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Alstroemeria (Alstroemeria spp.) is cultivated for cut flowers. Traditional propagation methods are by division of rhizomes from mature plants, so that viruses occurring in the crop can be multiplied and cause a decrease in the quality and production. The objective of this work was to obtain Alstroemeria cv. Rosario plants free of Alstromeria Mosaic Potyvirus (AlMV) by in vitro culture of shoots and thermotherapy. The best percentage of explants without contamination was obtained when adding the disinfectant PPM (1%) to the medium Murashige-Skoog (MS) while the best induction of buds was obtained when using explants of 1.5 cm. in length. In vitro multiplication of shoots was best in treatments with 2iP (isopentenyl adenine), BA (benzyladenine), and zeatin (4.4, 6.1, and 6.6 buds per explant, respectively). Rhizogenesis was observed in rhizomes growing in MS with 4.9 μM AIB (indole butyric acid) and 1.5 g·L^-1 of sugar. Sixty-seven percent of plants growing in vitro did not react to AlMV antiserum and did not show particles and viral inclusions. Thermotherapy treatments of 45, 50, and 55 °C during different periods of time produced from 25% to 87.5% of plants that did not react to AlMV antiserum and did not show virus particles or cytoplasmic inclusions.

Zucchini yellow fleck virus (ZYFV) is a potyvirus that occurs in cucurbits grown in some Mediterranean countries. `Marketer' cucumber responded to ZYFV infection with a severe mosaic, stunting, and leaf and fruit deformation. A high level of resistance to this virus was found in a single plant selection of `Taichung Mou Gua' (TMG) cucumber from Taiwan. In F₂ and backcross populations involving TMG × `Marketer', the resistance to ZYFV was determined to be conferred by a single recessive gene, to which the symbol zyf is assigned.

Quechua farmers have cultivated mashua (Tropaeolum tuberosum Ruiz & Pavon) and other tuber crops for thousands of years. The practice of trading seed tubers may have contributed to dispersal of viral diseases, such as the tropaeolum mosaic virus (TropMV). We surveyed 17 accessions of mashua collected from Quechua farmers in the provinces of Cuzco and Ayacucho, Peru. Most cross-reacted with the TropMV antibody and showed viral disease symptoms. Significant differences were observed between accessions from Cuzco and Ayacucho, with respect to virus infection and tuber yield under greenhouse conditions. Of the accessions from Cuzco, 87% displayed viral symptoms, while only 22% from Ayacucho showed symptoms. Fewer tubers from Cuzco generated mature plants. In turn, those mature plants produced lower tuber yields. The practice of trading seed tubers may be advantageous for promoting crop diversity but can be harmful when diseased seed tubers are being traded. A program to generate and distribute virus-free seed tubers among Andean farmers would contribute to higher crop yields while preserving local customs and crop diversity.

Cucumbers and other cucurbit crops are subject to severe losses due to an array of potyviruses, including zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), and the watermelon strain of papaya ringspot virus (PRSV-W). Sources of resistance to these viruses have been identified within the cucumber germplasm, including resistance to ZYMV, WMV, and PRSV in `TMG-l'; resistance to PRSV in `Surinam'; and to ZYMV in `Dina'. In this study, we sought to determine the allelic relationships between resistance to PRSV in `Surinam' and `TMG' and resistance to ZYMV in `Dina' and `TMG'. Segregation ratios among F<sub>1</sub>, F<sub>2</sub>, and backcross progeny of `Surinam' and `TMG' indicated that the alleles are at the same locus. Similarly, progeny analysis indicates that the alleles for ZYMV resistance in `Dina' and `TMG' are at the same locus. In each case, however, the alleles appear to differ from one another with respect to dominance relationships, symptom expression, and/or response to different viral strains. We are further characterizing these differences by screening progeny of crosses to a common susceptible parent.

Transgenic plum plants expressing the papaya ringspot virus (PRV) coat protein (CP) were produced by Agrobacterium-mediated transformation of hypocotyl slices. Hypocotyl slices were cocultivated with Agrobacterium tumefaciens strain C58/Z707 containing the plasmid pGA482GG/CPPRV-4. This plasmid carries the PRVCP gene construct and chimeric NPTII and GUS genes. Shoots were regenerated on Murashige and Skoog salts, vitamins, 2% sucrose, 2.5 μm indolebutyric acid, 7.5 μm thidiazuron, and appropriate antibiotics for selection. Integration of the foreign genes was verified through kanamycin resistance, GUS assays, polymerase chain reaction (PCR), and Southern blot analyses. Four transgenic clones were identified. Three were vegetatively propagated and graft-inoculated with plum pox virus (PPV)-infected budwood in a quarantine, containment greenhouse. PPV infection was evaluated over a 2- to 4-year period through visual symptoms, enzyme-linked immunosorbent assay, and reverse transcriptase PCR assays. While most plants showed signs of infection and systemic spread of PPV within l-6 months, one plant appeared to delay the spread of virus and the appearance of disease symptoms. Virus spread was limited to basal portions of this plant up to 19 months postinoculation, but, after 32 months symptoms were evident and virus was detected throughout the plant. Our results suggest that heterologous protection with PRVCP, while having the potential to delay PPV symptoms and spread throughout plum plants, may not provide an adequate level of long-term resistance.