Identification and Characterization of Pythium, Globisporangium, and Phytopythium Species Present in Floricultural Crops from Long Island, New York

Several Pythium, Globisporangium, and Phytopythium species cause Pythium diseases in greenhouse floricultural crops, resulting in significant seasonal losses. Four hundred and eighteen Pythium, Globisporangium, and Phytopythium isolates from flowering crops, growing media, or bench and floor debris were collected from Long Island greenhouses or clinic samples between 2002 and 2013. Isolates were identified to species based on morphology and internal transcribed spacer barcoding. Twenty-two species of Pythium, Phytopythium, and Globisporangium were identified, with Globisporangium irregulare sensu lato (s.l.) being the most common. To determine the origin of inoculum during the 2011 cropping season, 11 microsatellite loci were analyzed in 124 G. irregulare s.l. isolates collected in four greenhouses and six previously collected from clinic samples. Cluster analyses grouped G. irregulare s.l. isolates into four groups: G. irregulare sensu stricto, plus three G. cryptoirregulare clusters. The population structure defined by greenhouse and host was found in two clades. Additionally, the population dynamics of G. irregulare s.l. isolates associated with Pelargonium spp. from 2011 to 2013 were examined using 85 isolates and nine informative microsatellite loci to assess inoculum survival over multiple cropping seasons. Although most isolates had unique genotypes, closely related genotypes were found in the same locations over different years. Our results indicate that G. irregulare s.l. inocula have local as well as remote origins. Isolates may be initially brought into ornamental operations from common sources, such as infected plant materials or infested potting mixes. Our results support the hypothesis that established strains can serve as inocula and survive in greenhouse facilities over multiple seasons.

A Step Towards Validation of High-Throughput Sequencing for the Identification of Plant Pathogenic Oomycetes

The advancement in high-throughput sequencing (HTS) technology allows the detection of pathogens without the need for isolation or template amplification. Plant regulatory agencies worldwide are adopting HTS as a prescreening tool for plant pathogens in imported plant germplasm. The technique is a multipronged process and, often, the bioinformatic analysis complicates detection. Previously, we developed E-probe diagnostic nucleic acid analysis (EDNA), a bioinformatic tool that detects pathogens in HTS data. EDNA uses custom databases of signature nucleic acid sequences (e-probes) to reduce computational effort and subjectivity when determining pathogen presence in a sample. E-probes of Pythium ultimum and Phytophthora ramorum were previously validated only using simulated HTS data. However, HTS samples generated from infected hosts or pure culture may vary in pathogen concentration, sequencing bias, and data quality, suggesting that each pathosystem requires further validation. Here, we used metagenomic and genomic HTS data generated from infected hosts and pure culture, respectively, to further validate and curate e-probes of Pythium ultimum and Phytophthora ramorum. E-probe length was found to be a determinant of diagnostic sensitivity and specificity; 80-nucleotide e-probes increased the diagnostic specificity to 100%. Curating e-probes to increase specificity affected diagnostic sensitivity only for 80-nucleotide Pythium ultimum e-probes. Comparing e-probes with alternative databases and bioinformatic tools in their speed and ability to find Pythium ultimum and Phytophthora ramorum demonstrated that, although pathogen sequence reads were detected by other methods, they were less specific and slower when compared with e-probes.

Genetic Diversity of Phymatotrichopsis omnivora Based on Mating Type and Microsatellite Markers Reveals Heterothallic Mating System

Phymatotrichopsis omnivora is a member of Pezizomycetes and causes root rot disease on a broad range of dicotyledonous plants. Using recently generated draft genome sequence data from four P. omnivora isolates, we developed simple sequence repeat (SSR) markers and identified both mating type genes (MAT1-1-1 and MAT1-2-1) in this fungus. To understand the genetic diversity of P. omnivora isolates (n = 43) and spore mats (n = 29) collected from four locations (Oklahoma, Texas, Arizona, and Mexico) and four host crops (cotton, alfalfa, peach, and soybean), we applied 24 SSR markers and showed that of the 72 P. omnivora isolates and spore mats tested, 41 were distinct genotypes. Furthermore, the developed SSR markers did not show cross-transferability to other close relatives of P. omnivora in the class Pezizomycetes. A multiplex PCR detecting both mating type idiomorphs and a reference gene (TUB2) was developed to screen P. omnivora isolates. Based on the dataset we tested, P. omnivora is a heterothallic fungus with both mating types present in the United States in a ratio close to 1:1. We tested P. omnivora spore mats obtained from spatially distinct disease rings that developed in a center-pivot alfalfa field and showed that both mating types can be present not only in the same field but also within a single spore mat. This study shows that P. omnivora has the genetic toolkit for generating sexually diverse progeny, providing impetus for future studies that focus on identifying sexual morphs in nature.

Genetic Diversity and Potential Inoculum Sources of Fusarium Species Causing Cankers in Bareroot-Propagated Almond Trees in California Nurseries

Previous research determined that Fusarium acuminatum and F. avenaceum are important causal agents of a canker disease in bareroot-propagated fruit and nut trees in California that emerges during cold storage or after transplanting. The disease largely disappeared after 2001, but it reemerged in 2011 in almond trees in at least one nursery. This motivated further study of the etiology and epidemiology of the disease by undertaking studies to determine distribution of the pathogens throughout almond nursery propagation systems and trace possible sources of inoculum. Research initiated in 2013 detected pathogenic Fusarium spp. throughout the almond propagation system, including in healthy trees, in soils, on wheat rotation crops, on equipment, and in the cold-storage facility air. In addition to the two Fusarium spp. implicated previously, F. brachygibbosum and a new Fusarium species, F. californicum, were found to be pathogenic on almond trees. Multilocus sequence typing and somatic compatibility testing confirmed that isolates within a species collected from different materials in the nursery were all highly genetically similar and likely of one clonal lineage. These findings affirm that equipment surfaces, wheat rotation crops, soil, cold-storage facility air, and asymptomatic almond tree materials (i.e., rootstock cuttings, budwood, and scions) can potentially contribute inoculum to increase disease prevalence and severity.

The First Genomic Resources for Phymatotrichopsis omnivora, a Soilborne Pezizomycete Pathogen with a Broad Host Range

Phymatotrichopsis omnivora is a destructive plant pathogen causing root rot disease of alfalfa, cotton, pecan, grape, and many other important dicotyledonous species. A member of the family Rhizinaceae, in the class Pezizomycetes, P. omnivora is a soilborne ascomycete fungus that is difficult to maintain in culture, currently genetically intractable, and for which there are no publicly available genomic resources. We have generated draft genome sequences of four P. omnivora isolates obtained from cotton and alfalfa, growing in Texas and Oklahoma. These genome sequences will provide new insights into the biology of the fungus, including the factors responsible for its broad host range and pathogenicity.

Unique gene Pmhyp controlling melanization of pycnidia in Phoma medicaginis

Phoma medicaginis (syn. Ascochyta medicaginicola Qchen & L. Cai) causes spring black stem and leaf spot of alfalfa and the model legume Medicago truncatula. Phoma medicaginis produces uninucleate conidia in melanized pycnidia and is genetically tractable through Agrobacterium tumefaciens-mediated transformation (ATMT), which can result in insertional mutants. One T-DNA-tagged mutant, P1A17 produced conidia in non-melanized (hyaline) pycnidia. Pycnidial melanization recovered if the mutant was supplemented with melanin precursors or allowed to age. DNA sequences flanking the insertion did not predict any disrupted open reading frames (ORF) unless a Coccidioides prediction algorithm was used. Pmhyp gene was expressed in the wild type, but not the mutant, and has not been annotated in any genomes, to date. Expression of two conserved genes flanking the T-DNA disrupted Pmhyp was unchanged from the wild type. Knockout of Pmhyp strain displayed same cultural phenotype (non-melanized pycnidia). Complementation of Pmhyp strains with wild type PmHYP partially recovered pycnidial melanization. Both knockout and complementation transformants were confirmed using RT-PCR and southern blot analysis. Taken together, PmHYP appears to be a novel regulator of pycnidium specific melanization.

Inferring the presence of aflatoxin-producing Aspergillus flavus strains using RNA sequencing and electronic probes as a transcriptomic screening tool

E-probe Diagnostic for Nucleic acid Analysis (EDNA) is a bioinformatic tool originally developed to detect plant pathogens in metagenomic databases. However, enhancements made to EDNA increased its capacity to conduct hypothesis directed detection of specific gene targets present in transcriptomic databases. To target specific pathogenicity factors used by the pathogen to infect its host or other targets of interest, e-probes need to be developed for transcripts related to that function. In this study, EDNA transcriptomics (EDNAtran) was developed to detect the expression of genes related to aflatoxin production at the transcriptomic level. E-probes were designed from genes up-regulated during A. flavus aflatoxin production. EDNAtran detected gene transcripts related to aflatoxin production in a transcriptomic database from corn, where aflatoxin was produced. The results were significantly different from e-probes being used in the transcriptomic database where aflatoxin was not produced (atoxigenic AF36 strain and toxigenic AF70 in Potato Dextrose Broth).

Development of an RNA interference (RNAi) gene knockdown protocol in the anaerobic gut fungus Pecoramyces ruminantium strain C1A

Members of the anaerobic gut fungi (AGF) reside in rumen, hindgut, and feces of ruminant and non-ruminant herbivorous mammals and reptilian herbivores. No protocols for gene insertion, deletion, silencing, or mutation are currently available for the AGF, rendering gene-targeted molecular biological manipulations unfeasible. Here, we developed and optimized an RNA interference (RNAi)-based protocol for targeted gene silencing in the anaerobic gut fungus Pecoramyces ruminantium strain C1A. Analysis of the C1A genome identified genes encoding enzymes required for RNA silencing in fungi (Dicer, Argonaute, Neurospora crassa QDE-3 homolog DNA helicase, Argonaute-interacting protein, and Neurospora crassa QIP homolog exonuclease); and the competency of C1A germinating spores for RNA uptake was confirmed using fluorescently labeled small interfering RNAs (siRNA). Addition of chemically-synthesized siRNAs targeting D-lactate dehydrogenase (ldhD) gene to C1A germinating spores resulted in marked target gene silencing; as evident by significantly lower ldhD transcriptional levels, a marked reduction in the D-LDH specific enzymatic activity in intracellular protein extracts, and a reduction in D-lactate levels accumulating in the culture supernatant. Comparative transcriptomic analysis of untreated versus siRNA-treated cultures identified a few off-target siRNA-mediated gene silencing effects. As well, significant differential up-regulation of the gene encoding NAD-dependent 2-hydroxyacid dehydrogenase (Pfam00389) in siRNA-treated C1A cultures was observed, which could possibly compensate for loss of D-LDH as an electron sink mechanism in C1A. The results demonstrate the feasibility of RNAi in anaerobic fungi, and opens the door for gene silencing-based studies in this fungal clade.

A noncanonical poly(A) RNA polymerase gene affects morphology in Phoma medicaginis

Phoma medicaginis (syn. Ascochyta medicaginicola Qchen & L. Cai) causes spring black stem and leaf spot, an important disease of alfalfa and annual medics. P. medicaginis forms uninucleate conidia in melanized pycnidia and is genetically tractable using Agrobacterium mediated transformation (ATMT), resulting in random integration of T-DNA that occasionally generates pycnidial mutants. The T-DNA tagged mutant, P265 displayed smaller pycnidia and more aerial hyphae than the wild type. A single T-DNA disrupted a putative noncanonical poly(A) RNA polymerase gene, Pmncpap1, which in yeast interacts with ribonucleotide reductase (RNR). As in yeast mutants, P265 showed sensitivity to hydroxyurea (HU), a RNR inhibitor. To characterize the role of Pmncpap1, targeted ΔPmncpap1 mutants were created using a hygromycin selectable marker flanked by 1 Kbp regions of Pmncpap1. ΔPmncpap1 mutants possessed similar morphological features to those of P265. The plasmid for rescue of PmncPAP1, pCAM-Nat1 (nourseothricin selection) was constructed and used to introduce full-length PmncPAP1 into mutants. Rescued P265 showed partial recovery of wild type and the original T-DNA was lost due to homologous integration. To our knowledge, this is the first ncPAP to be examined in a filamentous fungus.

A new approach for detecting fungal and oomycete plant pathogens in next generation sequencing metagenome data utilising electronic probes

Early stage infections caused by fungal/oomycete spores may not be detected until signs or symptoms develop. Serological and molecular techniques are currently used for detecting these pathogens. Next-generation sequencing (NGS) has potential as a diagnostic tool, due to the capacity to target multiple unique signature loci of pathogens in an infected plant metagenome. NGS has significant potential for diagnosis of important eukaryotic plant pathogens. However, the assembly and analysis of huge amounts of sequence is laborious, time consuming, and not necessary for diagnostic purposes. Previous work demonstrated that a bioinformatic tool termed Electronic probe Diagnostic Nucleic acid Analysis (EDNA) had potential for greatly simplifying detecting fungal and oomycete plant pathogens in simulated metagenomes. The initial study demonstrated limitations for detection accuracy related to the analysis of matches between queries and metagenome reads. This study is a modification of EDNA demonstrating a better accuracy for detecting fungal and oomycete plant pathogens.

Infection and Colonization of Several Bermudagrasses by Ophiosphaerella korrae

Bermudagrass (Cynodon spp.) is the most commonly used turfgrass in the southern United States where it is severely affected by spring dead spot (SDS) caused by Ophiosphaerella herpotricha, O. korrae, and O. narmari. In this study, infection of bermudagrass roots and stolons by O. korrae was characterized using a transformant that expressed the red fluorescent protein tdTomato. Roots of interspecific hybrid cultivars Midlawn and Tifway 419, C. transvaalensis accessions Uganda and 3200, and C. dactylon cultivar U3 were inoculated and observed from 2 to 14 days postinoculation (DPI) while stolons were observed from 2 to 22 DPI. For all five cultivars tested, a similar level of root colonization was observed; however, differences were observed in the rate of necrosis development. Necrosis of Tifway 419 and Midlawn tissues was evident at 2 DPI, in Uganda and 3200 at 8 DPI, and in U3 necrosis was often absent as late as 14 DPI. The fungus rapidly penetrated the root epidermis and colonized the cortex of all cultivars by 4 DPI. Colonization of stele tissues by O. korrae was rare in hybrid cultivars but common in C. transvaalensis and C. dactylon accessions. On intact stolons, the fungus did not penetrate the epidermis 22 DPI though epidermal necrosis was evident on the surface of only the hybrid bermudagrasses. Wounded stolons became necrotic in all cultivars. Infection and colonization of various bermudagrasses by O. korrae was found to be similar to that by O. herpotricha, suggesting that host genetic resistance may be used for effective management of SDS caused by both species.

Population Structure of Pythium irregulare, P. ultimum, and P. sylvaticum in Forest Nursery Soils of Oregon and Washington

Pythium species are important soilborne pathogens occurring in the forest nursery industry of the Pacific Northwest. However, little is known about their genetic diversity or population structure and it is suspected that isolates are moved among forest nurseries on seedling stock and shared field equipment. In order to address these concerns, a total of 115 isolates of three Pythium species (P. irregulare, P. sylvaticum, and P. ultimum) were examined at three forest nurseries using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Analyses revealed distinct patterns of intraspecific variation for the three species. P. sylvaticum exhibited the most diversity, followed by P. irregulare, while substantial clonality was found in P. ultimum. For both P. irregulare and P. sylvaticum, but not P. ultimum, there was evidence for significant variation among nurseries. However, all three species also exhibited at least two distinct lineages not associated with the nursery of origin. Finally, evidence was found that certain lineages and clonal genotypes, including fungicide-resistant isolates, are shared among nurseries, indicating that pathogen movement has occurred.

Highly Sensitive End-Point PCR and SYBR Green qPCR Detection of Phymatotrichopsis omnivora, Causal Fungus of Cotton Root Rot

Phymatotrichopsis omnivora, the causal pathogen of cotton root rot, is a devastating ascomycete that affects numerous important dicotyledonous plants grown in the southwestern United States and northern Mexico. P. omnivora is notoriously difficult to isolate from infected plants; therefore methods for accurate and sensitive detection directly from symptomatic and asymptomatic plant samples are needed for disease diagnostics and pathogen identification. Primers were designed for P. omnivora based on consensus sequences of the nuclear ribosomal internal transcribed spacer (ITS) region of geographically representative isolates. Primers were compared against published P. omnivora sequences and validated against DNA from P. omnivora isolates and infected plant samples. The primer combinations amplified products from a range of P. omnivora isolates representative of known ITS haplotypes using standard end-point polymerase chain reaction (PCR) methodology. The assays detected P. omnivora from infected root samples of cotton (Gossypium hirsutum) and alfalfa (Medicago sativa). Healthy plants and other relevant root pathogens did not produce PCR products with the P. omnivora-specific primers. Primer pair PO2F/PO2R was the most sensitive in end-point PCR assays and is recommended for use for pathogen identification from mycelial tissue and infected plant materials when quantitative PCR (qPCR) is not available. Primer pair PO3F/PO2R was highly sensitive (1 fg) when used in SYBR Green qPCR assays and is recommended for screening of plant materials potentially infected by P. omnivora or samples with suboptimal DNA quality. The described PCR-based detection methods will be useful for rapid and sensitive screening of infected plants in diagnostic laboratories, plant health inspections, and plant breeding programs.

Fusarium spp., Cylindrocarpon spp., and Environmental Stress in the Etiology of a Canker Disease of Cold-Stored Fruit and Nut Tree Seedlings in California

The principal objective of this study was to determine the etiology of a canker disease in dormant stone fruit and apple tree seedlings maintained in refrigerated storage that has significantly impacted California fruit and nut tree nurseries. Signs and symptoms of the disease develop during storage or soon after planting, with subsequent decline and death of young trees. Isolations from both diseased and healthy almond and apple trees and Koch's postulates using stem segments of desiccation-stressed almond trees as hosts implicated Fusarium avenaceum and F. acuminatum as the primary causal agents. F. solani, Ilyonectria robusta, and Cylindrocarpon obtusiusculum were also capable of causing similar symptoms but were less frequently encountered in isolations of diseased tissue. Loss of bark turgidity in excised almond stem segments, as can occur in cold-stored seedlings, correlated with increased susceptibility to F. acuminatum, with maximum canker development occurring after relative bark turgidity dropped below a threshold of approximately 86%. Healthy almond trees, almond scion budwood, and a wheat cover crop used in fields where tree seedlings were grown and maintained until cold storage all possessed asymptomatic infections of F. acuminatum, F. avenaceum, and C. obtusiusculum as determined by activation following overnight freezing, cold storage, or desiccation.

Phymatotrichum (cotton) root rot caused by Phymatotrichopsis omnivora: retrospects and prospects

Phymatotrichum (cotton or Texas) root rot is caused by the soil-borne fungus Phymatotrichopsis omnivora (Duggar) Hennebert. The broad host range of the fungus includes numerous crop plants, such as alfalfa and cotton. Together with an overview of existing knowledge, this review is aimed at discussing the recent molecular and genomic approaches that have been undertaken to better understand the disease development at the molecular level with the ultimate goal of developing resistant germplasm.

TAXONOMY

Phymatotrichopsis omnivora (Duggar) Hennebert [synonym Phymatotrichum omnivorum (Shear) Duggar] is an asexual fungus with no known sexual stage. Mitosporic botryoblastospores occasionally form on epigeous spore mats in nature, but perform no known function and do not contribute to the disease cycle. The fungus has been affiliated erroneously with the polypore basidiomycete Sistotrema brinkmannii (Bres.) J. Erikss. Recent phylogenetic studies have placed this fungus in the ascomycete order Pezizales. HOST RANGE AND DISEASE SYMPTOMS: The fungus infects most dicotyledonous field crops, causing significant losses to cotton, alfalfa, grape, fruit and nut trees and ornamental shrubs in the south-western USA, northern Mexico and possibly parts of central Asia. However, this fungus does not cause disease in monocotyledonous plants. Symptoms include an expanding tissue collapse (rot) of infected taproots. In above-ground tissues, the root rot results in vascular discoloration of the stem and rapid wilting of the leaves without abscission, and eventually the death of the plant. Characteristic mycelial strands of the pathogen are typically present on the root's surface, aiding diagnosis.

PATHOGENICITY

Confocal imaging of P. omnivora interactions with Medicago truncatula roots revealed that infecting hyphae do not form any specialized structures for penetration and mainly colonize cortical cells and eventually form a mycelial mantle covering the root's surfaces. Cell wall-degrading enzymes have been implicated in penetration and symptom development. Global gene expression profiling of infected M. truncatula revealed roles for jasmonic acid, ethylene and the flavonoid pathway during disease development. Phymatotrichopsis omnivora apparently evades induced host defences and may suppress the host's phytochemical defences at later stages of infection to favour pathogenesis.

DISEASE CONTROL

No consistently effective control measures are known. The long-lived sclerotia and facultative saprotrophism of P. omnivora make crop rotation ineffective. Chemical fumigation methods are not cost-effective for most crops. Interestingly, no genetic resistance has been reported in any of the susceptible crop species.

Infection and colonization of turf-type bermudagrass by Ophiosphaerella herpotricha expressing green or red fluorescent proteins

Spring dead spot, caused by Ophiosphaerella herpotricha, is the most important disease of turf-type bermudagrass (Cynodon spp.) in the transition zone of the United States. Despite the importance of the disease, only limited information is available about the host-pathogen interaction at the cellular level. To evaluate the host plant interaction, an isolate of O. herpotricha expressing green fluorescent proteins (GFP) or red fluorescent proteins (tdTomato) was used to study the infection and colonization of roots and stolons of several bermudagrass cultivars. Roots of cultivars Tifway 419 and Midlawn were colonized similarly, resulting in extensive root necrosis, whereas an accession of Cynodon transvaalensis was less necrotic. The stele of C. transvaalensis roots was colonized but not those of Tifway 419 and Midlawn. For intact stolons, colonization was limited to the epidermis and defined macroscopic necrotic lesions were observed on Tifway 419 and Midlawn while C. transvaalensis stolon tissues remained mostly nonnecrotic. Internal colonization of stolons occurred when hyphae grew into wounds, resulting in necrosis in Tifway 419 and Midlawn, but not in C. transvaalensis. These studies suggest that the interaction of O. herpotricha with bermudagrass varies across host genotypes and the host tissues infected. The limited necrosis in C. transvaalensis tissues, though colonized, suggests an inherent tolerance to O. herpotricha.

Global gene expression profiling during Medicago truncatula-Phymatotrichopsis omnivora interaction reveals a role for jasmonic acid, ethylene, and the flavonoid pathway in disease development

Phymatotrichopsis omnivora (Duggar) Hennebert causes a destructive root rot in cotton, alfalfa (Medicago sativa), and many other dicot species. No consistently effective control measures or resistant host germplasm for Phymatotrichum root rot (PRR) are known. The relative genetic intractability of cotton and alfalfa precludes their use as model pathosystem hosts for P. omnivora. Therefore, we used the model legume M. truncatula and its available genetic and genomic resources to investigate PRR. Confocal imaging of P. omnivora interactions with M. truncatula roots revealed that the mycelia do not form any specialized structures for penetration and mainly colonize cortical cells and, eventually, form a mycelial mantle covering the root's surfaces. Expression profiling of M. truncatula roots infected by P. omnivora identified several upregulated genes, including the pathogenesis-related class I and class IV chitinases and genes involved in reactive oxygen species generation and phytohormone (jasmonic acid and ethylene) signaling. Genes involved in flavonoid biosynthesis were induced (2.5- to 10-fold over mock-inoculated controls) at 3 days postinoculation (dpi) in response to fungal penetration. However, the expression levels of flavonoid biosynthesis genes returned to the basal levels with the progress of the disease at 5 dpi. These transcriptome results, confirmed by real-time quantitative polymerase chain reaction analyses, showed that P. omnivora apparently evades induced host defenses and may downregulate phytochemical defenses at later stages of infection to favor pathogenesis.

Species composition and seasonal occurrence of Phyllophaga (Coleoptera: Scarabaeidae) infesting intensely managed Bermudagrass in Oklahoma

Larvae of Phyllophaga spp. (Coleoptera: Scarabaeidae) are important turfgrass pests in many regions of the United States. However, not all of the species associated with turfgrass are known, including species most likely to be of economic concern in Oklahoma turfgrasses, especially Bermuda grass. This study documented the species composition and seasonal occurrence of Phyllophaga associated with high maintenance Bermuda grass turf in Oklahoma over a 2-yr period. In 2005 and 2006, adult Phyllophaga spp. were collected with blacklight traps from selected golf courses throughout Oklahoma Phyllophaga larvae were obtained from Bermuda grass stands at selected sod production facilities adjacent to or near the light traps. We collected 20 species of Phyllophaga beetles in light traps, and nine species of Phyllophaga larvae from turfgrass. Peak flight periods for most species occurred in May and June, but some were captured as early as mid-April and others as late as September. The cytochrome c oxidase I (COI) gene from adults and larvae was amplified using polymerase chain reaction, sequenced, and then used to compare larval DNA against DNA from identified adults. These results confirmed the validity of using COI sequences to identify species of some Phyllophaga larvae. The identifications will aid in optimizing the timing of insecticide applications against Phyllophaga white grubs as discussed.

First Report of Dollar Spot of Buffalograss Caused by Sclerotinia homoeocarpa in Oklahoma

Buffalograss (Buchloe dactyloides (Nutt.) Engelm.) is a perennial, warm-season grass native to the central plains of North America and a dominant plant over much of the shortgrass prairie ecosystem. Its prostrate growth habit and excellent drought tolerance make it a commercially promising turfgrass species, and numerous turf-type cultivars have been released. In the spring of 2007, the southern plains states experienced prolonged periods of excessive precipitation during which numerous buffalograss swards throughout north-central Oklahoma exhibited symptoms of dollar spot (1). A fungus morphologically identical to Sclerotinia homoeocarpa Bennett was consistently isolated from diseased buffalograss leaves collected from three locations in Oklahoma, two from Payne County and one from Logan County. Thirty-day-old seedlings of B. dactyloides ('Cody' and 'Topgun') and Agrostis stolonifera ('SR1020') were inoculated by placing potato dextrose agar (PDA) plugs, colonized by mycelia of each S. homoeocarpa isolate, onto the seedlings' leaves. Sterile PDA plugs were placed on plants as controls. Leaf lesions developed after 4 days only on inoculated plants, and S. homoeocarpa was reisolated from lesions, satisfying Koch's postulates. The nuclear ribosomal internal transcribed spacer (ITS) region was amplified from DNA extracted from cultures of the three buffalograss isolates and a bentgrass isolate using primers ITS4 and ITS5 (2) and sequenced. Sequences were similar to one another (97 to 99% identical), however, two isolates shared a 420-bp, type I intron in the 18S small subunit rDNA. A search of GenBank at NCBI found the ITS sequences were most similar to the ITS regions of other S. homoeocarpa accessions (97% identical). The ITS sequences from the four isolates were deposited in GenBank (Accession Nos. EU123800-EU123803). To our knowledge, this is the first report of dollar spot on a native, warm-season grass in the United States and the disease appears to be endemic to buffalograss in Oklahoma and Kansas (N. A. Tisserat, personal communication). References: (1) R. W. Smiley et al. Page 22 in: Compendium of Turfgrass Diseases. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2005. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., New York, 1990.

Influence of Temperature and Time of Year on Colonization of Bermudagrass Roots by Ophiosphaerella herpotricha

The influence of temperature on the infection of bermudagrass seedlings by Ophiosphaerella herpotricha and colonization of plants in the field was investigated. Bermudagrass seedlings (cv. Jackpot) inoculated with O. herpotricha exhibited dark lesions after 8 days. Root lesion length was greatest at 17°C and was similar for all temperatures examined below 21°C. Seedlings grown at 25 or 30°C had small lesions that remained similar in size when evaluated at 8 and 10 days post inoculation. Colonization of bermudagrass roots from field plots were examined in July, October, and November of 2003 and 2004. In 2003, no differences between sampling dates were observed for plants sampled from the edge of the spring patch in 5.4-cm increments to a total distance of 21.6 cm. In 2004, July and October samples were similar; however, an increase in root colonization was found between the October and November samplings. These studies suggest that infection and colonization of bermudagrass roots by O. herpotricha occurs over a wide range of cool soil temperatures, occurs in the spring, and can be variable in the autumn.

First Report of Ergot of Bermudagrass Caused by Claviceps cynodontis in Oklahoma

During late June and early July of 2005, signs of bermudagrass ergot were reported from numerous northern and eastern counties in Oklahoma. Signs were observed primarily on forage-type bermudagrass (Cynodon dactylon (L.) Pers.), as well as bermudagrass turf. During the "honeydew" stage, honeydew was frequently observed exuding from most of the ovaries of infected inflorescences. These signs of ergot have been observed previously on bermudagrass in Oklahoma and Texas (1). Sphacelia-type conidia were abundantly produced during the honeydew stage and were single-celled, hyaline, averaged 14 × 5 μm in size, and were reniform to allantoid in shape. When streaked on water agar, conidia produced terminal holoblastic secondary conidia. Single-spore cultures were isolated from the honeydew of bermudagrasses from Logan and Muskogee counties in Oklahoma and grew slowly as white mycelium on potato dextrose agar (PDA). Koch's postulates were fulfilled for these two isolates by spray inoculating four bermudagrass inflorescences at anthesis with mycelium scraped from a PDA plate and homogenized in water. Control plants' inflorescences were sprayed with a water suspension of a similar amount of sterile PDA as inoculated plants. Plants were placed inside plastic bags to maintain humidity and incubated in a growth chamber at 22°C (14-h photoperiod) and 20°C (10 h of darkness). After 9 days, honeydew exuded from the inoculated inflorescences, but not from the controls. Single-spore cultures were reisolated from the honeydew, and conidia streaked on water agar formed identical secondary conidia. The complete nuclear ribosomal internal transcribed spacer (ITS) region was amplified from DNA extracted from honeydew and single-spore cultures using the ITS4 and ITS5 primers (4) and sequenced. All sequences were identical and a search of GenBank at NCBI found these sequences were most similar to the ITS regions of Claviceps cynodontis Langdon (100%, Accession No. AJ557074) and C. maximensis Theis (99%, Accession No. AJ133396). The ITS sequence from the Logan County isolate was deposited at Gen-Bank (Accession DQ187312). The morphology, secondary conidiation, and ITS sequences identify the causal fungus as C. cynodontis (2) and differentiate it from C. purpurea (Fr.) Tul., the previously identified cause of bermudagrass ergot (1). To our knowledge, this is the first report of C. cynodontis on bermudagrass in Oklahoma and may represent a recent introduction to the United States (2; S. Pažoutová and M. Flieger, personal communication). A Claviceps sp. isolated from bermudagrass has been shown to produce ergot alkaloids possibly causing "bermudagrass tremors" in cattle (3). In regions where bermudagrass is the predominant forage for livestock, the toxicological significance of bermudagrass ergot caused by C. cynodontis is unclear and requires further research. References: (1) K. E. Conway et al. Plant Dis. 76:1077, 1992. (2) S. Pažoutová et al. Can J. Plant Pathol. 27:541, 2005. (3) J. K. Porter et al. J. Agric. Food Chem. 22:838, 1974. (4) T. J. White et al. Pages 315-322 in: PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., New York, 1990.

Nuclear DNA degradation during heterokaryon incompatibility in Neurospora crassa

Many filamentous fungi are capable of undergoing conspecific hyphal fusion with a genetically different individual to form a heterokaryon. However, the viability of such heterokaryons is dependent upon vegetative (heterokaryon) incompatibility (het) loci. If two individuals undergo hyphal anastomosis, but differ in allelic specificity at one or more het loci, the fusion cell is usually compartmentalized and self-destructs. Many of the microscopic features associated with vegetative incompatibility resemble apoptosis in metazoans and plants. To test the hypothesis whether vegetative incompatibility results in nuclear degradation, a characteristic of apoptosis, the cytology of hyphal fusions between incompatible Neurospora crassa strains that differed at three het loci, mat, het-c and het-6, and the cytology of transformants containing incompatible het-c alleles were examined using fluorescent DNA stains and terminal deoxynucleotidyl transferase-mediated dUTP-X nick end labeling (TUNEL). Hyphal fusion cells between het incompatible strains and hyphal segments in het-c incompatible transformants were compartmentalized by septal plugging and contained heavily degraded nuclear DNA. Hyphal fusion cells in compatible self-pairings and hyphal cells in het-c compatible transformants were not compartmentalized and rarely showed TUNEL-positive nuclei. Cell death events also were observed in senescent, older hyphae. Morphological features of hyphal compartmentation and death during vegetative incompatibility and the extent to which it is genetically controlled can best be described as a form of programmed cell death.