Pennsylvania Floral Industry Association
Research Progress Report - February 2005

Title:

Pythium species and population identification and epidemiology using DNA markers

Principal Investigator:

Gary W. Moorman, Professor
The Pennsylvania State University, Department of Plant Pathology, 111 Buckhout Laboratory, University Park, PA 16802-4506. (voice: 814-863-7401; fax: 814-863-7217;
e-mail: gmoorman@psu.edu)

Co-Investigators:

David M. Geiser and Seogchan Kang, Associate Professors, The Pennsylvania State University, Dept. of Plant Pathology.

SeongHwan Kim, Chief Plant Pathologist, Pennsylvania Dept. of Agriculture, Bureau of Plant Industry, 2301 N. Cameron Street, Harrisburg, PA 17120.

Postdoctoral-Investigator:

Carla D. Garzón
The Pennsylvania State University, Department of Plant Pathology, 310 Buckhout Laboratory, University Park, PA

Progress:

Objective 1. Determine the DNA sequences of Pythium that can be used to identify species in the genus.

Work has been underway since 1999 to identify the species of Pythium involved in greenhouse crop losses in Pennsylvania. In research funded by PFIA (1999-2000), it was determined that Pythium irregulare is responsible for the majority of losses of many different crops other than poinsettias. Poinsettia losses are caused by Pythium aphanidermatum. Identification of species is based on DNA sequences as well as amplified fragment length polymorphism DNA fingerprints. Historically, Pythium ultimum was viewed as the most important plant pathogenic specieRs in greenhouse production. That species is associated with the use of field soil as a component of potting mix. We speculate that P. ultimum is no longer the most important species involved in damping-off and root rot because field soil is seldom used in modern greenhouse operations.

DNA sequences indicate that what has been called ‘Pythium irregulare’ based microscopic characteristics may actually be two or more different species. This is important to resolve because one group appears to be a local population with fungicide resistance while a second group may not be of local origin and may be spread within the industry on plant material shared among greenhouses. Currently, a graduate student is taking extensive measurements on isolates of two of the groups within P. irregulare to determine whether they can actually be separated morphologically if the correct structures are measured or ratios of measurements are calculated and compared.

Objective 2. Generate DNA data on populations Pythium species that cause significant crop losses in commercial floriculture.

Samples are being taken on a regular basis from selected greenhouses where Pythium crop losses are a chronic problem. Water, potting soil, stray soil (under, on, and between benches), crop debris, and infected plants are collected, cultured for Pythium and the DNA of each isolate is extracted for analysis.

Work to date indicates that disease outbreaks caused by Pythium irregulare are, in most cases, due to local populations of this species that are resident in or around the greenhouse. This species attacks a very wide variety of plants, generally under cool conditions. Root rot in poinsettias, usually caused by Pythium aphanidermatum under relative high temperature conditions, appears to be caused by select isolates of this species that are being moved on cuttings and pre-finished poinsettias within the industry and is not caused by local populations resident in individual greenhouses. Future work is designed to trace crop loss-causing isolated to their harbors.

Funding:

The majority of funding over the last 5 years has come from the USDA Floriculture and Nursery Crops Research Initiative ($50,000/yr to Penn State as a subcontractor to Margery Daughtrey at Cornell University who oversees the national Pythium/Phytophthora project). USDA projects are limited strictly to 5 years maximum duration. The current project terminates August 2005. We are waiting to be notified as to whether a new project should be proposed in order to continue the Pythium work. Moorman, Garzón, and Daughtrey submitted a proposal to the USDA Biology of Plant-Microbe Associations competitive grants program ($400,000 for 3 yr duration) in a further attempt to secure funding to continue the research. A decision on that proposal is expected in June 2005 with funding, if approved, to begin in September 2005. We also submitted a proposal to the American Floral Endowment ($55,000/yr for 3 years to be split between Moorman and Daughtrey). However at this time, it appears that AFE plans to refer that proposal to the USDA Floriculture and Nursery Crops Research Initiative for consideration rather than consider it for AFE funding.

One of the important spin-offs of this work has been to educate scientists to serve the floriculture industry. To date, this project has supported the education of 1 Ph. D., 1 Masters, and 1 Masters of Agriculture graduate students at Penn State in the Department of Plant Pathology. The M. S. (M. P. Ramon) recipient is currently working in the floriculture industry. The Ph. D. (C. D. Garzón) is applying for a faculty position at Ohio State University with responsibilities for floricultural crop disease research and Extension. The M. Agr. (J. Yanez) student anticipates completion in May and hopes to work in floriculture in her home country (Ecuador).