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Biodiversity of Antarctica includes climatically adapted microflora. Antarctic flora mainly contains cryptogams and are dominated by lichens, followed by mosses and algae. Among three bio-geographic zones of Antarctica, Sub-Antarctic zone is the most diverse and followed by Maritime and Continental zone. The Antarctic plant growth is largely limited to the coastal areas of Sub- and Maritime Antarctic regions. Two vascular plants; Deschampsia antarctica and Colobanthus quitensis are restricted along with other cryptogams at Antarctic Peninsula region. The average increase in temperature is the most prominent change in Antarctic Peninsula. Due to favorable conditions, cryptogams (lichens and mosses) are widely distributed in several localities of Antarctica. The algal growth is restricted to the semi permanent to permanent snow or melt ice and in floating water bodies of Antarctica. About 700 non-marine algal taxa were recorded from the different region of the Antarctica. Beside this, 200 additional taxa have been recorded from the continental Antarctica. The changes in temperature, pattern of cyclonic activity, availability of nutrients, water, high UV-B radiation along with other stresses posses obstacles for survival and distribution of Antarctic flora.

Surveys of commercial and seed potato fields for virus diseases (1998 to 2002) in Manitoba established that Potato virus Y (PVY) is of concern in seed potato production. To determine the prevalence of PVY strains, PVY-infected tubers identified by reverse transcription-polymerase chain reaction (RT-PCR) from surveys (2000 to 2001) were grown for symptom expression and strain characterization by strain-specific RT-PCR, bioassays, and serological assays. Of the samples collected (2000 to 2001) and tested by RT-PCR, 4.0% contained PVY. Further analysis of the PVY-positive samples by a duplex RT-PCR facilitating the simultaneous detection of common (PVYO) and tobacco veinal necrosis strains (PVYN/NTN) indicated that 37.5% contained PVYO and 63.5% contained PVYN-type isolates. Analysis of the PVYN-type samples using three monoclonal antibodies (MAbs) showed that all reacted with only the PVYO MAbs and not with the PVYN-specific MAb. Partial nucleotide sequences of both ends of PVY-RNA showed that the PVYN-type isolates resembled those reported in 1996 from Manitoba. These isolates are designated as PVYN:O. In view of the increased incidence of PVYN:O in one production area, seed tubers imported from other provinces of Canada and the neighboring United States were analyzed for PVYN:O. The PVYN:O was detected in imported seeds from Minnesota, Montana, and North Dakota.

Tomato chlorotic dwarf viroid (TCDVd), a member of the genus Pospivroid, family Pospiviroidae, was first identified on greenhouse tomato (Solanum lycopersicum) in Canada (2). Since then, it has also been reported elsewhere, e.g., on tomato in Colorado (4). During 2006 in Arizona, tomato plants in a large greenhouse facility with continuous tomato production exhibited viroid-like symptoms of plant stunting and chlorosis of the young leaves. Symptomatic plants were often located along the edge of the row, indicating the presence of a mechanical transmissible agent. Approximately 4% of the plants in this greenhouse were symptomatic in 2008. Symptoms were distinctly different from those caused by Pepino mosaic virus (PepMV), a virus that was generally present in this greenhouse and also in our test samples. Other commonly occurring tomato viruses were ruled out by serological, PCR, or reverse transcription (RT)-PCR tests in multiple laboratories. RT-PCR with two sets of universal pospiviroid primers, PospiI-FW/RE and Vid-FW/RE (4), yielded amplicons of the expected sizes of 196 and 360 bp in three samples collected from symptomatic plants. Direct sequencing of the amplicons revealed that the genome was 360 nt and 100% identical to the type TCDVd from Canada (GenBank Accession No. AF162131) (2). Mechanical inoculation with leaf tissue extract from four samples to plants of the tomato ‘Money-Maker’ resulted in the same viroid-like symptoms and TCDVd was confirmed in these plants by RT-PCR and sequencing. In both 2007 and 2008, 18 samples were tested using primers PSTVd-F and PSTVd-R (1), which are capable of amplifying the full TCDVd genome. Analysis of the sequences from the amplicons revealed two genotypes of TCDVd. The first genotype (GenBank Accession No. FJ822877) was identical to the type TCDVd and found in 11 samples from 2007 and one from 2008. The second genotype (GenBank Accession No. FJ822878) was 361 nt, differing from the first by nine nucleotide substitutions, 2 insertions, and 1 deletion. This second genotype was found in 7 and 17 samples from 2007 and 2008, respectively, and showed the highest sequence identity (97%) to a Japanese tomato isolate (AB329668) and a much lower sequence identity (92%) to a U.S. isolate previously identified in Colorado (AY372399) (4). The origin of TCDVd in this outbreak is not clear. The genotype identified first could have been introduced from a neighboring greenhouse where the disease was observed before 2006 and where this genotype also was identified in 2007. The second genotype may have been introduced from infected seed since TCDVd has recently been shown to be seed transmitted in tomato (3). To our knowledge, this is the first report of natural occurrence of TCDVd in Arizona. References: (1) A. M. Shamloul et al. Can. J. Plant Pathol. 19:89, 1997. (2) R. P. Singh et al. J. Gen. Virol. 80:2823, 1999. (3) R. P. Singh and A. D. Dilworth. Eur. J. Plant Pathol. 123:111, 2009. (4) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.

A field isolate of Potato virus Y (PVY) was collected in New Brunswick, Canada in 2007 due to unusual symptoms observed on different potato cultivars. To unveil the PVY strain identity, tobacco and potato bioassays, PVY

North American potato production differs from other geographical regions such as Europe in that it is essentially a closed system, i.e., seed potatoes are not imported and production is dominated by only a few cultivars. The lack of significant seed imports provides a mechanism for seed certification to be extremely effective at minimizing virus levels in seed lots, especially if the changes in seed laws, postharvest testing, and tolerance limits discussed above are adopted. This is an opportunity to effectively manage PVY at levels that are at or below detection and well below economic significance. Aiding the seed certification programs in the adoption of the Canada/US-Management Plan for Potato Viruses that Cause Tuber Necrosis has and continues to build consensus and cooperation within the industry to reform and modernize seed certification practices and, as importantly, modernize best management practices that growers can implement so that their production meets or exceeds virus tolerances set within the seed certification standards. Seed inspectors could also benefit from continually updated information from the research community to help them better recognize the spectrum of symptoms caused by the various strains and variants of PVY in all the different cultivars now being grown in their states and provinces. They could also benefit from improved field diagnostics that will assist them and the growers in identifying problem plants that should be rogued. If PVY levels in seed can be minimized and on-farm management strategies can be optimized, then PVY incidence in the potato crop will be marginalized. The restricted distribution of the tuber necrotic strains also offers an opportunity to prevent these strains from becoming economically significant if appropriate testing of seed lots in those areas could prevent them from being planted. Shipping point inspections of tubers will also help in identifying and eliminating tuber necrotic viruses. The dominance of a few cultivars has been eroding in recent years. Russet Burbank, a cultivar introduced over 100 years ago, still accounts for 40 to 50% of the U.S. acreage, but acreage in the Northwestern United States has been declining steadily as other russet cultivars come on the market and gain acceptance. Potato cultivar has had a significant impact on the PVY problem, as with the release and widespread acceptance of Shepody, Russet Norkotah, and other asymptomatic carriers of PVY (http://oregonstate. edu/potatoes/latenttoPVYlist.htm), which in 2008 comprised more than 15 and 12% of the total U.S. and Canadian seed acreage, respectively. These cultivars have certainly contributed to the overall increase in PVY in the seed potato crop and by extension the commercial potato crop. The increased diversity of potato cultivars grown in both countries has also introduced a wider spectrum of PVY symptoms, most notably the milder symptoms that are characteristic of the PVYN/NTN and PVYN-Wi strains on many cultivars. Since the success of seed certification is dependent upon visual assessment of the crop, mild or absent symptoms means that many more infected plants go unnoticed. The more symptomatic PVYO strains are observed and removed, but the other strains remain in the crop and are passed along in the seed, contributing to an overall increase in PVY incidence and more importantly to a shift in PVY strain composition. The U.S. and Canadian potato industry stakeholders are increasingly aware of the PVY-associated challenges and have been moving rapidly to work with researchers and all aspects of the industry to implement plans to suppress PVY incidence. Continued education of growers, seed certification officials, and researchers alike, coupled with the development and adoption of new or revised best management practices and diagnostic tools, and the renewed inter est of breeders to develop virus resistant cultivars, will be the keys to success in bringing PVY incidence under control and in minimizing tuber necrotic strains.

A field isolate of Potato virus Y (PVY) was collected in New Brunswick, Canada in 2007 due to unusual symptoms observed on different potato cultivars. To unveil the PVY strain identity, tobacco and potato bioassays, PVYO and PVYN-specific antibody-based enzyme-linked immunosorbent assays, and reverse-transcription polymerase chain reaction (PCR)-based genotyping were carried out. All the assays demonstrated that the isolate, designated as PVYO-FL in this study, belonged to the PVYO strain group. Greenhouse tests with the potato cvs. FL 1533 and Jemseg confirmed the severe nature of infection by PVYO-FL. The complete genome sequences of PVYO-FL and PVYO-RB, the latter a mild PVYO isolate, were determined. BLAST analysis revealed that the two isolates shared 97 and 98% sequence identities at the nucleotide and polyprotein levels, respectively. Further BLAST analysis unveiled that PVYO-FL shared 99.7% nucleotide sequence identity with PVYO-Oz, an isolate reported in New York, United States, whereas the PVYO-RB isolate shared 99.2% sequence identity with PVYO-139, a PVYO isolate reported in New Brunswick, Canada. A phylogenetic tree of available, full-length sequences of PVY isolates demonstrated two subgroups within the PVYO branch, one clustered with PVYO-RB and the other with PVYO-FL. Group-specific sense primers for differentiation of the two subgroups were developed and evaluated. A limited survey of potato tubers collected from a field plot at the Potato Research Centre, Agriculture and Agri-Food Canada, using the newly developed PCR primers, indicated that 65.3 and 2.4% of the PVYO-positive tubers were infected with PVYO isolates belonging to the PVYO-FL and PVYO-RB subgroups, respectively. Assessment of the pathogenicity of three representative isolates from each subgroup on the potato cv. Jemseg demonstrated that severe and mild symptoms were induced by the PVYO-FL-like and PVYO-RB-like isolates, respectively.

O Potato virus Y (PVY) tornou-se o maior problema nas áreas de produção de batata semente do Brasil. Somente as estirpes comum (PVYº) e necrótica (PVY N) eram detectadas infectando batata no Brasil. Esta situação mudou drasticamente a partir de 1997 quando um surto epidêmico de uma variante da estirpe necrótica de PVY causando arcos e anéis necróticos na superfície do tubérculo (PVY NTN) foi observado no país. Este estudo visou avaliar e validar uma metodologia de diferenciação de estirpes que causam necrose em tubérculos, proposta por Weilguny e Singh (1998). Vinte e oito isolados de PVY originários de tubérculos infectados de batata, provenientes de quatro estados brasileiros, foram analisados em sua reação em plantas de fumo, por Elisa, utilizando anti-soro policlonal e pelo método 3-primer RT-PCR. Quatro isolados induziram clareamento de nervuras e manchas peroladas em folhas de Nicotiana tabacum conforme esperado para a estirpe comum. Os 24 isolados restantes induziram necrose de nervuras neste hospedeiro portanto, classificados como da estirpe necrótica. Todos os 28 isolados de PVY reagiram positivamente contra o anti-soro policlonal de PVY por Elisa. Três métodos de extração de RNA foram testados, sendo que o método de hidrocloreto de guanidina mostrou-se o mais eficiente e de menor custo. Dos 28 isolados submetidos ao RT-PCR, um isolado de Santa Catarina e três do Rio Grande do Sul foram diferenciados como PVYº, confirmando os resultados do teste biológico. Um isolado de PVY N foi detectado no Estado de Santa Catarina e quatro no Rio Grande do Sul. O PVY NTN foi detectado em Minas Gerais (seis isolados), Santa Catarina (três isolados) e São Paulo (dez isolados). Estes resultados confirmam a presença dessa variante necrótica, PVY NTN, nas principais regiões produtoras de batata do Brasil.The Potato virus Y (PVY) has become the major virus problem in seed potato growing areas of Brazil. Only necrotic and ordinary PVY strains were found infecting potatoes in Brazil. This situation drastically changed around 1997 when an epidemic of a PVY necrotic variant causing necrotic rings on the potato tuber surface was observed in the country. This study aimed to test the tuber necrotic strain differentiation method proposed by Weilguny & Singh (1998). Twenty eight PVY isolates originated from infected tubers and leaves from four Brazilian States were analyzed by host reaction after inoculation in tobacco, by ELISA using polyclonal antiserum and by the 3-primer RT-PCR method. The ordinary strain type isolates induced vein clearing and chlorotic pearl spots on Nicotiana tabacum leaves. All 24 remaining isolates inducing vein necrosis in leaves were classified as necrotic strains. All 28 PVY isolates positively reacted to PVY polyclonal antiserum by Elisa. Three RNA extraction methods were compared and the guanidine hydrochloride method was the most efficient and of the lowest cost. One isolate from Santa Catarina State and three from Rio Grande do Sul out of 28 PVY isolates submitted to RT-PCR method were differentiated as PVYº, confirming the biological test. One isolate of PVY N was detected from Santa Catarina and four from Rio Grande do Sul State. The PVY NTN was detected in Minas Gerais (six isolates), Santa Catarina (three isolates) and São Paulo (ten isolates). These results confirmed the presence of this new variant, PVY NTN in the main potato growing areas of Brazil.

Potato (Solanum tuberosum L.) cv. Shepody is highly resistant to Potato virus A (PVA), yielding no visible symptoms after rub inoculation. In 'Shepody' rootstocks graft-inoculated by PVA-infected scions from a susceptible host, we found a resistance consisting of traces of necrosis (necrotic streaks) in stems and chlorosis in newly emerged leaves. The response was temperature dependent, appearing at 15 to 18 degrees C but not at 28 to 31 degrees C. Necrosis was also observed in tubers, appearing first in the bud end and spreading randomly throughout the majority of the tuber. Trace amounts of PVA in plant tissues were detected by a combination of reverse transcription polymerase chain reaction and Southern blot procedures. The virus concentration was significantly higher in visibly necrotic areas than in nonnecrotic areas, suggesting that presence of the necrosis may be concentration dependent. Pathogenesis-related gene expression showed that chitinase A and B, glucanase B, and PR-10a were associated with chlorotic or necrotic symptoms in leaves, stems, and tubers. Gene expression was markedly more evident in tuber tissues than in leaves and stems. Furthermore, generation of oxidants was also observed within the necrotic areas. Although PVA was detected in necrotic areas of tubers, newly emerged plants from the same tubers were PVA-free.

Potato is the fourth most important food crop in the world and it forms the diet of a billion consumers in developing countries, where potato production is increasing rapidly. However, potato virus diseases in developing countries are one of the major causes of lower yields. Their control requires the development of appropriate virus-detection and seed-production technologies for the region. Recent progress in developing nucleic acid based virus detection methods are reviewed. Refinements of the protocols applicable to the laboratories located in seed producing areas are discussed. Nucleic acid spot hybridization (NASH) and reverse transcription polymerase chain reaction (RT-PCR) methods are described for the detection of viruses and viroids in dormant seed tubers and insect vectors. Although the potato crop is susceptible to over 25 virus and viroid diseases, only universally economically important viruses have been dealt with here. The progress of pathogen-derived resistance for the control of potato virus diseases is elaborated, and the results of field tests indicate their feasibility in virus control.Key words: dot-blot, spot-hybridization, reverse transcription, polymerase chain reaction, transgenic plants.

In 1960s, potato spindle tuber was thought to be a viral disease. In 1971, the agent of the disease was characterised as a low-molecular weight infectious ribonucleic acid (RNA), which was named as ‘viroid’, specifically Potato spindle tuber viroid (PSTVd)). Since then, more than 30 plant diseases in horticultural and ornamental plants have been shown to be caused by different viroids globally. Viroids are single-stranded RNA, covalently closed circular molecule, without any protein coat. They are the smallest known plant pathogen containing RNA genome ranging from 246 nucleotides (Coconut cadang–cadang viroid) to 399 nucleotides (Chrysanthemum chlorotic mottle viroid). Some viroids are located in the plant cell nucleus (pospiviroids) and others in the chloroplast (avsunviroids). With the recognition of pathogenic nature of viroid, specific detection methodologies were developed, which enabled detection of PSTVd in seed-potato tubers prior to their planting in the field, and thus PSTVd was prevented from spreading the disease. As a result, PSTVd was eradicated from Canada in late 1980s. Viroids similar to PSTVd (Pospiviroid) have been discovered and they are detected in symptomless ornamental plants. Although, PSTVd has been eradicated from Canada, there is a strong possibility of viroid introduction from other plants besides potato and tomato and causing PSTVd like diseases.

In the highlands of Ethiopia, tillage methods and frequency affect drainage, soil erosion, moisture conservation, weeding and harvesting of crops. This is through their effects on soil physical, chemical and biological qualities. In this study, four tillage methods for land preparation, “broad bed and furrows”,” green manure”, “reduced tillage “and the traditional tillage “ridge and furrows” were evaluated for their effects on soil physical quality indicators. The study was superimposed on the field experiment conducted on a vertisol area at Caffee doonsa for five years (1998 to 2002) in the central highland of Ethiopia. Penetration resistance (PR), aggregate stability, water-holding capacity, crust strength and thickness, texture, porosity, saturated hydraulic conductivity, bulk density and water holding capacity were the soil physical quality indicators considered. The result indicated that only PR was significantly (p

Piche, L. M., Singh, R. P., Nie, X., and Gudmestad, N. C. 2004. Diversity among Potato virus Y isolates obtained from potatoes grown in the United States. Phytopathology 94:1368-1375. Potato field isolates (Solanum tuberosum) of Potato virus Y (PVY) collected from the midwestern and western United States were characterized using serological, molecular, and biological assays. PVY field isolates were grouped into the previously defined categories: PVY O , European PVYNTN, North American PVYNTN, and PVYN:O recombinant and four previously undefined groups. Studies reported here agree with published reports from Europe and elsewhere in North America as PVY isolates capable of causing veinal necrosis in tobacco indicator plants appear in high frequency. In contrast to European experiences, PVY tuber necrosis isolates have a PVY O coat protein rather than that of PVY N . Several PVYN:O recombinant isolates induced potato tuber necrotic ringspot disease (PTNRD) in the highly susceptible potato cv. Yukon Gold. The PTNRD symptoms produced by these PVYN:O recombinants were atypical compared with lesions found on the same cultivar infected with either the European or North American PVYNTN isolates. These PVYN:O isolates produced a roughly circular, sunken necrotic lesion on the surface of the tuber instead of the typical external sunken ring pattern displayed by PVY NTN isolates. This study establishes the complex nature of PVY populations within the U.S. potato industry and clearly demonstrates the diverse nature of PVY in the United States. Potato virus Y (PVY) belongs to the largest plant virus family, Potyviridae. The most common PVY strains affecting potatoes are differentiated by reaction on potato (Solanum tuberosum L.) and tobacco (Nicotiana tabacum L.). Several strains of PVY are known. PVY O (the “ordinary” strain) is ubiquitous among potato production areas, causing mild to severe mosaic symptoms, depending on the cultivar. This PVY strain was first classified in

O Potato virus Y (PVY) tornou-se o maior problema nas áreas de produção de batata semente do Brasil. Somente as estirpes comum (PVYº) e necrótica (PVY N) eram detectadas infectando batata no Brasil. Esta situação mudou drasticamente a partir de 1997 quando um surto epidêmico de uma variante da estirpe necrótica de PVY causando arcos e anéis necróticos na superfície do tubérculo (PVY NTN) foi observado no país. Este estudo visou avaliar e validar uma metodologia de diferenciação de estirpes que causam necrose em tubérculos, proposta por Weilguny e Singh (1998). Vinte e oito isolados de PVY originários de tubérculos infectados de batata, provenientes de quatro estados brasileiros, foram analisados em sua reação em plantas de fumo, por Elisa, utilizando anti-soro policlonal e pelo método 3-primer RT-PCR. Quatro isolados induziram clareamento de nervuras e manchas peroladas em folhas de Nicotiana tabacum conforme esperado para a estirpe comum. Os 24 isolados restantes induziram necrose de nervuras neste hospedeiro portanto, classificados como da estirpe necrótica. Todos os 28 isolados de PVY reagiram positivamente contra o anti-soro policlonal de PVY por Elisa. Três métodos de extração de RNA foram testados, sendo que o método de hidrocloreto de guanidina mostrou-se o mais eficiente e de menor custo. Dos 28 isolados submetidos ao RT-PCR, um isolado de Santa Catarina e três do Rio Grande do Sul foram diferenciados como PVYº, confirmando os resultados do teste biológico. Um isolado de PVY N foi detectado no Estado de Santa Catarina e quatro no Rio Grande do Sul. O PVY NTN foi detectado em Minas Gerais (seis isolados), Santa Catarina (três isolados) e São Paulo (dez isolados). Estes resultados confirmam a presença dessa variante necrótica, PVY NTN, nas principais regiões produtoras de batata do Brasil. The Potato virus Y (PVY) has become the major virus problem in seed potato growing areas of Brazil. Only necrotic and ordinary PVY strains were found infecting potatoes in Brazil. This situation drastically changed around 1997 when an epidemic of a PVY necrotic variant causing necrotic rings on the potato tuber surface was observed in the country. This study aimed to test the tuber necrotic strain differentiation method proposed by Weilguny & Singh (1998). Twenty eight PVY isolates originated from infected tubers and leaves from four Brazilian States were analyzed by host reaction after inoculation in tobacco, by ELISA using polyclonal antiserum and by the 3-primer RT-PCR method. The ordinary strain type isolates induced vein clearing and chlorotic pearl spots on Nicotiana tabacum leaves. All 24 remaining isolates inducing vein necrosis in leaves were classified as necrotic strains. All 28 PVY isolates positively reacted to PVY polyclonal antiserum by Elisa. Three RNA extraction methods were compared and the guanidine hydrochloride method was the most efficient and of the lowest cost. One isolate from Santa Catarina State and three from Rio Grande do Sul out of 28 PVY isolates submitted to RT-PCR method were differentiated as PVYº, confirming the biological test. One isolate of PVY N was detected from Santa Catarina and four from Rio Grande do Sul State. The PVY NTN was detected in Minas Gerais (six isolates), Santa Catarina (three isolates) and São Paulo (ten isolates). These results confirmed the presence of this new variant, PVY NTN in the main potato growing areas of Brazil.

In this work, we report cloning of two full-length 1-aminocyclopropane-1-carboxylate oxidase (ACO) cDNAs (ACO1 and ACO2) from potato (Solanum tuberosum) and their expression in potato tissues. The sequence data indicate that the two cDNAs share a high degree of homology with each other, and with known ACO genes from other plant species, including monocots and dicots. However, these potato genes lack homology at the 5' and 3' ends, despite similarities in their open reading frames and encoded amino acids. Phylogenetic analysis places them in two subfamilies of ACOs. The genes are tissue specific: expression is high in leaves and low in roots and tubers. In sprouts and tubers, ACO1 is induced by heat (40°C) and cold (0°C) stresses, whereas ACO2 is induced only by cold (0°C). ACO1 is markedly induced in leaves by wounding, soil-flooding, and exogenous application of 1-aminocyclopropane-1-carboxylic acid (ACC). In contrast, ACO2 induction is lower under these treatments. ACO1 and ACO2 are regulated very differently in potato leaves with respect to senescence. ACO2 expression is unaffected by senescence, whereas that of ACO1 is closely related to the age and senescence in both attached and detached leaves. Exogenous ACC not only induces ACO1, but also accelerates leaf senescence. ACO1 transcripts are induced significantly in leaves, stems, and tubers in the Potato virus A (PVA)-resistant potato cultivar Shepody when graft inoculated with PVA.Key Words: ACO, ethylene, gene isolation, phylogeny, Solanum tuberosum.

This study aimed to assess the impacts of ultraviolet-B (UV-B) radiation over a 28-day period on the levels of pigments of Umbilicaria aprina and Bryum argenteum growing in field. The depletion of stratospheric ozone is most prominent over Antarctica, which receives more UV-B radiation than most other parts of the planet. Although UV-B radiation adversely affects all flora, Antarctic plants are better equipped to survive the damaging effects of UV-B owing to defenses provided by UV-B absorbing compounds and other screening pigments. The UV-B radiations and daily average ozone values were measured by sun photometer and the photosynthetic pigments were analyzed by the standard spectrophotometric methods of exposed and unexposed selected plants. The daily average atmospheric ozone values were recorded from 5 January to 2 February 2008. The maximum daily average for ozone (310.7 Dobson Units (DU)) was recorded on 10 January 2008. On that day, average UV-B spectral irradiances were 0.016, 0.071, and 0.186 W m ­2 at wavelengths of 305, 312, and 320 nm, respectively. The minimum daily average ozone value (278.6 DU) was recorded on 31 January 2008. On that day, average UV-B spectral irradiances were 0.018, 0.085, and 0.210 W m ­2 at wavelengths of 305, 312, and 320 nm, respectively. Our results concludes that following prolonged UV-B exposure, total chlorophyll levels decreased gradually in both species, whereas levels of UV-B absorbing compounds, phenolics, and carotenoids gradually increased.

Columnea latent viroid, originating from ornamental plants, is known to be harmful to crop plants (2). Despite the potential threat to crop plants, the importance of ornamental plants in viroid evolution is not fully appreciated. Availability of a Pospiviroid genus-specific primer pair (1) to detect the most prevalent viroids in ornamental plants and a simplified nucleic acid preparation protocol (3) for use in reverse-transcription polymerase chain reaction (RT-PCR) have facilitated surveys of ornamental plants for pospiviroids. Using the above protocol in India, leaf and shoot samples were collected randomly from roadside beds consisting of ground covers or creepers/trailing plants at the IARI campus, New Delhi. These were extracted in 50 mM NaOH + 2.5 mM EDTA solution, centrifuged to sediment the coarse debris from sap, and 10 μl of the supernatant was spotted on a nitrocellulose membrane. Individual spots were eluted with distilled sterile water (30 μl) and the eluates were used for RT-PCR detection of viroids (3). Amplified fragments or subsequently cloned plasmids were also purified using NaOH-EDTA membrane protocol. Cloning and sequencing of amplicons (195 to 224 bp) revealed a very high sequence identity with specific viroids from the viroid sequence database (NCBI). Among the 19 plant samples assayed, only three plant species were infected by viroids, although none of them exhibited any symptoms. The three plant species included: (i) moss verbena, Glandularia puchella (Verbenaceae, native to Argentina and Chile, now established in several regions of the world), infected with a viroid (Accession No. DQ846884) having 99% sequence identity to Citrus exocortis viroid (CEVd) (Accession No. S67446); (ii) trailing verbena, Verbena × hybrida (Verbenaceae, ornamental plant), doubly infected with a viroid (Accession No. DQ846885) having 95% sequence identity to CEVd (Accession No. DQ094297) and infected with another viroid (Accession No. DQ846883) having 98% sequence identity to Tomato chlorotic dwarf viroid (TCDVd) (Accession No. AF162131); and (iii) red joyweed, Alternanthera sessilis (Amaranthaceae, a perennial weed herb) infected with a viroid (Accession No. DQ846886) having 96% sequence identity to Iresine viroid (IrVd) (Accession No. DQ094293). CEVd and TCDVd were mechanically transferred to tomato seedlings causing reduced growth of plants, smaller leaves, and bunchy-top appearance of plants, symptoms similar to those typically observed with other isolates of these viroids. As expected from previous studies, IrVd was not transmitted to tomato plants. Natural infection of verbena with CEVd has been detected in North America (2) but this was a novel observation in India. Additional novel observations include: A. sessilis as a new host for IrVd; and TCDVd is the first crop viroid to be isolated from a naturally infected ornamental plant. The significance of these viroid findings in ground cover and widely grown ornamental plants may lie in their potential role in spreading the viroids to citrus plants in citrus-growing countries such as India. References: (1) H. Bostan et al. J. Virol. Methods 116:189, 2004, (2) R. P. Singh and J. A. Teixeira da Silva. Floriculture, Ornamental Plant Biotechnol. 3:531, 2006. (3) R. P. Singh et al. J. Virol. Methods 132:204, 2006.

Using enzyme-linked immunosorbent assay (ELISA) and potato plantlets of cultivars Green Mountain, Red Pontiac, Russet Burbank and Shepody, potato virus S (PVS) was detected in primary infected plants under field conditions. Potato virus S was detected 3 wk postinoculation (p.i.) from the field-grown plants as compared to 2 wk p.i. from greenhouse-grown plants. Potato virus S concentration in infected plants remained high throughout the growing season. The ELISA test using dormant tubers was not reliable because A405 nm values overlapped between infected and healthy tubers. Exposure of healthy plants to PVS sources in the field resulted in high infections with PVS by the 9th wk of growth. This pattern of infection suggests involvement of aerial vectors in the transmission of PVS under conditions of the Atlantic region of Canada.Key words: Current year infection, ELISA, dormant tubers, spread of PVS