Managing Diseases of Ornamentals with Bicarbonates and Determining their Mode of Action 1993 Proposal
Bicarbonates
Associate
Concern bordering on alarm characterizes responses to imminent ecological,
even economical, crises that could result from undiminished use of present
day agrifungicides. On a more positive and wholesome note, the perceived
crises have spawned numerous searches for solutions. One approach to a
solution that has great potential focuses on a search/review for well-known
“natural” substances that also may bear sometimes profound antifungal properties.
Current work in our laboratories mobilizes a common, low-cost, biocompatible
substance, baking soda, for routine management of powdery mildew caused
by Spherotheca pannosa (Wallr. ex Fr.) Lerv. var rosae Wor., the most widely
distributed and destructive disease in the world of glasshouse grown roses.
Moreover, ongoing exploratory studies now indicate that bicarbonates also
may bear significant potentials for managing an array of common and costly
fungal diseases of many ornamentals.
Our preliminary research has given dramatic results. Bicarbonates may
not only be very effective and very safe, but they may also be very inexpensive.
Little is known about all this; significant research in this area is overwhelmingly
sparse. Therefore, our program is at a crossroads. Available, but modest,
in-house support is far from adequate to address the critical questions
that form the objectives of this proposal, viz.:
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 S. pannosa var. rosae?
This is low-risk research. We seek funds that will generate results
of guaranteed significance for the ornamentals industry.
Background and Review of Significant Literature
Powdery mildew caused by Sphaerotheca pannosa (Wallr. ex Fr.) Lerv.
var rosae Wor. is the most widely distributed and destructive disease of
greenhouse grown Rosa spp. in the world; and with blackspot caused by Diplocarpon
rosae Wolf, the most serious pair of diseases of nursery and garden grown
Rosa spp. Fungicide applications at 7 day intervals are the only means
of control. At Cornell University, annual control of powdery mildew in
cut rose production research has required up to 17 applications (2) at
an annual cost per ft^2 of $0.04 to $0.09, excluding labor. Because the
1987 market value of cut rose crops grown on 39.4 million ft^2 of production
space in the United States exceeded $180 million (1, 7), the annual cost
of fungicides for control of powdery mildew on production roses easily
exceeds $3.6 million, or about 2.0% of the wholesale market value. This
value does not include nursery and garden grown roses.
Present ecological concerns about frequent fungicide applications are
serious; they include (i) worker safety and reentry; (ii) contamination
of greenhouse drainage water; (iii) consumer exposure to fungicide residues;
and (iv) effects on crop photosynthesis and yield. Thus “biocompatible”
fungicides, which we define to be fungicides that exhibit low mammalian
and environmental toxicities, are particularly interesting for control
of powdery mildew and blackspot. Legitimate candidates are bicarbonates
and horticultural oils, which have individually been demonstrated to show
control activity against specific pathogenic fungi. Punja and Grogan (6)
found that carbonate and bicarbonate salts of ammonium, potassium, sodium
and lithium were fungicidal to Sclerotium rolfsii, and Homma et al. (5)
have found sodium bicarbonate to be inhibitive to powdery mildew on cucumber.
Film-forming polymers have been shown to inhibit powdery mildew on rose
and several others diseases caused by fungi (3, 4, 8). Recent investigations
in our laboratories (in press) have shown that powdery mildew and blackspot
were significantly controlled by weekly sprays of 0.05% (w/v) aqueous solution
of either potassium or sodium bicarbonate plus 0.5% or 1.0% (v/v) SunSpray
Ultra-fine Spray Oil, respectively. Bicarbonates appear to eradicate the
pathogens; analysis showed that combinations of bicarbonates plus oil were
more effective than either alone. Furthermore, current investigations in
our laboratories indicate that bicarbonates plus oil may be effective biocompatible
fungicides against numerous other fungal pathogens of ornamental plants.
Hypotheses have been suggested for the inhibitory mechanisms for both
bicarbonates and oils. Hydrogen ion concentrations of bicarbonate salts
have been shown to have a profound inhibitory influence on sclerotia germination
of S. rolfsii (6) where pH 8.6 but not 6.0 was fungicidal. Furthermore,
Homma et al. (5) found NaHCO3 to inhibit conidial formation and germination.
Bicarbonate may also influence host responses to the pathogen. Moreover,
film-forming polymers may form a physical barrier on leaf surfaces against
germ tube penetration by conidia of S. pannosa var. rosae (3, 4, 8). Obviously,
the mechanism(s) of antifungal activity have not been conclusively established
for bicarbonates and horticultural oils.
Specific Objectives:
1. To survey efficacy of bicarbonates for management of fungal diseases
of ornamental plants. 2. To establish the minimal dosage and frequency
of application of bicarbonate salts for disease management of powdery mildew
of rose. 3. To determine the mechanism(s) of antifungal activity of bicarbonates
against S. pannosa var. rosae.
Materials and Methods
Effectiveness against fungal pathogens. Preliminary investigations in
our laboratories reveal bicarbonates to have effective control potentials
against numerous fungal pathogens. Exciting possibilities include rusts,
downy mildews, and diseases caused by species of Fusarium, Colletotrichum,
and Alternaria. We do not know the breadth of control potential for bicarbonates.
Controlled and well-designed experiments are required to conclusively establish
this phenomenon. We will generally survey important fungal pathogens of
ornamental plants for sensitivity to bicarbonates. Selected fungal pathogens
will be screened in vitro and/or in greenhouse and field experiments.
Minimal Dosage and Application Frequency. We know from separate experiments
that powdery mildew on rose can be controlled by weekly sprays of 0.05%
(w/v) aqueous solution of either potassium or sodium bicarbonate plus 0.5%
(v/v) SunSpray Ultra-fine Spray Oil. We will now compare the disease control
effectiveness of potassium bicarbonate to sodium bicarbonate in the same
controlled experiments with powdery mildew on rose. However, we have not
yet determined whether lower concentrations and/or spraying less frequently
will give equally good results. We will also investigate 0.025% and 0.01%,
compared to 0.05% of sodium bicarbonate (determined in our previous investigations
to be effective), for their antifungal effectiveness against S. pannosa
var. rosae. In addition, applications at 1, 2, and 4 weeks will be compared
and contrasted for efficiency of disease control. We will also compare
the disease control effectiveness of potassium bicarbonate to sodium bicarbonate
in controlled experiments with powdery mildew on rose.
Mechanism(s) of activity. The particulars of how some synthetic organic,
even tailored, fungicides function have been known for some time, but the
mechanism for bicarbonate action can, at this junction, only be surmised.
The dilemma results in part from the fact that encounter events between
mildew and rose are severely isolated in time and space, particularly at
the (sub) microscopic, mechanistic level. Thus it is difficult to observe
and manipulate the sites and to analyze them using the averaging techniques
so common to modern biological research.
We propose to study thoroughly at the cellular level how the interactions
between two populations of cells - those of powdery mildew and those of
rose leaf epidermis - are affected by bicarbonates. To do this we will
need to establish by statistically significant methods what happens between
the two population in the absence of bicarbonates. We already know that
some encounters fail to materialize for a variety of reasons, including
host resistance, however, we must now describe precisely all possible outcomes
in order to predict accurately what will happen at any given encounter
site in the event bicarbonate ion, or any other experimental manipulation,
were withheld. Only then can we determine what the ion does. Questions
we will address in this research include: (i) Are mycelia actually killed?
(ii) Is the formation of conidia inhibited? (iii) If conidia are produced,
is germination inhibited? (iv) If conidia germinate, do they retain the
capability of forming penetration pegs followed by penetration through
leaf epidermal cells? (v) If penetration occurs, are haustoria formed in
epidermal cells? (vi) If haustoria are formed, do they cause disease and
further development of the pathogen on the host?
When these questions are answered and a foundation is established, we
will investigate the mechanism(s) of bicarbonate activity in greater detail.
The bicarbonates may have direct or indirect effects on the disease. Possible
direct effects include desiccation and toxicity of the fungi; indirect
effects may include alteration of the phyllosphere microflora and enhancement
of host resistance mechanisms. These effects can be studied, for example,
by initially substituting compounds with ionic strengths and pH similar
to the bicarbonates in order to determine which of these characteristics
are important.
We will devise a systematic analytical scheme based on fungal growth
curves and penetration efficiency data for controlled and experimental
examination of inoculated, detached leaves that will stress in the analysis
extensive application of cutting edge methods for in situ cytological research.
Brief Progress Report Since Project 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 stage of the rose powdery mildew cycle through which we will uncover
the mechanism(s) by which bicarbonates antagonize the fungal causal agent.
The systems have been constructed in such a way to permit us to microscopically
and quantiatively 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. Our evaluations
thus far indicate that our methodologies do work and that bicarbonates
function as eradicants and preventives.
We have begun investigations on minimum effective dosages of sodium,
potassium and ammonium bicarbonates against powdery mildew of rose in the
same experiment. Our results indicate that 0.05% and 0.5% concentrations
of sodium and potassium bicarbonate significantly reduce disease severity
of powdery mildew and that 0.5% concentrations are better than a 0.05%.
Ammonium bicarbonate was not as effective as sodium and potassium bicarbonate
in control of powdery mildew.
Additional progress details will be given in our progress report due
1 September 1992.
Literature Cited
1. Anonymous. 1989. Industry statistics from the USDA floriculture crops
1988 summary. Grower Talks 53(4):8-9.
2. Dreesen, D. R., and Walker, M. 1990. Investigations of environmental
effects of pesticides and fertilizers used at Cornell University greenhouse
facilities. Final Report, Results of Phase I Investigations. New York State
Water Resources Institute, Cornell University. June 30, 1990.
3. Elad, Y., Ziv, O., Ayish, N., and Katan, J. 1989. The effect of film-forming
polymers on powdery mildew of cucumber. Phytoparasitica 17:279-288.
4. Hagiladi, A., and Ziv, 0. 1986. The use of antitranspirants for the
control of powdery mildew of roses in the field. J. Envir. Hort. 4:69-71.
5. Homma, Y., Arimoto, Y., and Misato, T. 1981. Effect of sodium bicarbonate
on each growth stage of cucumber powdery mildew fungus (Sphaerotheca fuliginea)
in its life cycle. J. Pesticide Sci. 6:201-209.
6. Punja, Z. K., and Grogan, R. G. 1982. Effects of inorganic salts,
carbonate- bicarbonate anions, ammonia, and the modifying influence of
pH on sclerotia germination of Sclerotium rolfsii. Phytopathology 72:635-639.
7. U.S. Department of Commerce. 1989. 1987 Census of Agriculture.
8. Ziv, O. 1983. Control of powdery mildew of roses with antitranspirant
coating polymers. Hassadeh 53:1967-1969.
Detailed Budget
1992 1993 1994
Technical Support $15,457.00 $16,384.00 $17,367.00 EMP Benefits (fringes,
30.46%) 4,708.00 4,991.00 5,290.00 Supplies 2,000.00 2,000.00 2,000.00
Travel 2,000.00 2,000.00 2,000.00
Total $24,165.00 $25,375.00 $26,657.00
Project Leaders Qualifications:
R. K. Horst has worked with diseases of ornamental plants for 30 years.
His research efforts have been published in nearly 200 papers appearing
in scientific journals, book chapters, and trade journals. Included in
this list of publications are three books - 4th and 5th Editions of Westcott’s
Plant Disease Handbook and Compendium of Rose Diseases. Horst’s research
activities include investigations the past three years on bicarbonates
as an effective biocompatible control of fungal diseases of ornamental
plants.
H. W. Israel brings to this project more than 15 years of published
experience with comparable studies of powdery mildew of barley and Olpidium
infections of kohlrabi. Moreover, he coordinates the department’s Electron
Microscope Facility and is expert with most microscopic/cytological techniques.
However, to have the project hit the ground running we need to secure partial
support for his experienced technician of more than 20 years, S. J. Bucci,
in order that she direct her efforts specifically at one of the objectives
of this project, viz.,
To determine the basic mechanism(s) that account for the bicarbonate
control of powdery mildew on rose.
