The Top 10 Oomycete Pathogens in Molecular Plant Pathology

Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens that threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. The article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.

Principles of plant pathology; a text and laboratory manual.

Reproduced from typewritten copy.

Soviet publications in plant pathology and closely related fields; titles published from 1925 through early 1953 and available in the Library of the U.S. Department of Agriculture.

Mode of access: Internet.

A check list of the publications of the Department of Agriculture on the subject of plant pathology, 1837-1918.

Mimeographed.

Controlling Bacterial Wilt in Muskmelon with Perimeter Trap Cropping

Perimeter trap cropping (PTC) involves planting one or more rows of a cucurbit crop that is highly attractive to cucumber beetles around the border of a main cucurbit cash crop that is less attractive to the beetles. Cucumber beetles attempting to migrate into the field are concentrated in the relatively more attractive border crop, where they can be controlled by insecticides. In New England, perimeter trap cropping using Blue Hubbard squash as the border crop around pumpkin, cucumber, or butternut squash controlled cucumber beetle/bacterial wilt with as few as one border spray of insecticide. This strategy reduced insecticide use on the main crop by up to 94 percent, nearly eliminating sprays on the main cash crop. In on-farm trials, 8 of 10 Massachusetts growers found that using perimeter trap cropping saved them money. The same tactic also effectively managed cucumber beetles on muskmelon and squash in Oklahoma.

Development of a small-plant bioassay to assess banana grown from tissue culture for consistent infection by Fusarium oxysporum f. sp. cubense

Two reliable small-plant bioassays were developed using tissue-cultured banana, resulting in consistent symptom expression and infection by Fusarium oxysporum f. sp. cubense (Foc). One bioassay was based on providing a constant watertable within a closed pot and the second used free-draining pots. Culture medium for spore generation influenced infectivity of Foc. Inoculation of potted banana by drenching potting mix with a conidial suspension, consisting mostly of microconidia, few macroconidia and no chlamydospores, generated from one-quarter-strength potato dextrose agar + streptomycin sulfate, resulted in inconsistent infection. When a conidial suspension that consisted of all three spore types, microconidia, macroconidia and chlamydospores, prepared from spores generated on carnation leaf agar was used, all plants became infected, indicating that the spore type present in conidial suspensions may contribute to inconsistency of infection. Inconsistency of infection was not due to loss of virulence of the pathogen in culture. Millet grain precolonised by Foc as a source of inoculum resulted in consistent infection between replicate plants. Sorghum was not a suitable grain for preparation of inoculum as it was observed to discolour roots and has the potential to stunt root growth, possibly due to the release of phytotoxins. For the modified closed-pot system, a pasteurised potting mix consisting of equal parts of bedding sand, perlite and vermiculite plus 1 g/L Triabon slow release fertiliser was suitable for plant growth and promoted capillary movement of water through the potting mix profile. A suitable potting mix for the free-draining pot system was also developed.

Preface to Lesser Known Large dsDNA Viruses. Current Topics in Microbiology and Immunology 328

Several large dsDNA-containing viruses such as poxviruses (smallpox) and herpes viruses are well known among the scientific community, as well as the general populace, because they cause human diseases. The large dsDNA insect-infecting baculoviruses are also well known in the scientific community because they are used both as biological control agents and as protein expression systems. However, there are other large dsDNA-containing viruses, including the giant 1.2-Mb mimivirus, which are less well known even though all of them play important roles in everyday life. Seven of these virus families are reviewed in this book.

Effect of Fungicides and Plant Populations on Soybean Disease and Yield

Applications of foliar fungicides on soybeans have been shown to reduce disease pressure and protect yield under the right conditions, especially in environments that have very wet or humid conditions. In the past decade, fungicide use in Iowa has increased. Initially, growers were concerned with the potential threat of soybean rust, which is controlled effectively by foliar fungicides. In Iowa, however, there has not been any case of yield reduction due to soybean rust. New potential purposes for foliar fungicides include “plant health” benefits and the reduction of foliar diseases endemic in Iowa such as Septoria brown spot, Cercospora leaf blight, and frogeye leaf spot. Currently what is not known is how the efficacy of fungicides is affected when agricultural practices change. Our question: How does plant population affect the efficacy of fungicides?

Anti-quorum sensing agents from south Florida medicinal plants and their attenuation of Pseudomonas aeruginosa pathogenicity

With the difficulty in treating recalcitrant infections and the growing resistance to antibiotics, new therapeutic modalities are becoming increasingly necessary. The interruption of bacterial quorum sensing (QS), or cell-cell communication is known to attenuate virulence, while limiting selective pressure toward resistance. This study initiates an ethnobotanically-directed search for QS inhibiting agents in south Florida medicinal plants. Fifty plants were screened for anti-QS activity using two biomonitor strains, Chromobacterium violaceum and Agrobacterium tumefaciens. Of these plants, six showed QS inhibition: Conocarpus erectus L. (Combretaceae), Chamaecyce hypericifolia (L.) Millsp. (Euphorbiaceae), Callistemon viminalis (Sol.ex Gaertn.) G. Don (Myrtaceae), Bucida burceras L. (Combretaceae), Tetrazygia bicolor (Mill.) Cogn. (Melastomataceae), and Quercus virginiana Mill. (Fagaceae). These plants were further examined for their effects on the QS system and virulence of Pseudomonas aeruginosa, an intractable opportunistic pathogen responsible for morbidity and mortality in the immunocompromised patient. C. erectus, B. buceras, and C. viminalis were found to significantly inhibit multiple virulence factors and biofilm formation in this organism. Each plant presented a distinct profile of effect on QS genes and signaling molecules, suggesting varying modes of action. Virulence attenuation was observed with marginal reduction of bacterial growth, suggesting quorum quenching mechanisms unrelated to static or cidal effects. Extracts of these plants were also investigated for their effects on P. aeruginosa killing of the nematode Caenorhabditis elegans. Results were evaluated in both toxin-based and infection-based assays with P. aeruginosa strains PA01 and PA14. Overall nematode mortality was reduced 50-90%. There was no indication of host toxicity, suggesting the potential for further development as anti-infectives. Using low-pressure chromatography and HPLC, two stereoisomeric ellagitannins, vescalagin and castalagin were isolated from an aqueous extract of C. erectus . Structures were confirmed via mass spectrometry and NMR spectroscopy. Both ellagitannins were shown to decrease signal production, QS gene expression, and virulence factor production in P. aeruginosa. This study introduces a potentially new therapeutic direction for the treatment of bacterial infections. In addition, this is the first report of vescalagin and castalagin being isolated from C. erectus, and the first report of ellagitannin activity on the QS system.

Plant programmed cell death : Can't live with it; Can't live without it

The decision of whether a cell should live or die is fundamental for the wellbeing of all organisms. Despite intense investigation into cell growth and proliferation, only recently has the essential and equally important idea that cells control/programme their own demise for proper maintenance of cellular homeostasis gained recognition. Furthermore, even though research into programmed cell death (PCD) has been an extremely active area of research there are significant gaps in our understanding of the process in plants. In this review, we discuss PCD during plant development and pathogenesis, and compare/contrast this with mammalian apoptosis. © 2008 Blackwell Publishing Ltd.

Cloning and development of pathotype-specific SCAR marker associated with Sclerospora graminicola isolates from pearl millet

Downy mildew pathogen of pearl millet in India is associated with the spread of the highly virulent Sclerospora graminicola pathotype-1. Twenty-seven S. graminicola isolates were screened using 20 intersimple sequence repeats (ISSR). Dinucleotide repeat primer [17898A-(CA)(6) AC] amplified a similar to 600 bp fragment specific to five isolates of pathotype-1 (Sg 048, Sg 153, Sg 212, DM-11 and DM-90). The ISSR fragment linked with pathotype-1 was cloned successfully and sequenced. To convert ISSR fragments into pathotype-specific sequence characterised amplified region (SCAR) markers, PCR primers were designed using a sequence of the cloned DNA fragment. PCR amplification using SCAR primer pair (UOM3-Sg-Path1-F/R) amplified a single 284 bp band only in isolates of S. graminicola pathotype-1. This SCAR primer pair did not amplify the 284 bp product from the other five S. graminicola pathotypes or a negative control, which demonstrates primer specificity for pathotype-1. The SCAR primer pair (UOM3-Sg-Path1-F/R) obtained in this study will provide a valuable tool for rapid identification and specific detection of S. graminicola pathotype-1.

Field evaluation of a plant activator, captan, chlorothalonil, copper hydroxide, iprodione, mancozeb and strobilurins for the control of citrus brown spot of mandarin

Brown spot (caused by Alternaria alternata) is a major disease of citrus in subtropical areas of Australia. A number of chemicals, the strobilurins azoxystrobin, trifloxystrobin, pyraclostrobin and methoxycrylate, a plant activator (acibenzolar), copper hydroxide, mancozeb, captan, iprodione and chlorothalonil/pyrimthanil were tested in the field for its control. Over three seasons, trees in a commercial orchard received 16, 14 and 7 fungicide sprays, respectively, commencing at flowering in the first season, and petal fall in the later seasons. In all experiments, the strobilurins used alone, or incorporated with copper and mancozeb, were as effective as, or better than the industry standard of copper and mancozeb alone. The only exception was trifloxystrobin, which when used alone was less effective than the industry standard. Acibenzolar used alone was ineffective. Applying a mixture of azoxystrobin and acibenzolar was found to reduce the incidence of brown spot compared with applying azoxystrobin alone but, in either case, disease levels were not found to be significantly different to the industry standard. Captan, iprodione and chlorothalonil/pyrimthanil were as effective as the industry standard. The incidence and severity of rind damage were significantly lowest in the azoxystrobin, methoxycrylate, iprodione and chlorothalonil/pyrimthanil treatments. Medium and high rates of trifloxystrobin (0.07 g/L, 0 .15 g/L) and pyraclostrobin (0.8 g/L, 1.2 g/L) applied alone were the only treatments found to be IPM-incompatible as shown by the elevated level of scale infection on fruit.