Date 28 February 1992

Title of Project Managing Fungal Diseases of Ornamentals with Bicarbonates and Determining Their Mode of Action

Institution where work is being conducted Cornell University

Amount of Endowment Grant $ 20,000
Covering Period 1 January to 31 December 1992

Anticipated Date of Project Completion/Final Report 31 December 1994

Individual(s) Conducting Project:

(List Project Leader First)

R. K. Horst - Title Professor

Telephone Number 607-255-7894

H. W. Israel - Title Senior Research Associate

Managing Fungal Diseases of Ornamentals with Bicarbonates and Determining Their Mode of Action

R. K. Horst and H. W. Israel

Cornell University

Progress Report to the American Floral Endowment, 2/28/92

A. Project Objectives:

1. Which consequential diseases of ornamentals can be managed with bicarbonates?

2. What is the minimal effective bicarbonate treatment necessary for management of rose powdery mildew?

3. What is the mechanism(s) by which bicarbonate antagonizes Sphaerotheca pannosa var. rosae?

B. Summary of Work Since Project’s Inception (1 January 1992):

Four experimental near-optically ideal systems have been established to effectively and efficiently

determine the time/space window in the very early stages of the rose powdery mildew cycle through which

we will uncover the mechanism(s) by which bicarbonates antagonize the fungal causative agent. The

systems have been constructed in a way to permit us to microscopically and quantitatively determine: i)

whether bicarbonates function as eradicants and/or preventives; ii) whether, when, and how quickly

bicarbonates affect adversely spore viability, germinability, and/or penetrability; iii) bicarbonate dose-response

levels; and iv) adjuvant dose-response levels.

One system compares and contrasts intact, paired leaflets of mildew-susceptible or -resistant

cultivars that have been inoculated or not, bicarbonate treated or not, and floated “right side up” or “upside

down” on a 4% sucrose solution and sampled over a 24-hour incubation sequence.

A second system, similar to the first, capitalizes on the enhanced optics afforded by rose leaflets

partially dissected in a way that leaves only the lower epidermis as an intact functioning host tissue. The

leaves are mounted in a specially designed microscope-compatible apparatus that permits efficient ease

of handling and analysis.

A third system uses a specially coated, but optically clear, glass microscope slides as the

germination substrate for freshly formed and harvested fungal spores. The substrate is treated or untreated

pre- or post-”inoculation” in ways that effect controlled outcomes and objective interpretation.

The fourth system uses detached rose leaflets on moist filter paper in petri dish chambers which

have been inoculated or not, and bicarbonate treated or not. Development of conidia and coniophores is

evaluated by pressing clear adhesive tape to leaflet surfaces followed by mounting to microscope slides

for microscopic examination and quantification. Internal cellular fungal development is determined by leaflet

sectioning with a freezing microtome.

C. Results to Date:

Our observations and evaluations positively indicate that these four systems will provide the means

of determining the eradicative and/or preventive functions of bicarbonates against powdery mildew of rose.

D. Future Plans Covered by the Endowment Grant:

1. Previous in vitro tests showed bicarbonates to be effective against species of Fusarium, Colletotrichum,

and Alternaria. We will carry out in vitro sensitivity tests of selected bacterial pathogens to bicarbonates,

i.e., Erwinia, Xanthomonas, and Pseudomonas.

2. We will investigate minimal dosage and application frequency for control of powdery mildew of rose.

We now know that 0.05% bicarbonate sprayed weekly will not effectively control powdery mildew.

3. The methodology which is presently being developed will provide us the means for thoroughly studying

at the cellular level how the interactions between host and pathogen cells are affected by bicarbonates.

E. Anticipated Benefits for Floral Industry:

The bicarbonates which we term biocompatible chemicals will have an exciting impact on disease

control due to increased public and commercial concerns about environmental quality. The breadth of

effectiveness in disease control and the mechanism(s) by which bicarbonates inhibit pathogens are

important components in developing the optimal bicarbonate systems approach in disease control.

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