Weed Suppression by Release of Isothiocyanates from Turnip‐Rape Mulch

Abstract

wick et al., 1983). Living plants do not actively release high amounts of ITCs (Bö rner, 1961), because glucosi-The allelopathic potential of isothiocyanates (ITC) released by nolates are located in the vacuole and myrosinase is turnip-rape mulch [Brassica rapa (Rapifera Group)-Brassica napus L.] was evaluated. Six different ITCs were identified from chopped bound to the cell wall (Bjö rkman, 1976). As long as this turnip-rape by HPLC-DAD/HPLC-MS. All plant parts contained separation exists, there is only a low ITC content in the 2-phenylethyl-ITC. In the shoot n-butyl and 3-butenyl-ITC domicells (Tang, 1971). Larger amounts of ITCs can only nated. Younger leaves, flowers, and buds also contained small amounts be released by the breakdown of the cells, e.g., during of benzyl and allyl-ITC. Furthermore, marginal amounts of 4-pendecomposition of dead plant material (Bell and Muller, tenyl-ITC were detected. In the soil, where turnip-rape mulch was 1973), or even faster by incorporating green plant mateincorporated, only low amounts of ITCs were detected. It was shown rial into the soil. If Brassica spp. plant tissues are incorthat the DT 50 of ITCs in soil are very short. Germination tests with porated into the soil, it is possible to control weeds in weed seeds in aqueous ITC solutions showed, that aryl-ITCs were the following crop by ITCs released from the mulch the most suppressive compounds. Within the alkyl-ITCs, the activity decreased with increasing molecular mass. The susceptibility of differ- (Brown and Morra, 1995; Boydston and Hang, 1995; ent weed species to ITCs mainly depended on seed size. Smaller seeds Al-Katib et al., 1997). This might be a chance to reduce tended to be more sensitive. Further studies demonstrated a high the use of herbicides and could be an additional tool to biological activity of ITCs in the vapor phase. n-Butyl-ITC was more control herbicide-resistant weeds. suppressive in the vapor phase than in aqueous solution, while 2-The objectives of this study were to evaluate the allelphenylethyl-ITC showed the opposite effect. Results demonstrated opathic potential of ITCs released by turnip-rape that weed suppression observed in the field was probably due to the mulch. Therefore, the content of ITCs in different parts high amounts of ITCs identified in turnip-rape mulch. Isothiocyanates of turnip-rape, and in the soil after incorporation was were strong suppressants of germination on tested species-spiny determined, and the phytotoxicity of different ITCs on sowthistle [Sonchus asper (L.) Hill], scentless mayweed (Matricaria inodora L.), smooth pigweed (Amaranthus hybridus L.), barn-several weed species-spiny sowthistle [Sonchus asper yardgrass [Echinochloa crusgalli (L.) Beauv.], blackgrass (Alopec-(L.) Hill], scentless mayweed (Matricaria inodora L.), urus myosuroides Huds.), and wheat (Triticum aestivum L.)-and smooth pigweed (Amaranthus hybridus L.), barnprobably interact with weed seeds in the soil solution and as vapor yardgrass [Echinochloa crusgalli (L.) Beauv.], blackin so...

Potencial alelopático de extratos aquosos de genótipos de canola sobre Bidens pilosa

“…A família Brassicaceae caracteriza-se por produzir glucosinolatos (Oerlemans et al, 2006), que, quando decompostos, transformam-se em isotiocianatos e tiocianatos (Eberlein et al, 1998). Essas substâncias podem, em baixas concentrações, atrasar a germinação e, em altas concentrações, penetrar nas sementes, tornando-as inviáveis (Petersen et al, 2001). …”

The Biology of Canadian Weeds. 137. Brassica napus L. and B. rapa L.

“…For example, in aqueous extracts, arylisothiocyanate from domesticated winter B. rapa was the most potent inhibitors of germination in several species [T. aestivum L., Sonchus asper (L.) Hill, Matricaria inodora L., Amaranthus hybridus L., Echinochloa crus-galli (L.) Beauv., Alopecurus myosuroides Huds.] (Petersen et al 2001), while allyl-isothiocyanate and methyl-isothiocyanate were the most active allelopathic compounds in the volatile phase and consistently provided I 50 values (the concentration at which 50% of germination is inhibited) for germination of soybean [Glycine max (L.) Merr. ], corn (Zea mays L.), canola, alfalfa (Medicago sativa L.), dandelion (Taraxacum officinalis Weber), cucumber (Cucumis sativus L.), and wheat (Triticum aestivum L.) at concentrations below 1 ppm.…”

“…Leachates from domesticated spring B. napus residue were more potent to stinkweed (Thlaspi arvense L.), flixweed (Descurainia sophia L.), and downy brome (Bromus tectorum L.) than to winter wheat (Triticum aestivum L.), suggesting the possibility of selective management of these weeds in notill, direct-seeded farming systems in Alberta (Moyer and Huang 1997). Water soluble and volatile isothiocyanates have been identified as allelopathic compounds (Vaughn and Boydston 1997;Petersen et al 2001). Potency of isothiosyanates is dependent on form at each phase.…”

Effects of Plant Residue, Root Exudate and Juvenile Plants of Rapeseed (Brassica napus L.) on the Germination, Growth, Yield, and Quality of Subsequent Crops in Successive and Rotational Cropping Systems

“…Exposure to the volatiles from the leaves delayed seed germination and decreased subsequent growth of these species. Peterson et al (2001) reported that volatile isothiocyanates, one of the degradation products of glucosinolates, suppressed weed germination after the incorporation of turnip-rapeseed green mulch into the soil. They reported that the isothiocyanate produced in large amounts by the mulch suppressed weed germination.…”