Herbicidal effects of soil-incorporated wheat

The hydroxamic acid 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and the benzoxazolinones benzoxazolin-2-one (BOA) and 6-methoxybenzoxazolin-2-one (MBOA) have been identified as important allelochemicals in wheat. This study examines the possibility of exploiting the allelopathic properties of wheat as a weed control strategy by cultivating wheat as a precrop and incorporating plant residues into the soil before the next crop is sown. Different wheat varieties were cultivated in field plots during two seasons in both conventional and organic farming systems. Plants were sampled at various growth stages, and their contents of DIMBOA, MBOA, and BOA were determined by chemical analyses. The wheat samples were incorporated into soil, and the effect on germination and growth of 12 different weed species was examined in pot experiments under controlled conditions. In some cases significant effects were obtained, but the results were inconsistent and the effects were not correlated to the content of DIMBOA, MBOA, and BOA in the incorporated wheat plants. ED50 doses of the pure compounds were estimated in dose-response experiments in Petri dishes, and these turned out to be much higher than the predicted maximum concentrations of DIMBOA, MBOA, and BOA in the soil water following incorporation. The study shows that a prerequisite for exploiting the incorporation of wheat residues as a weed control strategy is the development of wheat varieties with an increased content of allelochemicals.     

Quantification of benzoxazinone derivatives in wheat (Triticum aestivum) varieties grown under contrasting conditions in Denmark

Three varieties of winter wheat (Triticum aestivum) were grown in both conventional and organic farming systems. The contents of the benzoxazinone derivatives 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), 2-beta-d-glucopyranosyloxy-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA-Glc), 6-methoxybenzoxazolin-2-one (MBOA), 2-hydroxy-7-methoxy-1,4-benzoxazin-3-one (HMBOA), benzoxazolin-2-one (BOA), and 2-hydroxy-1,4-benzoxazin-3-one (HBOA) were analyzed at five growth stages (BBCH 9-10, 12, 21, 31, and 53). Major differences were found between the varieties, with Stakado exhibiting the highest contents. In contrast, only minor and erratic differences were found between the two farming systems, suggesting that the inherent differences in the content of benzoxazinone derivatives of the varieties were not significantly affected by the use of pesticides and synthetic fertilizers. The concentration of benzoxazinone derivatives in the foliage was considerably higher at the early growth stages than later in the growing season, with DIMBOA being the most abundant of the benzoxazinone derivatives. An increase in the concentration was observed in early spring compared to late autumn, suggesting that plants synthesized benzoxazinone derivatives at the commencement of growth in early spring. The concentrations in the roots were considerably lower than in the foliage at the early growth stages but remained relatively constant over time, resulting in a higher concentration than in the foliage at the late growth stages. The results are discussed in relation to previous findings that predominantly originate from experiments done under controlled conditions in either growth cabinets or greenhouses.     

Qualitative characterization of benzoxazinoid derivatives in whole grain rye and wheat by LC-MS metabolite profiling

Benzoxazinoids are metabolites occurring in a restricted group of plant species including crops such as rye, wheat, and maize. Focus on the analysis of benzoxazinoid metabolites has typically been due to their importance to plant biochemistry and physiology as highly bioactive molecules that plants use as alleochemicals to defend themselves against predators and infections. However, the potential dietary contribution of these compounds has not been addressed. This study conducted a detailed qualitative characterization of benzoxazinoid metabolites present in the whole grain rye and processed fractions of rye bran, and their presence was also detected in whole grain wheat samples. Several novel benzoxazinoid metabolites of the hydroxamic acids (2,4-dihydroxy-1,4-benzoxazin-3-one, DIBOA; 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, DIMBOA), lactams (2-hydroxy-1,4-benzoxazin-3-one, HBOA), and benzoxazolinones (1,3-benzoxazol-2-one, BOA) were identified, including double-hexose derivatives of DIBOA, DIMBOA, and HBOA. This paper presents an important addition to the information on the phytochemical composition of rye and wheat grains, which deserves attention in the discussion of the potential health-promoting effects of these grains.     

Elucidating the transformation pattern of the cereal allelochemical 6-methoxy-2-benzoxazolinone (MBOA) and the trideuteriomethoxy analogue [D3]-MBOA in soil

To deduce the structure of the large array of compounds arising from the transformation pathway of 6-methoxybenzoxazolin-2-one (MBOA), the combination of isotopic substitution and liquid chromatography analysis with mass spectrometry detection was used as a powerful tool. MBOA is formed in soil when the cereal allelochemical 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) is exuded from plant material to soil. Degradation experiments were performed in concentrations of 400 microg of benzoxazolinone/g of soil for MBOA and its isotopomer 6-trideuteriomethoxybenzoxazolin-2-one ([D3]-MBOA). Previously identified metabolites 2-amino-7-methoxyphenoxazin-3-one (AMPO) and 2-acetylamino-7-methoxyphenoxazin-3-one (AAMPO) were detected. Furthermore, several novel compounds were detected and provisionally characterized. The environmental impact of these compounds and their long-range effects are yet to be discovered. This is imperative due to the enhanced interest in exploiting the allelopathic properties of cereals as a means of reducing the use of synthetic pesticides.     

Ecotoxicological effects of benzoxazinone allelochemicals and their metabolites on aquatic nontarget organisms

Before natural plant allelochemicals can be exploited as biological pesticides against weeds and for disease control, more than the effect on target organisms needs to be known. This study presents results of aquatic biotests using four organisms, namely, a water flea, a freshwater alga, a soil alga, and a luminescent bacterium. The tested substances were 10 benzoxazinone derivatives, 3 of them known to be wheat allelochemicals, benzoxazolin-2(3H)-one (BOA), 6-methoxybenzoxazolin-2(3H)-one (MBOA), and 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one (DIMBOA), and 7 identified degradation intermediates and metabolites. For comparison, two commercial pesticide formulations (BAS, Betanal) were tested by applying the same set of biotests. The data set produced could be seen as an ecotoxicological evaluation for effects of allelochemicals against nontarget organisms and as a base for further risk assessment.     

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA) levels in the wheat rhizosphere and their effect on the soil microbial community structure

Despite increasing knowledge of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA) as allelochemicals involved in the defense of wheat against pests, relatively little is known about their levels in the rhizosphere and interactions with the soil microbial community. This study quantified DIMBOA and MBOA in the wheat rhizosphere and analyzed the soil microbial community structure. MBOA rather than DIMBAO was found in the wheat rhizosphere, and its concentration varied with cultivars, plant densities, and growth conditions. Wheat could detect the presence of competing weeds and respond by increased MBOA in the rhizosphere. There was a linear positive relationship between the MBOA level in the wheat rhizosphere and soil fungi/bacteria. When DIMBOA was applied to soil, yielding MBOA increased soil fungi. There were different phospholipid fatty acid (PLFA) patterns in soil incubated with DIMBOA and MBOA. These results suggested that DIMBOA and MBOA could affect the soil microbial community structure to their advantage through the change in fungi populations.     

Degradation studies on benzoxazinoids. Soil degradation dynamics of (2R)-2-O-beta-D-glucopyranosyl-4-hydroxy-(2H)- 1,4-benzoxazin-3(4H)-one (DIBOA-Glc) and its degradation products, phytotoxic allelochemicals from Gramineae

Wheat (Triticum aestivum L.) has been found to possess allelopathic potential and studies have been conduced to apply wheat allelopathy for biological weed control. 2,4-Dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) is a common product found in wheat, corn, and rye exudates and it can be released to the environment by that way. In this report, the stability of DIBOA is studied in two soils from crop lands of wheat cv. Astron and cv. Ritmo. These varieties were selected by their concentrations of DIBOA and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) from aerial parts and by the bioactivities of their aqueous extracts in the growth of wheat coleoptile sections. The degradation rate of DIBOA in these soils was measured in laboratory tests during 90 h by high-pressure liquid chromatography methods. These analyses demonstrate that DIBOA was transformed primarily into 2-benzoxazolinone (BOA). This transformation was similar in both soil types with an average half-life of 43 h. The degradation studies for BOA show its biotransformation to 2-aminophenoxazin-3-one (APO) with a half-life of 2.5 days. Therefore, BOA is an intermediate product in the biotransformation from DIBOA to APO in these wheat crop soils and is consistent with previous findings. APO was not degraded after three months in soil, suggesting that its degradation rate in soil is very slow.     

Effect of 6-methoxybenzoxazolin-2-one (MBOA) on the reproduction rate of the grain aphid (Sitobion avenae F.)

Partial host-plant resistance could make a substantial contribution to reducing the damage caused by economically important grain aphids and, therefore, to reduced insecticide use. Naturally occurring hydroxamic acids, in particular 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), have been shown to be involved in the resistance of cereals to insects. DIMBOA is unstable in aqueous solutions and has been reported to decompose to 6-methoxybenzoxazolin-2-one (MBOA). MBOA was tested on grain aphids living on artificial diet incorporated with MBOA. From 0 to 0.1 mM, the intrinsic rate of increase (rm) increased. From 0.1 to 0.3 it decreased by 73%. The rm was calculated to be 0 at 1.0 mM. Consequently, even low concentrations of MBOA may reduce the aphid multiplication to a level below the economic damage threshold. Therefore, it is possible to breed wheat varieties with a sufficiently high content of DIMBOA to decrease grain aphid populations.     

Isolation and synthesis of allelochemicals from gramineae: benzoxazinones and related compounds

Compounds with a (2H)-1,4-benzoxazin-3(4H)-one skeleton have attracted the attention of phytochemistry researchers since 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) were isolated from plants belonging to the Poaceae family. These compounds exhibit interesting biological properties, such as phytotoxic, antimicrobial, antifeedant, antifungal, and insecticidal properties. These chemicals, in addition to a wide variety of related compounds involved in their metabolism, detoxification mechanisms, and degradation on crop soils and other systems, have high interest and in some cases potential agronomic utility. This paper presents a complete review of the methods employed for their synthetic obtention in addition to some of the authors' own contributions to their chemistry. The degradation and phytotoxicity experiments carried out in ongoing research into the potential agronomic utility of these compounds required large amounts of them, which were obtained from natural sources. This paper presents a modified methodology to access DIMBOA from Zea mays cv. Apache and to obtain 2-O-beta-D-glucopyranosyl-2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-Glc) and DIBOA from Secale cereale L. New synthetic methodologies were employed for the obtention of the lactams 2-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one and 2-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one and the malonamic acids N-(2-hydroxyphenyl)malonamic acid and N-(2-hydroxy-7-methoxyphenyl)malonamic acid. The aminophenoxazines 2-amino-7-methoxyphenoxazin-3-one and 2-acetamido-7-methoxyphenoxazin-3-one have been synthesized in the authors' laboratory by novel procedures. All of the methodologies employed allowed the desired compounds to be obtained in high yield and in an easy-to-scale manner.     

Fate of benzoxazinone allelochemicals in soil after incorporation of wheat and rye sprouts

Growing cereals (especially rye), which are incorporated into the soil to increase soil fertility or organic matter content, is a common practice in crop rotation. The additional sanitizing effect of this incorporation has often been appreciated and is said to be due to leaching of benzoxazinones and subsequent formation of benzoxazolinones. In this study wheat (Stakado) and rye (Hacada) sprouts were incorporated into soil in amounts that simulated agricultural practice. By extraction and subsequent LC-MS analysis the disappearance and appearance of benzoxazinones, benzoxazolinones, and phenoxazinones in soil were followed. In the wheat experiments 6-methoxybenzoxazolin-2-one (MBOA) was detected as the main compound. 2-Hydroxy-7-methoxy-1,4-benzoxazin-3-one (HMBOA) and 2-hydroxy-1,4-benzoxazin-3-one (HBOA) were detected as well. No phenoxazinones were detected. For the rye experiment the picture was more complex. In the first 2 days of incubation MBOA and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) were detected as the main allelochemicals along with HBOA, HMBOA, and benzoxazolin-2-one (BOA), in decreasing order. Later in the incubation period some 2-amino-3H-phenoxazin-3-one (APO) was detected and the amount of HBOA increased considerably and decreased again. The profiling of the benzoxazinone metabolites and their derivates in soil was dynamic and time-dependent. The highest concentrations of most of the compounds were seen at day 1 after incorporation. A maximum concentration was reached at day 4 for a few of the compounds. This study is the first of its kind that shows the dynamic pattern of biologically active benzoxazinone derivates in soil after incorporation of wheat and rye sprouts. Methods for organic synthesis of HBOA and HMBOA were developed as part of the study.     

Joint action of benzoxazinone derivatives and phenolic acids

The joint action of binary and ternary mixtures of benzoxazinone derivatives and phenolic acids was studied using the additive dose model (ADM) as reference model. The activity of fixed-ratio mixtures of phenolic acids [ferulic acid (FA), p-coumaric acid (CA), vanillic acid (VA), and p-hydroxybenzoic acid (HBA)] and benzoxazinone derivatives [2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), 6-methoxybenzoxazolin-2-one (MBOA), benzoxazolin-2-one (BOA), 2-aminophenol (AP), and N-(2-hydroxyphenyl)acetamide (HPAA)] on Lolium perenne and Myosotis arvensis root growth was assessed in Petri dishes. Root length was recorded 6 days after seeding, and EC(50) and EC(90) values were estimated using nonlinear regression analyses. The benzoxazinone derivatives were found to be more phytotoxic than the phenolic acids, particularly on M. arvensis. Binary mixtures of phenolic acids responded predominantly additively on both plant species. Deviations from additivity were species-specific with antagonistic responses on L. perenne and synergistic responses on M. arvensis. Similarly, binary mixtures of benzoxazinone derivatives also followed the ADM, although synergistic responses were observed for BOA + AP and BOA + HPAA. Binary and ternary mixtures of benzoxazinone derivatives and phenolic acids responded primarily antagonistically; however, a significant synergistic performance was observed with DIMBOA + FA and DIMBOA + VA on L. perenne. These results do not support the assumption that allelopathic effects of wheat can be attributed to synergistic effects of otherwise weakly active allelopathic compounds, and it is suggested that future research be directed toward identifying and studying the effects of other potential allelochemicals including the degradation products of the most abundant wheat allelochemicals.     

Structure-Activity Relationships (SAR) studies of benzoxazinones, their degradation products and analogues. phytotoxicity on standard target species (STS)

Benzoxazinones 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) and 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) have been considered key compounds for understanding allelopathic phenomena in Gramineae crop plants such as corn (Zea mays L.), wheat (Triticum aestivum L.), and rye (Secale cereale L.). The degradation processes in the environment observed for these compounds, in which soil microbes are directly involved, could affect potential allelopathic activity of these plants. We present in this work a complete structure-activity relationships study based on the phytotoxic effects observed for DIMBOA, DIBOA, and their main degradation products, in addition to several synthetic analogues of them. Their effects were evaluated on standard target species (STS), which include Triticum aestivum L. (wheat) and Allium cepa L. (onion) as monocots and Lepidium sativum L. (cress), Lactuca sativa L. (lettuce), and Lycopersicon esculentum Will. (tomato) as dicots. This permitted us to elucidate their ecological role and to propose new herbicide models based on their structures. The best phytotoxicity results were shown by the degradation chemical 2-aminophenoxazin-3-one (APO) and several 2-deoxy derivatives of natural benzoxazinones, including 4-acetoxy-(2H)-1,4-benzoxazin-3(4H)-one (ABOA), 4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIBOA), and 4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIMBOA). They showed high inhibitory activity over almost all species growth. The fact that APO is a degradation product from DIBOA with high phytotoxicity and stability makes it possible to assign an important ecological role regarding plant defense mechanisms. 2-Deoxy derivatives of natural benzoxazinones display a wide range of activities that allow proposing them as new leads for natural herbicide models with a 1,4-benzoxazine skeleton.     

Concentration of benzoxazinoids in roots of field-grown wheat (Triticum aestivum L.) varieties

Benzoxazinones are naturally occurring secondary metabolites of some Gramineae plants, responsible for their resistance to some pathogenic fungi and for their allelopathic action. Six varieties of winter wheat grown in fields under organic or conventional systems and 11 old accessions were tested for two consecutive seasons and three plant development stages for the concentration in their roots of cyclic hydroxamic acids and their degradation products. This is the first report of six benzoxazinones analyzed in plants grown in the field. An analytical technique employing LC-DAD was used for determination. It was shown that 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, its degradation product 6-methoxybenzoxazolin-2-one, and the lactam 2-hydroxy-7-methoxy-1,4-benzoxazin-2-one were predominant compounds in all tested samples. Their concentrations significantly differed with plant development stage and season, but no significant differences were found between varieties and between plant cultivation systems. The concentrations of 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and its degradation product benzoxazolin-2-one (BOA) were much lower, ranging from 60 to 430 mg/kg of dry matter, depending on accession, stage of development, and season. There was no significant difference found between plants grown in different cultivation systems, but there were significant differences between old and new varieties; concentrations of DIBOA and its derivatives were significantly lower in old accessions. It was concluded that the concentrations of DIBOA and BOA, which are precursors of highly fungicidal 2-aminophenol, 2-amino-3H-phenoxazin-3-one, and 2-acetylamino-3H-phenoxazin-3-one, are theoretically high enough to protect plants against some soilborne pathogens.     

Simple method for large scale isolation of the cyclic arylhydroxamic acid DIMBOA from maize (Zea mays L.)

The 2-beta-O-D-glucoside of the cyclic arylhydroxamic acid 2, 4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) that occurs in large amounts in young maize shoots (Zea mays L.) is converted enzymatically to its aglycone upon tissue damage. The aglycone DIMBOA possesses strong biologically activity toward various organisms whereas the glucoside is almost biologically inactive. A simple procedure yielding DIMBOA in gram quantities, from 7-day-old maize seedlings, was developed by using solid-phase extraction.     

Determination of benzoxazinone derivatives in plants by combining pressurized liquid extraction-solid-phase extraction followed by liquid chromatography-electrospray mass spectrometry

A new analytical method based on the use of pressurized liquid extraction (PLE) followed by solid-phase extraction with LiChrolut RP C18 cartridges was evaluated for the sample preparation, extraction, and cleanup of eight naturally occurring benzoxazinone derivatives, 2-beta-D-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one, 2-beta-D-glucopyranosyloxy-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one, 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, 2-hydroxy-1,4-benzoxazin-3-one, 2-hydroxy-7-methoxy-1,4-benzoxazin-3-one, benzoxazolin-2-one, and 6-methoxybenzoxazolin-2-one in plant samples. Afterward, liquid chromatography-electrospray mass spectrometry, using the selected ion monitoring mode and internal standard (2-MeO-DIBOA, indoxyl-beta-D-glucoside, and quercetin-3-O-rutinoside) quantification method was performed. This paper demonstrates the effectiveness of the PLE method, in conjunction with sensitive and specific mass spectrometric detection, for the quantitative recovery of compounds of the benzoxazinone class from plants. The recoveries of the analytes ranged from 66 to 110% with coefficients of variation ranging from 1 to 14%. This method gave detection limits between 1 and 27 microg/g. The method was applied to foliage and roots of three different wheat cultivars, and the analytes were detected in the range of 11-3261 microg/g of dry weight.     

Structure-activity relationship studies of benzoxazinones and related compounds. Phytotoxicity on Echinochloa crus-galli (L.) P. Beauv

Echinochloa crus-galli (E. crus-galli; barnyardgrass) is a weed widely distributed. It constitutes a serious weed problem in 42 countries and has been found in at least 27 more. It is the world's main weed of rice affecting up to 36 crops worldwide. Several biotypes of this plant, with resistance to herbicides with different modes of action have evolved. In our ongoing studies regarding the potential application of benzoxazinones and their soil degradation products for weed control, a complete structure-activity relationships (SARs) study was made by using barnyardgrass as the target plant. Compounds used in this study were previously tested on a wide variety of standard target species (STS), and they include natural allelochemicals 2-O-beta-D-glucopyranosyl-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-Glc), 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA), together with some degradation derivatives found in wheat crop soil and some synthetic analogues. Their phytotoxicity on E. crus-galli is discussed and compared with the results obtained from previous screening. This work constitutes the next step in the search for natural herbicide models based on benzoxazinones and their degradation products. The most active compounds were the degradation product 2-aminophenol (APH) and the synthetic analogue 4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIBOA). Their activities confirm the direction proposed in our previous SAR study, which establishes D-DIBOA to be the best lead for natural herbicide model development with benzoxazinone structure.     

Differential exudation of two benzoxazinoids--one of the determining factors for seedling allelopathy of Triticeae species

Benzoxazinoids (Bx) are natural phytotoxins that function as chemical defense compounds in several species. The release of Bx by intact plant roots associated these compounds with root allelopathy in Triticeae species; however, the significance of exudate concentrations of Bx for plant-plant interactions is still a controversial question. A biological screening of 146 cultivars of four Triticeae species (Triticum aestivum L., Triticum durum Desf., Triticum spelta L., and Secale cereale L.) demonstrated a high cultivar dependence to suppress the root growth of Sinapis alba L. by root allelopathy in a dose-response bioassay. Only a few cultivars possessed a marked high or low allelopathic activity, whereby high-performance liquid chromatography-diode array detection analysis of root exudates revealed that these cultivars differed considerably in their ability to exude the two Bx aglucones, DIBOA [2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one] and DIMBOA [2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one]. The total amount of DIBOA and DIMBOA exuded showed a significant correlation to the growth inhibition in bioassay with a statistically estimated contribution to the overall allelopathic effect of 48-72%. In a bioassay with pure phytotoxins, Bx concentrations consistent with the amounts quantified in the screening bioassay caused detrimental effects on S. alba and almost reproduced the statistically estimated contribution. The observed causal association between the allelopathic activity under laboratory conditions and the exudate concentrations of Bx suggests that this association might have implications for the interference of Triticeae species in natural plant communities.     

Structure-activity relationship (SAR) studies of benzoxazinones, their degradation products, and analogues. Phytotoxicity on problematic weeds Avena fatua L. and Lolium rigidum Gaud

Avena fatua L. (wild oat) and Lolium rigidum Gaud. (rigid ryegrass) are highly problematic weeds affecting a wide variety of cereal crops worldwide. The fact that both of these weeds have developed resistance to several herbicide groups made them optimal candidates as target organisms for ongoing research about the potential application of allelochemicals and analogue compounds as natural herbicide models. Benzoxazinones, a family of natural allelochemicals present in corn, wheat, and rye, including 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one, together with some degradation products, found in crop soils as well as in other systems, and some synthetic analogues of them were tested on wild oat and rigid ryegrass seeds; the results were statistically treated, and some structure-activity relationships, useful in further development of natural herbicide models, were elucidated. The most active compounds were the synthetic benzoxazinone 2-acetoxy-(2H)-1,4-benzoxazin-3(4H)-one and the degradation product 2-aminophenoxazin-3-one, with highly significant inhibition on the development of both weeds. The ecological role of these compounds is discussed by considering both degradability and phytotoxicity. The bioactivity of aminophenoxazines has been correlated by their aqueous solubility-lipophilicity predicted by means of computational methods.