Browsing by Author "McPhee, K.E."

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Erysiphe trifolii? a newly recognized powdery mildew pathogen of pea
(Plant Pathology, 2010) Attanayake, R.N.; Glawe, D.A.; McPhee, K.E.; Dugan, F.M.; Chen, W.
Diversity of powdery mildew pathogens infecting pea (Pisum sativum) in the US Pacific Northwest was investigated using both molecular and morphological techniques. Phylogenetic analyses based on rDNA ITS sequences, in combination with assessment of morphological characters, defined two groups of powdery mildews infecting pea. Group I (five field samples and three glasshouse samples) had ITS sequences 99% similar to those of Erysiphe pisi in GenBank and exhibited simple, mycelioid type of chasmothecial appendages typical of E. pisi. Erysiphe pisi is normally considered as the powdery mildew pathogen of pea. Group II (four glasshouse samples and two field samples) had ITS sequences 99% similar to those of E. trifolii and produced chasmothecia with dichotomously branched appendages similar to those of E. trifolii. There are fourteen nucleotide differences in the ITS region between the two groups. The correlation of rDNA ITS sequences with teleomorphic features for each of the two groups confirms their identity. Repeated samplings and artificial inoculations indicate that both E. pisi and E. trifolii infect pea in the US Pacific Northwest. Erysiphe trifolii is not previously known as a pathogen of pea. The existence of two distinct powdery mildew species infecting pea in both glasshouse and field environments may interfere with the powdery mildew-resistance breeding programmes, and possibly explains putative instances of breakdown of resistance in previously resistant pea breeding lines.
First Report of Powdery Mildew of Chickpea (Cicer arietinum) Caused by Leveillula taurica in Washington State
(Plant Health Progress, 2008) Chen, W.; Attanayake, R.N.; Glawe, D.A.; McPhee, K.E.; Dugan, F.M.
In Oct. 2007, powdery mildew was found in chickpea fields in an experimental farm near Pullman, Whitman County, Washington. Although disease signs were observed on all chickpea cultivars in the fields, high incidence was seen only on cvs. Dwelley and Spanish White. To our knowledge this is the first record of powdery mildew caused by Leveillula taurica on chickpea in WA. The pathogen has also been reported from chickpea in California and elsewhere, e.g., Ethiopia, India, Iran, Morocco, Pakistan, Sudan, Turkey, and the former USSR.
Potential alternative hosts for pea powdery mildew pathogen Erysiphetrifolii
(Pisum genetics, 2010) Attanayake, R.N.; Dugan, F.M.; Glawe, D.A.; McPhee, K.E.
Powdery mildew is an important disease of peas grown in both greenhouses and in the field. The latter is obviously important for commercial production, but greenhouses are often used to increase the number of generations per year in pea breeding programs. Even though Erysiphe pisi (often reported as E. communis or E. polygoni in earlier literature) is the most commonly documented pathogen species causing powdery mildew of peas, E. baeumleri (1) and E. trifolii (2) were recorded as powdery mildew pathogens on peas. It has been presumed that the putative breakdown of resistance in previously resistant pea cultivars observed in the US Pacific Northwest (US PNW) was actually due to the presence of more than one species of Erysiphe (2). Attanayake et al. (2) observed severe disease symptoms caused by E. trifolii on resistant pea cv. 'Lifter' grown in greenhouse conditions. Greenhouse-grown pea breeding materials often get infected with powdery mildew in the US PNW (K. McPhee, personal communication). However, the inoculum source, particularly for greenhouse-grown peas during the winter months, has not been determined. Since during winter months no pea crops are growing in fields in the PNW, inoculum would have to originate from pea debris of the previous growing season, volunteer pea plants or from powdery mildew-infected wild legume plants serving as alternative hosts. Many powdery mildew pathogens are known to have broad host ranges (3). E. trifolii has been reported on peas and lentils in the US PNW (2, 4) and on Trifolium (as the specific epithet indicates) and other genera of the Fabaceae such as Acacia, Arachis, Lathyrus, and Melilotus (5). Species of Arachis, Dolichos, Lathyrus, Lens, Lupinus, Medicago, Melilotus, Phaseolus, Trifolium and Vicia are known hosts for E. pisi (5). The above abbreviated host lists make it clear that E. trifolii and E. pisi have numerous hosts, including some hosts in common. Powdery mildew-infected Medicago lupulina, Melilotus spp., Lathyrus spp. and Vicia spp. plants are abundant along road sides, recreational areas and commercial fields during the periods of July-November in the Palouse region of Idaho and Washington. We hypothesized that these weedy legumes can serve as alternative hosts for E. trifolii. Detailed studies on host range of E. trifolii in the US PNW are lacking, so we tested these common weedy legumes from the region as potential alternative hosts of E. trifolii.
Taxonomic complexity of powdery mildew pathogens found on lentil and pea in the U.S. Pacific Northwest
(Phytopathology, 2008) Attanayake, R.N.; Glawe, D.A.; McPhee, K.E.; Dugan, F.M.; Chen, W.
and field production conditions in the U.S. Pacific Northwest was investigated using morphological and molecular characters. Isolates collected from lentil plants grown in the greenhouse or field displayed morphologies in substantial agreement with descriptions of Erysiphe trifolii, but sometimes with more extensively branched chasmothecial appendages resembling those of E. diffusa. ITS sequences of the lentil fungi were identical to each other, and more similar to GenBank accessions of E. trifolii (99.5%) than of E. diffusa (97%). The data suggest there may be more than one Erysiphe species causing lentil powdery mildew. The fungus on field-grown pea plants was determined to be E. pisi. However, powdery mildew samples obtained from greenhouse pea plants were either E. pisi or E. trofolii depending on the time of sampling and greenhouse location. Therefore, the powdery mildews infecting lentil and pea are more diverse than previously assumed. Powdery mildews from black medic (Medicago sp.) and sweet clover (Melilotus sp.) found near the greenhouses exhibited ITS sequences with 99.9 to 100% similarity to isolates from lentil and pea in the greenhouses, and to isolates from lentil from the field. These weedy legumes could be inoculum sources for powdery mildew of lentil and pea in the greenhouses, and serve as alternative hosts for cultivated legumes.