Effects of lodging of Echinochloa crus-galli L. on the herbicidal efficacy of MTB-951, a mycoherbicide using Drechslera monoceras (Drechsler) Subram. et Jain (= Exserohilum monoceras [Drechsler] Leonard et Suggs)

MTB-951 is a plant pathogen ( Drechslera monoceras ), which was isolated from native Echinochloa spp. in Japan. The conidia of this pathogen were used as the herbicidal active ingredient to control Echinochloa crus-galli L. The herbicidal efficacy of MTB-951 on E. crus-galli was drastically increased with an increasing water depth of between 1 and 10 cm. The efficacy also was increased when shoots were lodged by pushing down on them with a stainless steel net so that all parts of the weed were submerged. These results suggest that the contact area of the leaf surface of E. crus-galli with water is important for infection and that lodging the shoots of E. crus-galli might be effective in increasing the herbicidal efficacy. In order to find other methods to lodge the weed, we investigated several materials, of which diisononyl phthalate (DINP) was found to be the most effective. Using this material as a model, the effect of lodging on the herbicidal efficacy of MTB-951 was examined. The lodging ratio (ratio of the number of the plants lodged on the water surface to that of the total plants) was increased with an increased amount of DINP, between 0.5 and 8 kg ha⁻¹. The herbicidal efficacy of MTB-951 also was increased by DINP and a positive correlation was observed between the lodging ratio and herbicidal efficacy. These results indicate that lodging, which can increase the contact area between the leaf surface and water, enhances the herbicidal efficacy of MTB-951.     

Biotransformation of clomazone in rice (Oryza sativa) and early watergrass (Echinochloa oryzoides)

Rice (Oryza sativa), a relatively tolerant species, and early watergrass (Echinochloa oryzoides; EWG), a relatively susceptible species, were exposed to ¹⁴C-labeled clomazone to determine accumulation, biotransformation, and mass balance. On a total mass basis, rice absorbed more clomazone than EWG (p < 0.05), but on a nmol/g basis, there was no significant difference between the two species (p > 0.05). Rice contained more extractable ¹⁴C residues (7.7 ± 0.5 vs. 4.8 ± 0.5 nmol in rice vs. EWG, respectively; p < 0.5), but the concentration in EWG was significantly higher (4.2 ± 0.5 vs. 1.8 ± 0.1 nmol/g in EWG vs. rice, respectively; p < 0.01). More metabolized residue was measured in EWG compared to rice (84.1% vs. 67.9%; p < 0.01). Both species produced hydroxylated forms, β-d-glucoside conjugates, and several other unidentified polar metabolites, but EWG generally produced higher metabolite concentrations. The concentration of the suspected active metabolite, 5-ketoclomazone, was significantly higher in EWG vs. rice (21 ± 2 vs. 5.7 ± 0.5 pmol/g, respectively; p < 0.01). Differences in sensitivity to clomazone between rice and EWG appear to be due to differential metabolism, but in this case the more susceptible EWG qualitatively and quantitatively metabolized more clomazone than the more tolerant rice. This is consistent with the action of a metabolically activated herbicide. This metabolic difference could be exploited to develop herbicide safeners for use with clomazone.     

Differential ability of alcohol fermentation between the seeds of flooding-tolerant and flooding-susceptible varieties of Echinochloa crus-galli (L.) Beauv.

Seed germination and respiratory metabolism under aerobic and anaerobic conditions were studied in the flooding-tolerant and flooding-susceptible varieties of Echinochloa crus-galli with an identical genome and common ancestry . In the flooding-tolerant E. crus-galli var. formosensis , the seeds imbibed under nitrogen could germinate and exhibited an I/N quotient > 0.6. They accelerated glycolysis and concomitantly produced large and equimolar quantities of carbon dioxide and ethanol, suggesting that the seeds of this variety showed operation of the Pasteur effect and respired through alcohol fermentation under anaerobic conditions. The seeds excreted most of the toxic fermentation product. In contrast, the seeds of the flooding-susceptible E. crus-galli var. praticola were capable of germinating only under aerobic conditions through the conventional aerobic respiration and were unable to anaerobically respire to germinate through alcohol fermentation regardless of the presence of both sufficient alcohol dehydrogenase activity and a high redox charge of the pyridine nucleotides.     

Competition of Barnyardgrass with Rice Varieties

A field study was conducted to examine the competition of barnyardgrass with various rice varieties and its effect on propanil effectiveness. Six rice varieties, Ispaniki A', Strymonas and Roxani (Japonica type) and Rea, Skybonnet and Blue belle (Indica type), were grown in a silty loam soil, in 1994 and 1995. The varieties had different 1000 seed weights, which varied from 24 to 40 g. The herbicide propanil was applied at the four-leaf stage of barnyardgrass on half the plot area. Japonica type varieties emerged earlier and had lower numbers of barnyardgrass plants compared to Indica varieties. The time of seedling emergence was significantly and negatively correlated with the seed weight and positively with the number of barnyardgrass plants. The delayed establishment of Indica type varieties favoured rapid barnyardgrass growth at the early stages and resulted in lower effectiveness of propanil, compared to Japonica type varieties. Thus, in controlling barnyardgrass in rice fields it is necessary to take into account the variety grown in order to reduce production costs and the pollution risk to the environment.     

稗草(Echinochloa crusgalli)根型ppc基因对水稻的遗传转化及其对光合速率的调节效应

稗草(Echinochloa crusgalli)是稻田中的C4光合型杂草,为了探索稗草ppc基因(Eppc)对水稻遗传转化的可行性及其对光合速率的调节效应,首次将含有稗草根型磷酸烯醇式丙酮酸羧化酶(phosphoenolpyruvate carboxylase,PEPC)基因ppc c DNA的2个植物表达载体p Ubi-Eppc、p Rbc S-Eppc通过农杆菌介导法对水稻进行了遗传转化。对分化植株进行的PCR、RT-PCR、克隆测序和Western杂交等结果均表明稗草ppc基因已经整合到了水稻基因组中,并且在转录和翻译水平都得到了表达。转基因水稻PEPC活性和气体交换参数测定结果表明T0代多数植株的PEPC活性高于对照,最高达到了对照的5.85倍;T0代大多数转基因植株叶片的净光合速率(Pn)比对照提高了20.00%,最大地提高了47.16%,同时叶片水分利用效率(WUE)也得到增强;T6代大部分转化植株的PEPC活性及Pn仍保持高于对照,本研究表明C3根型ppc基因过量表达也可以提高水稻的Pn,且证明稗草PEPC对光合作用具有较强的调节作用。     

60Co-γ辐射对谷稗幼苗生长和微量元素吸收的影响

用不同剂量⁶⁰Co-γ辐射对‘朝牧1号’谷稗（Echinochloa crusgalli）种子进行处理,研究⁶⁰Co-γ射线辐射对谷稗幼苗生长和微量元素含量的影响。结果表明：50~200 Gy辐射组促进了最长根的生长,但抑制了幼苗株高和总长度;随着辐射剂量的增加,茎叶Fe、Mn、Zn、B、Ni元素含量和根部B元素含量呈先增后减趋势,根Fe、Mn、Ni元素含量随辐射剂量增加而呈增加趋势,Zn元素含量呈降低趋势。     

A novel screening method for rice allelopathic potential: the inhibitory‐circle method

Screening crop accessions for allelopathic activity is of paramount importance for crop allelopathy research. Previous bioassays often did not use a mixed culture of donor and target plants, did not use soil and were not conducted under natural conditions. In this study, we designed an inhibitory‐circle method in which a rice accession (donor plant) and Echinochloa crus‐galli (target plant) were cultured together in paddy soil under natural conditions. First, we determined that the highest allelopathic activity of allelopathic rice accession PI312777 was at the 5‐leaf stage, and the suitable distance of rice seedlings and E. crus‐galli was 12 cm apart. This method was then validated by a field test. A further 40 rice accessions were evaluated for allelopathic activity to E. crus‐galli using this method. Two rice accessions, PI312777 and Taichung Native 1, had highly allelopathic activity to E. crus‐galli (inhibitory rate > 50%), while another accession, Lemont, had non‐allelopathic activity. These experimental results were in accordance with previous studies using direct field experiments. The inhibitory‐circle method integrated three necessary conditions, that is donor and target plants grown together, with soil as the medium and under natural conditions for reliable results. The ‘inhibitory‐circle method’, which combined donor and target plants, soil medium and field conditions, can give reliable results in one step, compared with laboratory screening methods. Also, the ‘inhibitory‐circle method’ gave results in 30‐35 days, thereby substantially reducing the requirements for time, labour and cost.     

Survey and examination of the potential alternative hosts of Villosiclava virens,the pathogen of rice false smut,in China

Rice false smut is caused by ascomycete Villosiclava virens, whose potential alternative hosts have been assumed previously. Here its potential alternative hosts were surveyed and identified from 2008 to 2013 in the main rice-growing regions in China. Two common weeds in paddy fields, Digitaria sanguinalis Scop. and Echinochloa crusgalli(L.) Beauv., were found to present the similar symptoms to smut diseases in a few individuals in 2012 and 2013 in Zhejiang and Sichuan provinces of China, respectively. After the examinations of the spore morphology, their infection and extension mode in hosts, pathogen cell wall components, and molecular identification, the two pathogens were identified to be the Basidiomycetes, Ustilago syntherismae and Ustilago trichophora, respectively. So far there has been no alternative host of V. virens to be identified in China. These suggest that the alternative hosts of V. virens, if they do exist, are not possible to play an important role in the pathogen life cycle and the disease epidemics.