Behavioral and physiological responses of cabbage looper,Trichoplusia ni (Hübner), to steam distillates from resistant versus susceptible soybean plants

Soybean plant volatiles, extracted as steam distillates, significantly affected the behavior and biology of the cabbage looper,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). Distillates from the susceptible Davis variety attractedT. ni larvae and female adults, whereas those from resistant PI 227687 plants repelled them. When mixed in an artificial diet, steam distillates from PI 227687 plants caused mortality of first-instar larvae. Adults emerging from pupae topically treated with 5 g of such PI 227687 extractable showed developmental abnormalities. Larval feeding was significantly less on Davis leaves treated with PI 227687 volatiles as compared to solvent (acetone) or such Davis extractables. However, Davis volatiles on PI 227687 leaves did not increase larval feeding. HPLC analyses of steam distillates from susceptible Davis versus resistant PI 227687 indicated differences.     

Plant Growth Inhibiting Flavonoids in Exudate of Cistus ladanifer and in Associated Soils

Of the aglycone flavonoids identified in the exudate of cistus ladanifer, two, the flavone apigenin-4-(O)-methyl and the flavonol kaempferol-3,7-di(O)-methyl inhibit development of the seedlings of Rumex crispus at 0.5 and 1 mM. Additive effects were observed between the major flavonols of the exudate kaempferol-3-(O)-methyl and kaempferol-3,7-di-(O)-methyl in inhibiting the size of the cotyledons and delaying the germination and cotyledon emergence. The presence of apigenin-4-(O)-methyl, kaempferol3,7-di-(O)-methyl, and kaempferol-3-(O)-methyl was detected in the soils associated with C. ladanifer during the summer and autumn months. That these compounds are present in the soil and are not restricted to the leaves provides support for the hypothesis that C. ladanifer has allelopathic potential.     

Effects of Monoterpenoids, Acting Alone or in Pairs, on Seed Germination and Subsequent Seedling Growth

We compared the potential allelopathic activity of 47 monoterpe- noids of different chemical groups, by estimating their effect on seed germination and subsequent growth of Lactuca sativa seedlings. Apart from individual compounds, eleven pairs at different proportions were also tested. As a group, the hydrocarbons, except for (+)-3-carene, were the least inhibitory. Of the oxygenated compounds, the least inhibitory were the acetates; whenever the free hydroxyl group of an alcohol turned into a carboxyl group, the activity of the resulting ester was markedly lower (against both germination and seedling growth). Twenty-four compounds were extremely active against seedling growth (inhibiting it by more than 85%), but only five against seed germination. The compounds that were most active against both processes belonged to the groups of ketones and alcohols; they were terpinen-4-ol, dihydrocarvone, and two carvone stereoisomers. We used a model to investigate whether compounds acted independently when applied in pairs. The combined effect varied. In half of the cases, it followed the pattern expected under the assumption of independence; in the rest, either synergistic or antagonistic interactions were found in both germination and elongation. However, even in cases of synergistic interactions, the level of inhibition was not comparable to that of a single extremely active compound, unless such a compound already participated in the combination. The specific structural factors that operate and determine the activity of monoterpenoids still remain rather obscure. The same holds true for the combined effect; its character cannot in general be predicted on the basis of individual compounds acting alone.     

Allelochemicals in soil from no-tillage versus conventional-tillage wheat (Triticum aestivum) fields

Putative allelochemicals found in the soil of no-tillage and conventional-tillage wheat plots near Stillwater, Oklahoma, were obtained by a mild alkaline aqueous extraction procedure, bioassayed to determine their biological activity, purified, and analyzed with a capillary gas chromatography-mass spectrometry-data analysis system. The most significant inhibition was found in bioassays of extracts from soil collected immediately after harvest in June, July, and August. No-tillage soils produced significant inhibition during the rest of the year also. Mass spectrometry showed fatty acids as the most abundant compounds. However, when bioassayed authentic samples of the five free fatty acids showed no significant biological activity toward wheat.Journal Article No. 5650 of the Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, Oklahoma 74078.     

Hydrodynamic constraints on evolution of chemically mediated interactions between aquatic organisms in unidirectional flows

Two hydrodynamic habitats can be defined in unidirectional flow: (1) A boundary where molecular diffusion dominates is found within roughly 1 mm of solid substrates. The actual thickness of this diffusion boundary is a function of current velocity and topography of the substrates. (2) A zone of turbulent flow is present outside the diffusion boundary where chemicals are rapidly diluted and transported downstream. The mode of chemically mediated interaction between organisms in streams is constrained differently depending on which of these two habitats they occupy. Within a diffusion boundary, reciprocal interaction between small organisms is possible because mixing is low, diffusion flux high, and organisms share the same water. Outside a diffusion boundary, in unidirectional flow, organisms unable to move effectively against flow are only chemically influenced by upstream organisms and can only influence downstream organisms. Organisms that are able to move upstream can interact reciprocally with other organisms, even if one or both organisms are found primarily in areas of turbulent mixing.     

Identification of Phytotoxic Substances from Early Growth of Barnyard Grass (Echinochloa crusgalli) Root Exudates

Barnyard grass is a problematic weed worldwide. It competes with crops and causes reduction in crop yields. In this study, barnyard grass suppressed rice emergence, and the degree of rice inhibition was proportional to the density of barnyard grass. Root exudates of barnyard grass reduced germination and growth of lettuce, rice, and monochoria. Fifteen compounds potentially involved in the phytotoxic activities of barnyard grass were isolated and identified, including phenolics, long-chain fatty acids, lactones, diethyl phthalate, acenaphthene, and derivatives of phthalic acids, benzoic acid, and decane. Quantities of diethyl phthalate, decanoic acid, myristic acid, stearic acid, 7,8-dihydro-5,6-dehydrokavain, and 7,8-dihydrokavain were 2.7, 11.1, 19.6, 35.5, 10.3, and 15.5 μg/ml of barnyard grass root exudates, respectively. The two lactones exhibited the greatest inhibition, followed by the phenolics and the derivatives of phthalic acids. Fatty acids had stronger suppression than diethyl phthalate and ethyl ester-4-ethoxy-benzoic acid. The acenaphthene and decane derivatives were the least phytotoxic. The phytotoxins released by barnyard grass roots showed strong inhibition on growth of broadleaf indicator plants and paddy weeds, but were less effective on barnyard grass itself and rice. Our study revealed that in addition to competition, barnyard grass also interferes with rice and other plants in its surroundings by chemical means.T. D. Khanh and I. M. Chung are members of the research team of Friendly Environmental Low Input Natural Herbicide New Material Study of the Konkuk University.     

Interactions of <Emphasis Type="Italic">Bacillus mojavensis</Emphasis> and <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> with a Benzoxazolinone (BOA) and its Transformation Product,APO

The benzoxazolinones, specifically benzoxazolin-2(3H)-one (BOA), are important transformation products of the benzoxazinones that can serve as allelochemicals providing resistance to maize from pathogenic bacteria, fungi, and insects. However, maize pathogens such as Fusarium verticillioides are capable of detoxifying the benzoxazolinones to 2-aminophenol (AP), which is converted to the less toxic N-(2-hydroxyphenyl) malonamic acid (HPMA) and 2-acetamidophenol (HPAA). As biocontrol strategies that utilize a species of endophytic bacterium, Bacillus mojavensis, are considered efficacious as a control of this Fusarium species, the in vitro transformation and effects of BOA on growth of this bacterium was examined relative to its interaction with strains of F. verticillioides. The results showed that a red pigment was produced and accumulated only on BOA-amended media when wild type and the progeny of genetic crosses of F. verticillioides are cultured in the presence of the bacterium. The pigment was identified as 2-amino-3H-phenoxazin-3-one (APO), which is a stable product. The results indicate that the bacterium interacts with the fungus preventing the usual transformation of AP to the nontoxic HPMA, resulting in the accumulation of higher amounts of APO than when the fungus is cultured alone. APO is highly toxic to F. verticillioides and other organisms. Thus, an enhanced biocontrol is suggested by this in vitro study.     

Antifungal Activity of a New Phenolic Compound from Capitulum of a Head Rot-resistant Sunflower Genotype

In a previous study, we observed that bract and corolla extracts from a Sclerotinia sclerotiorum-resistant sunflower contained high amounts of the known coumarins scopoletin, scopolin, and ayapin. There was a correlation between coumarin concentration and disease resistance. Thin layer chromatography showed higher concentrations of three other compounds in the resistant genotype when compared to the susceptible. A bioassay-directed purification that used column chromatography and HPLC allowed the isolation of a new compound, 3-acetyl-4-acetoxyacetophenone, and known compounds, demethoxyencecalin and 3-acetyl-4-hydroxyacetophenone. Structures were assigned from spectral data, and bioactivities were characterized by in vitro bioassays against S. sclerotiorum. The new compound, 3-acetyl-4-acetoxyacetophenone, had an antifungal activity similar to the coumarin ayapin, previously described as a potent Sclerotinia inhibitor. The speed and simplicity by which these compounds can be detected make them suitable for use in screening procedures that may identify genotypes with valuable levels of resistance. A screening of seven sunflower genotypes in a field experiment showed a correlation between these compounds and resistance to Sclerotinia.     

Potentials for exploiting allelopathy to enhance crop production

Strategies for utilizing allelopathy as an aid in crop production include both avoidance and application protocols. There are immediate opportunities for management of weed and crop residues, tillage practices, and crop sequences to minimize crop losses from allelopathy and also to use allelopathic crops for weed control. Varieties of grain and forage sorghums (Sorghum Spp.), sunflower (Helianthus annuus L.), oats (Avena sativa L.), wheat (Triticum sativum L.),rye (Secale cereale L.), and others may provide weed control and in some instances crop stimulation from their residues. Our four-year field study with cultivated sunflower resulted in no differences in weed biomass between plots with and without herbicide (EPTC) applications. Strip cropping that included sorghum showed that in the subsequent year weed density and biomass were significantly lower in the previous-year sorghum than in soybean strips. Possibilities exist for modification of crop plant metabolism to alter production of allelochemicals. Allelochemical-environmental interactions must be considered in efforts to benefit from allelopathy. Under greenhouse conditions, joint application of low levels of atrazine, trifluralin, alachlor, or cinmethylin with a phenolic allelochemical showed that these two categories of inhibitors acted in concert to reduce plant growth. Allelochemicals may also be adapted as yield stimulants or environmentally sound herbicides, such as cinmethylin and methoxyphenone. Isolation of bialophos, tentoxin, and others shows that bacteria and fungi are good sources of biologically active compounds.     

Photosynthesis and Water Relations in Tomato Plants Cultivated Long-Term in Media Containing (+)-Usnic Acid

The influence of (+)-usnic acid on rates of gas exchange (photosynthesis, respiration, and transpiration) in long-term cultivation of tomato plants was studied. The effect was dose-dependent. Plants grown in media containing the maximum concentration of (+)-usnic acid (30 μM) had photosynthetic and respiration rates reduced by 41% and 80%, respectively. The effect on photosynthesis rate may be the result of a multidirectional effect at various stages of this process, which at the highest usnic acid concentration underwent reduction: content of chlorophylls by 30%, carotenoids by 35%, and Hill reaction activity by 75%. Usnic acid also raises the susceptibility of chlorophyll to photodegradation. Under some conditions, transpiration was reduced by 2.1-fold in light and 3.7-fold in dark. This result was correlated with (1) an increase in the diffusive resistance of the stomata (3.1-fold in upper and 1.5-fold in lower surface of leaf), (2) a reduction of stomata density (by 60% on upper and 40% on lower surface), and (3) a 12.3-fold decrease in root hydraulic conductance.