Molecular phylogeny of Leptosphaeria and Phaeosphaeria

The objectives of this study were to determine the phylogenetic relationships of species of Leptosphaeria and Phaeosphaeria and evaluate the phylogenetic significance of morphological characters of the teleomorph, anamorph, and host. Sequences of the entire ITS region, including the 5.8S rDNA, of 59 isolates representing 54 species were analyzed and the phylogeny inferred using parsimony and distance analyses. Isolates grouped into three well-supported clades. The results of this study support the separation of Phaeosphaeria from Leptosphaeria sensu stricto. Leptosphaeria bicolor and the morphologically similar Leptosphaeria taiwanensis formed a separate, well-supported clade. We conclude that peridial wall morphology, anamorph characteristics, and to a lesser extent host, are phylogenetically significant at the generic level. Ascospore and conidial morphology are taxonomically useful at the species level.

A revision of the genus Lomaantha, with the description of a new species

Lomaantha phragmitis sp. nov. is described and illustrated from a specimen collected on dead culms of Phragmites communis in southern China. The fungus differs from other described Lomaantha species in its conidiophores, conidiogenous cells and conidial appendages. Conidial morphology and presence or absence of percurrent proliferation of conidiogenous cells are the main characters distinguishing species within this genus. We provided a key and synoptic table of morphological characters of all three Lomaantha species.

Elevated atmospheric carbon dioxide concentrations amplify Alternaria alternata sporulation and total antigen production

BACKGROUND

Although the effect of elevated carbon dioxide (CO2) concentration on pollen production has been established in some plant species, impacts on fungal sporulation and antigen production have not been elucidated.

OBJECTIVE

Our purpose was to examine the effects of rising atmospheric CO2 concentrations on the quantity and quality of fungal spores produced on timothy (Phleum pratense) leaves.

METHODS

Timothy plants were grown at four CO2 concentrations (300, 400, 500, and 600 micromol/mol). Leaves were used as growth substrate for Alternaria alternata and Cladosporium phlei. The spore abundance produced by both fungi, as well as the size (microscopy) and antigenic protein content (ELISA) of A. alternata, were quantified.

RESULTS

Leaf carbon-to-nitrogen ratio was greater at 500 and 600 micromol/mol, and leaf biomass was greater at 600 micromol/mol than at the lower CO2 concentrations. Leaf carbon-to-nitrogen ratio was positively correlated with A. alternata spore production per gram of leaf but negatively correlated with antigenic protein content per spore. At 500 and 600 micromol/mol CO2 concentrations, A. alternata produced nearly three times the number of spores and more than twice the total antigenic protein per plant than at lower concentrations. C. phlei spore production was positively correlated with leaf carbon-to-nitrogen ratio, but overall spore production was much lower than in A. alternata, and total per-plant production did not vary among CO2 concentrations.

CONCLUSIONS

Elevated CO2 concentrations often increase plant leaf biomass and carbon-to-nitrogen ratio. Here we demonstrate for the first time that these leaf changes are associated with increased spore production by A. alternata, a ubiquitous allergenic fungus. This response may contribute to the increasing prevalence of allergies and asthma.

Ulocladium cantlous sp. nov. isolated from northwestern China: its morphology and molecular phylogenetic position

A new species of Ulocladium was isolated from diseased leaves from two Cucumis sp. growing in Sinkiang and Gansu provinces of China. Conidia were isolated from necrotic leaves and used to establish single-spore pure cultures. Conidia were harvested from cultures 7 d after incubation for morphological comparisons. The morphology of this species resembles that of U. botrytis and U. consortiale. However it is distinguished from these two species by the sizes of obovoid to broadly ellipsoidal conidia and longer conidiophores. A taxonomic description of U. cantlous, comparison with related species in this genus, and a species phylogeny based on the partial nucleotide sequence of the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene and the Alternaria alternata major allergen (Alt a 1) gene are provided.

Functional analysis of Pcipg2 from the straminopilous plant pathogen Phytophthora capsici

Phytophthora capsici causes serious diseases in numerous crop plants. Polygalacturonases (PGs) are cell wall-degrading enzymes that play an important role in pathogenesis in straminopilous pathogens. To understand PGs as they relate to the virulence of P. capsici, Pcipg2 was identified from a genomic library of a highly virulent P. capsici strain. Pcipg2 was strongly expressed during symptom development after the inoculation of pepper leaves with P. capsici. The wild protein (PCIPGII) was obtained from the expression of pcipg2 and found that increasing activity of PGs in PCIPGII-treated pepper leaves was consistent with increasing symptom development. Asp residues in active sites within pcipg2 affected PCIPGII activity or its virulence on pepper leaves. Results show that pcipg2 is an important gene among pcipg genes, and illustrate the benefit of analyzing mechanisms of pathogenicity during the period of host/parasite interaction.

Lima Bean Downy Mildew Epiphytotics Caused by New Physiological Races of Phytophthora phaseoli

Before 1995, race D of Phytophthora phaseoli, the causal agent of downy mildew on lima bean (Phaseolus lunatus), was the prevalent physiological race in the mid-Atlantic region of the United States. Since 1995, however, new physiological races of P. phaseoli have been responsible for downy mildew outbreaks in previously resistant cultivars in this region. Cultivar differential testing of 180 isolates of P. phaseoli collected between 1994 and 2005 from Delaware and the eastern shore of Maryland has confirmed the presence of two new physiological races. The detection of race E in 1995 and race F only 5 years later in 2000, plus the lack of resistant cultivars to manage the epiphytotics in lima bean, have led to millions of dollars of crop losses. Intra- and interspecific genetic variation of Phytophthora spp. and isolates were assessed using amplified fragment length polymorphism DNA fingerprinting. Primer groups EcoRI+AG and MseI+C distinguished P. phaseoli and P. capsici from P. infestans but did not distinguish among different races of P. phaseoli.

Comparison of Colletotrichum orbiculare and Several Allied Colletotrichum spp. for mtDNA RFLPs, Intron RFLP and Sequence Variation, Vegetative Compatibility, and Host Specificity

ABSTRACT Based on spore morphology, appressorium development, sequence similarities of the rDNA, and similarities in amplified restriction fragment length polymorphism (AFLP), it has been proposed that Colletotrichum orbiculare, C. trifolii, C. lindemuthianum, and C. malvarum represent a single phylogenetic species, C. orbiculare. In the current study, the phylogenetic relationship among isolates in the C. orbiculare species complex was reassessed. In all, 72 isolates of C. orbiculare from cultivated cucurbit or weed hosts, C. trifolii from alfalfa, C. lindemuthianum from green bean, and C. malvarum from prickly sida (Sida spinosa) were examined for mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs), RFLPs and sequence variation of a 900-bp intron of the glutamine synthetase gene and a 200-bp intron of the glyceraldehyde-3-phosphate dehydrogenase gene, and vegetative compatibility. In addition, host specificity was examined in foliar inoculations on cucurbit, bean, and alfalfa hosts. Inoculations also were conducted on cucumber fruit. Genetically distinct isolates, based on vegetative compatibility, within the species complex (C. orbiculare, C. trifolii, and C. malvarum) had an identical mtDNA haplotype (haplotype A) when examined with each of three different restriction enzymes. Isolates of C. lindemuthianum had a very similar mtDNA haplotype to haplotype A, with a single polymorphism detected with the enzyme HaeIII. The four species represent a phylogenetically closely related group based on a statistical analysis of the 900- and 200-bp intron sequences. However, distinct RFLPs in the 900-bp intron were consistently associated with each species and could be used to qualitatively and quantitatively distinguish each species. Furthermore, each of the species showed distinct host specificity, with isolates of C. orbiculare (from cucurbits), C. lindemuthianum, and C. trifolii being pathogenic only on cucurbits, green bean, and alfalfa, respectively. Consequently, distinct and fixed nucleotide, or genotypic (intron sequences and RFLPs) and phenotypic (host specificity) characteristics can be used to distinguish C. orbiculare, C. lindemuthianum, and C. trifolii from one another; therefore, they should be recognized as distinct species. This species delineation is consistent with the most current species concepts in fungi. More isolates and further characterization is needed to determine whether C. orbiculare from cocklebur and C. malvarum represent distinct species. RFLPs of the 900-bp intron may represent a relatively inexpensive, reliable, and useful diagnostic tool for general species differentiation in the genus Colletotrichum.

Systematics and mating systems of two fungal pathogens of opium poppy: the heterothallic Crivellia papaveracea with a Brachycladium penicillatum asexual state and a homothallic species with a Brachycladium papaveris asexual state

This paper presents a systematic revision of the fungal opium poppy (Papaver somniferum L.) pathogens formerly known as Pleospora papaveracea (de Not.) Sacc., along with allied asexual states formerly placed in Dendryphion . The revision is based on analysis of phylogenetic relationships, comparative morphology, and analysis of mating systems. Using morphology, 18S and ITS rDNA, we established that these species belong to the Alternaria group rather than to Pleospora, a conclusion supported by the Shimodaira–Hasegawa test. For these fungi, we erect the new genus Crivellia , with Crivellia papaveracea as type. ITS rDNA analyses suggested with moderate support Alternaria brassicicola (Schw.) Wiltshire, Alternaria japonica Yoshii, and Ulocladium alternariae (Cooke) Simmons as Crivellia’s closest relatives. Combined ITS, partial GPD and EF-1 alpha analyses confirmed earlier studies that show that asexual isolates in the Crivellia lineage of poppy pathogens represent two closely related species. Because Dendryphion was determined to be polyphyletic, the former genus Brachycladium was resurrected for B. penicillatum Corda and B. papaveris (K. Sawada) Shoemaker & Inderbitzin, the Crivellia asexual states that had been in Dendryphion. Molecular and morphological comparison with isolates from field-collected ascomata and morphological comparison with the type specimen of P. papaveracea indicated that B. penicillatum , and not B. papaveris , is the anamorph of C. papaveracea. The mycelia from single conidium or single ascospore isolates, including mycelia from 14 single ascospores from one field-collected C. papaveracea ascoma, either have a MAT1-1 or MAT1-2 gene and are thus heterothallic. In contrast, each single-conidium isolate of B. papaveris has an incomplete MAT1-2 gene fused to a MAT1-1 region and is inferred to be homothallic. We speculate that ancestral MAT fusion might have led to speciation in Crivellia.

Genetic Diversity Among Ophiosphaerella agrostis Strains Causing Dead Spot in Creeping Bentgrass

Dead spot (Ophiosphaerella agrostis) is a relatively new disease of young creeping bentgrass and hybrid bermudagrass putting greens in the United States. Little is known about the biology or genetic diversity of the pathogen. O. agrostis is unusual in that it produces prodigious numbers of pseudothecia in the field throughout the summer months and has no known asexual state. A total of 77 O. agrostis isolates were collected from 21 different bentgrass putting greens and one hybrid bermudagrass green in 11 states. DNA fingerprint analysis revealed that 78 out of 97 markers were polymorphic (80.4%), providing 57 unique profiles. Genetic variation of O. agrostis was diverse, and isolates separated into three distinct clades with ≥69% similarity. Analysis of molecular variance indicated that the geographic origins of the isolates and the ability to produce pseudothecia were the best indicators for genetic similarity among O. agrostis isolates. Colony color varied among the isolates, but generally was similar for isolates residing within two clades (B and C). Colony color of isolates within clade A appeared to be a mixture of the colony colors exhibited by clades B and C. Isolates examined within each clade generally had varying levels of pseudothecia production and varying colony colors when grown on PDA. Although O. agrostis is a homothallic species, it is unclear if outcrossing among strains occurs.

A New Biotype of Phaeosphaeria sp. of Uncertain Affinity Causing Stagonospora Leaf Blotch Disease in Cereals in Poland

A new Phaeosphaeria sp. biotype was isolated from winter ryes in Poland during 1995. Two isolates, Sn23-1 and Sn48-1, were obtained from diseased leaves of cvs. Motto and Dańkowskie, respectively. The rye Phaeosphaeria sp. represented by isolate Sn48-1 has similar pycnidiospore morphology and induces disease symptoms in cereals similar to Phaeosphaeria nodorum, the causal agent of Stagonospora nodorum blotch disease (4). The pathogen (Sn48-1) produces hyaline, cylindrical pycnidiospores that are mostly three-septate and measure 12.8 to 23.7 × 2.1 to 3.2 μm (average size = 16 × 2.6 μm) on water agar. A molecular comparison of several genes in isolates Sn23-1 and Sn48-1 revealed that the rye Phaeosphaeria sp. was different from P. nodorum. In the conserved alpha-box sequence (1,93 bp) of the MAT1-1 gene, a four nucleotide difference occurred between the wheat-biotype P. nodorum and isolates Sn23-1 and Sn48-1 (GenBank Accession Nos. AY072933 and AF322008). In addition, the length of the internal transcribed spacer (ITS) region of the nuclear rDNA was the same for the wheat-biotype P. nodorum and the two rye Phaeosphaeria sp. isolates. However, a six nucleotide discrepancy was found in the ITS region (GenBank Accession Nos. U77362 and AF321323). The beta-glucosidase (bgl1) and beta-tubulin (tubA) genes differ in length between the wheat-biotype P. nodorum and two rye Phaeosphaeria sp. isolates (2,3). The main difference was due to the intron sizes of these two genes. One extra nucleotide was found in the intron2 of the bgl1 gene (GenBank Accession Nos. AY683619 and AY683620) and the intron1 of the tubA gene (GenBank Accession Nos. AY786337 and AY786331), respectively, in these two rye Phaeosphaeria sp. isolates. Disease severity on the fifth leaf (GS15) of Polish wheat (Alba, Begra, and Liwilla), triticale (Bogo and Pinokio), and rye (Zduno) cultivars was assessed with one (resistant) to nine (susceptible) scales 14 days after inoculation. Aggressiveness of wheat-biotype P. nodorum isolate Sn26-1 and rye Phaeosphaeria sp. isolate Sn48-1 was significant (P < 0.01) in five cultivars except in the moderately resistant wheat cv. Liwilla. The rye Phaeosphaeria sp. isolate Sn48-1 severely affected Polish rye Zduno (8.3) and two triticale cultivars (6.5), while the infection by isolate Sn26-1 was moderate (3-4). On the contrary, the wheat-biotype P. nodorum isolate Sn26-1 was more aggressive on wheat (4.1 on moderately resistant Alba and 6.2 on highly susceptible Begra) than the rye Phaeosphaeria sp. isolate Sn48-1, which had a scale of 2.2 and 4.3, respectively. Under laboratory conditions, the rye isolate Sn48-1 was able to cross with the wheat-biotype P. nodorum isolate Sn26-1 that has an opposite mating-type (MAT1-2) gene, but few viable ascospores were produced (1). References: (1) P. C. Czembor and E. Arseniuk. Mycol. Res. 104:919, 2000. (2) A. Malkus et al. FEMS (Fed. Eur. Microbiol. Soc.) Lett. 249:49, 2005. (3) E. Reszka et al. Can. J. Bot. 83:1001, 2005. (4) M. J. Richardson and M. Noble. Plant Pathol. 19:159, 1970.

Environmental Influences on the Release of Ophiosphaerella agrostis Ascospores Under Controlled and Field Conditions

ABSTRACT Ophiosphaerella agrostis, the causal agent of dead spot of creeping bentgrass (Agrostis stolonifera), can produce prodigious numbers of pseudothecia and ascospores throughout the summer. The environmental conditions and seasonal timings associated with O. agrostis ascospore release are unknown. The objectives of this research were to (i) determine the influence of light and relative humidity on ascospore release in a controlled environment, (ii) document the seasonal and daily discharge patterns of ascospores in the field, and (iii) elucidate environmental conditions that promote ascospore release under field conditions. In a growth chamber, a sharp decrease (100 to approximately 50%; 25 degrees C) in relative humidity resulted in a rapid (1- to 3-h) discharge of ascospores, regardless of whether pseudothecia were incubated in constant light or dark. In the field, daily ascospore release increased between 1900 and 2300 h and again between 0700 and 1000 h local time. The release of ascospores occurred primarily during the early morning hours when relative humidity was decreasing and the canopy began to dry, or during evening hours when relative humidity was low and dew began to form. Few ascospores were released between 1100 and 1800 h when the bentgrass canopy was dry. The release of ascospores also was triggered by precipitation. Of the ascospores collected during precipitation events, 87% occurred within 10 h of the beginning of each event.

A PCR-Based Method for the Detection of Ophiosphaerella agrostis in Creeping Bentgrass

Dead spot is a relatively new disease of creeping bentgrass and hybrid bermudagrass that is incited by Ophiosphaerella agrostis. Initial symptoms are difficult to diagnose and clinicians generally rely on the presence of pseudothecia within infected tissue or isolation of O. agrostis on an artificial medium. The main goal of this study was to develop a polymerase chain reaction-based technique capable of quickly identifying O. agrostis within infected creeping bentgrass tissues. Oligonucleotide primers specific for O. agrostis were developed based on the internal transcribed spacer (ITS) rDNA regions (ITS1 and ITS2) of three previously sequenced isolates of O. agrostis. The 22-bp primers amplified a 445- or 446-bp region of 80 O. agrostis isolates collected from creeping bentgrass and bermudagrass in 11 states. Primers did not amplify DNA from other common turfgrass pathogens, including three closely related species of Ophiosphaerella. Selective amplification of O. agrostis was successful from field-infected creeping bent-grass samples and primers did not amplify the DNA of noninfected, field-grown creeping bent-grass or hybrid bermudagrass plants. Amplification of purified O. agrostis DNA was successful at quantities between 50 ng and 5 pg. The entire process, including DNA isolation, amplification, and amplicon visualization, may be completed within 4 h. These results indicate the specificity of these primers for assisting in the accurate and timely identification of O. agrostis and the diagnosis of dead spot in both bentgrass and bermudagrass hosts.

Genetic Diversity of Sclerotinia homoeocarpa Isolates from Turfgrasses from Various Regions in North America

Sixty-seven isolates of Sclerotinia homoeocarpa, causing dollar spot disease in creeping bentgrass, annual bluegrass, Bermudagrass, and perennial ryegrass turf, collected from 23 golf courses in various geographical regions of the United States and Canada between 1972 and 2001, were characterized by vegetative compatibility, genetic diversity, and pathogenicity. Eleven vegetative compatibility groups (VCGs A to K) were identified among the isolates tested in this study, and five of them (VCGs G to K) were new. VCG B was the most predominant group, typifying 33 isolates (51%) tested. S. homoeocarpa isolates collected from golf courses in Pennsylvania belonged to seven VCGs (A, B, E, F, G, I, and K), whereas three groups were observed in those collected from New York (B, E, and G) and New Jersey (E, H, and I). Two isolates, one each from Pennsylvania and Canada, were incompatible when paired with the tester isolates in all possible combinations, and did not fall into any known VCG. An isolate collected from Canada was compatible with tester isolates from two VCGs (C and D). Genetic analyses using amplified fragment length polymorphism (AFLP) showed the presence of two genetically distinct groups, designated as major group and the minor group. The major group included 36 isolates collected from various golf courses in the United States and Canada. Two isolates collected from bermudagrass in Florida formed a separate cluster, the minor group. Isolates that belonged to the major group were further divided into two subgroups (1 and 2). Subgroup 1 consisted of all the isolates that belonged to VCGs A, E, G, H, and I. Three of the four isolates that belonged to VCG K also were clustered with isolates of subgroup 1. Subgroup 2 consisted of all the isolates from VCG B, and one each from VCGs F and K. Pathogenicity assays on Penncross creeping bentgrass showed significant differences (P = 0.05) in virulence among the isolates. Overall, a relationship between virulence and VCGs was observed, in which certain virulence groups corresponded to specific VCGs; however, such a relationship was not observed between virulence and AFLPs. Close similarity among isolates of S. homoeocarpa collected from different locations in the United States and Canada suggests that isolates of the same genotype could be involved in outbreaks of dollar spot epidemics at multiple locations.

Reactions in the Annual Medicago spp. Core Germ Plasm Collection to Phoma medicaginis

The annual Medicago spp. core collection, consisting of 201 accessions, represents the genetic diversity inherent in 3,159 accessions from 36 annual Medicago spp. This germ plasm was evaluated for resistance to spring black stem and leaf spot caused by Phoma medicaginis. Spring black stem and leaf spot is a major destructive disease in perennial alfalfa (Medicago sativa) grown in North America, Europe, and other temperate regions. Disease control is based principally on the use of cultivars with moderate levels of resistance. Evaluation of the core collection was conducted using standardized environmental conditions in growth chambers, and included the M. sativa standard reference cultivars Ramsey (resistant) and Ranger (susceptible). The degree of resistance found among accessions within species was variable, but most annual species and accessions were susceptible. Most accessions from 10 species exhibited high disease resistance. These included accessions of M. constricta, M. doliata, M. heyniana, M. laciniata, M. lesinsii, M. murex, M. orbicularis, M. praecox, M. soleirolii, and M. tenoreana. Most of the accessions within M. arabica, M. minima, M. lanigera, M. rotata, M. rugosa, M. sauvagei, and M. scutellata were highly susceptible. Disease reactions among some accessions within species were highly variable. On a 0-to-5 disease severity scale, ratings ranged from 0.67 (PI 566873) to 4.29 (PI 566883) within accessions of M. polymorpha. Most of the M. truncatula accessions were susceptible, with a mean of 3.74. Resistant reactions were similar to those found in incompatible interactions with P. medicaginis and alfalfa, which have been associated with specific genes leading to the production of isoflavonoid phytoalexins. The large genetic variability in annual Medicago spp. offers potential for locating and utilizing disease resistance genes through breeding or genetic engineering that will enhance the utilization of Medicago spp. as a forage crop.

Reactivation of Bentgrass Dead Spot and Growth, Pseudothecia Production, and Ascospore Germination of Ophiosphaerella agrostis

Ophiosphaerella agrostis incites bentgrass dead spot (BDS) of creeping bentgrass. Little is known about the biology of O. agrostis; hence the primary goal of this study was to determine some basic biological properties of the pathogen and epidemiological components of the disease. Winter-dormant creeping bentgrass field samples showing symptoms of BDS were incubated at temperatures ranging from 15 to 30°C. Between 12 and 28 days of incubation, reactivation of BDS symptoms occurred at temperatures ≥20°C, but the greatest expansion in BDS patch diameter occurred at 25 and 30°C. The optimum temperatures for growth of hyphae among 10 O. agrostis isolates ranged from 25 to 30°C, and growth was suppressed at 35°C. Pseudothecia of O. agrostis were produced in vitro on a mixture of tall fescue seed and wheat bran. Pseudothecia developed under constant fluorescent light at 13 to 28°C, but no pseudothecia developed in darkness at any temperature. Pseudothecia developed in as few as 4 days, but the highest numbers appeared about 30 days after incubation began. Ascospores incubated at 25°C germinated in as little as 2 h, with germ tubes generally emerging from the terminal rather than interior cells of ascospores. Germination during the first 4 h of incubation was enhanced by both light and the presence of bentgrass leaves or roots. After 18 h of incubation, however, there were few differences in the percentage of ascospores germinated regardless of light treatment or presence of plant tissue.

AFLP Comparisons Among Claviceps africana Isolates from the United States, Mexico, Africa, Australia, India, and Japan

Eighty-seven isolates of the sorghum ergot pathogen, Claviceps africana, from diverse geographic locations were analyzed using four different amplified fragment length polymorphism (AFLP) primer combinations to determine genetic relationships among isolates. Most isolates showed unique AFLP haplotypes, indicating that substantial genetic variation is present within C. africana populations. Two major groupings of isolates were observable, with ca. 70% similarity between the two groups. One group consisted of Australian, Indian, and Japanese isolates and the other of U.S., Mexican, and African isolates. In spite of overall high levels of genetic diversity observed in C. africana, isolates within the two major groups were between 75 and 100% similar. The observed associations of C. africana isolates from worldwide sources could be the result of intercontinental trade and/or movement of seed. The data indicate that Africa was the likely source of C. africana that has become established in the Americas since 1996. Analysis of additional isolates in future studies will reveal whether these groupings are being maintained or whether population subdivision or reshuffling may occur.

Genetic analysis of pathogenic and nonpathogenic Fusarium oxysporum from tomato plants

Forty-three Fusarium oxysporum strains and one Fusarium solani strain were analyzed for genetic diversity. These strains represent a wide range of geographic locations and were collected primarily from tomato (Lycopersicon esculentum) roots. Among all 43 F. oxysporum strains, 21 were not pathogenic to tomato, 20 were pathogenic, including 13 strains of Fusarium oxysporum lycopersici and seven strains of Fusarium oxysporum radicis-lycopersici, and two were other formae speciales of the fungus. Genetic diversity of all 43 strains was assessed by vegetative compatibility group (VCG), sequence analysis of the rDNA internal transcribed spacers (ITS1 and ITS2) and the 5.8S rRNA gene, and amplified fragment length polymorphism (AFLP). Most of the F. o. lycopersici strains were assigned to VCG 0030, while most nonpathogenic ones were incompatible with each other. ITS region analysis grouped the strains into four clusters. The nonpathogenic F. oxysporum strains were in two groups, while the pathogenic strains were placed in two different groups. Pathogenic and nonpathogenic strains were also separated into different clusters based on AFLP data, although some nonpathogenic strains grouped with pathogenic strains. The population of pathogenic strains was less diverse than that of the nonpathogenic strains, suggesting that the pathogenic strains were possibly of monophyletic origin. For both pathogenic and nonpathogenic F. oxysporum strains, no relationship was observed between the genetic profiles and geographic origin; this may indicate that pathogens did not originate independently at each locality.Key words: Fusarium oxysporum, VCG, rDNA (ITS) sequence, AFLP.

Assessment of Diversity in Claviceps africana and Other Claviceps Species by RAM and AFLP Analyses

ABSTRACT Genetic diversity among isolates of Claviceps africana, the sorghum ergot pathogen, and isolates of other Claviceps spp. causing ergot on sorghum or other hosts, was analyzed by random amplified microsatellite (RAM) and amplified fragment length polymorphism (AFLP) analyses. Of the RAM primer sets tested, one revealed polymorphism in C. africana isolates, with Australian and Indian isolates possessing a unique fragment. AFLP analysis, in addition to clearly distinguishing Claviceps spp., revealed polymorphisms in C. africana. A group of isolates from the United States, Puerto Rico, and South Africa exhibited 95 to 100% similarity with one another. Several isolates from Isabela, Puerto Rico were 100% similar to an isolate from Texas, and another isolate from Puerto Rico was identical with one from Nebraska. Australian and Indian isolates showed greater than 90% similarity with isolates from the United States., Puerto Rico, and South Africa. A number of polymorphisms existed in the United States group, indicating that the recently introduced population contains multiple genotypes. Isolates of C. sorghicola, a newly described sorghum pathogen from Japan, were very distinct from other species via RAM and AFLP analyses, as were isolates from outgroups C. purpurea and C. fusiformis. Both RAM and AFLP analysis will be useful in determining future patterns of intercontinental migration of the sorghum ergot pathogen, with the AFLP method showing greater ability to characterize levels of intraspecific variation.

Nep1 Protein from Fusarium oxysporum Enhances Biological Control of Opium Poppy by Pleospora papaveracea

ABSTRACT The fungus Pleospora papaveracea and Nep1, a phytotoxic protein from Fusarium oxysporum, were evaluated for their biocontrol potential on opium poppy (Papaver somniferum). Four treatments consisting of a control, P. papaveracea conidia, Nep1 (5 mug/ml), and P. papaveracea conidia plus Nep1 (5 mug/ml) were used in detached-leaf and whole-plant studies. Conidia of P. papaveracea remained viable for 38 days when stored at 20 or 4 degrees C. Nep1 was stable in the presence of conidia for 38 days when stored at 4 degrees C or for 28 days at 20 degrees C. The presence of Nep1 did not affect conidia germination or appressoria formation. Nep1 was recovered from drops applied to opium poppy leaves in greenhouse and field studies 24 h after treatment. Opium poppy treated with the combination of Nep1 and P. papaveracea had higher necrosis ratings than the other treatments. There were changes in the intercellular protein profiles, determined by sodium dodecyl sulfate gel electrophoresis and silver staining, due to application of treatments; the most intense occurred in response to the combination of Nep1 and P. papaveracea. The combination of Nep1 and P. papaveracea enhanced the damage caused to opium poppy more than either component alone.

Evaluation of Infection Processes and Resulting Disease Caused by Dendryphion penicillatum and Pleospora papaveracea on Papaver somniferum

ABSTRACT Two pathogenic fungi of opium poppy, Pleospora papaveracea and Dendryphion penicillatum, were isolated from field material in Beltsville, MD. The processes of infection by these two fungi were studied to determine the optimal environmental conditions for infection. Both fungi formed appressoria capable of penetrating directly through the plant epidermal layer. Of the two fungi, P. papaveracea was more aggressive, causing more rapid necrosis. Appressorial formation by P. papaveracea occurred as early as 4 h after application of a conidial suspension to poppy leaves. P. papaveracea formed more appressoria than did D. penicillatum, especially at cool temperatures (7 to 13 degrees C). In greenhouse studies, P. papaveracea caused more damage to opium poppy than did D. penicillatum when applied in 10% unrefined corn oil. In the field, P. papaveracea was more consistent in its effects on opium poppy from a local seed source designated Indian Grocery. P. papaveracea caused higher disease ratings, more stem lesions, and equal or greater yield losses than did D. penicillatum on Indian Grocery. The late-maturing opium poppy variety White Cloud was severely damaged by disease, regardless of formulation or fungal treatment. P. papaveracea was the predominant fungus isolated from poppy seed capsules and the only fungus reisolated from the field the following year. These studies provide a better understanding of the infection process and the differences between these two pathogenic fungi and will be beneficial for the development of the fungi as biological control agents.

Dendryphion penicillatum and Pleospora papaveracea, Destructive Seedborne Pathogens and Potential Mycoherbicides for Papaver somniferum

ABSTRACT Dendryphion penicillatum and Pleospora papaveracea were isolated from blighted Papaver somniferum and Papaver bracteatum plants grown in growth chambers and the field in Beltsville, MD. The etiology of the diseases was determined, and the fungi are being investigated as potential mycoherbicides to control the narcotic opium poppy plant. P. papaveracea is known to be a highly destructive seedborne pathogen of Papaver somniferum, causing seedling blight, leaf blight, crown rot, and capsule rot. Single conidia and ascospores were isolated and cultures established from naturally infested seed and diseased foliage and pods of opium poppy from Iran, Colombia, Venezuela, Sweden, India, and the United States (Maryland and Washington). Mycelia and conidia of P. papaveracea and D. penicillatum produced on necrotic leaf tissues appear morphologically similar, and the fungi were previously considered to be anamorph and teleomorph. However, no anamorph/teleomorph connection could be established, and the fungi appear to be distinct taxa. P. papaveracea produced conidia, mature pseudothecia, and chlamydospores in vitro and on infected stems. D. penicillatum produced conidia, microsclerotia, and macronematous conidiophores. Although both fungi were pathogenic to three poppy cultivars, conidial inoculum from P. papaveracea cultures was more virulent than conidial inoculum from D. penicillatum. Eight-week-old plants became necrotic and died 8 days after inoculation with a conidial suspension of P. papaveracea at 2 x 10(5) spores per ml. Disease severity was significantly enhanced by inoculum formulations that contained corn oil, by higher conidial inoculum concentrations, and by increased wetness periods. Symptoms on plants inoculated with either pathogen included leaf and stem necrosis, stem girdling, stunting, necrotic leaf spots, and foliar and pod blight. Inoculated seedlings exhibited wire stem, damping-off, and root rot. Conidia, and less frequently pseudothecia, of P. papaveracea and conidia of D. penicillatum were produced abundantly on inoculated, necrotic foliage, pods, and seedlings. Cultures from conidia or ascospores reisolated from these tissues consistently produced fungi whose morphologies were typical of the fungus from which the inoculum was derived.

Sources of Resistance to Anthracnose in the Annual Medicago Core Collection

The annual genus Medicago core collection, consisting of 201 accessions, represents the genetic diversity inherent in 3,159 accessions from 36 annual Medicago species. This germ plasm was evaluated for resistance to anthracnose caused by Colletotrichum trifolii. Anthracnose is a major disease in perennial alfalfa (Medicago sativa L.) grown in North America and disease control is based principally on the use of resistant varieties. Evaluation of the core collection was conducted using standardized environmental conditions in growth chambers, and included the M. sativa standard reference cvs. Arc (resistant) and Saranac (susceptible). The degree of resistance found among accessions within species was highly variable; however, most annual species and accessions were susceptible. Only 14 accessions from seven species exhibited resistance greater than 40% seedling survival. These included accessions of M. murex, M. muricoleptis, M. polymorpha var. brevispina, M. polymorpha var. polymorpha, M. radiata, M. soleirolii, M. truncatula, and M. turbinata. Of the 12 accessions of M. polymorpha var. polymorpha, 4 exhibited more than 50% resistance, but 3 accessions were 100% susceptible. Most of the M. truncatula and M. turbinata accessions exhibited significantly more resistance than accessions of other species. Plant introduction (PI) accession number PI 495401 of M. muricoleptis exhibited 90.3% resistance. Accessions of M. scutellata were uniformly susceptible. Histological examinations of 14 of the most anthracnose-resistant accessions revealed that C. trifolii spores germinated and produced typical appressoria, but failed to penetrate and produce the primary and secondary hyphae characteristic of susceptible interactions. Resistant reactions were similar to those found in incompatible interactions with C. trifolii and alfalfa, which have been associated with specific genes leading to the production of isoflavonoid phytoalexins. The large genetic variability in annual Medicago spp. offers potential for locating and utilizing disease resistance genes through breeding or genetic engineering that will enhance the utilization of Medicago spp. as a forage crop.

A New Disease of Agrostis palustris Incited by an Undescribed Species of Ophiosphaerella

Creeping bentgrass (Agrostis palustris; syn. Agrostis stolonifera) is widely used on golf course putting greens. In September and October 1998, samples of diseased creeping bentgrass were received from golf courses in Maryland, Virginia, and Ohio. Disease symptoms developed in August or September 1998, and appeared initially as 1.0- to 2.0-cm-diameter, reddish brown spots that enlarged to about 8.0 cm in diameter. Leaves of plants in the center of diseased patches were tan and those on the periphery were reddish brown. Dark, ectotrophic hyphae were not observed on roots. Numerous pseudothecia were embedded in necrotic leaf and stolon tissues. A fungus was isolated from leaves, stems, and roots, and single-spore isolates were obtained from pseudothecia. Colonies of all isolates were identical in appearance and were initially rose-quartz to pinkish brown, developing a gray color as they aged. Inoculum was prepared by placing mycelium from a single-spore isolate on an autoclaved medium consisting of 50% tall fescue (Festuca arundinacea) seed, and 50% wheat (Triticum aestivum) bran (vol/vol) and grown at 28°C for 8 days. Putter and Crenshaw creeping bentgrass seedlings were grown for 14 days in 12 cm² pots containing an autoclaved topdressing mix with a mechanical analysis of 95% sand, 1% silt, and 4% clay. The inoculum (200 mg) was mixed into the upper 5 mm of the sandy soil. Pots were placed in plastic bags and incubated during the daytime on a windowsill bench (20 to 24°C), and were maintained at 25°C at night in a darkened growth chamber. After 7 days, 2.0-cm-diameter patches of blighted leaves were observed on both cultivars in nearly all pots, and pseudothecia were found on the inoculum or on blighted foliage in some pots after 20 days. Blighted leaves were covered with a pale pinkish white mycelium and newly infected leaves at the periphery of the dead spot were a pale reddish brown. Most plants were dead 20 days after inoculation. The fungus was reisolated from blighted leaves of both cultivars and all isolates produced colonies identical in appearance and growth rate to those produced by the single-spore isolate. Pseudothecia produced in vivo were sectioned with a freezing microtome and examined microscopically. Bitunicate asci were observed and contained light-brown, 6- to 15-septate, filiform ascospores that were usually spirally twisted in the ascus and measured 70 to 150 × 2.0 to 2.5 μm. Characteristics of the pseudothecia and the ascospores fit those of the genus Ophiosphaerella Speg. (1). Based on morphometric studies of 12 collections from three different states, this fungus can be distinguished from O. graminicola by the lack of periphyses and fewer septa in ascospores (i.e., 12 to 20 septa in O. graminicola). It was distinguished from O. herpotricha by characteristics of the pseudothecia neck, ascospores, and colony color. Because of these differences, we suggest that this fungus represents a new species attacking creeping bentgrass, which will be described after further morphometric and molecular analyses. Reference: (1) J. Walker. Mycotaxon 11:1, 1980.

Alfalfa (Medicago sativa L.) resistance to the root-lesion nematode, Pratylenchus penetrans: defense-response gene mRNA and isoflavonoid phytoalexin levels in roots

Alfalfa (Medicago sativa) varieties with antibiosis-based resistance to the root-lesion nematode (Pratylenchus penetrans), a migratory endoparasite of many crops, have been developed by recurrent selection. Individual plants from these varieties that support significantly lower nematode reproduction were identified for molecular and biochemical characterization of defense responses. Before nematode infection, RNA blot analysis revealed 1.3-1.8-fold higher phenylpropanoid pathway mRNA levels in roots of three resistant plants as compared to three susceptible alfalfa plants. The mRNAs encoded the first enzyme in the pathway (phenylalanine ammonia-lyase), the first in the pathway branch for flavonoid biosynthesis (chalcone synthase), a key enzyme in medicarpin biosynthesis (isoflavone reductase) and a key enzyme in the pathway branch for biosynthesis of lignin cell wall precursors (caffeic acid O-methyltransferase). After nematode infection, the mRNAs declined over 48 h in resistant roots but rose in susceptible plants during the first 12 h after-infection and then declined. Acidic beta-1,3-glucanase mRNA levels were initially similar in both root types but accumulated more rapidly in resistant than in susceptible roots after nematode infection. Levels of a class I chitinase mRNA were similar in both root types. Histone H3.2 mRNA levels, initially 1.3-fold higher in resistant roots, declined over 6-12 h to levels found in susceptible roots and remained stable in both root types thereafter. Defense-response gene transcripts in roots of nematode-resistant and susceptible alfalfa plants thus differed both constitutively and in inductive responses to nematode infection. HPLC analysis of isoflavonoid-derived metabolites of the phenylpropanoid pathway revealed similar total constitutive levels, but varying relative proportions and types, in roots of the resistant and susceptible plants. Nematode infection had no effect on isoflavonoid levels. Constitutive levels of the phytoalexin medicarpin were highest in roots of the two most resistant plants. Medicarpin inhibited motility of P. penetrans in vitro.

Application of amplified restriction fragment length polymorphism for genetic characterization of colletotrichum pathogens of alfalfa

ABSTRACT Amplified restriction fragment length polymorphism (AFLP) was used to assess the levels of genomic variations among species and isolates of the genus Colletotrichum. Our objective was to characterize at the molecular level two alfalfa pathogens, isolates Arl-NW and 57RR, which are unusually aggressive to anthracnose-resistant alfalfa cultivars and whose taxa has been uncertain based on morphological criteria. The fingerprint patterns obtained were complex but did enable us to place these two isolates within the species C. trifolii and C. gloeosporioides, respectively. The diversity detected with AFLP among and within Colletotrichum species from alfalfa and other crops corroborated their published taxonomy based on morphology, ribosomal DNA sequence, and random amplified polymorphic DNA analyses. Similarity matrices generated with three primer pairs were highly correlated and, thus, were combined to determine the similarity among the fungal species and isolates that were analyzed. Analysis of the data generated with each of the primer pairs individually and application of either distance or parsimony methods supported the placement of these two isolates. The parsimony method of data analysis was more confirmatory in the placement of Phoma medicaginis as an out-group than the distance method, using either simple matching or Jaccard's coefficients to generate the similarity matrices. Our conclusion is that the AFLP technique will be useful for identification of individual isolates within complex genera such as Colletotrichum because of its ability to generate large numbers of polymorphisms and the consistency of polymerase chain reaction amplification.