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Rice bran application is practically used by Japanese organic rice farmers as a common measure in controlling Monochoria vaginalis, a known weed in organic rice production. To elucidate the inhibitory mechanisms of rice bran application on M. vaginalis germination, we focused on volatile fatty acids (VFAs) and aromatic carboxylic acids (ACAs) as organic acids produced through rice bran decomposition in the soil, which can possibly suppress M. vaginalis germination. Both solo solutions of 1 mM VFAs (propionic or isobutyric acid) and 0.2 mM ACAs (3-phenylpropionic or 4-phenylbutyric acid) exhibited M. vaginalis germination suppression, especially at pH 4.6, the lowest pH tested. In the 0.5–3 mM VFA solutions at pH 4.6, germination was strongly suppressed in the order of isobutyric > propionic > butyric > acetic acid. With the 0.05–0.2 mM ACA solutions at pH 4.6, the germination was strongly suppressed in the order of 3-phenylpropionic > 4-phenylbutyric > 2-phenylpropionic acid. Benzoic acid did not exhibit significant germination suppression. The solutions of 0.5 mM VFAs and 0.05 mM ACAs exhibited no suppression when applied separately; however, the certain mixture of a VFA and an ACA at the aforementioned concentration, for example, 0.5 mM isobutyric acid and 0.05 mM 3-phenylpropionic acid, exhibited significant germination suppression. These results showed the several combinations of VFAs and ACAs at even non-effective concentrations synergistically suppressed M. vaginalis germination. Abbreviations:2PPA: 2-phenylpropionic acid; 3PPA: 3-phenylpropionic acid; 4PBA: 4-phenylbutyric acid; ACA: aromatic carboxylic acid; EC: electrical conductivity; M. vaginalis: Monochoria vaginalis; VFA: volatile fatty acid

Growth of the weed Monochoria vaginalis (Burm. f.) Kunth under the conditions of organic rice production is a serious problem. The reason for the growth of M. vaginalis being dominant, especially in organic rice production, is not fully understood. In this study, laboratory experiments were conducted to analyze soil and seed factors in relation to the promotion of germination. (1) After incubation of flooded soil with or without the addition of rice bran (0.3%, 0.6%, and 0.9% in an air-dried soil basis), soil solutions were recovered and seeds of M. vaginalis were incubated in the soil solutions. Germination in the soils solutions without and with 0.3% rice bran was greater than that in distilled water. However, germination was suppressed in the presence of 0.6% and 0.9% of rice bran. These findings indicate that the solution from the soils with rice bran has different effects that may either increase or decrease germination. (2) A mixture of air-dried soil and distilled water was filtered to obta...

Although weeds cause serious yield losses in agriculture, relatively few studies have been conducted on the relationship between weeds and yield loss in no-input rice production systems, where no herbicides are used. This study investigated weed communities in rice paddy fields and their influence on rice yield, by comparing 16 no-input paddy fields in northern Japan. The weed seed community in the paddy field soils, before transplanting, were analyzed using a spontaneous germination test, and the established weed communities in the fields were examined at the full heading growth stage of the rice. The weed community structures showed a marked difference between the seeds in the soil and the established weed communities. Although eight weed species germinated from the soil, only four weed species were observed in the fields at the full heading stage of the rice. The two dominant weed species, Monochoria vaginalis and Cyperaceae, accounted for 84% of the total weed biomass in the field. The multipl...

We investigated the effect of poultry manure (PM) on the occurrence and early growth of Monochoria vaginalis in relation to soil solution electrical conductivity (SSEC). PM was applied at rates corresponding to 0 g of nitrogen (N) m−2 (PM-0), 1 g N m−2 (PM-1), 3 g N m−2 (PM-3), and 5 g N m−2 (PM-5). At 7 d post-seeding, the soil solution was sampled to measure EC, and also the emergence and growth of M. vaginalis were evaluated. The emergence rate of M. vaginalis decreased with increasing application rate of PM and SSEC. SSEC was significantly negatively correlated with the emergence rate of M. vaginalis seedlings. The average leaf number and length of M. vaginalis did not differ between PM-0, PM-1, and PM-3, but were significantly lower in PM-5. In summary, PM would allow to better control the emergence and early growth of M. vaginalis.

Field experiments were conducted to analyze the relationship between the settled soil volume in water (SSVW) and the growth of Monochoria vaginalis (Burm. f.) Kunth under organic farming conditions. SSVW corresponds to the mud volume per dry matter weight. Soil was sampled from the superficial layer of the topsoil (

Phosphoenolpyruvate carboxylase (PEPC) undergoes activity regulation through reversible phosphorylation. The day/night phosphorylation of leaf PEPC in 27 C3 plant species was analyzed by immunoblotting. PEPC was phosphorylated in the daytime in 12 species, whereas it was phosphorylated at night in three species, rice, Monochoria vaginalis, and Sagittaria trifolia, all of which are hygrophytic monocots. Immunoblot analysis of isolated chloroplasts of M. vaginalis identified a PEPC protein inside the chloroplast in addition to cytosolic isozyme(s) as previously shown in genus Oryza. Using transgenic rice overexpressing the maize PEPC in the cytosol, we confirmed that the cytosolic PEPC underwent the nocturnal phosphorylation. These results suggest the interrelationship between the presence of chloroplastic PEPC and the nocturnal phosphorylation of cytosolic isozyme(s).

Laboratory experiments were conducted to investigate (1) the effects of the addition of rice (Oryza sativa. L.) bran to paddy soil on the germination of Monochoria vaginalis (Burm. f.) Kunth, and (2) the relationship between the electric conductivity (EC) of the soil solution and germination. Soil samples were collected at 4 sites in Japan. After flooded soils with rice bran had been incubated for 7 d at 30°C, the soil solution was collected using a porous cup and the EC of the soil solution was measured. The amounts of rice bran added to the soil were 0%, 0.3%, 0.6% and 0.9% (weight(w)/w). In the soil solution obtained, seeds of M. vaginalis were incubated for 3 d at 30°C, and the germination percentage was then analyzed. The addition of rice bran suppressed germination, and the degree of suppression increased with increasing content of rice bran. Although the same amount of rice bran was applied to each soil, the degree of growth suppression by rice bran as well as the EC of the soil solution differed a...

Monochoria vaginalis (Burm. f.) C. Presl. is a common weed in Oryza sativa L. fields that has use as a vegetable. The objective of the study was to evaluate the nutritional composition of leaves and flowers of M. vaginalis. Almost all essential and nonessential amino acids were present in leaves and flowers. The amount of nonessential amino acids, especially aspartic acid and glutamic acid, was higher in flowers than leaves. There was more nitrogen in leaves (9.7 mg/100 g) than flowers (6.3 mg/100 g). Phosphorus, potassium, magnesium copper, manganese, and calcium were found in samples in levels that would allow this plant to provide adequate nutrition. Proteins (10.8 g/100 g) and carbohydrates (4.6 g/100 g) in flowers were higher than in leaves. Antinutritional compounds total free phenolics and tannins were also estimated. The amount of nutrition in M. vaginalis indicates that it can be used as a nutritional food supplement.

Soil and water contaminated with arsenic (As) pose a major environmental and human health problem in Bangladesh. Phytoremediation, a plant-based technology, may provide an economically viable solution for remediating the As-polluted sites. The use of indigenous plants with a high tolerance and accumulation capacity for As may be a very convenient approach for phytoremediation. To assess the potential of native plant species for phytoremediation, plant and soil samples were collected from four As-contaminated (groundwater) districts in Bangladesh. The main criteria used for selecting plants for phytoremediation were high bioconcentration factors (BCFs) and translocation factors (TFs) of As. From the results of a screening of 49 plant species belonging to 29 families, only one species of fern (Dryopteris filix-mas), three herbs (Blumea lacera, Mikania cordata, and Ageratum conyzoides), and two shrubs (Clerodendrum trichotomum and Ricinus communis) were found to be suitable for phytoremediation. Arsenic bioconcentration and translocation factors > 1 suggest that these plants are As-tolerant accumulators with potential use in phytoextraction. Three floating plants (Eichhornia crassipes, Spirodela polyrhiza, and Azolla pinnata) and a common wetland weed (Monochoria vaginalis) also showed high BCF and TF values; therefore, these plants may be promising candidates for cleaningup As-contaminated surface water and wetland areas. The BCF of Oryza sativa, obtained from As-contaminated districts was > 1, which highlights possible food-chain transfer issues for As-contaminated areas in Bangladesh.

Yield and weed growth in dry-seeded rice (Oryza sativa L.) were unaffected by method of seeding. Weeds depressed rice yields by 95%. Fourteen weed species were found growing in association with dry-seeded rice at maximum flowering of the weeds. Echinochloa colona (L.) Link and Leptochloa chinensis (L.) Nees were the major weeds. A dramatic change in the weed flora was observed in transplanted rice planted immediately after the harvest of the dry-seeded crop. Only five species grew in association with the transplanted crop. Monochoria vaginalis (Burm.) Presl. dominated. E. colona and L. chinensis were present in transplanted rice but were only minor weeds. The number of weeds in the transplanted crop was less than 50%, and weighed only 5% as much as those in the dry-seeded crop. There was no carryover of the weed control treatments from the dry-seeded crop to the transplanted crop.

Three fields with different weed floras were selected for the study. Weed species suppressed by azolla (Azolla pinnata R.Br.) were Monochoria vaginalis (Burm.f.) Presl., Echinochloa glabrescens Munro ex Hook.f., Cyperus difformis L. and Paspalum sp. The effect of azolla was assessed at two different stages of crop growth. At rice flowering the weeds were suppressed by 69–100%, and at harvest by 86–95%, depending on the weed species. Azolla failed to suppress the growth of Scirpus maritimus L. and Echinochloa crus‐galli ssp. hispidula (Retz.) Honda. When weeds were adequately controlled by azolla, yields from azolla‐treated plots were comparable with those from the hand‐weeded plots, and significantly higher than that from the non‐weeded control. When azolla failed to suppress the weeds, the yields from the azolla‐treated plots were similar to those from the non‐weeded control and significantly less than that from the hand‐weeded control.

There was little difference in the weed flora between transplanted and wet‐seeded rice (Oryza sativa L.). The weed control methods used greatly influenced the weed flora. Echinochloa glabrescens Munro ex Hook.f. was dominant in the unweeded and herbicide‐treated plots while Monochoria vaginalis (Burm. f.) Presi was dominant in the hand weeded plots. Weed weights were similar in both planting methods. Weed weight was reduced and rice yield was increased by hand weeding and herbicide treatments but the efficiency of weed control with herbicides decreased due to the buildup of weeds in the later plantings.

smuts on account of their rarity and the interesting types of lifecycles in many of the species. The rarity of these smuts is often due to the very obscure symptoms they produce on the host, which might range from an almost inconspicuous paling of the infected portions to definite discolored spots. In very few cases there is the formation of tumor-like excrescences on the host. In India, three species of Doassansia have been known by the determinations of Sydow and Butler. Another species, Doassansia Hygrophilae Thirumalachar, was added by the writer (1946). It is based on a collection of a leaf smut made near Nandi, Mysore, on Hygrophila sp. No species of Burrillia was hitherto known to occur in India, and a first report of an undescribed species of Burrillia, viz. B. Narasimhanii, was made recently by Thirumalachar and Mundkur (1946) on Alisma reniformis G. Don. This has been followed up by the finding of another species of Burrillia on Monochoria vaginalis Presl. by the writer and it appears to be undescribed. The life-cycle of the smut has been worked out in some detai.l, and in this paper an account of it is presented. Some of the observations made on the other species of Doassansia and Burrillia are also included.