Joseph S. Semancik

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Nucleotide sequences were determined for two hop stunt viroid-related Group II citrus viroids characterized as either a cachexia disease non-pathogenic variant (CVd-IIa) or a pathogenic variant (CVd-IIb). Sequence identity between the two variants of 95.6% indicated a conserved genome with the principal region of nucleotide difference clustered in the(More)
ABSTRACT Citrus viroid (CVd) group II is comprised of hop stunt viroid (HSVd)-related variants of 295 to 302 nucleotides. Included in this group are the cachexia-inducing agents citrus cachexia viroid (or CVd-IIb), CVd-IIc, Ca-903, and Ca-909 as well as the non-cachexia-inducing variant CVd-IIa. The cachexia indexing hosts 'Parson's Special' mandarin and(More)
An unusual variant of citrus exocortis viroid (CEV) was detected when an inoculum source from Gynura aurantiaca D.C. was used to infect a hybrid tomato (Lycopersicon esculentum Mill. x L. peruvianum). The 92 nucleotide larger variant, CEV D-92, which displayed the characteristic circular and linear viroid structural forms, contained two repeated sequences(More)
The nucleotide sequence and secondary structure of two representative variants from the Group III citrus viroids. CVd-IIIa (297 bases) and CVd-IIIb (294 bases) were determined. The variants are related to the apple scar skin viroid (ASSVd) family. Although smaller in size than any of the ASSVd-related viroids, the central conserved region as well as most of(More)
Isolates of citrus exocortis viroid (CEV) from a single sweet orange citrus source have been selected by sequential passage through the alternative hosts citron, Gynura aurantiaca, a hybrid tomato Lycopersicon esculentum x L. peruvianum, and from disorganized callus culture of the hybrid tomato. The distinctions in symptom expression, titre and(More)
Variants of avocado sunblotch viroid (ASBVd) of between 247 and 250 nucleotides in length have been recovered from diseased avocado tissues. The sunblotch syndrome covers a complex pattern of disease symptoms which are associated with infection by variants of ASBVd. The viroid species are designated ASBVd-B, ASBVd-V and ASBVd-Sc from their association with(More)
Evidence of post-transcriptional gene silencing (PTGS) in avocado infected by Avocado sunblotch viroid (ASBVd), the type species of family Avsunviroidae, was suggested by detection of ASBVd-specific 22-nucleotide RNAs. PTGS was observed in infected bleached and variegated symptomatic tissues as well as symptomless carrier foliar sources and fruit with(More)
Recovery of highly purified citrus cachexia viroid (CCaV) was accomplished by serial elution following CF-11 cellulose chromatography of a 2 i-LiCl-soluble nucleic acid preparation. The alternative herbaceous host, cucumber (Cucumis sativus cv. Suyo), yielded greater quantities of the viroid than the highest yielding citrus host, citron (Citrus medica cv.(More)