Search results

255

Recurrent epiphytotics of X-disease, caused by ‘Candidatus Phytoplasma pruni’, have inflicted significant losses on commercial cherry and peach production across North America in the last century. During this period, there have been multiple studies reporting different disease phenotypes, and more recently, identifying different strains through sequencing core genes, but the symptoms have not, to date, been linked with genotype. Therefore, in this study we collected and assessed differing disease phenotypes from multiple U.S. states and conducted multi-locus sequence analysis on these strains. We identified a total of five lineages associated with the induction of X-disease on commercial Prunus species and two lineages that were associated with wild P. virginiana. Despite a century of interstate plant movement, there were regional trends in terms of lineages present, and lineage-specific symptoms were observed on P. avium, P. cerasus, and P. virginiana, but not on P. persica. Cumulatively, these data have allowed us to define ‘true’ X-disease-inducing strains of concern to the stone fruit industry across North America, as well as potential sources of infection that exist in the extra-orchard environment.

Chia (Salvia hispanica L., Lamiaceae) is an important commercial and medicinal crop recently popularized in India and widely cultivated in Karnataka (Joy et al., 2022). During the field survey of chia crop diseases, characteristic virescence like symptoms were observed at Main Agricultural Research Station, UAS, Raichur as well as at Mysuru and HD Kote region. The incidence was ranged from 2 – 4 per cent in an area of 30 hectares. Typical symptoms associated with chia are malformed shoot and/or inflorescence axis with reduced floral parts with greenish florets. The stem axis become thick, flattened, leaves are reduced towards terminal region. A total of five phytoplasma suspected samples and five suspected healthy samples were used for identification purpose. The Plant Genomic DNA Miniprep Kit (Sigma Aldrich, USA) was used to extract the DNA from five symptomatic and five asymptomatic samples and the DNA was used as template to amplify the phytoplasma-specific 16S rDNA gene using P1/P7 primers (Deng and Hiruki, 1991; Schneider et al., 1995) followed by nested PCR using R16F2n/R16R2 primers (Gundersen and Lee 1996). The expected 1.25-kb amplicon was detected from the suspected symptomatic samples. Nested PCR products were purified and sequenced from both the directions using ABIX370 Genetic Analyzer (Applied Biosystems, Waltham, MA). The analysis revealed that all five sequences shared 100 per cent identity with Candidatus Phytoplasma aurantifolia (OM649850, ON975012) and Tomato big bud phytoplasma (EF193359). The in-silico RFLP pattern of F2n/R2 primed region of 16S rDNA gene analyzed by using iPhyClassifier (Zhao et al. 2009) revealed that the sequence shared 98.72 per cent nucleotide sequence similarity with coefficient value of 1.00 to the reference strain RFLP pattern of 16Sr group II, subgroup D (witches'-broom disease of lime; U15442). Based on 16SrDNA sequences and in-silico RFLP analysis, the phytoplasma associated with the chia virescence was identified as a member of 16SrII-D group. Further, SecA gene was also amplified from the samples using SecAfor1/SecArev3 primer pair (Hodgetts et al., 2008). All samples produced ~400 bp products and sequenced as detailed above. Sequence analysis by nBLAST revealed 100 per cent similarity to Ca. P. australasia (MW020545) and Ca. P. aurantifolia isolate Idukki Kerala 1 (MK726369) both representing 16SrII-D group phytoplasma. The representative sequence (16Sr: PP359693, PP359694; secA:PP386558, PP386559) were deposited in GenBank. Chia virescence phytoplasma belonging to Ca. phytoplasma australasia has not been reported anywhere. The phytopathological studies associated with chia crop are very limited. Joy et al. (2022) reported the occurrence of foot rot disease caused by Athelia rolfsii. Several hosts are recorded to be associated with 16SrII D phytoplasma which includes china aster, eggplant and crotalaria (Mahadevakumar et al., 2017, Yadav et al., 2016a, b). Now the wide occurrence of the phytoplasma in the area might have transmitted by vectors. The occurrence of virescence is of great importance as it affects the overall yield which reduces the market value. To our knowledge, this is the first report of a group 16SrII-D phytoplasma associated with chia virescence in India.

Lingonberries (Vaccinium vitis-idaea L.) are low-growing, evergreen shrubs of cooler, northern regions of North America and Europe. These plants produce berries that are unique in flavor, bear high economic significance, and play a vital role in maintaining the diversity of the northern ecosystems (Kowalska, 2021). In October 2023 diseased plants of lingonberry were discovered in Labanoras Forest (55°14′N 25°42′E) (Lithuania). The plants expressed symptoms of stunting, yellowing, little leaf, shortened internodes, and stem distortions. Samples (leaves) were collected and tested from ten asymptomatic and ten symptomatic lingonberry plants. Total genomic DNAs of all samples were extracted by a CTAB protocol. Extracted DNAs were used as a template in direct and nested PCRs using the universal primer pairs P1/P7 and R16F2n/R2, respectively, to amplify phytoplasma 16S rRNA gene 1.2 kb fragments (Lee et al. 1998). The primer pairs SecAFor1/SecARev3 and SecAFor2/SecARev3 were used in direct and semi-nested PCRs, respectively, to amplify phytoplasma secA genes 0.5 kb fragment (Dickinson and Hodgetts, 2013). PCR amplicons of the 16S rRNA and secA genes specific for the phytoplasmas were only obtained from all sampled symptomatic plants. Three R16F2n/R2 and three SecAFor2/SecARev3 amplicons were cloned and submitted for Sanger sequencing (Nature Research Centre, Vilnius, Lithuania by 3500 Genetic Analyser). The three 16S rDNAs as well as the three secA gene fragments were identical. The BLAST analysis (NCBI) of the obtained sequences showed a similarity percentage, ranging from 99.75% to 100% (1247-1250 bp from 1250 bp) for 16SrRNA, and 98.13% to 99,15% (473-478 bp from 482 bp) for secA amplicons, with numerous strains of ‘Candidatus (Ca.) Phytoplasma (P.) trifolii’ (first hit MT674293 and KR906724, respectively). Additionally, 16S rDNA sequences by using iPhyClassifier were used to create virtual RFLP pattern (Zhao et al. 2009). The generated pattern was identical (similarity coefficient 1.00) to the reference pattern of 16Sr group VI, subgroup A. The phytoplasma strain detected in lingonberries was designated as lingonberry stunted yellows, LingbSY. Furthermore, the enzymatic RFLP analysis was performed with the 14 restriction enzymes (Lee et al., 1998), and obtained profiles were compared with virtually generated using iPhyClassifier. This yielded the same classification of detected phytoplasma to the 16SrVI-A phytoplasma subgroup. The phylogenetic analysis of both marker gene sequences revealed the same LingbSY phytoplasma classification. Selected sequences were deposited in GenBank (NCBI) with Accession No: PP237769 (16S rRNA gene) and No: PP238489 (secA gene). Phytoplasmas of 16SrI phytoplasma group were identified in lingonberries in Canada (Brochu et al. 2022). Strains of 16SrVI phytoplasma group were reported in Vaccinium myrtillus in Austria (Fernandez et al. 2007). This is the first report of ‘Ca. P. trifolii’ strain belonging to 16SrVI-A phytoplasma subgroup infecting lingonberry worldwide. Also, this is the first report of 16SrVI phytoplasma group in Lithuania. The presence of this phytoplasma poses a threat to the natural ecosystem and could eventually spread into agricultural settings in our country. Therefore, it’s crucial to conduct surveillance for insect vectors, and assess effective control methods. Without proactive action, long term sustainability of lingonberries and their ecosystems may be jeopardized.