Rice ( Oryza sativa L.) is a principal source of food for more than half of the world population, especially in South and Southeast Asia and Latin America. Elsewhere, it represents a high‐value commodity crop. Change in the method of crop establishment from traditional manual transplanting of seedlings to direct‐seeding has occurred in many Asian countries in the last two decades in response to rising production costs, especially for labor and water. Direct‐seeding of rice (DSR) may involve sowing pregerminated seed onto a puddled soil surface (wet‐seeding) or into shallow standing water (water‐seeding), or dry seed into a prepared seedbed (dry‐seeding). In Europe, Australia, and the United States, direct‐seeding is highly mechanized. The risk of crop yield loss due to competition from weeds by all seeding methods is higher than for transplanted rice because of the absence of the size differential between the crop and weeds and the suppressive effect of standing water on weed growth at crop establishment. Of 1800 species reported as weeds of rice, those of the Cyperaceae and Poaceae are predominant. The adoption of direct‐seeding has resulted in a change in the relative abundance of weed species in rice crops. In particular, Echinochloa spp., Ischaemum rugosum, Cyperus difformis , and Fimbristylis miliacea are widely adapted to conditions of DSR. Species exhibit variability in germination and establishment response to the water regime postsowing, which is a major factor in interspecifically selecting constituents of the weed flora. The relatively rapid emergence of “weedy” (red) rice, rice phenotypically similar to cultivars but exhibiting undesirable agronomic traits, has been observed in several Asian countries practicing DSR, and this poses a severe threat to the sustainability of the production system. Stale seedbeds, tillage practices for land leveling, choice of competitive rice cultivars, mechanical weeders, herbicides, and associated water management are component technologies essential to the control of weeds in DSR. Herbicides in particular are an important tool of weed management, but hand weeding is either partially or extensively practiced in countries of Asia, Africa, and Latin America. Though yet to be globally commercialized, transgenic rice varieties engineered for herbicide resistance are a potential means of weed control. The release of herbicide‐resistant rice for red rice control in the United States has indicated the need to critically examine mitigation methods for the control of gene flow. Integrating preventive and interventional methods of weed control remains essential in managing weed communities in DSR, both to prohibit the evolution of herbicide resistance and to maximize the relative contributions of individual components where herbicides are not widely used. There remains a need to further develop understanding of the mechanisms and dynamics of rice weed competition and of the community dynamics of weed populations in DSR to underpin sustainable weed management practices.

Weed Management in Direct‐Seeded Rice

Cofactor requirement was determined for the heterologous expressed phytoene desaturases from the cyanobacterium Synechococcus and the higher plant Gentiana lutea. The cyanobacterial enzyme is depen...

Bleaching Herbicide Norflurazon Inhibits Phytoene Desaturase by Competition with the Cofactors

This review represents systematic and integrated picture of pesticide exposure to plant and its effect on growth and metabolism. Decades ago, agrochemicals were introduced aiming at enhancing crop yields and protecting crops from pests. Due to adaptation and resistance developed by pests to chemicals, every year higher amounts and new chemical compounds are used to protect crops, causing undesired side effects and raising the costs of food production. Biological chemical free agriculture is gaining also more and more support but it is still not able to respond to the need for producing massive amounts of food. The use of agrochemicals, including pesticides, remains a common practice especially in tropical regions and South countries. Cheap compounds, such as DDT, HCH, and Lindane, that are environmentally persistent, are today banned from agriculture use in developed countries, but remain popular in developing countries. As a consequence, persistent residues of these chemicals contaminate food and disperse in the environment. Therefore, the thrust of this paper was to review the application of pesticides effect early from germination to growth of the plant, leading to alteration in biochemical, physiological and different enzymatic and non-enzymatic antioxidants which ultimately affect the yield and resulted in residues in plant, vegetables, and fruits.

Selective Effect of Pesticides on Plant—A Review

Rice (Oryza sativa L.) is one of the most important food crops worldwide. However, it is also a valuable tool in assessing toxicity of organic and inorganic compounds. For more than 20 years, it has been an approved species for standardized phytotoxicity experiments. The objective of this study is to determine germination and radicle (root) and coleoptile (shoot) growth of rice seeds exposed to three insecticides and two herbicides, commonly used in the agricultural production landscape. Although no germination effects of pesticide exposure were observed, significant growth effects were noted between pesticide treatments. Coleoptile growth was significantly (p ≤ 0.05) lowered in metolachlor/atrazine mixture, diazinon, and lambda-cyhalothrin exposures when compared with controls. Radicles of fipronil-exposed seeds were significantly larger (p ≤ 0.05) when compared with controls. This research contributes to the phytotoxicity assessment database, in addition to laying the foundation for the use of rice as a phytoremediation tool for agricultural pesticide runoff.

Effect of Three Insecticides and Two Herbicides on Rice (Oryza sativa) Seedling Germination and Growth

At present the use-rate of modern herbicides is in the range of 100-300 g AI ha-1, with a tendency to decline. The low use-rate (ca 10 g AI ha-1) of the original sulfonylurea and cyclic imide herbicides prompted agrochemical scientists to look for even more active compounds which led to the successive discoveries of many new herbicidal acetolactate synthase inhibitors and no less than 18 cyclic imides in the class of protoporphyrinogen-IX oxidase inhibitors in the 1990s. In this paper, mechanisms of action related to function and biosynthesis of chlorophylls, carotenoids, plastoquinone, amino acids, fatty acids and photosynthetic electron transport and other metabolic processes are discussed as plant-specific herbicidal target domains.

Target sites for herbicides: entering the 21st century.

A mode of action study of herbicidal diphenylpyrrolidinones was carried out through carotenoid analyses in intact Scenedesmus cells and by a cell-free plant-type phytoene desaturase assay using Escherichia coli transformants. A series of forty-eight diphenylpyrrolidinones decreased the carotenoid content of Scenedesmus cells in the light and inhibited phytoene desaturase. The relationship between substituents at various positions and inhibition of phytoene desaturase is discussed. Using very active bleaching diphenylpyrrolidinones, a 10−5 M concentration affected neither the ζ-carotene desaturase nor the protoporphyrinogen-IX oxidase. Although some differences in their inhibitory activity were found between the in vivo and cell-free assays, it is concluded that the compounds are essentially bleachers affecting carotenoid biosynthesis in plants. Enzyme kinetics studies with recombinant phytoene desaturase revealed a non-competitive inhibition with respect to the substrate phytoene. A competition against the inhibitor was shown by the cofactor NADP+, suggesting an interaction of pyrrolidinones at the cofactor-binding site of phytoene desaturase.



© 2001 Society of Chemical Industry

Mode of bleaching phytotoxicity of herbicidal diphenylpyrrolidinones

MTB-951 is a potential mycoherbicide using a fungal plant pathogen (Drechslera monoceras) isolated from native Echinochloa species in Japan. Conidia of this pathogen were used as the active ingredient and its herbicidal performance was examined in a greenhouse. The efficacy of MTB-951 on Echinochloa crus-galli L. was higher in deep water (7–9 cm) than in relatively shallow water (3–5 cm). In a postemergence application, the efficacy decreased as the leaf stage of E. crus-galli proceeded between the 1 and 2.5 leaf stage. For example, the control ratio (%) of E. crus-galli was 95% when applied at the 1 leaf stage, and 72% at the 2.5 leaf stage in 5 cm water. Generally, mycoherbicidal efficacy was less when applied pre-emergence rather than postemergence. Efficacy was also influenced by the duration of submergence in deep water. For example, when water depth was kept at 5 cm for more than 7 days after application and then decreased down to 3 cm, the efficacy was high. However, when the water depth was kept at 5 cm for less than 7 days, the efficacy was low. Efficacy was lower under high temperatures (35°C/25°C, day/night) than under low temperatures (25°C/15°C, day/night). Water management, application timing and temperature are important factors on herbicidal efficacy of MTB-951 to control E. crus-galli.

Influence of water management, application timing and temperature on efficacy of MTB-951, a mycoherbicide using Drechslera monoceras to control Echinochloa crus-galli L.

The effects of MT-101 and its herbicidally active form, NOP, on the germination and seedling growth of hemp sesbania and rice were investigated. MT-101 decreased the germination of hemp sesbania by 57 and 90% at 0.05 and 0.5 mM, respectively, 1 d after treatment (DAT) in petri dishes. The germination, however, recovered such that there was no significant difference between treatments 4 to 6 DAT. NOP completely inhibited the germination of hemp sesbania at both 0.05 and 0.5 mM 1 DAT. However, germination also similarly recovered, and there was no difference between treatments 4 to 6 DAT. Neither MT-101 nor NOP decreased the germination of rice 3 to 6 DAT. In greenhouse trials preemergence (PRE) application of MT-101 at 2.25 kg ai ha−1 decreased the density (number of plants pot−1), plant height, and dry weight of hemp sesbania by 85, 67, and 91%, respectively. When applied postemergence (POST), MT-101 at 2.25 kg ha−1 decreased the density, plant height, and dry weight by a maximum of 58, 61, and 8...

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Effects of MT-101 and NOP on germination and seedling growth of hemp sesbania and rice

Novel tricyclic 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran (TFB) derivatives were synthesized, and their herbicidal activities were elucidated. They were synthesized from D-glucose as a natural chiral source. The formation of the TFB skeleton was achieved by a Friedel-Crafts type intramolecular cyclization of methyl 5-deoxy-2,3-O-dibenzyl-5-C-methyl-D-xylofranosides. The intramolecular cyclization was dependent upon the electronic effects of the substituents at the C-2 benzyloxy group of methyl xylofranosides. Some TFBs exhibited a remarkable herbicidal activity to annual paddy weeds, such as Echinochloa sp, without injury to the rice.

Novel 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2] benzopyran derivatives: synthesis of chiral glycol benzyl ether herbicides.

Herbicidal formulations used in paddy fields in Japan have historically been mainly granules and f lowable. Granules are usually applied by hand or with a granule applicator in the amount of 30kg/ha. Many attempts have been made at labor saving in herbicide application, for example, the amount of formulation applied has been reduced by increasing the content of active ingredient in granules13). Herbicide application amount in Japan is based on an area of 10a; therefore, granules applied at 10kg/ha are called '1kg granules' in this study. This type of granule can be conveniently applied from a levee with a power granule applicator which saves labor. Granules applied at 30kg/ha are referred to here as '3kg granules'. The number of 1kg granules in a unit area on the surface of a paddy field is naturally smaller than that of 3kg granules. Decrease in the number affects herbicidal efficacy6). It is important that the active ingredient be diffused uniformly for reliable control. The dispersion of several diphenylether herbicides1,17) and pyrazolate14) affects herbicidal efficacy. Formulation type3,4) and physical properties5) are also important for herbicidal efficacy. We tried to produce granules of naproanilide [2-(2-naphthyloxy) propionanilide] to be applied at an amount of 1kg/10a. Because the herbicidal properties of naproanilide were well studied, we selected this compound as a test compound for a formulation trial. The water solubility of naproanilide is 0.74ppm at 27C, which is not enough for effective diffusion in water when formulated into 1kg granules by the usual recipe. This compound is similar to diphenylether herbicides in respect to low water solubility17). Naproanilide is hydrolyzed to NOP, its active form, by soil bacteria and by several plants9,12). Pyrazolate15) is also hydrolyzed to a destosylpyrazolate, DTP, in paddy water which is the active form. Both herbicides have a common chemical property in the sense that they are hydrolyzed in water to produce the active form. Thus, the herbicidal efficacy of naproanilide granules changes according to its formulation type as shown in diphenylether herbicides1,17) and pyrazolate16). We reported that herbicidal efficacy of naproanilide 1kg granules2) was the same as that of 3kg granules. That was attributed to high release of the active ingredient in the 1kg granules. The purpose of this study is to prove that * Life Science Laboratory, Mitsui Chemicals, INC.

https://www.jstage.jst.go.jp/article/weed1962/43/1/43_1_49/_pdf

Kangetsu Hirase

Papers

Mode of bleaching phytotoxicity of herbicidal diphenylpyrrolidinones

Influence of water management, application timing and temperature on efficacy of MTB-951, a mycoherbicide using Drechslera monoceras to control Echinochloa crus-galli L.

Effects of MT-101 and NOP on germination and seedling growth of hemp sesbania and rice

Novel 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2] benzopyran derivatives: synthesis of chiral glycol benzyl ether herbicides.

Diffusion of Naproanilide in Water from High Release Granules and Their Herbicidal Efficacy.