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S.T. Nameth and S.L. Cheng

Double-stranded ribonucleic acid (dsRNA) analysis of apparently healthy red mulberry (Morus rubra L.) yielded four distinct dsRNA banding profiles. dsRNA type 1 contained three dsRNA bands with approximate molecular weights (MWs) of 12.0, 1.0, and 0.9 × 106, respectively. dsRNA type 2 contained two dsRNA bands with MWs of 1.0 and 0.9 × 106. dsRNA type 3 contained four dsRNA bands with MWs of 1.0, 0.9, 0.89, and 0.88 × 106. dsRNA type 4 contained three dsRNA bands with MWs of 1.0, 0.88, and 0.87 × 106. No virus particles were associated with any of the samples analyzed. All four types of dsRNA were resistant to DNase I and RNase A in high salt and susceptible to RNase A in low salt. Mulberry dsRNAs were somewhat similar to endogenous dsRNAs (edsRNA) associated with other hosts. This is the first report of edsRNA associated with a deciduous tree.

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J.R. Fisher and S.T. Nameth

Ajuga reptans L. is an herbaceous ornamental mint grown in borders or as a groundcover, and is commonly propagated vegetatively and by seed. Three hundred and fifty-six A. reptans samples were obtained from growers in Washington, Michigan, Iowa, and Ohio, and screened for alfalfa mosaic virus (AMV), tobacco streak ilarvirus (TSV), cucumber mosaic cucumovirus (CMV), tomato aspermy cucumovirus (TAV), tomato spotted wilt tospovirus (TSWV), impatiens necrotic spot tospovirus (INSV), tobacco mosaic tobamovirus (TMV), potato virus × potexvirus (PVX), and 80 potyviruses, using direct antibody sandwich (DAS) and indirect enzyme-linked immunosorbent assay (ELISA). Viral-associated double-stranded ribonucleic acid (dsRNA) analysis was used to detect an apparent satellite (sat) RNA, and northern hybridization using a digoxigenin (DIG) labeled (S) CARNA-5 cDNA probe was used to confirm the identity of the apparent satRNA. No incidences of TAV, TMV, TSWV, INSV, PVX, or potyviruses were detected. CMV was detected in 11%, AMV in 22.2%, TSV in 3.7%, and mixed infections of CMV and AMV in 1.1% of the samples. SatRNA was detected in 36 A. reptans `Royalty', two `Rainbow', and two `Burgundy Glow' samples by dsRNA analysis, and confirmed by hybridization in 29 `Royalty' and one `Burgundy Glow' samples. Sixteen A. reptans `Royalty' seedlings grown from seed harvested from CMV-infected plants were tested by ELISA for CMV, AMV, and TSV. All were positive for CMV, and two were positive for a mixed infection of CMV and AMV. SatRNA was detected in all 16 seedlings by RT-PCR.

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J.R. Fisher and S.G.P. Nameth

Cucumber mosaic virus (CMV) was isolated from the perennial ornamental mint, Ajuga reptans L. `Royalty', using melon aphids (Aphis gossypii Glover). The isolate and its associated satellite RNA (satRNA) were biologically and chemically characterized. The satRNA was cloned and sequenced and is 338 nucleotides long and does not induce lethal necrosis on `Rutgers' tomato (Lycopersicon esculentum Mill.) or severe chlorosis on tobacco (Nicotiana L. spp.). The virus is ≈28 to 30 nm in diameter and reacts to CMV serological subgroup I antibodies. The virus is able to infect `Black Beauty' squash (Cucurbita pepo L.), cucumber (Cucumis sativus L.), and `Howden' pumpkin (Cucurbita pepo) but is not able to infect green bean (Phaseolus vulgaris L.) or cowpea [Vigna unguiculata (L.) Walp. ssp. unguiculata]. The virus is able to efficiently replicate its satRNA in tobacco and `Black Beauty' squash but replication is less efficient in cucumber, based on accumulation of double-stranded satRNA.

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C.C. Pasian, F. Varela Ramirez and S. Nameth

Evaluation of disease severity in root systems is usually subjective, based on observation and categorization into an arbitrary scale of several categories. Results obtained using this approach can vary according to the observer's experience. A new, simple method for evaluating and quantifying the root severity index (RSI) was developed. This method consists of surrounding the root pan with a transparent film and tracing all roots with a marker. On a second transparency, only healthy roots are traced. Lengths of both healthy and diseased roots are measured with a root length/area meter (Dias II). The method of peripheral root-ball root tracings was evaluated with poinsettias infected with Pythium ultimum (Trow.). Results indicated that it was as effective as the traditional method of determining RSI for total and peripheral roots.

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M-C Sanchez-Cuevas and S.G.P. Nameth

Double petunia plants expressing virus-like symptoms were collected in greenhouses and garden centers throughout Ohio in Spring 1997 and 1998 in an effort to determine the frequency and distribution of petunia viruses present in the state. Direct antibody-sandwich and indirect enzyme-linked immunosorbent assay (ELISA) were conducted with commercial antisera made against 13 viruses, a potyvirus kit capable of detecting 80 different potyviruses, and our antiserum raised against a tobamo-like virus inducing severe mosaic in double petunia. Viral-associated double-stranded ribonucleic acid (dsRNA) analysis and light microscopy for detection of inclusion bodies were also carried out. ELISA, dsRNA analysis, and light microscopy revealed the presence of tobacco mosaic tobamovirus, an unknown tobamo-like petunia virus, tomato ringspot nepovirus, tobacco streak ilarvirus, and tobacco ringspot nepovirus. Tomato aspermy cucumovirus, tomato spotted wilt tospovirus, impatiens necrotic spot tospovirus, alfalfa mosaic virus, cucumber mosaic cucumovirus, potato virus X potexvirus, and chrysanthemum B carlavirus were not detected. No potyviruses were identified. A number of plants with virus-like symptoms tested negative for all viruses.

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A.E. Lighthiser, S.G.P. Nameth and L.H. Rhodes