Composition and some biological activities of the essential oil of Callicarpa americana (L.)
ABSTRACT The essential oil profile of Callicarpa americana was examined. Samples were collected from Lafayette county in north central Mississippi, and GC-MS data and retention indices were used to identify 67 oil components. Humulene epoxide II (13.9%), alpha-humulene (10.0%), 7-epi-alpha-eudesmol (9.4%), beta-pinene (8.8%), and 1-octen-3-ol (8.5%) were the major components of the steam-distilled oil. The oil was selectively toxic toward the cyanobacterium Oscillatoria perornata compared to Oscillatoria agardhii and the green alga Selenastrum capricornutum, with complete growth inhibition at 28.5 microgram/mL. The oil was only mildly phytotoxic and antifungal.
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ABSTRACT: The continuing development of fungicide resistance in plant and human pathogens necessitates the discovery and development of new fungicides. Discovery and evaluation of natural product fungicides is largely dependent upon the availability of miniaturized antifungal bioassays. Essentials for natural product bioassays include, sensitivity to microgram quantities, selectivity to determine optimum target pathogens, and adaptability to complex mixtures. Experimental accuracy and precision must be stable between assays over time. These assays should be relevant to potential pathogen target sites in the natural infection process of the host and applicable to the agrochemical industry. Bioassays should take advantage of current high-throughput technology available to evaluate dose-response relationships, commercial fungicides standards, modes of action, and structure activity studies. As part of a program to discover natural product-based fungicides, two sensitive detection systems were developed for evaluation of antifungal agents as agrochemical plant protectants. Bioautography assays using Colletotrichum acutatum, C. fragariae, and C. gloeosporioides were used to identify antifungal components from plant extracts, eliminate commonly occurring nuisance compounds, and characterize antifungal activity of pure compounds. A microbioassay using conidia from Botrytis cinerea, Colletotrichum spp., Fusarium oxysporum, Phomposis obscurans, and P. viticola in a 96-well microtiter format was also developed to evaluate growth effects of active fractions or pure compounds identified by bioautography. These microbioassays allow for the evaluation of microgram quantities, determine dose-response relationships; compare antifungal activity with fungicide standards of known mode of action. This coupled approach to natural product discovery combines the simple and visual nature of direct bioautography with the rapid, sensitive, and high throughput capabilities of a microtiter system. Ultimately, development of safer plant protectants with selective antifungal activity and low environmental and mammalian toxicity is sought. INTRODUCTION Since the early 1970s, agriculture has struggled with the evolution of pathogen resistance to antimicrobial disease control agents. Increased necessity for repeated chemical applications, development of pesticide cross-resistance, and disease resistance management strategies have overshadowed the use of agricultural chemicals. Scientists are currently attempting to control agricultural pests with fewer effective chemical controls. In addition, the desire for safer pesticides with less environmental toxicity is a major public concern. Particularly desirable is the discovery of totally novel, prototype pesticidal agents representing new chemical classes with different toxicities that operate by different modes of action and, consequently, lack cross-resistance with currently used chemicals. In this respect, evaluating natural products and extracts to identify potential new pesticides offers an approach to discover new chemical entities that have never been synthesized by chemists. Antibiotics, antineoplastics, herbicides, and insecticides often originate from plant Proc. WOCMAP III, Vol. 3: Perspectives in Natural Product Chemistry Eds. K.