@article{ristaino_groves_parra_2001, title={PCR amplification of the Irish potato famine pathogen from historic specimens}, volume={411}, ISSN={["1476-4687"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035822055&partnerID=MN8TOARS}, DOI={10.1038/35079606}, abstractNote={Late blight, caused by the oomycete plant pathogen Phytophthora infestans, is a devastating disease of potato and was responsible for epidemics that led to the Irish potato famine in 1845 (refs 1,2,3,4,5). Before the 1980s, worldwide populations of P. infestans were dominated by a single clonal lineage, the US-1 genotype or Ib mitochondrial DNA (mtDNA) haplotype, and sexual reproduction was not documented outside Mexico, the centre of diversity of the pathogen. Here we describe the amplification and sequencing of 100-base-pair fragments of DNA from the internal transcribed spacer region 2 from 28 historic herbarium samples including Irish and British samples collected between 1845 and 1847, confirming the identity of the pathogen. We amplified a variable region of mtDNA that is present in modern Ib haplotypes of P. infestans, but absent in the other known modern haplotypes (Ia, IIa and IIb). Lesions in samples tested were not caused by the Ib haplotype of P. infestans, and so theories that assume that the Ib haplotype is the ancestral strain need to be re-evaluated. Our data emphasize the importance of using historic specimens when making inferences about historic populations.}, number={6838}, journal={NATURE}, author={Ristaino, JB and Groves, CT and Parra, GR}, year={2001}, month={Jun}, pages={695–697} }
 @article{parra_ristaino_2001, title={Resistance to mefenoxam and metalaxyl among field isolates of Phytophthora capsici causing Phytophthora blight of bell pepper}, volume={85}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.2001.85.10.1069}, abstractNote={ Incidence of Phytophthora blight in bell pepper fields that were sprayed for the first time with Ridomil Gold (mefenoxam) according to labeled recommendations was higher in North Carolina in 1997 than in previous years. Mefenoxam is the more active enantiomer contained in the racemic fungicide metalaxyl. A total of 150 isolates were obtained from 17 fields at eight grower locations. Among isolates from all locations, 30% were classified as sensitive, 10% as intermediate, and 59% were resistant to mefenoxam. Mefenoxam-resistant isolates were found in 82% of the fields sampled (14 of 17 fields). The proportion of resistant isolates in individual (fields ranged from 28 to 100%. The mean effective concentration (EC50) values for mefenoxam-sensitive isolates was 0.568 μg ml-1 (ranging from 0.12 to 1.1 μg ml-1), whereas the mean EC50 value for mefenoxam-resistant isolates was 366.5 μg ml-1 (ranging from 3 to 863 μg ml-1). The mean EC50 value for metalaxyl-sensitive isolates was 0.27 μg ml-1 (ranging from 0.00002 to 1.3 μg ml-1) and for metalaxyl-resistant isolates was 470.34 μg ml-1 (ranging from 10 to 966 μg ml-1). The greatest proportion of resistant isolates came from fields where mefenoxam was used alone rather than in combination with other fungicides. Both mating types were found among resistant isolates, suggesting that these isolates may persist in soil in subsequent years. Field isolates of Phytophthora capsici resistant to mefenoxam on pepper have not been reported previously and now pose new challenges for management of this important disease. }, number={10}, journal={PLANT DISEASE}, author={Parra, G and Ristaino, JB}, year={2001}, month={Oct}, pages={1069–1075} }
 @article{sujkowski_parra_gumpertz_ristaino_2000, title={Temporal dynamics of Phytophthora blight on bell pepper in relation to the mechanisms of dispersal of primary inoculum of Phytophthora capsici in soil}, volume={90}, ISSN={["0031-949X"]}, DOI={10.1094/phyto.2000.90.2.148}, abstractNote={ The effect of components of primary inoculum dispersal in soil on the temporal dynamics of Phytophthora blight epidemics in bell pepper was evaluated in field and growth-chamber experiments. Phytophthora capsici may potentially be dispersed by one of several mechanisms in the soil, including inoculum movement to roots, root growth to inoculum, and root-to-root spread. Individual components of primary inoculum dispersal were manipulated in field plots by introducing (i) sporangia and mycelia directly in soil so that all three mechanisms of dispersal were possible, (ii) a plant with sporulating lesions on the soil surface in a plastic polyvinyl chloride (PVC) tube so inoculum movement to roots was possible, (iii) a wax-encased peat pot containing sporangia and mycelia in soil so root growth to inoculum was possible, (iv) a wax-encased peat pot containing infected roots in soil so root-to-root spread was possible, (v) noninfested V8 vermiculite media into soil directly as a control, or (vi) wax-encased noninfested soil as a control. In 1995 and 1996, final incidence of disease was highest in plots where sporangia and mycelia were buried directly in soil and all mechanisms of dispersal were operative (60 and 32%) and where infected plants were placed in PVC tubes on the soil surface and inoculum movement to roots occurred with rainfall (89 and 23%). Disease onset was delayed in 1995 and 1996, and final incidence was lower in plants in plots where wax-encased sporangia (6 and 22%) or wax-encased infected roots (22%) were buried in soil and root growth to inoculum or root-to-root spread occurred. Incidence of root infections was higher over time in plots where inoculum moved to roots or all mechanisms of dispersal were possible. In growth-chamber studies, ultimately all plants became diseased regardless of the dispersal mechanism of primary inoculum, but disease onset was delayed when plant roots had to grow through a wax layer to inoculum or infected roots in tension funnels that contained small volumes of soil. Our data from both field and growth-chamber studies demonstrate that the mechanism of dispersal of the primary inoculum in soil can have large effects on the temporal dynamics of disease. }, number={2}, journal={PHYTOPATHOLOGY}, author={Sujkowski, LS and Parra, GR and Gumpertz, ML and Ristaino, JB}, year={2000}, month={Feb}, pages={148–156} }
 @article{parra_ristaino_1998, title={Insensitivity to Ridomil Gold (Mefenoxam) found among field isolates of phytophthora capsici causing phytophthora blight on bell pepper in North Carolina and New Jersey}, volume={82}, DOI={10.1094/pdis.1998.82.6.711d}, abstractNote={ Phytophthora blight caused by the pathogen Phytophthora capsici has caused economic losses in bell pepper and cucurbit fields in the U.S., and the prevalence of the disease has increased in recent years. The pathogen can be dispersed in soil, with surface water, and via splash dispersal from the soil to foliage. Management of the disease relies on modifications in cultural practices, crop rotation, and judicious use of fungicides. Disease occurred in fields that were sprayed with multiple applications of Ridomil Gold (mefenoxam) according to labeled recommendations in 1997. Mefenoxam is the active enantiomer contained in the racemic fungicide metalaxyl. Mefenoxam was widely used on bell pepper for the first time in 1997, but disease was widespread. Insensitivity to mefenoxam and metalaxyl has not been reported previously in field isolates of P. capsici. However, selection for metalaxyl insensitive isolates in the laboratory after mutagenesis has been reported. Insensitivity to metalaxyl has been reported among other Oomycete pathogens including Phytophthora infestans, Pseudoperonospora cubensis, Peronospora tabacina, Bremia lactucae, and Pythium spp. Infected plants were collected from 12 fields in North Carolina by the authors and one additional field in New Jersey (courtesy of Steve Johnston). Infected plants (10 to 30 per field) were surface disinfested in 10% bleach and plated on selective media to isolate P. capsici. Colonies of the pathogen were transferred to V8 juice agar or maintained on cornmeal agar slants. Mefenoxam-amended V8 juice agar was prepared at levels of 0, 5, and 100 ppm. Screening for sensitivity was conducted by placing agar plugs containing the pathogen onto two replicate plates of mefenoxam-amended media at each concentration. Isolates were categorized as sensitive if growth was less than 40% of the unamended control at 5 ppm. Intermediate isolates exhibited growth greater than 40% of the unamended control at 5 ppm but less than 40% of the unamended control at 100 ppm mefenoxam. Insensitive isolates exhibited growth greater than 40% of the unamended control at 100 ppm mefenoxam. Concentrations of the fungicide used to screen for insensitivity were within the range applied in the field. Thus far, 161 isolates have been screened for sensitivity. Of these, 54 isolates were classified as sensitive, 15 as intermediate, and 92 or 57% of the isolates were insensitive. Three quarters of the fields sampled contained insensitive isolates and insensitivity ranged from 11 to 80% within fields. Both A1 and A2 mating types were recovered from some fields and insensitive isolates occurred among both mating types. Isolates that were insensitive to mefenoxam were also insensitive to metalaxyl. A significant proportion of the isolates obtained from infected plants in fields where Ridomil Gold has been used recently were insensitive. The ability of insensitive isolates to cause disease on fungicide-treated plants will be studied in further experiments. Isolates collected between 1988 and 1994 were screened and all isolates were sensitive to metalaxyl (Ridomil 2E). A dramatic shift in populations of P. capsici to insensitivity to the new metalaxyl substitute mefenoxam has occurred in bell pepper fields in a 3-year period. }, number={6}, journal={Plant Disease}, author={Parra, G. and Ristaino, Jean}, year={1998}, pages={711} }
 @article{ristaino_madritch_trout_parra_1998, title={PCR amplification of ribosomal DNA for species identification in the plant pathogen genus Phytophthora}, volume={64}, number={3}, journal={Applied and Environmental Microbiology}, author={Ristaino, J. B. and Madritch, M. and Trout, C. L. and Parra, G.}, year={1998}, pages={948–954} }
 @inproceedings{ristaino_parra_campbell_1997, title={Effect of inoculum source type and cultural practices on the spread of Phytophthora capsici in bell pepper}, number={1997}, booktitle={Soil solarization and integrated management of soilborne pests: Proceedings of the Second International Conference on Soil Solarization and Integrated Management of Soilborne Pests, Aleppo, Syrian Arab Republic, 16-21 March 1997}, publisher={Rome: Food and Agriculture Organization of the United}, author={Ristaino, J. B. and Parra, G. and Campbell, C. L.}, editor={J. J. Stapleton, J. E. DeVay and Elmore, C. L.Editors}, year={1997} }
 @article{ristaino_parra_campbell_1997, title={Suppression of Phytophthora blight in bell pepper by a no-till wheat cover crop}, volume={87}, ISSN={["0031-949X"]}, DOI={10.1094/PHYTO.1997.87.3.242}, abstractNote={ Four mechanisms of dispersal of propagules of Phytophthora capsici were investigated through modifications in cultural practices and fungicide applications in field plots of bell pepper (Capsicum annuum). Dispersal of soil inoculum was suppressed, and final incidence of disease was 2.5 to 43% when stubble from a fall-sown, no-till, wheat cover crop was present. Final disease incidence was 71 to 72% and pathogen spread occurred within and across rows when all dispersal mechanisms were operative in plots of pepper planted into bare soil. Final disease incidence was 42 to 78% with black plastic mulch when a sporulating pepper fruit placed on the surface served as the source of initial inoculum. The fungicide metalaxyl applied in the irrigation system did not suppress within-row spread of surface inoculum from a sporulating fruit on plastic, but did limit across-row spread; final disease incidence in metalaxyl-treated plots was 11.5 to 14%. Pathogen dispersal mechanisms were modified most dramatically by the no-till cropping system. Thus, simple changes in cultural practices can have dramatic effects on the development of Phytophthora epidemics. Ecologically based disease management strategies have the potential to reduce our reliance on agrichemicals in this and similar pathosystems. }, number={3}, journal={PHYTOPATHOLOGY}, author={Ristaino, JB and Parra, G and Campbell, CL}, year={1997}, month={Mar}, pages={242–249} }