Exploring the Mycovirus Sclerotinia sclerotiorum Hypovirulence-Associated DNA Virus 1 as a Biocontrol Agent of White Mold Caused by Sclerotinia sclerotiorum.

Sclerotinia sclerotiorum is a necrotrophic fungal pathogen causing white mold on many important economic crops. Recently, some mycoviruses such as S. sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1) converted S. sclerotiorum into a beneficial symbiont that helps plants manage pathogens and other stresses. To explore the potential use of SsHADV-1 as a biocontrol agent in the United States and to test the efficacy of SsHADV-1-infected United States isolates in managing white mold and other crop diseases, SsHADV-1 was transferred from the Chinese strain DT-8 to United States isolates of S. sclerotiorum. SsHADV-1 is readily transmitted horizontally among United States isolates of S. sclerotiorum and consistently conferred hypovirulence to its host strains. Biopriming of dry bean seeds with hypovirulent S. sclerotiorum strains enhanced resistance to white mold, gray mold, and Rhizoctonia root rot. To investigate the underlying mechanisms, endophytic growth of hypovirulent S. sclerotiorum in dry beans was confirmed using PCR, and the expression of 12 plant defense-related genes were monitored before and after infection. The results indicated that the endophytic growth of SsHADV-1-infected strains in plants stimulated the expression of plant immunity pathway genes that assisted a rapid response from the plant to fungal infection. Finally, application of the seed biopriming technology with SsHADV-1-infected hypervirulent strain has promise for the biological control of several diseases of wheat, pea, and sunflower.

Suitable Methods of Inoculation and Quantification of Fusarium Root Rot in Lentil.

Lentil (Lens culinaris L. subsp. culinaris) is an important grain legume grown worldwide. As its popularity grows among consumers and more acres are produced, new root rot complexes have become more prevalent. This work sought to develop methods for studying root rot caused by Fusarium avenaceum in lentil using controlled environments. The objectives were to (i) find an effective and seed-safe sterilization technique, (ii) optimize the inoculation technique and lentil growing environment, and (iii) develop visual and automated disease scoring systems. Results showed the use of detergent and a low concentration (0.1%) of NaClO (the active ingredient in bleach) maintained germinability and effectively eliminated bacterial and fungal contamination on seeds. Other treatments, such as ethanol, reduced seed germination or failed to kill pathogenic fungi such as Fusarium spp. Placing inoculum at a moderate rate of 1 × 106 spores both directly on the seed and on top of the media covering the seed improved severity scores and reduced escapes compared with placement on top of the media only. Visual severity scoring systems and diagrammatic scales were developed for scoring the cotyledon region and roots. A computer vision algorithm was designed to improve the efficiency of scoring the cotyledon region and roots for disease severity using a simple RGB camera and lightbox. Visual and computer scores were best correlated when images were visually scored on a monitor, and multiple images were averaged. The scores generated from the computer vision algorithm had better correlations with visual scores for cotyledon rot (r = 0.92 and ß1 = 0.96) than root rot (r = 0.62 and ß1 = 0.67).

Phenotypic and Genetic Characterization of the Lentil Single Plant-Derived Core Collection for Resistance to Root Rot Caused by Fusarium avenaceum.

Lentil (Lens culinaris) is a pulse crop grown for its amino acid profile, moderate drought tolerance, and ability to fix nitrogen. As the global demand for lentils expands and new production regions emerge so too have the complement of diseases that reduce yield, including the root rot complex. Although the predominant causal pathogen varies based on growing region, Fusarium avenaceum is often found to be an important contributor to disease. This study screened part of the lentil single plant-derived core collection for resistance to F. avenaceum in a greenhouse. Plants were phenotyped for disease severity using three scoring scales and the differences in biomass traits due to pathogen presence were measured. Lentil accessions varied in disease severity and differences in biomass traits were found to be correlated with each visual severity estimate (r = -0.37 to -0.63, P < 0.001), however, heritability estimates were low to moderate among traits (H2 = 0.12 to 0.43). Results of a genome-wide association study (GWAS) using single nucleotide polymorphism (SNP) markers derived from genotyping-by-sequencing revealed 11 quantitative trait loci (QTL) across four chromosomes. Two pairs of QTL colocated for two traits and were found near putative orthologs that have been previously associated with plant disease resistance. The identification of lentil accessions that did not exhibit a difference in biomass traits may serve as parental material in breeding or in the development of biparental mapping populations to further validate and dissect the genetic control of resistance to root rot caused by F. avenaceum.

Identification of Root Rot Resistance QTLs in Pea Using Fusarium solani f. sp. pisi-Responsive Differentially Expressed Genes.

Pisum sativum (pea) yields in the United States have declined significantly over the last decades, predominantly due to susceptibility to root rot diseases. One of the main causal agents of root rot is the fungus Fusarium solani f. sp. pisi (Fsp), leading to yield losses ranging from 15 to 60%. Determining and subsequently incorporating the genetic basis for resistance in new cultivars offers one of the best solutions to control this pathogen; however, no green-seeded pea cultivars with complete resistance to Fsp have been identified. To date, only partial levels of resistance to Fsp has been identified among pea genotypes. SNPs mined from Fsp-responsive differentially expressed genes (DEGs) identified in a preceding study were utilized to identify QTLs associated with Fsp resistance using composite interval mapping in two recombinant inbred line (RIL) populations segregating for partial root rot resistance. A total of 769 DEGs with single nucleotide polymorphisms (SNPs) were identified, and the putative SNPs were evaluated for being polymorphic across four partially resistant and four susceptible P. sativum genotypes. The SNPs with validated polymorphisms were used to screen two RIL populations using two phenotypic criteria: root disease severity and plant height. One QTL, WB.Fsp-Ps 5.1 that mapped to chromosome 5 explained 14.8% of the variance with a confidence interval of 10.4 cM. The other four QTLs located on chromosomes 2, 3, and 5, explained 5.3-8.1% of the variance. The use of SNPs derived from Fsp-responsive DEGs for QTL mapping proved to be an efficient way to identify molecular markers associated with Fsp resistance in pea. These QTLs are potential candidates for marker-assisted selection and gene pyramiding to obtain high levels of partial resistance in pea cultivars to combat root rot caused by Fsp.

KASP Markers Reveal Established and Novel Sources of Resistance to Pea Seedborne Mosaic Virus in Pea Genetic Resources.

Pea seed-borne mosaic virus (PSbMV) is both seedborne and aphid-transmitted and can cause economic losses for pea (Pisum sativum L.) production by reducing yield through decreased seed weight and number. The P1 pathotype is especially virulent, affecting this important vegetable crop across the United States and internationally in regions of West Asia, North Africa, Europe, and Australia. Previously, two kompetitive allele-specific PCR (KASP) genotyping markers (eIF4E resistant 1 and 2) were developed and validated on P. sativum accessions identifying two PSbMV pathotype P1 resistance alleles in the eukaryotic translation initiation factor gene, eIF4E. The current study utilized these novel markers to rapidly evaluate 318 genetic resource accessions maintained as part of the United States Department of Agriculture National Plant Germplasm System's Pea Single Plant Collection (PSPC). The evaluations also included 58 commercial and other plant introduction (PI) lines that were assessed for the two eIF4E resistance alleles. All genotyping results were validated in greenhouse assays by confirmation of observable disease symptoms after inoculations and by enzyme-linked immunosorbent assays. The eIF4E resistant 1 and 2 alleles were found in 18 accessions from the PSPC, five commercial lines, and 14 other PI accessions. A single PSPC accession showed resistance to PSbMV pathotype P1 that is believed to be a novel source of resistance based on sequencing analysis of eIF4E. Sources of resistance were identified in the PSPC and in commercial cultivars that can be introgressed into breeding lines using traditional techniques to reduce the time and cost required to generate germplasm with superior disease-resistant traits.

Analysis and Identification of QTL for Resistance to Sclerotinia sclerotiorum in Pea (Pisum sativum L.).

White mold caused by Sclerotinia sclerotiorum is an important constraint to field pea (Pisum sativum L.) production worldwide. To transfer white mold resistance into an adapted background, and study the genetics of the disease, two recombinant inbred line (RIL) populations (PRIL17 and PRIL19) were developed by crossing two partially resistant plant introductions with two susceptible pea cultivars. PRIL17 (Lifter × PI240515), and PRIL19 (PI169603 × Medora) were evaluated for resistance to white mold by measuring lesion expansion inhibition (LEI) and nodal transmission inhibition (NTI) at 3, 7, and 14 days post inoculation (dpi) under controlled environmental conditions. Lesion expansion inhibition percentage (LEIP), survival rate (SR), and area under disease progress curves (AUDPC) were also calculated accordingly. Because of a positive correlation between LEI and NTI with height, short and long internode individuals of each population were analyzed separately to avoid any confounding effect of height to pathogen response. A total of 22 short genotypes demonstrated partial resistance based on at least two Porter's resistance criteria. Only two pea genotypes with partial resistance to white mold (PRIL19-18 and PRIL19-124) had both semi-leafless (afila) and short internode traits. Both the RIL populations were genotyped using genotyping by sequencing (GBS). For PRIL17 and PRIL19, genetic maps were constructed from a total of 1,967 and 1,196 single nucleotide polymorphism (SNP) and spanned over 1,494 cM and 1,415 cM representing seven and nine linkage groups, respectively. A consensus map constructed using data from both populations, had 1,486 unique SNPs over 2,461 cM belonging to seven linkage groups. Inclusive composite interval mapping (ICIM) identified thirteen quantitative trait loci (QTL) associated with white mold resistance traits in both populations. Three of them were co-located with height genes (a morphological trait that reduces infection risk and acts as disease avoidance) and the other ten QTL were associated with two forms of physiological resistance (seven for LEI and three for NTI) with LOD and r2 ranging from 3.0 to 28.5 and 5.1 to 64.3, respectively. The development of resistance lines, genetic dissection and identification of markers associated will help accelerate breeding efforts for white mold resistance using molecular breeding approaches.

Identification of Fusarium solani f. sp. pisi (Fsp) Responsive Genes in Pisum sativum.

Pisum sativum (pea) is rapidly emerging as an inexpensive and significant contributor to the plant-derived protein market. Due to its nitrogen-fixation capability, short life cycle, and low water usage, pea is a useful cover-and-break crop that requires minimal external inputs. It is critical for sustainable agriculture and indispensable for future food security. Root rot in pea, caused by the fungal pathogen Fusarium solani f. sp. pisi (Fsp), can result in a 15-60% reduction in yield. It is urgent to understand the molecular basis of Fsp interaction in pea to develop root rot tolerant cultivars. A complementary genetics and gene expression approach was undertaken in this study to identify Fsp-responsive genes in four tolerant and four susceptible pea genotypes. Time course RNAseq was performed on both sets of genotypes after the Fsp challenge. Analysis of the transcriptome data resulted in the identification of 42,905 differentially expressed contigs (DECs). Interestingly, the vast majority of DECs were overexpressed in the susceptible genotypes at all sampling time points, rather than in the tolerant genotypes. Gene expression and GO enrichment analyses revealed genes coding for receptor-mediated endocytosis, sugar transporters, salicylic acid synthesis, and signaling, and cell death were overexpressed in the susceptible genotypes. In the tolerant genotypes, genes involved in exocytosis, and secretion by cell, the anthocyanin synthesis pathway, as well as the DRR230 gene, a pathogenesis-related (PR) gene, were overexpressed. The complementary genetic and RNAseq approach has yielded a set of potential genes that could be targeted for improved tolerance against root rot in P. sativum. Fsp challenge produced a futile transcriptomic response in the susceptible genotypes. This type of response is hypothesized to be related to the speed at which the pathogen infestation advances in the susceptible genotypes and the preexisting level of disease-preparedness in the tolerant genotypes.

Development and Validation of KASP Markers for the Identification of Pea seedborne mosaic virus Pathotype P1 Resistance in Pisum sativum.

As pesticides have become heavily relied on for management of insect pests vectoring economically important pathogens of vegetable crops, development of pathogen-resistant germplasm remains a promising alternative to reduce or eliminate costly and timely chemical inputs. Molecular markers can be used to rapidly identify resistant genotypes to aid breeders in advancing germplasm. This study developed two kompetitive allele-specific PCR (KASP) genotyping markers for rapid screening of Pisum sativum genotypes for resistance to Pea seedborne mosaic virus pathotype P1 (PSbMV-P1), the most economically devastating strain worldwide. The KASP markers differentiate two eIF4E PSbMV-P1-resistant allelic variants from susceptible eIF4E variants. A single nucleotide polymorphism (Resistant 1) and a 3-basepair deletion (Resistant 2) present in either of the two resistant alleles were used for marker design. Forty-four P. sativum lines previously characterized for resistance to PSbMV were inoculated with PSbMV-P1 in a greenhouse, observed for visual symptoms, assayed for virus susceptibility by enzyme-linked immunosorbent assay (ELISA), and genotyped by KASP marker analysis. The KASP markers were 100% accurate in characterizing PSbMV-P1-susceptible and PSbMV-P1-resistant genotypes when correlated with the ELISA results. The Resistant 1 marker also correlated with resistance to PSbMV pathotypes P2 and P4 completely, making this marker a new advanced tool for P. sativum breeding programs.

Dissecting the Genetic Architecture of Aphanomyces Root Rot Resistance in Lentil by QTL Mapping and Genome-Wide Association Study.

Lentil (Lens culinaris Medikus) is an important source of protein for people in developing countries. Aphanomyces root rot (ARR) has emerged as one of the most devastating diseases affecting lentil production. In this study, we applied two complementary quantitative trait loci (QTL) analysis approaches to unravel the genetic architecture underlying this complex trait. A recombinant inbred line (RIL) population and an association mapping population were genotyped using genotyping by sequencing (GBS) to discover novel single nucleotide polymorphisms (SNPs). QTL mapping identified 19 QTL associated with ARR resistance, while association mapping detected 38 QTL and highlighted accumulation of favorable haplotypes in most of the resistant accessions. Seven QTL clusters were discovered on six chromosomes, and 15 putative genes were identified within the QTL clusters. To validate QTL mapping and genome-wide association study (GWAS) results, expression analysis of five selected genes was conducted on partially resistant and susceptible accessions. Three of the genes were differentially expressed at early stages of infection, two of which may be associated with ARR resistance. Our findings provide valuable insight into the genetic control of ARR, and genetic and genomic resources developed here can be used to accelerate development of lentil cultivars with high levels of partial resistance to ARR.

Protein, weight, and oil prediction by single-seed near-infrared spectroscopy for selection of seed quality and yield traits in pea (Pisum sativum).

BACKGROUND: Pea (Pisum sativum) is a prevalent cool-season crop that produces seeds valued for their high protein content. Modern cultivars have incorporated several traits that improved harvested yield. However, progress toward improving seed quality has received less emphasis, in part due to the lack of tools for easily and rapidly measuring seed traits. In this study we evaluated the accuracy of single-seed near-infrared spectroscopy (NIRS) for measuring pea-seed weight, protein, and oil content. A total of 96 diverse pea accessions were analyzed using both single-seed NIRS and wet chemistry methods. To demonstrate field relevance, the single-seed NIRS protein prediction model was used to determine the impact of seed treatments and foliar fungicides on the protein content of harvested dry peas in a field trial. RESULTS: External validation of partial least squares (PLS) regression models showed high prediction accuracy for protein and weight (R2 = 0.94 for both) and less accuracy for oil (R2 = 0.74). Single-seed weight was weakly correlated with protein and oil content in contrast with previous reports. In the field study, the single-seed NIRS predicted protein values were within 10 mg g-1 of an independent analytical reference measurement and were sufficiently precise to detect small treatment effects. CONCLUSION: The high accuracy of protein and weight estimation show that single-seed NIRS could be used in the dual selection of high-protein, high-weight peas early in the breeding cycle, allowing for faster genetic advancement toward improved pea nutritional quality. © 2020 Society of Chemical Industry.

Confirmation of Fusarium root rot resistance QTL Fsp-Ps 2.1 of pea under controlled conditions.

BACKGROUND: Dry pea production has increased substantially in North America over the last few decades. With this expansion, significant yield losses have been attributed to an escalation in Fusarium root rots in pea fields. Among the most significant rot rotting pathogenic fungal species, Fusarium solani fsp. pisi (Fsp) is one of the main causal agents of root rot of pea. High levels of partial resistance to Fsp has been identified in plant genetic resources. Genetic resistance offers one of the best solutions to control this root rotting fungus. A recombinant inbred population segregating for high levels of partial resistance, previously single nucleotide polymorphism (SNP) genotyped using genotyping-by-sequencing, was phenotyped for disease reaction in replicated and repeated greenhouse trials. Composite interval mapping was deployed to identify resistance-associated quantitative trait loci (QTL). RESULTS: Three QTL were identified using three disease reaction criteria: root disease severity, ratios of diseased vs. healthy shoot heights and dry plant weights under controlled conditions using pure cultures of Fusarium solani fsp. pisi. One QTL Fsp-Ps 2.1 explains 44.4-53.4% of the variance with a narrow confidence interval of 1.2 cM. The second and third QTL Fsp-Ps3.2 and Fsp-Ps3.3 are closely linked and explain only 3.6-4.6% of the variance. All of the alleles are contributed by the resistant parent PI 180693. CONCLUSION: With the confirmation of Fsp-Ps 2.1 now in two RIL populations, SNPs associated with this region make a good target for marker-assisted selection in pea breeding programs to obtain high levels of partial resistance to Fusarium root rot caused by Fusarium solani fsp. pisi.

Exploring the genetics of lesion and nodal resistance in pea (Pisum sativum L.) to Sclerotinia sclerotiorum using genome-wide association studies and RNA-Seq.

The disease white mold caused by the fungus Sclerotinia sclerotiorum is a significant threat to pea production, and improved resistance to this disease is needed. Nodal resistance in plants is a phenomenon where a fungal infection is prevented from passing through a node, and the infection is limited to an internode region. Nodal resistance has been observed in some pathosystems such as the pea (Pisum sativum L.)-S. sclerotiorum pathosystem. In addition to nodal resistance, different pea lines display different levels of stem lesion size restriction, referred to as lesion resistance. It is unclear whether the genetics of lesion resistance and nodal resistance are identical or different. This study applied genome-wide association studies (GWAS) and RNA-Seq to understand the genetic makeup of these two types of resistance. The time series RNA-Seq experiment consisted of two pea lines (the susceptible 'Lifter' and the partially resistant PI 240515), two treatments (mock inoculated samples and S. sclerotiorum-inoculated samples), and three time points (12, 24, and 48 hr post inoculation). Integrated results from GWAS and RNA-Seq analyses identified different redox-related transcripts for lesion and nodal resistances. A transcript encoding a glutathione S-transferase was the only shared resistance variant for both phenotypes. There were more leucine rich-repeat containing transcripts found for lesion resistance, while different candidate resistance transcripts such as a VQ motif-containing protein and a myo-inositol oxygenase were found for nodal resistance. This study demonstrated the robustness of combining GWAS and RNA-Seq for identifying white mold resistance in pea, and results suggest different genetics underlying lesion and nodal resistance.

Pythium Species Associated with Damping-off of Pea in Certified Organic Fields in the Columbia Basin of Central Washington.

Organic vegetable production accounted for 19% of the total organic acreage in Washington State in 2013, with 1,700 ha of certified organic vegetable pea. However, production is challenged constantly with the threat of poor emergence after planting due to damping-off caused by Pythium spp. A survey of Pythium spp. in organic vegetable production areas of the semiarid Columbia Basin of central Washington was carried out in fall 2009 to identify species associated with damping-off during early spring planting. Of 305 isolates baited from soil sampled from 37 certified organic fields, 264 were identified to 16 Pythium spp. by sequencing the internal transcribed spacer region of ribosomal DNA. A soil DNA-CFU regression curve was developed using real-time quantitative polymerase chain reaction assays for each of the three predominant pathogenic species (Pythium abappressorium, the P. irregulare complex, and P. ultimum var. ultimum) found in soil sampled from the 37 fields. The P. irregulare complex, P. abappressorium, and P. ultimum var. ultimum were detected in 57, 78, and 100% of the fields sampled, respectively. A regression analysis was used to determine that P. ultimum var. ultimum ranged from 14 to 332 CFU/g of soil in the 37 fields, the P. irregulare complex ranged from 25 to 228 CFU/g of soil, and P. abappressorium DNA was below the quantifiable limit. In summary, P. ultimum var. ultimum was the most prevalent pathogenic Pythium sp. detected in certified organic fields in the semiarid Columbia Basin of central Washington but multiple Pythium spp. may be associated with damping-off in cool and wet, early spring planting conditions.

Characterization and Pathogenicity of Rhizoctonia and Rhizoctonia-Like spp. From Pea Crops in the Columbia Basin of Oregon and Washington.

Isolates of Rhizoctonia and Rhizoctonia-like spp. (n = 179) were baited selectively from soil and plant samples collected from irrigated pea crops in the semiarid Columbia Basin of Oregon and Washington from 2011 to 2013, and characterized to species, subspecies, and anastomosis groups (AG) based on sequences of the internal transcribed spacer region of ribosomal DNA. Rhizoctonia solani comprised 76% of all isolates, and included isolates of AG 4 (31% of all isolates), AG 2-1 (18%), AG 3 (10%), AG 8 (8%), AG 5 (5%), AG 10 (3%), and AG 9 (1%). The isolates of Ceratobasidium spp. (20%) comprised four AGs: AG K (11%), AG A (6%), AG I (2%), and AG I-like (1%). Waitea circinata isolates (4%) comprised two subspecies: W. circinata var. circinata (approximately 4%) and W. circinata var. zeae (<1%). Repeated pathogenicity tests of isolates of the 10 most frequently detected AGs and subspecies on 'Serge' pea at 15°C revealed that R. solani AG 2-1 caused the greatest reduction in pea emergence, followed by R. solani AG 4. R. solani AG 4 caused the most severe root rot, stunting, and reduction in pea seedling biomass, followed by isolates of AG 2-1. R. solani AG 8 did not affect emergence, plant height, and total biomass compared with noninoculated control plants; however, root rot caused by isolates of AG 8 was ranked the third most severe among isolates of the 10 Rhizoctonia subgroups, after that caused by isolates of AG 4 and AG 2-1. Isolates of other AGs and subspecies were either weakly virulent or nonpathogenic on pea. The most common AGs (AG 4 and AG 2-1) detected in pea fields in the Columbia Basin were also the most virulent. In a growers' pea crop grown for seed ('Prevail') planted 5 days after herbicide application and incorporation of a preceding winter wheat crop, severe stunting caused by Rhizoctonia spp. resulted in an average 75% yield loss within patches of stunted plants. In contrast, the yield of processing pea from a green pea crop of Serge did not differ significantly for plants sampled within versus outside patches of stunted plants; however, plants within patches were significantly more mature. In the Prevail seed crop, a greater frequency of R. solani AG 8 was detected than AG 2-1 or AG 4 from within patches of stunted plants, indicating that isolates of AG 8 may be associated with the root rot complex in some pea crops in the Columbia Basin.

Complex patterns of speciation in cosmopolitan "rock posy" lichens--discovering and delimiting cryptic fungal species in the lichen-forming Rhizoplaca melanophthalma species-complex (Lecanoraceae, Ascomycota).

A growing body of evidence indicates that in some cases morphology-based species circumscription of lichenized fungi misrepresents the number of existing species. The cosmopolitan "rock posy" lichen (Rhizoplaca melanophthalma) species-complex includes a number of morphologically distinct species that are both geographically and ecologically widespread, providing a model system to evaluate speciation in lichen-forming ascomycetes. In this study, we assembled multiple lines of evidence from nuclear DNA sequence data, morphology, and biochemistry for species delimitation in the R. melanophthalma species-complex. We identify a total of ten candidate species in this study, four of which were previously recognized as distinct taxa and six previously unrecognized lineages found within what has been thus far considered a single species. Candidate species are supported using inferences from multiple empirical operational criteria. Multiple instances of sympatry support the view that these lineages merit recognition as distinct taxa. Generally, we found little corroboration between morphological and chemical characters, and previously unidentified lineages were morphologically polymorphic. However, secondary metabolite data supported one cryptic saxicolous lineage, characterized by orsellinic-derived gyrophoric and lecanoric acids, which we consider to be taxonomically significant. Our study of the R. melanophthalma species-complex indicates that the genus Rhizoplaca, as presently circumscribed, is more diverse in western North American than originally perceived, and we present our analyses as a working example of species delimitation in morphologically cryptic and recently diverged lichenized fungi.

Development of codominant simple sequence repeat, single nucleotide polymorphism and sequence characterized amplified region markers for the pea root rot pathogen, Aphanomyces euteiches.

Three kinds of genetic markers including simple sequence repeats (SSRs), single nucleotide polymorphisms (SNPs) and sequence characterized amplified regions (SCARs) were developed from Aphanomyces euteiches. Of 69 loci tested, seven SSR, two SNP and two SCAR markers were codominantly polymorphic. These codominant markers and dominant markers described herein will facilitate population genetic and evolutionary studies of this important plant pathogen.

Survival of Phytophthora infestans in Surface Water.

ABSTRACT Coverless petri dishes with water suspensions of sporangia and zoospores of Phytophthora infestans were embedded in sandy soil in eastern Washington in July and October 2001 and July 2002 to quantify longevity of spores in water under natural conditions. Effects of solar radiation intensity, presence of soil in petri dishes (15 g per dish), and a 2-h chill period on survival of isolates of clonal lineages US-8 and US-11 were investigated. Spores in water suspensions survived 0 to 16 days under nonshaded conditions and 2 to 20 days under shaded conditions. Mean spore survival significantly increased from 1.7 to 5.8 days when soil was added to the water. Maximum survival time of spores in water without soil exposed to direct sunlight was 2 to 3 days in July and 6 to 8 days in October. Mean duration of survival did not differ significantly between chilled and nonchilled sporangia, but significantly fewer chilled spores survived for extended periods than that of nonchilled spores. Spores of US-11 and US-8 isolates did not differ in mean duration of survival, but significantly greater numbers of sporangia of US-8 survived than did sporangia of US-11 in one of three trials.