Herbicidal activity of clove oil and its main constituents eugenol, β-caryophyllene, and α-humulene was studied by measuring their effects on cell membrane integrity in broccoli and common lambsquarters plants at the three- and nine-leaf stage, respectively. Roles of essential oil constituents in the overall phytotoxicity of clove oil, dose-response (10 to 160 mM) relationships of their phytotoxicity, and the effect of light intensity on phytotoxicity of clove oil and eugenol were studied. Most of the phytotoxicity of clove oil (2.5% solution) was due to eugenol, its largest constituent. β-caryophyllene and α-humulene played little or no role. Dose-response relationships showed that at equimolar concentration, eugenol was the most phytotoxic essential oil constituent of the clove oil. On a per unit biomass basis, membrane damage in response to clove oil and eugenol sprays decreased with increasing light intensity. This suggests that efficacy of essential oil in causing plant damage could be affected by light intensity experienced by plants prior to the oil spray.

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The Franciszek Górski In sti tute of Plant Phys i ol ogy, Pol ish Acad emy of Sci ences, Niezapominajek 21, 30-239 Kraków, Po land ** De part ment of Soil Man age ment and Plant Cul ti va tion, Ag ri cul tural Uni ver sity of Kraków, Al. Mickiewicza 21, 31-120 Kraków, Po land Cor re spon dence to: hura@ifr-pan.krakow.pl Key words: allelopathy, buck wheat, Echinochloa crus-galli, oat, phe no lic ac ids, rye, spring bar ley, white mus tard Ab stractThe pur pose of this study was to de ter mine the con tent of selected phe no lic com pounds in white mus tard, buck wheat, spring bar ley, oat and rye grown un der field con di tions. Moreover, the allelopathic ef fi ciency of these com pounds was evalu ated by sen si tiv ity of Echinochloa crus-galli. The ar o matic ac ids: trans-cinnamic, sal i cylic, ferulic, chlorogenic, p-hydroxy benzoic, protocatechuic, p-coumaric and vanillic were sep a rated from crop plants by TLC and de ter mined spec tropho to met ri cally.Dif fer ences in con cen tra tions of ana lysed com pounds were ob served for most of the ex am ined plant spe cies. The high est con cen tra tion was no ticed for cinnamic acid and ranged from 360 µg·g -1 DW in rye to 2770 µg·g -1 DW in spring bar ley. The rel a tively high con cen tra tion was no ticed for ferulic acid (from 73.8 µg·g -1 DW in buck wheat to 1046 µg·g -1 DW in spring barley) and p-coumaric acid (from 50 µg·g -1 DW in oat to 1499 µg·g -1 DW in buck wheat). The ob served dif fer ences in the phenolics con tent be tween two suc ces sive veg e ta tion sea sons can re flect the ef fect of abiotic and bi otic en vi ron men tal factors on the phenolics level in stud ied plants.In the green house ex per i ment the ef fect of par tic u lar compounds on the growth of Echinochloa crus-galli was also studied. It has been found that the ex am ined phenolics, and es pecially trans-cinnamic acid and mix ture of phe no lic compounds, sig nif i cantly in hibit the growth of Echinochloa crus-galli. The ob tained re sults may con trib ute to the ex pla nation of the bi o log i cal ac tiv ity of some phe no lic com pounds.List of ab bre vi a tions: TLC, thin -layer chro ma togra phy; AE, allelopathic ef fi ciency; x, x/2, x/4, concen tra tions of the phe no lic com pounds. In tro duc tionPlants pro duce many or ganic com pounds which play a sig nif i cant role in plant-plant in ter ac tions and are used as her bi cides. Re cently, a range of second ary me tab o lites have been in ten sively stud ied for allelochemical prop er ties. So far sev eral cat ego ries of allelochemicals in plants have been identi fied, namely, phe no lic ac ids, phenylpropanoids, hydroxamic ac ids, and short-chain fatty ac ids. Beside these, catechins, epicatechins, rutin and quercitin were rec og nized as com pounds highly contrib ut ing to in hib i tory ef fects in some plant spe cies 537

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The study aimed to determine the usefulness of isothermal calorimetry and FT-Raman spectroscopy for the early evaluation of rigid ryegrass resistance to fenoxaprop-P ethyl (active ingredient one of aryloxyphenoxypropionate herbicides). The calorimetric measurements were done on the 4-day-old seedlings of susceptible and resistant biotypes of rigid ryegrass (Lolium rigidum Goud.) for 72 h, at 20°C. It was observed that the specific thermal powertimecurves of the susceptible and resistant biotypes growing on water (control) were qualitatively similar. Herbicides changed the shape of the specific thermal power-time curves of both biotypes. Furthermore, the total specific thermal energy was significantly higher for the seedlings of resistant biotype, growing both on water or herbicide, as compared to the susceptible ones. The analysis of the seedlings' endosperm, conducted using FT-Raman spectroscopy, showed a weaker intensity of the bands in the spectra derived from the resistant biotype. Differences in the specific thermal power-time curves and FT-Raman spectra between susceptible and resistant biotypes growing on water indicate that the sensitive and resistant biotypes are metabolically and chemically different already in the early stages of the seedling growth. We conclude that isothermal calorimetry and FT-Raman spectroscopy are efficient tools for the early detection of rigid ryegrass resistance to fenoxaprop-P ethyl.