: 996 Information© 2020 The American Phytopathological SocietyKeywordsblackberryPeronospora sparsadowny mildewoomycete pathogenThe author(s) declare no conflict of interest.

The genus Tospovirus is unique within the family Bunyaviridae in that it is made up of viruses that infect plants. Initially documented over 100 years ago, tospoviruses have become increasingly important worldwide since the 1980s due to the spread of the important insect vector Frankliniella occidentalis and the discovery of new viruses. As a result, tospoviruses are now recognized globally as emerging agricultural diseases. Tospoviruses and their vectors, thrips species in the order Thysanoptera, represent a major problem for agricultural and ornamental crops that must be managed to avoid devastating losses. In recent years, the number of recognized species in the genus has increased rapidly, and our knowledge of the molecular interactions of tospoviruses with their host plants and vectors has expanded. In this review, we present an overview of the genus Tospovirus with particular emphasis on new understandings of the molecular plant-virus and vector-virus interactions as well as relationships among genus members.

Xylella fastidiosa is a xylem-limited gram-negative plant pathogen that affects numerous crop species, including grape, citrus, peach, pecan, and almond. Recently, X. fastidiosa has also been found to be the cause of bacterial leaf scorch on blueberry in the southeastern United States. Thus far, all X. fastidiosa isolates obtained from infected blueberry have been classified as X. fastidiosa subsp. multiplex; however, X. fastidiosa subsp. fastidiosa isolates are also present in the southeastern United States and commonly cause Pierce's disease of grapevines. In this study, seven southeastern U.S. isolates of X. fastidiosa, including three X. fastidiosa subsp. fastidiosa isolates from grape, one X. fastidiosa subsp. fastidiosa isolate from elderberry, and three X. fastidiosa subsp. multiplex isolates from blueberry, were used to infect the southern highbush blueberry 'Rebel'. Following inoculation, all isolates colonized blueberry, and isolates from both X. fastidiosa subsp. multiplex and X. fastidiosa subsp. fastidiosa caused symptoms, including characteristic stem yellowing and leaf scorch symptoms as well as dieback of the stem tips. Two X. fastidiosa subsp. multiplex isolates from blueberry caused more severe symptoms than the other isolates examined, and infection with these two isolates also had a significant impact on host mineral nutrient content in sap and leaves. These findings have potential implications for understanding X. fastidiosa host adaptation and expansion and the development of emerging diseases caused by this bacterium.