Crus-galli Var Research Articles

Sequencing report of the rRNA amplicons of Echinochloa crus-galli in Iraq

This study was conducted to identify the genetic polymorphisms of one wild grass sample species and assess the phylogenetic distribution these isolates occupy based on their internal transcribed (ITS) ribosomal sequences. This study amplified one genetic locus covering a portion of the ITS rRNA sequences. A direct sequencing strategy was performed for the observed PCR amplicons in the amplified genetic locus. Subsequently, a comprehensive phylogenetic tree was constructed in the observed variants for these sequences to reveal the accurate phylogenetic distances alongside other relative sequences. Our results indicated the identity of the investigated wild grass samples (assigned S1 and S2). Sequencing reactions indicated that our investigated samples belonged to Echinochloa crusgalli var. crus-galli (panicum grass), a common wild grass dominated in tropical Asia. Two ribosomal variations were identified in the investigated wild grass samples, 61C>T, observed in the S2 sample and 408C>A, observed in both the S1 and S2 samples. According to the identified results, the investigated samples were positioned within one distinct phylogenetic clade of these identified wild grass sequences in the currently generated comprehensive tree. These positionings were observed within the main clade of Echinochloa crus-galli. Based on the identified ribosomal sequences, it was found that the currently investigated samples may exhibit variable extents of diversities originating from several Asian and South American ancestors. Also, the currently constructed tree revealed that the investigated wild grass sequences belonged to one distinct clade of Echinochloa crus-galli, having many sequences of close phylogenetic connections. This clade occupied far away phylogenetic positions from the other comparable grasses within the same tree. Keywords: rRNA amplicons, Echinochloa crus-galli, Rice

Detection of Resistance in Echinochloa spp. to Three Post-Emergence Herbicides (Penoxsulam, Metamifop, and Quinclorac) Used in China

In this study, rapid resistance in-season quick (RISQ) tests were developed for detecting the resistance in Echinochloa spp. to penoxsulam, metamifop, and quinclorac, which are widely used in rice fields to control E. spp. biotypes. Seedlings in 1–2 leaf stages from nine biotypes of E. crusgalli, E. crusgalli var. zelayensis, and E. glabrescens, with different susceptibility to the three herbicides tested, were transplanted to plates containing nutrient agar and different rates of herbicides. The survival rates were recorded at 8 days after treatment when no more new roots emerged for all the treatments. By comparing the results from RISQ tests and whole-plant pot bioassays statistically, discrimination rates could be determined to distinguish resistant plants from susceptible plants. For penoxsulam, metamifop, and quinclorac, the discrimination rates were 0.3, 0.6, and 2.4 µmol/L, respectively. Two additional biotypes of E. crusgalli collected in rice fields were used to confirm the validation of the RISQ test and the obtained results by the RISQ test were consistent with that of the whole-plant pot bioassay. Therefore, the developed RISQ test would be a possible alternative method to determine the susceptibility of E. spp. to certain herbicides.

Weed Control, Rice Safety, and Mechanism of the Novel Paddy Field Herbicide Glyamifop

Glyamifop (R&D code: FG001), (R)-(2-(4-(6-chlorobenzoxazol-2-oxy) phenoxy) propionyl) glycine ethyl ester is a newly developed aryloxyphenoxypropionate (HRAC Group 1) herbicide for weed control in paddy fields. This work determined the effect of Glyamifop on weeds and its safety for rice in the glasshouse. Glyamifop controlled the common gramineous weeds in paddy fields at 100 g a.i. ha−1: the fresh weight inhibition rates of Echinochloa crus-galli, Leptochloa chinensis, Setaria viridis, Eragrostis japonica, Digitaria sanguinalis and Panicum bisulcatum were all above 90%. It has almost no inhibitory effect on broad-leaved and cyperaceae weeds, such as Eclipta prostrata and Cyperus iria. Glyamifop inhibited cyhalofop-butyl-resistant L. chinensis, penoxsulam-resistant E. crus-galli and quinclorac-resistant E. crusgalli var. zelayensis by 100%, 99.98% and 96.37%, respectively, at 100 g a.i. ha−1, based on the fresh weight. The selectivity index of Glyamifop foliage treatment in the rice varieties japonica ‘Huaidao 5’, indica ‘Xiangliangyou 900’ and glutinous ‘Zhennuo 29’ was 5.93, 6.81 and 4.91, respectively; therefore, Glyamifop is safe for the 3 different rice varieties. Fresh weight rice inhibition rates were 7.18%, 2.99% and 7.93% at the 2.5-, 3.5- and 5.5-leaf stage, respectively, and the selectivity index was 5.18, 6.04 and 7.93, respectively, indicating that Glyamifop was safe for rice at these leaf stages. L. chinensis ACCase activity decreased with increasing Glyamifop concentration, and the inhibitory effect was similar to that of cyhalofop acid; this confirmed that Glyamifop is an ACCase inhibitor. In conclusion, Glyamifop has potential for the management of gramineous weeds as it has good activity against weeds that are resistant to common herbicides in paddy fields.

Comparative Analysis of Whole Chloroplast Genomes of Three Common Species of Echinochloa (Gramineae) in Paddy Fields.

Echinochloa crus-galli var. crus-galli, E. crus-galli var. zelayensis, and E. glabrescens, morphologically similar at the seedling stage, are the most pernicious barnyard grass species in paddy fields worldwide. Chloroplast (cp) genomes could be conducive to their identification. In this study, we assembled the complete cp genome sequences of Echinochloa crus-galli var. crus-galli (139,856 bp), E. crus-galli var. zelayensis (139,874 bp), and E. glabrescens (139,874 bp), which exhibited a typical circular tetramerous structure, large and small single-copy regions, and a pair of inverted repeats. In Echinochloa crus-galli var. crus-galli, there were 136 simple sequence (SSRs) and 62 long (LRs) repeats, and in the other two species, 139 SSRs and 68 LRs. Each cp genome contains 92 protein-encoding genes. In Echinochloa crus-galli var. crus-galli and E. glabrescens, 321 and 1 single-nucleotide polymorphisms were detected compared to Echinochloa crus-galli var. zelayensis. IR expansion and contraction revealed small differences between the three species. The phylogenetic tree based on cp genomes demonstrated the phylogenetic relationship between ten barnyard grass species and other common Gramineae plants, showing new genetic relationships of the genus Echinochloa. This study provides valuable information on cp genomes, useful for identifying and classifying the genus Echinochloa and studying its phylogenetic relationships and evolution.

Different regulation of auxin homeostasis would be a possible mechanism conferring quinclorac resistance in Echinochloa crusgalli var. zelayensis

AbstractDifferences in ethylene biosynthesis and cyanide detoxification have been reported to be mechanisms of quinclorac resistance in Echinochloa crusgalli var. zelayensis. Resistant phenotypes could be a consequence of the altered endogenous indole acetic acid (IAA) homeostasis induced by the herbicide. In this study, we determined the IAA content and expression levels of auxin homeostasis‐related genes in susceptible and resistant biotypes of E. crusgalli var. zelayensis after quinclorac treatment. The results showed that the IAA content of JNNX‐S (susceptible biotype) was significantly higher than that of SSXB‐R (resistant biotype) after treatment with 50 μM quinclorac. To better understand this rise in IAA, the expression profiles of seven genes (one for auxin synthesis, five for IAA conjugation and one for IAA oxidation) and the biochemical activities of two oxidases involved in IAA homeostasis were measured. The expression of EcYUCCA10 was significantly higher in JNNX‐S than in SSXB‐R. The expression levels of the EcGH3s were significantly lower in JNNX‐S than in SSXB‐R. These expression profiles were consistent with the elevation of IAA levels in the susceptible biotype. In contrast, EcUGT and EcDAO were induced in each biotype, but a smaller increase was observed in SSXB‐R than in JNNX‐S. The enzymatic activities of IAA oxidases and peroxidases were higher in SSXB‐R than in JNNX‐S 24 h after treatment. It was inferred that altered expression of specific genes involved in IAA synthesis, conjugation and oxidation resulted in less IAA being induced in the resistant biotype, resulting in a lower ethylene burst and the associated quinclorac resistance. These results suggest novel layers of complexity in the mechanism of quinclorac resistance.

Comparison of quintrione and quinclorac on mechanism of action

Quintrione is a new post-emergence herbicide developed for use in rice; however, the mechanism of action remains unclear. We determined the phytotoxicity of quintrione, and the contributions of hormone levels and lipid peroxidation to phytotoxicity, by comparing them to those induced by quinclorac. We also investigated 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity and carotenoid content following treatment with quintrione by comparing them to those induced by quinclorac and mesotrione. We found that quintrione and quinclorac both inhibited the growth of Echinochloa crusgalli var. zelayensis, but that quinclorac was a little more effective. At 24 h, quintrione and quinclorac significantly increased ethylene production and the contents of abscisic acid (ABA) and indole acetic acid (IAA) compared with the control. No significant differences were observed between quintrione and quinclorac on the three plant hormones. Quintrione and quinclorac also induced the formation of malondialdehyde (MDA), which is associated with lipid peroxidation, with no significant difference between them. Carotenoid content was reduced in E. crusgalli var. zelayensis following treatments with quintrione, quinclorac, and mesotrione. At 120 h, carotenoid contents were significantly higher following the quintrione and quinclorac treatments, in comparison with mesotrione treatment. There were no significant differences between quintrione and quinclorac in the inhibition of HPPD activity, and the effects of both were significantly less than the effect of mesotrione. In summary, E. crusgalli var. zelayensis was susceptible to both quintrione and quinclorac. The mechanism of action of quintrione, like that of quinclorac, was related to levels of plant hormones and lipid peroxidation; however, quintrione was a poor inhibitor of HPPD activity compared to mesotrione.

Intraspecific differentiation in seed flooding tolerance of Echinochloa crusgalli var. zelayensis population in shores of a giant reservoir along altitudinal gradients

Abstract Aims In a large dam-regulated reservoir with regular hydrological pattern and strong flooding gradients across shore elevations, plants inhabiting in different shore elevations have to confront long-lasting flooding of differential intensities every year. Such persistent stress may lead to intraspecific differentiation of flooding tolerance in seeds. Echinochloa crusgalli var. zelayensis is a dominant annual plant in the shores of the Three Gorges Reservoir (TGR), which plays an important role in the shore vegetation. The objective of this study is to check whether intraspecific differentiation of seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores and whether such differentiation is associated with weak seed dispersal. Methods We collected seeds of E. crusgalli var. zelayensis from different populations in the TGR shores, and then placed them at four elevations in the shores flooded by reservoir impoundment. Parameters reflecting seed flooding tolerance including post-flooding percentage of intact seeds, seed germinability and seedling emergence rate were investigated for the seeds from different populations and undergoing flooding of different intensities. Floating time of seeds and speed of water level rise during impoundment were examined, and used to quantify dispersal potential of seeds in the shores of the TGR when flooded. Important Findings Both intact seed percentage and final seedling emergence rate after flooding significantly declined with increasing shore elevations where the seeds were collected, indicating that intraspecific differentiation in seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores after 7-year operation of the reservoir. The distance of seeds transported by rising water during reservoir impoundment was limited due to short-floating time of the seeds and relatively low speed of water level rise in the reservoir. This would be favourable to the development of intraspecific differentiation in seed flooding tolerance.

Ethylene Biosynthesis Inhibition Combined with Cyanide Degradation Confer Resistance to Quinclorac in Echinochloa crus-galli var. mitis.

Echinochloa crus-galli var. mitis has rarely been reported for herbicide resistance, and no case of quinclorac resistance has been reported so far. Synthetic auxin-type herbicide quinclorac is used extensively to control rice weeds worldwide. A long history of using quinclorac in Chinese rice fields escalated the resistance in E. crus-galli var. mitis against this herbicide. Bioassays in Petri plates and pots exhibited four biotypes that evolved into resistance to quinclorac ranking as JS01-R > AH01-R > JS02-R > JX01-R from three provinces of China. Ethylene production in these biotypes was negatively correlated with resistance level and positively correlated with growth inhibition. Determination of the related ethylene response pathway exhibited resistance in biotypes that recorded a decline in 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase oxidase activities, and less inducible ACS and ACO genes expressions than the susceptible biotype, suggesting that there was a positive correlation between quinclorac resistance and ethylene biosynthesis inhibition. Cyanides produced during the ethylene biosynthesis pathway mainly degraded by the activity of β-cyanoalanine synthase (β-CAS). Resistant biotypes exhibited higher β-CAS activity than the susceptible ones. Nucleotide changes were found in the EcCAS gene of resistant biotypes as compared to sensitive ones that caused three amino acid substitutions (Asn-105-Lys, Gln-195-Glu, and Gly-298-Val), resulting in alteration of enzyme structure, increased binding residues in the active site with its cofactor, and decreased binding free energy; hence, its activity was higher in resistant biotypes. Moreover, these mutations increased the structural stability of the enzyme. In view of the positive correlation between ethylene biosynthesis inhibition and cyanide degradation with resistance level, it is concluded that the alteration in ethylene response pathway or at least variation in ACC synthase and ACC oxidase enzyme activities—due to less relative expression of ACS and ACO genes and enhanced β-CAS activity, as well as mutation and increased relative expression of EcCAS gene—can be considered as a probable mechanism of quinclorac resistance in E. crus-galli var. mitis.

Fitness of Echinochloa crusgalli var. mitis biotypes susceptible and resistant to imazapyr + imazapic herbicide

The continuous use of herbicides with the same mechanism of action has caused the selection of resistant weed biotype that may present differences in fitness when compared with susceptible biotype. The objective of the present study was to identify and distinguish the fitness of barnyardgrass biotypes resistant and susceptible to imazapyr + imazapic herbicide under controlled and noncompetitive conditions. For that, there were used barnyardgrass biotype susceptible (ECH1 and ECH38) and resistant (ECH14 and ECH44) to ALS inhibitors, collected at Pelotas/RS and Rio Grande/RS cities, respectively, in experiment installed in a greenhouse in a completely randomized experimental design during the months from October to December 2015. The biotype were evaluated during the period of 15 to 120 days after the emergence related to plant height, foliar area, shoot dry matter mass and root dry matter mass. The results showed insignificant differences between the biotypes during the development of the plants. The susceptible biotype ECH44 showed a higher number of panicles per plant and seeds along with the resistant ECH1. There is variability among Echinochloa crusgalli var. mitis biotypes resistant and susceptible to ALS inhibitors, indicating an absence in fitness penalty caused by resistance when cultivated without the selection of pressure (herbicide).

Is the protection of photosynthesis related to the mechanism of quinclorac resistance in Echinochloa crus-galli var. zelayensis?

Echinochloa crus-galli var. zelayensis, a variety of E. crus-galli (L.) Beauv. has evolved resistance to quinclorac, but the mechanism of resistance remains unclear. Treatments with quinclorac, cause rapid leaf chlorosis, continuous decrease in the chlorophyll content to about 0.4 times, and rapid decline in biomass by about 20% in sensitive E. crus-galli var. zelayensis within 72 h. Then transcriptome sequencing for quinclorac-sensitive and -resistant E. crus-galli var. zelayensis biotypes was performed, and more differentially expressed genes (DEGs) were observed in the sensitive biotype (1115 DEGs, including 548 up-regulated and 567 down-regulated) than that in the resistant biotype (901 DEGs, including 373 up-regulated and 528 down-regulated). Thirty-four photosynthesis-related candidate genes were screened, in which twenty-nine genes were more affected by quinclorac in the sensitive biotype than that in the resistant biotype. The qPCR verification involving more sampling time-points revealed that on continuous treatment with 50 μ mol/L quinclorac, expression levels of 34 photosynthesis-related genes dropped significantly by 2–1000 times within 12 h in the sensitive biotype. Following significant or marginal decline in expression at 6 h after quinclorac treatment, recovery of the expression levels of 21 genes was observed after 12 h and the expression levels of another 13 genes remained unaltered in the resistant biotype. It is hypothesized that the sustained sharp decrease in the expression of photosynthesis-related genes is a major cause of death in the sensitive biotype. Further, it is inferred that there may be a regulatory mechanism in the resistant biotype that allowed the expression of these genes to be significantly unaffected or to rapidly recover, in turn preventing severe damage to the plants caused by quinclorac.

Resistance of Echinochloa crusgalli var. mitis to Imazapyr+Imazapic Herbicide and Alternative Control in Irrigated Rice

ABSTRACT: The introduction of Clearfield® system for irrigated rice production provided an effective management strategy in the selective control of weeds. However, the selection pressure caused by the continuous use of herbicides such as imazapyr+imazapic belonging to the imidazolinone chemical group, without the proper integrated management of weeds, has favored the selection of resistant accessions. The goals of this work were to confirm the resistance to ALS inhibitors in accessions of E. crusgalli var. mitis collected in rice fields of the state of Rio Grande do Sul and to evaluate the control with alternative herbicides registered for weed control. Three experiments were conducted in a greenhouse using plant seeds that survived the application of the herbicide imazapyr+imazapic, collected in irrigated rice producing regions with suspected resistance escapes. For dose-response curve study, three resistant accessions (ECH1 - Pelotas/Rio Grande do Sul, ECH27 - Arroio Grande/Rio Grande do Sul and ECH38 - Rio Grande/Rio Grande do Sul) and two susceptible accessions (ECH14 - Pelotas/Rio Grande do Sul and ECH44 - Rio Grande / Rio Grande do Sul) (factor A) and 11 doses of the herbicide imazapyr+imazapic (factor B) were selected. The results indicate that barnyardgrass resistant accessions present a high resistance level to imazapyr+imazapic. ALS inhibiting herbicides such as imazethapyr+imazapic, bispyribac-sodium and penoxsulam did not control the resistant accessions either. Integrated weed management should be adopted and alternative mechanisms of action as ACCAse (cyhalofop-butyl, profoxydim and clethodim) and EPSPS (glyphosate) inhibitors are still eficients controlling barnyardgrass ALS resistant accessions.

Quinclorac resistance induced by the suppression of the expression of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase genes in Echinochloa crus-galli var. zelayensis

We previously reported that the mechanism of quinclorac resistance in Echinochloa crus-galli var. zelayensis may be closely related to ethylene biosynthesis and the detoxification of cyanide. Differences in EcCAS gene sequences and expression levels may result in higher capacity to detoxify cyanide in resistant biotypes, which may avoid cyanide accumulation and avoid more ethylene and cyanide production and then avoid damage. In the present study, we focused on the mechanism of resistance related to ethylene biosynthesis in E. crus-galli var. zelayensis. The fresh weight of susceptible and moderately resistant biotypes were significantly reduced after treatment with quinclorac. However, AOA, an ethylene biosynthesis inhibitor, reduced the impact of quinclorac. On pretreatment with AOA, ethylene production was significantly reduced in the three biotypes. The highly resistant biotype produced less ethylene compared to the other two biotypes. Three ACS and seven ACO genes, which are the key genes in ethylene biosynthesis, were obtained. The expression levels of EcACS-like, EcACS7, and EcACO1 varied in the three biotypes upon treatment with quinclorac, which could be manipulated by AOA. In summary, it is inferred that the expression of EcACS-like, EcACS7, and EcACO1 can be stimulated to varying extent after quinclorac treatment in three E. crus-galli var. zelayensis biotypes, which consequently results in varying levels of ethylene production. Lower expression of these three genes results in more resistance to quinclorac, which may also be related to quinclorac resistance in E. crus-galli var. zelayensis.

Effects of common Echinochloa varieties on grain yield and grain quality of rice

Barnyard grass, such as Echinochloa crus-galli var. mitis, Echinochloa crus-galli var. zelayensis and Echinochloa colonum, are the main troublesome weeds in rice (Oryza sativa) paddies. This study aimed to investigate the rice yield (quality and quantity) when grown with these common barnyard grass varieties. A 2-year field experiment was conducted using two high-yielding rice cultivars, Liangyoupeijiu (an O. sativa indica hybrid cultivar) and Nanjing 9108 (an O. sativa japonica cultivar) at different developmental stages from transplant to maturity. Treatments included a weed-free (control), rice grown with Echinochloa. crus-galli var. mitis (Ecm), rice grown with E. crus-galli. crusgali var. zelayensis (Ecz), and rice grown with E. colonum (Ec). The results showed that when barnyard grasses were grown with the same rice cultivar, the order of plant height of the three barnyard grass varieties was Ecz>Ecm>Ec, the growth duration was Ecm>Ecz>Ec and the dry matter accumulation of both Ecm and Ecz was greater than Ec. Compared with the weed-free control, there was no significance difference in rice tiller numbers among the treatments within the same rice cultivar. The Ecm and Ecz treatments for both rice cultivars and the Ec treatment of Nanjing 9108 had significantly lower leaf photosynthetic rate, root biomass, root oxidation activity, and dry matter accumulation at both the heading and maturity stages. Lower rice yield loss was detected for all rice grown with barnyard grass, but the loss in yield differed by treatments. Losses in grain yield of rice were 12.7–42.6% in the Ecm treatment, 22.3–55.2% in the Ecz treatment, and 1.5–12.1% in the Ec treatment. For both rice cultivars, Ecm and Ecz treatments had significantly lower grain yield compared with the control. The Ec treatment for Nanjing 9108 had significantly lower grain yield compared to the control, but there was not a significant difference between Ec and the control for Liangyoupeijiu. In general, the japonica cultivar had a greater loss in grain yield compared with the indicia hybrid cultivar under the same treatment. The degree of yield loss by barnyard grass cultivar was Ecz>Ecm>Ec. Grain quality in head rice, chalky kernel, chalky size, and gel consistency was significantly lower for both rice cultivars in the Ecm and Ecz treatments and also for Nanjing 9108 but not for Liangyoupeijiu in the Ec treatment. We conclude that the reduction in leaf photosynthetic rate, root biomass, root oxidation activity at the grain filling stage, and dry matter accumulation at maturity was caused by interference in canopy light transmission caused by barnyard grass and that these factors resulted in losses in grain yield and quality.

Effects of different baynyardgrass varieties on grain yield formation of rice at different nitrogen application levels.

This study aimed to investigate the effects of different barnyardgrass varieties on yield formation of rice. A Japonica rice cultivar, Nanjing 9108, was used and co-cultured with three barnyardgrass varieties from transplanting to maturity under different nitrogen (N) levels of 0, 120, 240, and 360 kg N·hm-2, taking baynyardgrass free as control. The three barnyardgrass varieties were Echinochloa crusgalli var. mitis, E. crusgali var. zelayensis and E. colonum. The results showed that, at the same N level, the plant height of the three barnyardgrass varieties was E. crusgali var. zelayensis > E. crusgalli var. mitis > E. colonum, and the growth duration was E. crusgalli var. mitis > E. crusgali var. zelayensis > E. colonum. The biomass of baynyardgrass increased with the increase of N application rates and reached a peak at the N rate of 240 kg N·hm-2, and it decreased at 360 kg N·hm-2. The biomass of either E. crusgalli var. mitis or E. crusgali var. zelayensis was significantly higher than that of E. colonum. At the 0 kg N· hm-2 level, all barnyardgrass varieties showed no significant effect on rice yield. At the 120 kg N· hm-2 level, rice yield was not significantly different among the three treatments of barnyardgrass free, co-cultured with E. crusgalli var. mitis, and co-cultured with E. colonum, but it was significantly decreased when co-cultured with E. crusgali var. zelayensis. At the 240 kg N·hm-2 level, all treatments of co-cultured with barnyardgrass significantly decreased the rice yield. At the 360 kg N·hm-2 level, rice yield was significantly decreased under the treatments of co-cultured with E. crusgali var. zelayensis or with E. crusgalli var. mitis, and showed no significant difference between barnyardgrass free and co-cultured with E. colonum. All these data indicated an interaction between barnyardgrass and N fertilizer, which mediated the formation of grain yield of rice. Furthermore, at the 120 kg N· hm-2 level, the co-cultured E. crusgali var. zelayensis treatment significantly reduced leaf nitrate reductase activity and photosynthetic rate and root oxidation activity during the grain filling period, and decreased nitrogen accumulation and dry matter accumulation at the maturity stage, but other two treatments showed no significant effect when compared with barnyardgrass free treatment. These physiological indices of rice were significantly reduced by both E. crusgalli var. mitis and E. crusgali var. zelayensis treatments at either 240 or 360 kg N·hm-2 level, and showed no significant difference among all treatments at the 0 kg N·hm-2 level. Regression analysis showed that the order of effects of barnyardgrass phenotypes on rice grain yield was biomass, plant height, growth duration and tiller number. All these results suggested that the coexistence with large biomass of barnyardgrass inhibited the leaf photosynthetic rate, nitrate reductase activity, root oxidation activity, nitrogen accumulation and dry matter accumulation of rice, and consequently, reduced the rice grain yield.

Food Preference of Pecky Rice Bugs Is Influenced by Experience

This study investigated whether prior experience influences the plant food preference of Trigonotylus caelestialium and Stenotus rubrovittatus which cause pecky rice grain, by using rice plants and 2 poaceous weeds. In a choice experiment between Digitaria ciliaris and the rice plants, both T. caelestialium and S. rubrovittatus adults that were reared on D. ciliaris plants showed significant initial preference for D. ciliaris over rice. In a choice experiment between Echinochloa crus-galli var. aristata and rice plants, T. caelestialium adults reared on E. crus-galli var. aristata strongly preferred E. crus-galli var. aristata over rice throughout the experiment. However, at and after 24 h, T. caelestialium adults reared on rice showed no food preference, although T. caelestialium initially preferred E. crus-galli var. aristata. In contrast, S. rubrovittatus adults reared on rice showed no preference between E. crus-galli var. aristata and rice. However, S. rubrovittatus reared on E. crus-galli var. aristata initially preferred E. crus-galli var. aristata to rice, with this preference waning with time. The same results were obtained for both sexes. Although the effect of experience differed with food source and the species of mirid bug, prior experience initially had a noticeable effect, which disappeared with time (1 d).

피속 잡초 종자의 등온흡습곡선 특성

The equilibrium moisture contents (EMC) in seeds of four Echinochloa (E. crus-galli var. crus-galli, E. crus-galli var, echinata, E. crus-galli var. praticola, E. esculenta) were measured at 20oC with equilibration over a series of lithium chloride solutions with relative humidities ranging from 0.11 to 0.8 to determine sorption isotherms and safe storage relative humidity. Standard seed sorption isotherm models i.e. modified Henderson, modified Chung-Pfost, modified Halsey, modified Oswin and Guggenheim-Anderson-deBoer (GAB) equations were adopted to evaluate the goodness of fit to sorption isotherms. This study indicated that EMC of seeds was significantly different in four Echinochloa species at various relative humidity. The modified Oswin equations for E. crus-galli var. crou-galli, E. crus-galli var, echinata, E. esculenta and GAB equation for E. crus-galli var. praticola were adequate models for the EMC data. Seeds of four Echinochloa species have monolayer moisture contents when stored at RH < 0.1. These results show that seed moisture isotherm model should be selected according to genetic variation.

Effects of Different Species in Echinochloa on Photosynthetic Characteristics and Grain Yield in Rice under Alternate Wetting and Moderate Drying Condi-tion

In order to investigate the effects of different barnyardgrass species on photosynthetic characteristic and grain yield of rice, two rice cultivars, Liangyoupeijiu (an indica hybrid cultivar) and Nanjing 9108 (a japonica cultivar), were co-cultured with four barnyardgrass species from transplanting to maturity under alternate wetting and moderate drying condition. The treatments were designed as follow: weed free (control), rice with Echinochloa crusgalli var. mitis (T1), rice with Echinochloa crusgalli (T2), rice with Echinochloa crusgali var. zelayensis (T3), and rice with Echinochloa colonum (T4). The results showed that the degree of interference of barnyardgrass on rice yield depended on different barnyardgrass species and rice cultivars. The interference intensity of barnyardgrass was in the order of T3>T1>T2>T4, and grain yield loss rate in Liangyoupeijiu was less than that in Nanjing 9108. T1, T2, T3, and T4 treatments respectively reduced 11.16%-13.78%, 10.19%-10.60%, 19.00%-23.79%, and 0.50%-1.57%, for Liangyoupeijiu of the grain yield and 38.44%-45.51%, 31.29%-36.86%, 54.88%-60.65%, and 8.28%-15.14% for Nanjing 9108, T1, T2, and T3 significantly reduced rice grain yield, while the effect of T4 was significant for Nanijng 9108 but not for Liangyoupeijiu when compared with CK. Moreover T1, T2, and T3 had no effects on leaf area index and contents of photosynthetic pigments for Liangyoupeijiu, but Nanjing 9108 significantly reduced leaf area index and increased contents of photosynthetic pigments under the same treatment condition. Furthermore, four treatments significantly reduced rice canopy light transmission, leaf photosynthetic rate, stomata conductance, transpiration rate and dry matter accumulation during grain filling stage. The results indicated that the decrease in canopy light transmission, photosynthetic rate, transpiration rate, stomata conduc- tance and the increase in some degree in contents of photosynthetic pigments during grain filling stage may contribute to grain

The Effect of Transitional Organic Production Practices on Soilborne Pests of Tomato in a Simulated Microplot Study

The perceived risk of pest resurgence upon transition from conventional to organic-based farming systems remains a critical obstacle to expanding organic vegetable production, particularly where chemical fumigants have provided soilborne pest and disease control. Microplots were used to study the effects of soil amendments and cropping sequences applied over a 2-year transitional period from conventional to organic tomato (Solanum lycopersicum) cultivation on the incidence of bacterial wilt caused by Ralstonia solanacearum, purple nutsedge (Cyperus rotundus) reproduction, root galling by Meloidogyne incognita, and soil nematode populations. A continuation of tomato monoculture during the transitional period resulted in a disease incidence of 33%, as compared with 9% in microplots that were rotated with sunn hemp (Crotalaria juncea) and Japanese millet (Echinochloa crusgalli var. frumentacea). The benefits of disease control from a crop rotation extended into to a second season of organic tomato cultivation season, where bacterial wilt declined from 40% in microplots with a tomato monoculture to 17% in plots with a crop rotation sequence. Combining applications of urban plant debris with a continued tomato monoculture increased the incidence of bacterial wilt to 60%. During the transition period, tomato plants following a cover crop regime also had significantly lower levels of root galling from root-knot nematode infection compared with plants in the continuous tomato monoculture. Nutsedge tuber production was significantly increased in plots amended with broiler litter but not urban plant debris. Compared with a continuous monoculture, the results illustrate the importance of a systems-based approach to implementing transitional organic practices that is cognizant of their interactive effects on resident soilborne disease, weed, and pest complexes.

A resistance mechanism dependent upon the inhibition of ethylene biosynthesis

The highly selective auxin-type herbicide quinclorac is widely used to control important dicotyledon and monocotyledon weeds in rice fields. Echinochloa crusgalli var. zelayensis is one of the most troublesome weeds in China, and is very difficult to control in east China due to misuse of herbicides. The JZD -R, JTJ -R, JCW -R and SSX -R biotypes of E. crusgalli var. zelayensis had resistance to quinclorac with resistance levels ranked as JZD -R < JTJ -R < JCW -R < SSX -R. Growth reduction in different biotypes was positively correlated with ethylene production. Stimulated levels of ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) and activities of ACC synthase and ACC oxidase in resistant biotypes were less than the susceptible biotype, and were negatively correlated with quinclorac resistance levels, suggesting that inhibition of ethylene biosynthesis was positively correlated with resistance levels. Considering the resistance-dependent inhibition in the ethylene biosynthetic pathway, the mechanisms of resistance to quinclorac in E. crusgalli var. zelayensis involved alteration(s) in the ethylene response pathway, consisting of at least alteration in induction of the enzymes activity of ACC synthase and ACC oxidase.

벼 무경운 직파 논에서 뚝새풀 발생밀도에 따른 잡초 발생

벼 무경운 직파 재배는 노동력을 절감하고 쟁기 및 로타리 경운을 생략함으로서 에너지를 절약하는 이점이 있다. 또 토양 및 토양수분을 보전하고 논 표층에 토양유기물을 축적시키는 장점이 있다. 이는 벼 무경운 재배 논에서 동계에 많이 발생하는 뚝새풀로 인함이다. 본 시험에서 벼 무경운 재배를 한 논에서 동계에 뚝새풀이 많이 발생하였는데, 피복정도가 식양질에서 97.6%, 사양질에서 95.2%로 아주 심하게 발생을 하였다. 이로 인해 벼룩나물, 황새냉이, 개갓냉이, 선씀바귀 등 월년생 잡초나 숙근초의 발생이 줄어들었으며, 그리고 봄철 일찍 발생하는 1년생 잡초 좀명아주, 여뀌 뿐 아니라, 관개 후 논에서 발생하는 피, 알방동산이, 물달개비, 밭뚝외풀 등의 1년생 하계 논잡초들의 발생도 줄어들었다. 결론적으로 벼 무경운 직파 시 동계에 발생하는 뚝새풀로 인해 하계 논잡초 발생을 관리할 수 있는 이점도 있는 것이다. No-tillage direct seeding of rice is consumed less labor and oil energy by no plowing and rotary tillage. And it has other advantages of soil and water conservation and accumulation of organic matter on paddy surface due to crowded water foxtail (Alopecurus aequalis var. amurensis). When no-tillage seeding of rice, many water foxtail occurred in winter paddy field. In this experiment their covering degrees were 97.6% and 95.2% in clay loam and sandy loam paddy soils, respectively. Because of this, Stellaria alsine var. undulata, Cardamine flexuosa, Rorippa indica and Ixeris chinensis etc. annual and perennial wintering weeds occurrence was reduced. And annual weeds Chenopodium serotinum and Polygonum hydropiper that occurred early in spring were also reduced. As well as Echinochloa crusgalli var. praticola, Cyperus difformis, Monochoria vaginalis and Lindernia procumbens etc. summer annual weeds that occurred after irrigation were also reduced. In conclusion, no-tillage direct seeding of rice has another advantages of weed management by water foxtail.