Allelochemicals Biologica... - Name

NATURAL PRODUCT BASED FUNGICIDES 3
in a lipid-based signaling system where jasmonates induce the synthesis of a family of
wound-inducible defensive proteinase inhibitors (Farmer and Ryan, 1992) and low
and high molecular weight phytoalexins such as flavonoids, alkaloids, and terpenoids
(Gundlach et al., 1992; Mueller et al., 1993).
Several plant and bacterial natural products have novel applications as plant
protectants through the induction of systemic acquired resistance (SAR) processes.
Commercial products that appear to induce SAR include Messenger® (EDEN
Biosciences, Inc., Bothell, WA) and the bioprotectant fungicides Serenade®
(AgraQuest, Davis, CA), Sonata® (AgraQuest, Davis, CA), and Milsana® (KHH
BioSci, Inc., Raleigh, NC). Messenger is a harpin protein which switches on natural
plant defenses in response to bacterial leaf spot, wilt, and blight and fungal diseases
such as Botrytis brunch rot, and powdery mildew. Serenade is a microbial-protectant
derived from Bacillus subtilis, with SAR activity that controls Botrytis, powdery and
downy mildews, early blight, and bacterial spot. Sonata is also a microbial-biopesticide
with activity against Botrytis, downy and powdery mildews, rusts, Sclerotinia blight,
and rots. Milsana® is an extract from Reynoutria sachalinensis (giant knotweed)
that induces phytoalexins able to confer resistance to powdery mildew and other
diseases such as by Botrytis. However, elicitors with no innate antifungal activity
will not appear active in most current screening high throughput screening systems.
Many experimental approaches have been used to screen compounds and extracts
from plants and microorganisms in order to discover new antifungal compounds.
The focus of this paper is on laboratory methods and field procedures that we use to
evaluate naturally occurring antifungal compounds produced by plants, pathogens,
and other terrestrial and marine organisms. As part of a program to discover and
develop naturally occurring fungicides, several new in vitro detection systems and a
detached leaf assay were developed to evaluate small amounts of compound. Our
fungicide field protocol used to test potential lead fungicides using commercial
strawberry is also presented.
2.1. Pathogen Production
2. MATERIAL AND METHODS
Isolates of Colletotrichum acutatum, C. fragariae and C. gloeosporioides, Phomopsis
viticola and P. obscurans, Botrytis cinerea and Fusarium oxysporum are maintained
on silica gel at 4-6 °C. The three Colletotrichum species and P. obscurans strain were
isolated from strawberry (Fragaria x ananassa Duchesne). Phomopsis viticola and
B. cinerea were isolated from commercial grape (Vitis vinifera L.) and F. oxysporum
from orchid (Cynoches sp.). Fungal cultures were grown on potato-dextrose agar
(PDA, Difco, Detroit, MI) in 9-cm petri dishes and incubated in a growth chamber at
24 ± 2 °C under cool-white fluorescent lights (55 ± 5 µmols/m 2 /sec) with a 12h photoperiod.