Plant Disease magazine, February 2005 issue, Volume 89, Number 2
Selection of interpretive summaries of articles relevant to seed professionals

Characterization of Phytophthora capsici Isolates from Processing Pumpkin in Illinois
S. Z. Islam, M. Babadoost, K. N. Lambert, and A. Ndeme, Department of Crop Sciences, University of Illinois, Urbana 61801; and H. M. Fouly, Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana 61801. Plant Dis. DOI: 10.1094/PD-89-0191, 2004 (online). Accepted for publication 26 September 2004.

ABSTRACT

Illinois ranks first in pumpkin production in the United States, producing about 90% of the country’s commercial processing pumpkins. Phytophthora blight, caused by Phytophthora capsici, has become one of the most serious threats to processing pumpkin production in Illinois and has caused complete crop loss in some fields. P. capsici can attack the host plant at any growth stage, and it causes seedling death, crown rot, foliar blight, and fruit rot. The pathogen also causes severe crop losses in other cucurbits, eggplant, pepper, and tomato. During the past 5 years, we observed differences in the severity of Phytophthora blight and yield losses in the fields, and growth and sporulation of P. capsici in the laboratory. Growers of processing pumpkin reported losses due to seedling death caused by P. capsici. In some pumpkin fields, seedling death was so widespread that the growers had to replant fields two or three times. These reports and observations raised the question of whether the isolates of P. capsici in different processing pumpkin fields vary in virulence. Through this study, the P. capsici isolates examined from processing pumpkin fields in Illinois were demonstrated to belong to six genetic groups and to vary in virulence and morphology. Random amplified polymorphic DNA markers were employed to assess genetic variation among 24 isolates of P. capsici from 10 individual fields at six locations. Inoculation of pumpkin seedlings in the greenhouse revealed that the isolates belonged to six distinct genetic groups differing significantly in virulence. Isolates tested exhibited four growth patterns in culture: cottony, rosaceous, petaloid, and stellate. P. capsici isolates with cottony growth pattern did not grow at 36°C. Nine of 24 isolates tested produced chlamydospores (thick-walled spores), which has not been reported for P. capsici from pumpkin. Chlamydospores enable the pathogen to survive over winter in the field.

DISEASE NOTES (excerpts, relevant to seed professionals)
Subscribers to Plant Disease magazine can follow the links to the full articles

First Report of Southern blight Incited by Sclerotium rolfsii on Dichondra repens in Italy. A. Garibaldi, A. Minuto, and M. L. Gullino. Page 203. DOI: 10.1094/PD-89-0203B.

First Report of Root Rot of Bean and Soybean Caused by Rhizoctonia zeae in Turkey. I. Erper, G. Karaca, and I. Özkoç. Page 203. DOI: 10.1094/PD-89-0203C.

First Report of Summer Patch of Creeping Bentgrass Caused by Magnaporthe poae in North Carolina. L. P. Tredway. Page 204. DOI: 10.1094/PD-89-0204A.

First Report of Foliar Infection of Maianthemum racemosum by Phytophthora ramorum. D. Hüberli, K. L. Ivors, A. Smith, J. G. Tse, and M. Garbelotto. Page 204. DOI: 10.1094/PD-89-0204C.

Nicotiana occidentalis: A New Herbaceous Host for Blueberry scorch virus. D. T. Lowery, C. J. French, and M. Bernardy. Page 205. DOI: 10.1094/PD-89-0205A.

First Report of Root Rot Incited by Thielaviopsis basicola on Lamb’s Lettuce (Valerianella olitoria) in Europe. A. Garibaldi, G. Gilardi, and M. L. Gullino. Page 205. DOI: 10.1094/PD-89-0205B.

First Report of Onion yellow dwarf virus, Leek yellow stripe virus, and Garlic common latent virus in Garlic in Washington State. H. R. Pappu, B. C. Hellier, and F. M. Dugan. Page 205. DOI: 10.1094/PD-89-0205C.

First Report of a Leaf Spot Caused by Cercospora bizzozeriana on Lepidium draba subsp. draba in Tunisia. T. Souissi, D. K. Berner, and H. J. Dubin. Page 206. DOI: 10.1094/PD-89-0206A.

First Report of the Root-Knot Nematode Meloidogyne arenaria Race 2 from Several Vegetable Crops in Jordan. M. Karajeh, W. Abu-Gharbieh, and S. Masoud. Page 206. DOI: 10.1094/PD-89-0206B.

First Report of Soybean Rust Caused by Phakopsora pachyrhizi on Dry Beans in South Africa. E. D. du Preez, N. C. van Rij, K. F. Lawrance, M. R. Miles, and R. D. Frederick. Page 206. DOI: 10.1094/PD-89-0206C.

First Report of Gray Leaf Spot Caused by Alternaria brassicae on Canola in Argentina. S. Gaetán and M. Madia. Page 207. DOI: 10.1094/PD-89-0207A.

First Report of Stunting and Root Rot of Potato Associated with Pratylenchus penetrans in the Columbia Basin of Washington. R. E. Ingham, P. B. Hamm, E. Riga, and K. J. Merrifield. Page 207. DOI: 10.1094/PD-89-0207B.

First Report of White Rust of Arugula Caused by Albugo candida in Argentina. R. Zapata, A. M. Romero, and P. H. Maseda. Page 207. DOI: 10.1094/PD-89-0207C.

First Report of Soft Rot Caused by Sclerotinia sclerotiorum on Borage in North Dakota. C. A. Bradley, L. E. del Río, C. D. Chesrown, and B. L. Johnson. Page 208. DOI: 10.1094/PD-89-0208B.

First Report of Rust Caused by Puccinia carthami on Safflower in Oman. M. L. Deadman, A. M. Al Sadi, S. Al Jahdhami, and M. C. Aime. Page 208. DOI: 10.1094/PD-89-0208C.