Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation. Allelochemical structures and modes of action are diverse and may offer potential for the development of future herbicides. We have focused our review on a variety of weed and crop species that establish some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are ...

Weed and Crop Allelopathy

Development of capitate glands on the leaves of annual wormwood (Artemisia annua L.) was monitored with scanning and transmission electron microscopy. Differentiation of foliar cells into gland cells began in the youngest leaf primordia. After differentiation into a 10-celled biseriate structure of two stalk cells, two basal cells, and three pairs of secretory cells, the cuticle of the six secretory cells separated from the cell walls to form a bilobed sac that eventually splits to release its contents. At every developmental stage, the cells of the the gland contained relatively little vacuolar volume. The secretory cells contained extensive endoplasmic reticulum. The plastids of each cell pair were different. At maturity, the apical cells contained proplastids or leucoplasts with only occasional thylakoids. The cell pair below the apical cell pair contained amorphous chloroplasts without starch grains. The basal cell pair contained proplastids or leucoplasts and the stalk cells contained chloroplasts. T...

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Development and Fine Structure of the Glandular Trichomes of Artemisia annua L.

The tissue localization of the antimalarial sesquiterpenoid compound artemisinin in annual wormwood (Artemisia annua L.) was determined by differential extraction of a glanded biotype and through the use of a glandless biotype. A 5-s dip in chloroform extracted 97% of the artemisinin from glanded A. annua leaf tissue. In addition, all of the detectable artemisitene, an artemisinin analog, was extracted. This extraction method caused collapse of the subcuticular space of the capitate glands on the leaf surface, whereas no other damage to the leaf surface was observed with SEM. Light microscopy and TEM revealed that this extraction method, despite causing some organelle structural changes, did not disrupt cell membranes. An A. annua biotype without glands contained neither artemisinin nor artemisitene. These results indicate that artemisinin and artemisitene present in foliar tissue are localized entirely in the subcuticular space of capitate glands of A. annua.

Localization of artemisinin and artemisitene in foliar tissues of glanded and glandless biotypes of artemisia annua l.

Essential oils of Artemisia absinthium L. and Tanacetum vulgare L. were extracted by three methods, a microwave assisted process (MAP), distillation in water (DW) and direct steam distillation (DSD), and tested for their relative toxicity as contact acaricides to the twospotted spider mite, Tetranychus urticae Koch. All three extracts of A. absinthium and of T. vulgare were lethal to the spider mite but to variable degrees. The LC50 obtained from the DSD oil of A. absinthium was significantly lower (0.04 mg/cm2) than that of the MAP (0.13 mg/cm2) and DW (0.13 mg/cm2) oil of this plant species. DSD and DW extracts of T. vulgare were more toxic (75.6 and 60.4% mite mortality, respectively, at 4% concentration) to the spider mite than the MAP extract (16.7% mite mortality at 4% concentration). Chromatographic analysis indicated differences in composition between the more toxic DSD oil of A. absinthium and the other two extracts of this plant, indicating that a sesquiterpene (C15H24) compound present in the DSD oil and absent in the other two may enhance the toxicity of the DSD oil. Chemical analysis of the T. vulgare extracts indicated that β-thujone is by far the major compound of the oil (>87.6%) and probably contributes significantly to the acaricidal activity of the oil.

https://bioone.org/journals/journal-of-economic-entomology/volume-94/issue-1/0022-0493-94.1.167/Acaricidal-Properties-of-Artemisia-absinthium-and-Tanacetum-vulgare-Asteraceae-Essential/10.1603/0022-0493-94.1.167.pdf

S. M. Lee

Papers

Terpenoids from the Genus Artemisia as Potential Pesticides