Showing papers by "Jean B. Ristaino published in 2012"

Recent Genotypes of Phytophthora infestans in the Eastern United States Reveal Clonal Populations and Reappearance of Mefenoxam Sensitivity.

Abstract: Isolates of Phytophthora infestans (n = 178) were collected in 2002 to 2009 from the eastern United States, Midwestern United States, and eastern Canada. Multilocus genotypes were defined using allozyme genotyping, and DNA fingerprinting with the RG-57 probe. Several previously described and three new mulitilocus genotypes were detected. The US-8 genotype was found commonly on commercial potato crops but not on tomato. US-20 was found on tomato in North Carolina from 2002 through 2007 and in Florida in 2005. US-21 was found on tomato in North Carolina in 2005 and Florida in 2006 and 2007. US-22 was detected on tomato in 2007 in Tennessee and New York and became widespread in 2009. US-22 was found in 12 states on tomato and potato and was spread on tomato transplants. This genotype accounted for about 60% of all the isolates genotyped. The US-23 genotype was found in Maryland, Virginia, Pennsylvania, and Delaware on both tomato and potato in 2009. The US-24 genotype was found only in North Dakota in 2009. A1 and A2 mating types were found in close proximity on potato and tomato crops in Pennsylvania and Virginia; therefore, the possibility of sexual reproduction should be monitored. Whereas most individuals of US-8 and US-20 were resistant to mefenoxam, US-21 appeared to be intermediately sensitive, and isolates of US-22, US-23, and US-24 were largely sensitive to mefenoxam. On the basis of sequence analysis of the ras gene, these latter three genotypes appear to have been derived from a common ancestor. Further field and laboratory studies are underway using simple sequence repeat genotyping to monitor current changes in the population structure of P. infestans causing late blight in North America.

A universal microarray detection method for identification of multiple Phytophthora spp. using padlock probes.

Abstract: The genus Phytophthora consists of many species that cause important diseases in ornamental, agronomic, and forest ecosystems worldwide. Molecular methods have been developed for detection and identification of one or several species of Phytophthora in single or multiplex reactions. In this article, we describe a padlock probe (PLP)-based multiplex method of detection and identification for many Phytophthora spp. simultaneously. A generic TaqMan polymerase chain reaction assay, which detects all known Phytophthora spp., is conducted first, followed by a species-specific PLP ligation. A 96-well-based microarray platform with colorimetric readout is used to detect and identify the different Phytophthora spp. PLPs are long oligonucleotides containing target complementary sequence regions at both their 5' and 3' ends which can be ligated on the target into a circular molecule. The ligation is point mutation specific; therefore, closely related sequences can be differentiated. This circular molecule can then be detected on a microarray. We developed 23 PLPs to economically important Phytophthora spp. based upon internal transcribed spacer-1 sequence differences between individual Phytophthora spp. Tests on genomic DNA of many Phytophthora isolates and DNA from environmental samples showed the specificity and utility of PLPs for Phytophthora diagnostics.

Parallels in intercellular communication in oomycete and fungal pathogens of plants and humans.

Abstract: Sexual reproduction is one of the most fascinating evolutionary outcomes in nature. Sexual development is paradoxical, conferring both benefits and costs, which makes sex an attractive subject in evolutionary biology. In pathogenic microbes, sexual development generates progeny with diverse genetic repertoires and can contribute to create more virulent genotypes. Sexual reproduction is ubiquitous in eukaryotic organisms, from single-celled yeasts to humans. Mating systems are highly adapted in each group and vary from species to species, which results in extremely diverse sexual modes throughout nature. However, in some cases, quite divergent groups share similar mechanisms. This review describes a similarity in pheromone synthesis routes in two group of microbial pathogens of historic importance that are evolutionarily quite distinct: zygomycete pathogenic fungi that belong to the kingdom Fungi in the opisthokonts clade, and Phytophthora oomycete species that belong to the stramenopile supergroup [1] (Figure 1). Figure 1 Eukaryotic tree of life (adapted from Baldauf, Science, 2003 [1], with her permission). Historical Aspects of the Two Evolutionarily Distinct Pathogenic Molds: Mucoralean Fungi and Phytophthora Mucorales of the fungal Zygomycota and Phytophthora in the oomycetes have historical significance. One of the Mucor species belonging to the Mucoralean order was the first microbe ever observed in detail by the human eye via Robert Hooke's microscope. Hooke described the microscopic structures of this mold in his book Micrographia [2]. In addition, the first description of sexual development in fungi was of a Mucoralean species nearly two hundred years ago [3]. Several fungal species in the Mucoralean order are the causal agents of mucormycosis, a deadly fungal infection. These species include Rhizopus spp., Mucor spp., Rhizomucor spp., Absidia spp., Cunninghemella spp., and others [4]. Mucormycosis is an emerging, serious fungal infection with high mortality rates. A recent mucormycosis outbreak occurred in victims of the tornadoes in Joplin, Missouri, United States. Oomycetes such as Phytophthora spp. were previously considered members of the fungal kingdom. However, more recent molecular analyses revealed oomycetes are not true fungi but instead divergent stramenopiles that are more closely related to the diatoms and brown alga, with only one known human pathogen in the group: Blastocystis hominis [5]. Phytophthora spp are known as notorious plant destroyers. Phytophthora infestans exemplifies this threat; it was the first species described in the genus and left a path of devastation in its wake on potato crops in the US, Ireland, and Europe in the 19th century [6]. Movement of infected potato tubers led to the potato famine epidemics of the 19th century, which resulted in widespread human hunger, disease, and ultimately the death of 2 million people in Ireland. The pathogen is still a threat to food security in the developing world.

A Lucid Key to the Common Species of Phytophthora.

Abstract: The Key to the Common Phytophthora species (Lucid v 3.4) is a matrix-based computerized identification key and includes important morphological and molecular characters that are useful for identification of 55 common species of Phytophthora. A set of 20 features are used to make a correct species identification. Once a culture is obtained, the user enters responses to known character state options into Lucid Player, and the correct species is identified. Illustrations of each character state for a feature are included in the key. The main morphological features included in the key are: asexual structures, sexual structures, and chlamydospore, hyphae, and cultural characteristics. The user can read an illustrated “Fact Sheet” on each species that includes pictures of morphological characters, disease symptoms, host range, and relevant references. A cross-linked glossary of terminology is included in each fact sheet. In addition, a DNA search function that contains a simple search of internal trans...

Ten polymorphic microsatellite loci identified from a small insert genomic library for Peronospora tabacina.

Abstract: Ten polymorphic microsatellite loci for the obligate biotrophic, oomycete pathogen of tobacco, Peronospora tabacina, were identified from a small insert genomic library enriched for GT motifs. Eighty-five percent of the 162 loci identified were composed of dinucleotide repeats, whereas only 4% and 11% were tri- and tetra-nucleotide repeats respectively. About 82% of all the microsatellites were perfect and within the library; only about 7% of the loci were duplicated. Primers were designed for 63 loci; 10 loci were polymorphic, 19 were monomorphic and 34 either failed to amplify or produced ambig- uous/inconsistent results. The 10 polymorphic loci were characterized with 44 isolates of P. tabacina collected from tobacco plants growing in Europe, the Near East and North and South America. The number of alleles per locus was either three or four with a mean of 3.2, and the mean number of genotypes per locus was 3.6. Observed heterozygosity was 0.32-0.95, whereas expected heterozygosity was 0.44-0.69 for these loci. All loci except PT054 did not conform to the Hardy-Weinberg distribution. Poly- morphic information content (PIC) for the loci was 0.35-0.69 with a mean of 0.50. These microsatellite loci provide a set of markers sufficient to perform genetic diversity and population studies of P. tabacina, and possibly other species of Peronospora.