Date 8/30/91

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 $ 11,300
Covering Period 1/1/91 to 1/1/92

Anticipated Date of Project Completion/Final Report 12/31/92

Individual(s) Conducting Project:

(List Project Leader First)

Dr. Mary K. Hausbeck - Title Visiting Assistant Prof.

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, 8/30/91

A. Project Objecitves:

The production of a cost-effective, high quality product

delivered in the quantities wanted and at the time they are wanted will enable

the floriculture industry 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 proposal

pertains to the achievement of both of these goals.

B. Summary of Work Conducted and Results to Date:

The influence of temperature on germination, rate of

germination, and infection by conidia of Botrytis cinerea was investigated.

In order to simulate as closely as possible a naturally occurring situation,

dry conidia were used to inoculate geranium leaf discs using a spore settling

tower. Three leaf discs were used for each replication and three replications

were used for each treatment. Following inoculation, leaf discs were placed

in the dew chamber for 1, 2, 4, 6, 8, 10, 12, or 24 hours. Leaf discs were

fixed in FAA, cleared, stained, and germinated conidia counted. This

experiment has been conducted three times at 20′C. After only 2 hours of leaf

wetness as many as 5% of the conidia germinated. By 6 hours nearly 11% of the

conidia, germinated. At 8 and 10 hours a maximum of 22% and 72%, respectively,

of the conidia had germinated. Leaf wetness beyond beyond 10 hours did not

increase conidial germination beyond the maximum of 72%. According to this

data, just 6 hours of leaf wetness that might occur during the early morning

hours in a greenhouse is suitable for a substantial number of conidia. to

germinate. For instance, in this study, 11% germination meant that 271

conidia germinated potentially causing as many infection sites.

The influence of dew period and temperature on lesion production on

wounded stems of geranium stock plants was also investigated. Three stems on

each of twelve plants were cut with a razor blade. Each stem was between 0.5

and 1.0 cm in diameter. On six of the plants the stems were inoculated with

conidia collected from cultures of B. cinerea. The spores were applied to the

cut stem ends with a camel’s hair brush. Six plants were placed in

continuous dew and six in the growth chamber set at 60% relative humidity.

Each environment was set for 15′C. Measurements of disease were taken from

the cut stem end to the furthest point of progression as seen by the

blackening of the stem tissue. At the termination of the experiment, the

number of leaves of each plant were observed for disease symptoms and counted.

The reduced relative humidity limited infection by a minimum of 33%.

Progression of stem blight was not hindered. However, leaf infection were

limited by the reduced relative humidity. In low relative humidity, only 2 to

8% of the leaves became infected in comparison to the 36 to 58% of the leaves

infected in the dew chamber. Additional experiments were carried out to

determine the effect of temperature on stem infection and progression of

blight. Although infection of stems was not affected by temperatures of 15,

20, or 25′C, blight progression was greatest at 25′C.

C. Future Plans Covered by the Endowment Grant:

Verify where known and determine where not known the level and

duration of temperature and relative humidity necessary to interrupt the

disease cycle of B. cinerea on (a) necrotic geranium leaves and (b) wounded

stems of geranium stock plants.

D. Anticipated Benefits for Floral Industry:

Increasing the number of stock

plants per unit area could increase the production of cuttings and could apply

to all growing systems utilizing stock plants for cutting production.

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