Kevin K. Schrader

Invited Paper: Chemicals from nature for weed management

Abstract Natural products represent a vast repository of materials and compounds with evolved biological activity, including phytotoxicity. Some of these compounds can be used directly or as templates for herbicides. The molecular target sites of these compounds are often unique. Strategies for the discovery of these materials and compounds are outlined. Numerous examples of individual phytotoxins and crude preparations with weed management potential are provided. An example of research to find a natural product solution of a unique pest management problem (blue-green algae in aquaculture) is described. Finally, the problems associated with natural products for pest control are discussed.

Novel Derivatives of 9,10-Anthraquinone Are Selective Algicides against the Musty-Odor Cyanobacterium Oscillatoria perornata

ABSTRACT Musty “off-flavor” in pond-cultured channel catfish (Ictalurus punctatus) costs the catfish production industry in the United States at least

Natural Toxins for Use in Pest Management

30 million annually. The cyanobacterium Oscillatoria perornata (Skuja) is credited with being the major cause of musty off-flavor in farm-raised catfish in Mississippi. The herbicides diuron and copper sulfate, currently used by catfish producers as algicides to help mitigate musty off-flavor problems, have several drawbacks, including broad-spectrum toxicity towards the entire phytoplankton community that can lead to water quality deterioration and subsequent fish death. By use of microtiter plate bioassays, a novel group of compounds derived from the natural compound 9,10-anthraquinone have been found to be much more selectively toxic towards O. perornata than diuron and copper sulfate. In efficacy studies using limnocorrals placed in catfish production ponds, application rates of 0.3 μM (125 μg/liter) of the most promising anthraquinone derivative, 2-[methylamino-N-(1′-methylethyl)]-9,10-anthraquinone monophosphate (anthraquinone-59), dramatically reduced the abundance of O. perornata and levels of 2-methylisoborneol, the musty compound produced by O. perornata. The abundance of green algae and diatoms increased dramatically 2 days after application of a 0.3 μM concentration of anthraquinone-59 to pond water within the limnocorrals. The half-life of anthraquinone-59 in pond water was determined to be 19 h, making it much less persistent than diuron. Anthraquinone-59 appears to be promising for use as a selective algicide in catfish aquaculture.

The Effect of Pomegranate (Punica granatum L.) Byproducts and Ellagitannins on the Growth of Human Gut Bacteria

Natural toxins are a source of new chemical classes of pesticides, as well as environmentally and toxicologically safer molecules than many of the currently used pesticides. Furthermore, they often have molecular target sites that are not exploited by currently marketed pesticides. There are highly successful products based on natural compounds in the major pesticide classes. These include the herbicide glufosinate (synthetic phosphinothricin), the spinosad insecticides, and the strobilurin fungicides. These and other examples of currently marketed natural product-based pesticides, as well as natural toxins that show promise as pesticides from our own research are discussed.

Environmental and nutritional factors affecting geosmin synthesis by Anabaena sp.

The consumption of pomegranate products leads to a significant accumulation of ellagitannins in the large intestines, where they interact with complex gut microflora. This study investigated the effect of pomegranate tannin constituents on the growth of various species of human gut bacteria. Our results showed that pomegranate byproducts and punicalagins inhibited the growth of pathogenic clostridia and Staphyloccocus aureus. Probiotic lactobacilli and bifidobacteria were generally not affected by ellagitannins, while relatively small growth inhibition by ellagic acid likely resulted from decreasing media quality due to the formation of tannin-protein complexes. The effect of pomegranate ellagitannins on bifidobacteria was species- and tannin-dependent. The growth of Bifidobacterium animalis ssp. lactis was slightly inhibited by punicalagins, punicalins, and ellagic acid. POMx supplementation significantly enhanced the growth of Bifidobacterium breve and Bifidobacterium infantis.

Extracts of Flourensia cernua (L): volatile constituents and antifungal, antialgal, and antitermite bioactivities.

A cyanobacterium isolated from a source-water reservoir during a spring odor and taste episode and identified as Anabaena sp. consistently produced geosmin during laboratory culture on modified BG-11 liquid medium. Maximal geosmin/biomass occurred at 20 degrees C and a light intensity of 17 microE/m2/s; geosmin/chla values directly correlated with increasing light intensity (r2 = 0.95, P < 0.01). It was concluded that at 20 degrees C, increasing light intensity favors less chla synthesis and higher geosmin synthesis; at 17 microE/m2/s, increasing temperature stimulates chla production (to 25 degrees C) while repressing geosmin synthesis (above 20 degrees C). Nutritional factors promoting biomass, chla, and geosmin synthesis by Anabaena sp. were also investigated. For cultures grown at 17 microE/m2/s and 20 degrees C for 20 days, both ammonium-N and nitrate-N generally enhanced the growth of Anabaena sp. Nitrate-N promoted more chla production (r2 = 0.99) than ammonium-N. Geosmin synthesis was directly correlated with ammonium-N concentrations (r2 = 0.89), with low nitrate-N (123.5 micrograms/l) favoring maximal geosmin production (2.8 micrograms/l). Increasing nitrate-N concentrations promoted a three-fold increase in chla content with geosmin synthesis decreased by two-fold. Geosmin/mg biomass was directly related to ammonium-N concentration; high nitrate-N levels suppressed geosmin production. No geosmin was detected at or below 118 micrograms phosphate-phosphorus/l. Geosmin, dry weight biomass, and chla production were correlated with increasing phosphorus (P) concentration (r2 = 0.76, 0.96 and 0.98, respectively). No geosmin was detected when copper was present in growth media at or above 6.92 micrograms Cu2+/l (CuSO4.5H2O). Dry weight biomass and chla production were negatively correlated with Cu2+ ion concentrations.

Composition of the essential oil of Lepidium meyenii (Walp).

The chemical components of tarbush (Flourensia cernua) leaves were fractionated by extracting successively with hexanes, diethyl ether, and ethanol. Volatile profiles of each fraction were identified by using GC-MS. The hexanes fraction contained mostly monoterpenoids, while the ethanol fraction volatiles were primarily sesquiterpenoids. Crude fractions were tested for activity against fungi, algae, and termites. Application of as little as 1 μg of the essential oil from the hexanes fraction was sufficient to provide visible antifungal activity in bioautography assays. The diethyl ether fraction showed selective activity against the cyanobacterium responsible for the 2-methylisoborneol-induced off-flavor sometimes associated with catfish farming operations. All three fractions exhibited a high degree of antitermite activity.

Distribution of Off-Flavor Compounds and Isolation of Geosmin-Producing Bacteria in a Series of Water Recirculating Systems for Rainbow Trout Culture

The essential oil profile of maca (Lepidium meyenii) obtained from Lima, Peru, was examined. Steam distillates of the aerial parts of L. meyenii were continuously extracted with pentane and the pentane extracts analyzed by GC/MS. Retention indices and mass spectral data were used to identify 53 oil components. Phenyl acetonitrile (85.9%), benzaldehyde (3.1%), and 3-methoxyphenylacetonitrile (2.1%) were the major components of the steam distilled oil. The oil of L. meyenii was tested for phytotoxic, cyanobactericidal, and antitermite activity. The oil was selectively toxic towards the cyanobacterium Oscillatoria perornata compared to the green alga Selenastrum capricornutum, with complete growth inhibition at 100 microg/ml. Mortality of the Formosan subterranean termite, Coptotermes formosanus, was numerically, but not significantly, higher when held on filter paper treated with maca oil. At 1% (w/w), maca oil also appeared to act as a feeding deterrent to termites. Several minor components of the essential oil of maca including 3-methoxyphenylacetonitrile and benzylthiocyanate were significantly active against the Formosan termite. This is the first report on the essential oil composition of L. meyenii.

Algicidal Activity of Stilbene Analogues

Abstract Preharvest off-flavor in aquaculture products results in large economic losses to producers due to delayed harvest. The common off flavors “earthy” and “musty” are due to the presence of geosmin and 2-methylisoborneol (MIB), respectively. Although certain species of cyanobacteria are responsible for these problems in pond-cultured fish, the microbial sources of geosmin and MIB in recirculating aquaculture systems (RASs) are still being explored. In this study, we investigated (1) the distribution of geosmin and MIB within six replicated RASs producing rainbow trout Oncorhynchus mykiss and (2) the microorganisms responsible for earthy off-flavor in the flesh of RAS-cultured trout. Water, biosolids, and fish samples were collected when fish were at maximum feed levels and before harvest. Each RAS contained a fluidized-sand biofilter, a cascade aeration column, a low-head oxygenation (LHO) unit, an LHO sump, a 5.3-m3 culture tank, a drum filter, a pump sump, and a heat exchanger. Solid phase microex...

Geosmin and 2-Methylisoborneol Cause Off-Flavors in Cultured Largemouth Bass and White Sturgeon Reared in Recirculating-Water Systems

Continuing our search for natural product and natural product-based compounds for the control of off-flavor in catfish, 29 stilbene analogues were synthesized and evaluated for algicidal activity against the 2-methylisoborneol (MIB)-producing cyanobacterium Oscillatoria perornata. The cis and trans isomers of 4-(3,5-dimethoxystyryl)aniline showed moderate and selective algicidal activity toward O. perornata with the lowest observed inhibitory concentration and lowest complete inhibition concentrations of 10 muM. This is the first report on selective stilbene algicidal activity toward a MIB-producing cyanobacteria species.