Host Range Data Research Articles

Host range and impact of the stem- and leaf-deforming thrips, Liothrips tractabilis: a biological control agent for Campuloclinium macrocephalum, in South Africa

We report on the host range and impact of Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripinae), the first biological control agent to be considered for Campuloclinium macrocephalum (Less.) DC. (Asteraceae) (pompom weed) in South Africa. Laboratory host-range tests were conducted on 45 Asteraceae species. Field host range studies included 16 Asteraceae species. Results of both laboratory tests and field host range data indicated that L. tractabilis is suitably host specific to C. macrocephalum and hence safe for release in South Africa. Laboratory impact studies on both seedlings and regrowth showed that, even under low inoculation densities, L. tractabilis had a significant impact on plant height, number of leaves, flower production and biomass. Based on the above data, permission for the release of the thrips was applied for, and in June 2013, granted by South African authorities. First releases of L. tractabilis were made in the summer of 2013/2014, and in November 2014 its establishment was confirmed.

Successes We May Not Have Had: A Retrospective Analysis of Selected Weed Biological Control Agents in the United States

AbstractIn this paper, we describe five successful classical biological weed control agents released in the United States. For each of the five arthropod species, we compared data from prerelease studies that experimentally predicted the agent's host range with data collected postrelease. In general, experimental host range data accurately predicted or overestimated risks to nontarget plants. We compare the five cases with insects recently denied for introduction in the United States and conclude that none of the discussed agents would likely be approved if they were petitioned today. Three agents would be rejected because they potentially could attack economic plants, and two because of potential attack on threatened or endangered plants. All five biocontrol agents have contributed significantly to the successful management of major weeds with no or minimal environmental risk. We believe that the United States may miss opportunities for sustainable and environmentally benign management of weeds using biological control if the regulatory framework only considers the risks of agents as potential plant pests and treats any host-range data regarding economic or threatened and endangered species as a binary decision (i.e., mandates rejection if there is any chance of feeding or development). As a way forward we propose the following: (1) the addition of risk and benefit analyses at the habitat level with a clear ranking of decision-making criteria as part of the U.S. Department of Agriculture Animal and Plant Health Inspection Service Technical Advisory Group's evaluation process of biocontrol agents; (2) recognition of the primacy of realized host range data for potential agents that considers the insect's host selection behavior instead of emphasizing fundamental host range data during release evaluations, and (3) development of formalized postrelease monitoring of target and nontarget species as part of the release permit. These recommendations may initially be advanced through reassessment of current policies but may in the longer term require the implementation of dedicated biocontrol legislation.

Plasmopara sphagneticolae sp. nov. (Peronosporales) on Sphagneticola (Asteraceae) in Australia

A specimen of downy mildew on leaves of Sphagneticola trilobata found in northern Queensland was identified by a systematic approach as a novel species of Plasmopara. A new species, Plasmopara sphagneticolae, is proposed for this specimen, which differs from other species of Plasmopara by morphology, host range, and sequence data from nuclear-ribosomal DNA and mitochondrial DNA. Plasmopara sphagneticolae, together with P. halstedii, are downy mildews found on host species in the tribe Heliantheae (Asteraceae). Plasmopara halstedii causes downy mildew on Helianthus annuus, and is not present on sunflower in Australia. Phylogenetic analysis of the large subunit region of ribosomal DNA showed that P. sphagneticolae was sister to P. halstedii on sunflower.

A promising biological control agent for the invasive alien plant, Pereskia aculeata Miller (Cactaceae), in South Africa

Pereskia aculeata Miller (Cactaceae) is an invasive alien plant from Central and South America that has become a problematic environmental weed in South Africa. A potential biological control agent, the stem-wilter, Catorhintha schaffneri Brailovsky & Garcia (Coreidae), was collected in southern Brazil and imported into quarantine in South Africa. Field host range data suggested that C. schaffneri has a host range restricted to P. aculeata. No-choice nymph survival tests were then conducted on 27 test plant species in 9 families. Survival to the adult stage was only recorded on P. aculeata and the closely related Pereskia grandifolia Haw. (Cactaceae). Mortality was significantly higher on P. grandifolia with only 3% of the nymphs reaching the adult stage compared with 74% on P. aculeata indicating that P. aculeata is the primary host plant. P. grandifolia is native in South America and is of no agricultural importance in South Africa so any feeding on P. grandifolia in South Africa would have no negative environmental or economic consequences. In other tests, adult survival on P. aculeata [25.8 days (SE ± 3.74)] was significantly longer than on other test plant species [4.3 days (SE ± 0.36)] further confirming the host specificity of the species. Impact studies conducted in quarantine indicated that C. schaffneri is damaging to P. aculeata, significantly reducing the number of leaves and the shoot lengths of plants, even at relatively low insect densities. C. schaffneri is safe for release in South Africa and is likely to be a damaging and effective agent.

VerticilliumSystematics and Evolution: How Confusion Impedes Verticillium Wilt Management and How to Resolve It

Verticillium wilts are important vascular wilt diseases that affect many crops and ornamentals in different regions of the world. Verticillium wilts are caused by members of the ascomycete genus Verticillium, a small group of 10 species that are related to the agents of anthracnose caused by Colletotrichum species. Verticillium has a long and complicated taxonomic history with controversies about species boundaries and long overlooked cryptic species, which confused and limited our knowledge of the biology of individual species. We first review the taxonomic history of Verticillium, provide an update and explanation of the current system of classification and compile host range and geographic distribution data for individual species from internal transcribed spacer (ITS) GenBank records. Using Verticillium as an example, we show that species names are a poor vehicle for archiving and retrieving information, and that species identifications should always be backed up by DNA sequence data and DNA extracts that are made publicly available. If such a system were made a prerequisite for publication, all species identifications could be evaluated retroactively, and our knowledge of the biology of individual species would be immune from taxonomic changes, controversy and misidentification. Adoption of this system would improve quarantine practices and the management of diseases caused by various plant pathogens.

Prioritisation of potential agents for the biological control of the invasive alien weed, Pereskia aculeata (Cactaceae), in South Africa

Pereskia aculeata Miller (Cactaceae) is an invasive alien species in South Africa that is native in Central and South America. In South Africa, P. aculeata outcompetes native plant species leading to a reduction in biodiversity at infested sites. Herbicidal and mechanical control of the plant is ineffective and unsustainable, so biological control is considered the only potential solution. Climatic matching and genotype matching indicated that the most appropriate regions in which to collect biological control agents were Santa Catarina and Rio de Janeiro provinces in Southern Brazil. Surveys throughout the native distribution resulted in 15 natural enemy species that were associated with the plant. Field host range data, as well as previous host plant records, were used to prioritise which of the species were most likely to be suitably host specific for release in South Africa. The mode of damage was used to determine which species were most likely to be damaging and effective if released. The most promising species prioritised for further study, including host specificity and impact studies, were the stem-wilter Catorhintha schaffneri Brailovsky & Garcia (Coreidae); the stem boring species Acanthodoxus machacalis Martins & Monné (Cerambycidae), Cryptorhynchus sp. (Curculionidae) and Maracayia chlorisalis (Walker) (Crambidae) and the fruit galler Asphondylia sp. (Cecidomyiidae). By prioritising the potential biological control agents that are most likely to be host-specific and damaging, the risk of conducting host specificity testing on unsuitable or ineffective biological control agents is reduced.

A New Genus and Species of Delphacini (Hemiptera: Fulgoromorpha: Delphacidae) Associated with Hydrophytic Plants in Argentina

A new delphacid genus and species from Argentina, Lepidelphax pistiae Remes Lenicov, gen. et sp. nov.(Hemiptera: Fulgoromorpha: Delphacidae: Delphacini), is described and illustrated, and biological, distribution and experimental host range data are provided. Males of the new genus are easily distinguished from all other Neotropical Delphacini by being pale cream to white in color with a distinctive pair of longitudinal stripes on the face and symmetrical dark brown to black spots on the thorax and abdomen; very slender, laterally compressed, with long legs, narrow and short vertex with a small sub-apical areola continued by a distinctively simple frontal median carina. It also has unique malegenital structures. Laboratory and field data indicate this species is a specialized herbivore that feeds and oviposits exclusively on Pistia stratiotes (Alismatales: Araceae), a floating macrophyte native to South America. Lepidelphax pistiae was found throughout the distribution of P. stratiotes in Argentina.

The Prevalence of the Citrus tristeza virus Trifoliate Resistance Breaking Genotype Among Puerto Rican Isolates.

Citrus tristeza virus (CTV) isolates have been grouped into six genotypes: T3, T30, T36, VT, B165, and resistance breaking (RB) based on symptoms, host range, and genomic sequence data. The RB genotype has recently been identified with the novel property of replicating in trifoliate orange trees, a resistant host for the other five genotypes. Puerto Rican CTV isolate B301 caused mild vein clearing symptoms in Mexican lime but did not induce seedling yellows or stem pitting reactions in appropriate indicator Citrus spp., which are typical host reactions of the isolate T30. The isolate B301 was not detected by the genotype specific primer (GSP), which identifies the CTV-T3, -T30, -T36, -VT, and B165 genotypes. A primer pair for reverse transcription polymerase chain reaction (RT-PCR) amplification of the CTV-RB genotype was designed from the heat shock protein (p65) region based on the complete genomic sequences of trifoliate RB isolates from New Zealand available in the GenBank databases. The amplicon sequence from isolate B301 was 98% identical to that of the other trifoliate RB isolates. In addition, B301 was successfully inoculated into 'Carrizo citrange' (a trifoliate hybrid) but did not induce any symptoms. Furthermore, the complete genome sequence of B301 followed by the phylogenetic analysis revealed that the isolate is part of the RB clade with other CTV-RB isolates from New Zealand and Hawaii. Additional CTV isolates obtained from Puerto Rico were tested with the RB-GSP and confirmed the presence of trifoliate RB isolates in mixed infection with known CTV genotypes. Although this is the first report of a CTV trifoliate RB genotype from Puerto Rico, this genotype was present there prior to 1992.

Evolutionary tools for phytosanitary risk analysis: phylogenetic signal as a predictor of host range of plant pests and pathogens

Assessing risk from a novel pest or pathogen requires knowing which local plant species are susceptible. Empirical data on the local host range of novel pests are usually lacking, but we know that some pests are more likely to attack closely related plant species than species separated by greater evolutionary distance. We use the Global Pest and Disease Database, an internal database maintained by the United States Department of Agriculture Animal and Plant Health Inspection Service – Plant Protection and Quarantine Division (USDA APHIS-PPQ), to evaluate the strength of the phylogenetic signal in host range for nine major groups of plant pests and pathogens. Eight of nine groups showed significant phylogenetic signal in host range. Additionally, pests and pathogens with more known hosts attacked a phylogenetically broader range of hosts. This suggests that easily obtained data – the number of known hosts and the phylogenetic distance between known hosts and other species of interest – can be used to predict which plant species are likely to be susceptible to a particular pest. This can facilitate rapid assessment of risk from novel pests and pathogens when empirical host range data are not yet available and guide efficient collection of empirical data for risk evaluation.

Comparing predictions from mixed model equations with host range determinations from historical disease evaluation data of two previously released weed biological control pathogens

Host range determination is essential to risk assessments of classical biological weed control agents and needed for petitions to release of agents into non-native areas. Recently Henderson’s mixed model equations (MME) were adapted to evaluating host ranges of two biological control pathogens. This was accomplished by incorporating genetic relatedness, in the form of DNA sequences, with disease evaluation data among target and non-target plants to generate best linear unbiased predictors (BLUPs) of disease reaction among these plant species. Although qualities of MME analysis provide inherent validation of the approach, it has been difficult to validate by comparison with historical host range determination or field data. These types of data are virtually non-existent, because original, raw host range data from replicated tests have, for the most part, been lost, and host-range data from tests or monitoring of multiple plant species in the field are extremely limited. In this study, the host-ranges of two biological weed control pathogens previously released in the USA were re-evaluated with the MME and historical host-range data. Results showed that: BLUPs confirmed the narrow host range of the two pathogens; BLUPs supported and substantiated currently available information on host range; BLUPs were accurate predictors of host range, particularly concerning susceptibility of any non-target species in the field; and no new, unforeseen non-target effects could be expected in nature on the basis of BLUPs. Thus, validation was made for MME analysis in predicting known field host-range from greenhouse data.

Portal protein diversity and phage ecology

Recent whole-genome cyanophage sequencing (Sullivan et al., 2010) has revealed that the sequences of some genes do not match those published previously as single-gene sequences derived from DNA fragments PCR-amplified from phage isolates. Specifically, the g20 gene sequences for S-SSM7 (gene GI:189397276, protein GI:189397277) and Syn33 (gene GI:189397306, protein GI:189397307) in Sullivan and colleagues (2008) were incorrect. The revised sequences do not alter g20 tree topology or the conclusions of Sullivan and colleagues (2008). The source of error for these gene sequences is not certain, but could have its origin in either a clerical error, PCR contamination and/or mixed phage stocks. On this latter point, it has recently come to light that triplicate plaque purifications do not always result in pure stocks for these cyanophages, possibly due to the fluid consistency of the agarose plates (0.28% agarose) required for growth of the host. More reliable purification procedures have subsequently been developed. However, as mixed phage stock preparations could influence host range, we recommend that published host range data (Sullivan et al., 2003) be verified before their use in further research.

Reconstructing host range evolution of bacterial plant pathogens using Pseudomonas syringae pv. tomato and its close relatives as a model

Several lines of evidence suggest that highly virulent bacterial human pathogens evolved from less virulent wider host range animal pathogens since human migration out of Africa. To investigate evolution of host specificity of bacterial plant pathogens, here we report a molecular evolutionary analysis of the model plant pathogen Pseudomonas syringae pv. tomato DC3000 and of close relatives that are pathogens of a diverse set of crop plants. Extensive host range tests on five different plant species were performed. Combining phylogenetic data with host range data, a reconstruction of host range of all putative ancestors was performed. In particular, the hypothesis was tested that highly virulent narrow host range pathogens of today’s crops grown in monoculture evolved from ancestors with wider host range that were adapted to natural mixed plant communities of pre-agricultural times. We found support for this hypothesis in individual clades. However, reconstruction of host range of the most recent common ancestor of all analyzed strains was not conclusive. Based on the obtained results we stress the importance of including pathogens from wild plants when reconstructing the evolution of plant pathogenic bacteria.

Host range testing of a prospective classical biological control agent against cabbage maggot, Delia radicum, in Canada

The introduction of a European natural enemy, Aleochara bipustulata L. (Coleoptera: Staphylinidae), is being considered for control of cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae) in canola in Canada, and the host specificity of this pupal parasitoid must first be studied. Contemporary guidelines were used to select 18 species of Diptera to represent non-target species taxonomically related or ecologically similar to reported hosts of A. bipustulata, or beneficial species. No-choice tests were used to determine which of the 18 species are within A. bipustulata’s fundamental host range, and whether puparial structure or mass or duration of pupal development influence their acceptability and suitability as hosts. Five species were consistently suitable as hosts, and these were either relatively small or were taxonomically closely related to the target host. The probability that a puparium would be entered by a parasitoid larva was greatest for small puparia, but was unaffected by pupal duration. The probability of completing parasitoid development once a puparium was entered was influenced by both puparial mass and duration of pupal development. Pitfall traps to assess habitat associations caught A. bipustulata adults in a variety of crop habitats but none were caught in forests. Host range and habitat data are used to argue that there is little risk of parasitism to beneficial taxa. Non-target species taxonomically closely related to the target D. radicum or with small puparia may fall within the fundamental host range of A. bipustulata. However, risk to many of these species may be minimal because of the habitat preferences of the parasitoid and its cues for host-finding and recognition.

Bidens mottle virus and Apium virus Y Identified in Ammi majus in Florida.

Ammi majus (bishop's weed), a member of the Apiaceae, is grown from seed for cut flowers in South Florida. In March 2005, plants were found to be showing virus-like symptoms including mosaic, vein clearing, and leaf rugosity (3) that rendered their flowers unmarketable. Inclusion morphology in epidermal strips from these infected plants indicated the presence of one or more potyviruses. This was confirmed by ELISA with commercially available antiserum for potyvirus identification (Agdia, Elkhart, IN). Clover yellow vein virus (ClYVV) was identified by sequencing and confirmed with specific antiserum (4). However, ClYVV was not identified in all potyvirus-infected samples from 2005, indicating the presence of one or more additional potyviruses. Bidens mottle virus (BiMoV) was subsequently identified in one of three potyvirus-infected samples by immunodiffusion tests using specific antiserum for BiMoV (Department of Plant Pathology, University of Florida), cylindrical inclusion morphology in epidermal strips, host range data, and sequencing of cloned reverse transcription (RT)-PCR products from degenerate potyvirus primers (2). Nucleotide and deduced amino acid sequences of a partial polyprotein gene sequence (GenBank Accession No. EU255631) were 95 and 98% identical, respectively, to a Florida isolate of BiMoV recently reported from tropical soda apple (1). Similar virus-like symptoms were again observed in A. majus in January 2007 and persisted through March. ELISA testing again indicated the presence of a potyvirus. However, neither ClYVV nor BiMoV were identified in the initial 2007 samples. Instead, sequence analysis of the cloned RT-PCR products amplified with degenerate potyvirus primers (2) from seven potyvirus-infected samples collected on two dates in January and one each in February and March revealed the presence of Apium virus Y (ApVY). The 3' terminal portion of the genome (GenBank Accession No. EU255632) was found to be 90 to 91% identical to ApVY sequences in GenBank at the nucleotide level. Deduced amino acid sequences of the NIb and CP regions of these RT-PCR products were 96 and 95% identical, respectively, to ApVY sequences in GenBank. One of these seven ApVY-infected samples (collected in March 2007) was determined to be coinfected with BiMoV by sequence analysis of the cloned RT-PCR products. Six clones were sequenced. Three were determined to be ApVY as indicated above. Nucleotide and deduced amino acid sequences of a partial polyprotein gene sequence from the other three clones were 95 and 97% identical, respectively, to the 2005 A. majus BiMoV isolate. Although ClYVV and BiMoV have previously been reported in other hosts in Florida, to the best of our knowledge, this is the first report of BiMoV and ApVY in A. majus anywhere and the first report of ApVY in North America.

Identification and Partial Characterization of a New Luteovirus Associated with Rose Spring Dwarf Disease.

A number of viruses in the genera Ilarvirus and Nepovirus have been shown to be associated with specific diseases in rose, but many graft-transmissible rose diseases still have unknown etiologies. One of these diseases originally was detected by grafting from nonsymptomatic roses to Rosa multiflora indicator plants. Double-stranded RNAs (dsRNAs) were recovered and used as templates for cDNA synthesis and generating a cDNA library. Analysis of deduced amino acid sequences clearly positioned this virus as a member of the family Luteoviridae. The name rose spring dwarf associated virus (RSDaV) is tentatively proposed for the novel virus because the symptoms of this virus on R. multiflora are consistent with previous descriptions of rose spring dwarf disease (RSD). Phylogenetic analysis revealed a close relationship of RSDaV with members of the genus Luteovirus. Aphid transmission studies identified the rose-grass aphid (Metapolophium dirhodum) and yellow rose aphid (Rhodobium porosum) as vectors for this new virus. Host range data showed that RSDaV has a host range including both monocots and dicots. A specific reverse-transcription polymerase chain reaction assay was developed and revealed the presence of the RSDaV in several rose cultivars. RSDaV-inoculated rose plants developed RSD symptoms, confirming its role in the etiology of the disease.

Bidens mottle virus Identified in Tropical Soda Apple in Florida.

Tropical soda apple (TSA) (Solanum viarum Dunal), a plant native to South America, was first identified in Florida in 1988 (4). It rapidly became a noxious weed in pastures throughout the state and it is known to be a reservoir for Cucumber mosaic virus, Potato leafroll virus, Potato virus Y (PVY), Tobacco etch virus (TEV), Tomato mosaic virus, and Tomato mottle virus, viruses that infect important vegetable crops in Florida (3). During a routine survey of Florida weeds during May of 2004, a TSA plant with chlorotic, young leaves found near Okeechobee, FL was determined to be infected with a potyvirus by using a commercially available enzyme linked immunosorbent assay kit (Agdia, Elkhart, IN). The results of a host range study indicated this potyvirus was neither PVY nor TEV. The virus caused local lesions in Chenopodium amaranticolor and systemic symptoms in C quinoa, Coreopsis sp. (C. A. Baker, unpublished), Helianthus annus, Nicotiana benthamiana, Petunia × hybrida, Verbena hybrida, and Zinnia elegans. It did not infect Gomphrena globosa, N. glutinosa, Pisum sativum, or Phaseolus vulgaris (1). Cylindrical inclusions consistent with those observed in plants infected with Bidens mottle virus (BiMoV) were observed in Z. elegans. Immunodiffusion tests with antiserum to BiMoV (Department of Plant Pathology, University of Florida) gave a reaction of identity with leaf extracts of the symptomatic zinnia, a known sample of BiMoV originally isolated from Bidens pilosa and a recent isolate of BiMoV from lettuce in Belle Glade, FL (C. A. Baker and R. Raid, unpublished). A partial polyprotein gene fragment (GenBank Accession No. EF467235) was amplified from total RNA of an inoculated C. quinoa plant by reverse transcription (RT)-PCR with previously described degenerate potyvirus primers (2). Analysis of the RT-PCR product sequence confirmed the host range results and indicated that the potyvirus infecting TSA was neither PVY nor TEV. However, the nucleotide and deduced amino acid sequences of a 247-bp portion of the RT-PCR product were 94 and 98% identical, respectively, with the coat protein sequence (GenBank Accession No. AF538686) of Sunflower chlorotic spot virus (SCSV). SCSV is a tentative potyvirus species described from Taiwan that is not yet recognized as an accepted species by the International Committee on Taxonomy of Viruses. On the basis of our concurrent host range, inclusion body, and serological data, it is likely that SCSV is in actuality the previously described and currently accepted potyvirus species BiMoV, for which no previous sequence data existed. As part of a comprehensive viral disease management plan, it is recommended that TSA plants growing in and around lettuce-production areas be controlled along with other weed hosts of this virus.

Inonotus dryadeus in North America: new records, hosts, distribution and incidence

Summary Inonotus dryadeus is newly reported in eastern Canada (Ontario) on Acer platanoides and Acer saccharinum, both new hosts, and Ulmus americana. The host range, incidence, and available distributional data in continental North America are summarized in a table. The fungus occurs primarily on Quercus, Abies, and Tsuga. Occasionally, it is found on Picea and Pinus as well as many other hardwood trees. Colder climates and host differences in the boreal forests may be limiting distributional factors. Inonotus dryadeus appears to favour very old trees. The maximum known width of the fruiting body is revised upward to 74.9 cm.

Can Host Susceptibility to Baculovirus Infection be Predicted from Host Taxonomy or Life History?

Host range is a fundamental aspect of host-pathogen population dynamics and is a vital determinant of the risks associated with the use of a pathogen for biological control. Yet even for widely studied baculoviruses we often do not know which hosts they infect under natural conditions. Baculoviruses are primarily pathogens of Lepidoptera and Hymenoptera and exhibit great variation in host range. Some are apparently monospecific, whereas others are able to infect numerous hosts from diverse families. In this report, I review host range data, concentrating on two generalist viruses, Autographa californica (Speyer) multicapsid nucleopolyhedrovirus (AcMNPV) and Mamestra brassicae L. multicapsid NPV (MbMNPV). To my knowledge, 145 and 78 host species have been assayed with AcMNPV and MbMNPV, respectively. I examined susceptibility of these species according to various life history parameters using a phylogenetic analysis. Host susceptibility was poorly predicted by taxonomic relationships. Host susceptibility was correlated with some life history traits; of the species tested, a significantly higher proportion of polyphagous species and pest species were susceptible to AcMNPV compared with mono- or oligophagous species or nonpest species, respectively. A higher proportion of multivoltine species were susceptible to MbMNPV compared with univoltine species, although the opposite trend was shown for AcMNPV. Providing convincing explanations for these patterns is problematic and highlights the inadequacies in our understanding of the ecology of baculoviruses. Some possible explanations are discussed. I suggest that current patterns of host susceptibility may, in part, reflect an ongoing evolutionary arms race between numerous host species and each baculovirus, in which the virus repeatedly colonizes new host populations and new species while others evolve resistance.

Molecular identification of anamorphic powdery mildews (Erysiphales)

The powdery mildew fungi (Erysiphales) are a common group of obligate plant pathogens that can be extremely difficult to identify, depending on the reproductive stage encountered, The ribosomal DNA Internal Transcribed Spacer (ITS) region was assessed for its usefulness to link anamorphic Erysiphales with their respective teleomorphs. PCR primers for the rDNA ITS region were designed and found to have enhanced specificity for the 12 genera tested, even in the presence of contaminating fungi. Recent herbarium specimens of both anamorphic and teleomorphic material yielded sufficient DNA for amplification using a Chelex-based extraction method. The ITS regions from 25 anamorphic specimens were sequence d and compared with the ITS sequences of their suspected teleomorphs. In most cases, an ITS region sequence similarity of above 99% indicated that a correct match had been made, although a specimen on Phlox could not be identified and a somewhat unexpected match was made between a specimen on Convolvulus and the celery powdery mildew (Erysiphe heraclei). Although this technique will not always unambiguously identify an anamorphic specimen, it will provide valuable information to use in conjunction with morphological and host range data to aid in the final identification.

Advances in the identification of emerging powdery mildew fungi using morphological and molecular data.

Recently, the classical morphological criteria and host range data used in the identification of powdery mildew fungi were supplemented with scanning electron microscope (SEM) and molecular phylogenetic analyses. This paper discusses the joint use of these methods in the identification of powdery mildew anamorphs causing new or emerging plant diseases in different parts of the world.