Date 2/27/93

Title of Project The Effect of Modifying the Microenvironment Among Geranium Stock

Plants Within a Greenhouse on Botrytis Blight and Sporulation of

Botrytis Cinerea

Institution where work is being conducted Michigan State University

Amount of Endowment Grant $ 17,000
Covering Period 1/1/93 to 12/31/93

Anticipated Date of Project Completion/Final Report 12/31/95

Individual(s) Conducting Project:

(List Project Leader First)

Dr. Mary K. Hausbeck -Title Assistant Professor

Telephone Number 517-355-4534

The Effect of Modifying the Microenvironment Among Geranium Stock Plants Within a Greenhouse on

Botrytis Blight and Sporulation of Botrytis Cinerea

Mary K. Hausbeck

Michigan State University

Progress Report to the American Floral Endowment, 3/1/93

A. Project Objectives:

The production of a cost-effective, high quality product

delivered in the quantities desired and at the time they are needed will enable

the floriculture industry to become revitalized. To achieve this goal, the

following two objectives must be met:

(1) pathogen-free planting stock, and

(2)

computerized plant growth optimization strategies.

This research pertains to the

achievement of both of these goals. The objectives will be achieved through the

following research:

1) Verify the level and duration of temperature and relative

humidity necessary to interrupt the disease cycle of B. cinerea on geranium stock

plants,

2) Construct computerized software to regulate the level and duration of

temperature and relative humidity necessary to interrupt the disease cycle of B.

cinerea, and

3) Validate the computer software within a research and commercial

greenhouse.

B. Summary of Work Conducted:

Data gathered thus far clearly show that environmental

modification will not only reduce B. cinerea among stock plants, thereby reducing

stem blight and increasing cutting production, but that the leaf blight on the

cuttings removed from these stock plants will also be limited. Recently

conducted studies show the when cuttings are removed from geranium stock plants

grown in a modified environment and exposed to optimum conditions for disease

development, leaf blight can be substantially reduced in comparison to untreated

control. These experiments have been replicated four times with similar results.

Based on these studies, it appears that the longer the leaves are wet within the

stock plant canopy prior to the removal of cuttings, the more likely that the

leaves of the cuttings will become blighted. In one study, the stock plants in

the modified environment did not experience any duration of leaf wetness as

measured within the canopy, whereas the stock plants growing in the unmodified

environment experienced a minimum of 3 days of leaf wetness prior to the removal

of the cuttings. The resulting leaf blight on the cuttings was approximately 55%

and 22% respectively for the unmodified and modified treatments, respectively.

Studies also show that stock plants grown in a modified environment are

healthier and have the potential to produce more cuttings than those stock plants

grown in an unmodified environment. In this study, the environment was modified

using plastic mulch on top of the pots, forced heated air through a PVC tube

placed within the canopy, and a combination of plastic mulch and forced heated

air. The average number of stems that became infected following the removal of

cuttings for plants grown in the unmodified environment was nearly six. The

plastic mulch improved plant health slightly with approximately 4.5 stems per

plant becoming infected. The greatest reduction in disease was observed with the

environmental modification occurring as either heated air through the PVC tubes,

or as a combination of plastic mulch plus heated air through the PVC tubes where

the number of infected stems per plant was reduced to 2.0 and 1.5, respectively.

It is expected that this reduction in stem blight would allow further breaks to

occur on the stem thereby resulting in an increase of subsequent cuttings.

C. Future Plans Covered by the Endowment Grant:

The environmental parameters necessary for the

critical stages of the pathogens lifecycle including spore germination, infection

of the plant, and production of spores as defined by recent studies will be

incorporated into a data set collected from a commercial propagator of geraniums

that contains relative humidity, temperature, irradiance, spore concentrations,

and plant disease. This information will form the basis for a predictive system

that will be tested and validated in a commercial greenhouse.

D. Anticipated Benefits for Floral Industry:

Controlling disease caused by B.

cinerea through modification of the greenhouse environment is an attractive

addition to traditional control methods. Although event-driven, interactive

computers are available with the capacity for predicting disease epidemics and

altering the greenhouse environment, the data base necessary for the development

of software that will provide predictions is lacking. The environmental

parameters necessary to deter Botrytis blight will be formulated into a

forecasting system to provide growers with an economical disease management tool

that improves plant quality by reducing disease and pesticide applications.

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