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United States Department of Agriculture

Agricultural Research Service

Research Project: Early Detection of Pythium Stress in Floriculture Crops Using Minimally Invasive Techniques

Location: Application Technology Research Unit

2010 Annual Report


1a.Objectives (from AD-416)
The objective is to detect and evaluate the early stress response of seed geranium following exposure to Pythium, a microorganism that is ubiquitous in greenhouse setting, and can easily spread through the use of infested soil and reuse of contaminated irrigation water. The implementation of non-destructive or minimally invasive techniques to detect and evaluate plant performance early in the interaction process has become possible through the use of portable and computer-based devices. The techniques allow for real time monitoring and evaluation of periodical progression of stress response of the same plant or the same part of the plant. Data generated from the study should give us insight into developing strategies that could be implemented in order to lessen the biotic stress from such pathogens and to improve and optimize plant quality and profitability.


1b.Approach (from AD-416)
Geranium seed cv. Red Maverick will be sown in Oasis Cubes for ~2 weeks before being transplanted into 6” pots containing soilless medium into either greenhouse or growth chamber environments. Controlled environmental conditions such as light level of 200-400 micromol m-2 s-1 PAR, and temperature at 23 C will be maintained throughout the duration of the study. Other aspects of plant maintenance such as watering, fertilization, and insect control will be implemented as required. The system will utilize computer-based data monitoring and recording of temperature, humidity, light, and soil moisture.

Pythium ultimum and P. aphanidermatum will be utilized, and were originally isolated from infected plants and kept in Potato Dextrose Agar (PDA) in Toledo. Tested pathogens will be cultured in artificial media (PDA) for 1-2 weeks prior to inoculation at 23 C. The inoculum density will be adjusted to 104 spores ml-1. The inoculation procedure will be done by adding 100 ml of spore suspension from each of the tested pathogen to each pot. Two major control treatments will be included. One is the negative control where no pathogen will be tested. And the other will include treating of the plants with the fungicide Subdue Maxx prior to adding the spore suspension of each of the pathogen.

Periodic response of the challenged plants to treatments will be evaluated using non-destructive techniques which include visual inspection of symptom development and disease severity, chlorophyll content using a hand-held chlorophyll content meter (CCM200), leaf fluorescence with a portable fluorometer (OP-30), soil moisture, and whole-plant gas exchange with a system developed at Ohio State.


3.Progress Report

During the first year of the project, our effort was focusing on establishing experimental procedure, and developing instrumentation. A preliminary study was conducted under environmentally controlled growth conditions that included appropriate light level, temperature, fertilization, watering, and pest control. The study was conducted to fine tune plant growing, pathogen inoculation, and disease evaluation procedures. A weekly visual evaluation was used to rate symptom development and disease severity of Phythium on the geranium. The plants were started, transplanted, and inoculated with the pathogens at Toledo, OH by USDA scientists before transporting to Wooster, OH where the plants were grown in a 12-chamber phytotron facility and the stress symptom were evaluated weekly jointly by USDA and Ohio State University (OSU) scientists. At week 4 of this study, the plants challenged with Pythium ultimum showed slightly more visual disease severity than the ones treated with Phytophthora nicotianae. The observation was somewhat counter intuitive that warrants further investigation. Also collected was plant canopy temperature, and chlorophyll fluorescence as potential indicators of root damage due to the pathogen attack. Higher canopy temperature and higher fluorescent signal are expected as root damage severity increases. Another major effort during this time period was to improve our gas exchange measurement and data acquisition capability. We were successful in acquiring a CO2/H2O analyzer through Ohio Agriculture Research and Development Center funding to improve our gas exchange analysis capability for this project. A Li-Cor Li-7000 closed path CO2/H2O gas analyzer was acquired, checked-out, and mounted in a protective enclosure. The analyzer will be integrated with an existing data acquisition and control system in the phytotron building to collect data from gas exchange studies. This project was monitored by frequent (once a week) email communication, monthly phone calls, and face-to-face meetings about six times per year.


Last Modified: 9/29/2014
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