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G.E. Holcomb and R.A. Valverde

Salvia uliginosa Benth. plants, in an experimental planting of Salvia species, exhibited virus-like symptoms of chlorotic line patterns and ringspots. The suspect virus was mechanically transmitted to several experimental hosts and was identified as cucumber mosaic cucumovirus (CMV) based on dsRNA gel patterns, positive reaction with CMV antiserum, and particle morphology as observed by transmission electron microscopy.

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A.Q. Villordon, C.A. Clark, R.A. Valverde, R.L. Jarret, and D.R. LaBonte

Previous work by our group has detected the presence of a heterogeneous population of Ty1-copia-like reverse transcriptase retrotransposon sequences in the sweetpotato genome. Recently, we detected the presence of putatively active Ty1-copia-like reverse transcriptase sequences from a virus-infected `Beauregard' sweetpotato clone. In the current study, we report the differential detection of putatively stress-activated sequences in clones from seedling 91-189. The clones were infected with different combinations of virus isolates followed by extraction of leaf RNA samples at three sampling dates (weeks 2, 4, and 6) after inoculation. After repeated DNAse treatments to eliminate contaminating DNA, the RNA samples were subjected to first strand cDNA synthesis using random decamer primers followed by PCR analysis utilizing Ty1-copia reverse transcriptase-specific primers. Through this approach, we detected amplified fragments within the expected size range (280-300 bp) from clones infected with isolates of sweetpotato leaf curl (SPLC) and feathery mottle viruses (FMV) (week 2 and 6) and FMV (week 4). We were unable to detect PCR products from the noninfected clones or the other infected samples. The data suggests that specific viruses may be involved in the expression of these Ty1-copia-related reverse transcriptase sequences. It also appears that sampling at various dates is necessary to detect putative activity over time. This preliminary information is essential before proceeding to the construction and screening of cDNA libraries to isolate and fully characterize the putatively active sweetpotato Ty1-copia-like retrotransposon sequences. Through the partial or complete characterization of sweetpotato Ty1-copia elements, sequences that correspond to cis-regulatory element(s) can be identified and further studied for their roles in responding to specific stress factors.

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C. A. Clark, R. A. Valverde, J. A. Wilder-Ayers, and P. E. Nelson

Symptoms of chlorotic leaf distortion (CLD) develop on vigorously growing sweetpotato (Ipomoea batatas) plants during sunny weather. They include chlorosis and twisting of young, expanding leaves and the appearance of white material on the adaxial leaf surfaces. The white material consisted of extramatrical fungal mycelia and Fusarium macroconidia. Fusarium lateritium Nees was isolated from surface-sterilized vine segments, leaf primordia, apical meristems, flower parts and true seeds of plants with CLD. Meristem-tip-culture-derived plants (mericlones) did not develop symptoms when grown for extended periods under disease-conducive conditions in the greenhouse. The fungus was not isolated from mericlones or other plants which had remained symptomless in the greenhouse but was isolated from lower nodes of symptomless plants from growers' fields. Symptoms developed on 84% of 185 mericlones of nine sweetpotato genotypes inoculated with F. lateritium isolated from CLD-affected plants. The pathogen was reisolated only from inoculated mericlones.