Integrated effect of allelochemicals and herbicides on weed suppression and soil microbial activity in wheat (Triticum aestivum L.)

To evaluate the allelopathic effects of major crops and weeds, studies were conducted during 2011–12 and 2012–13 by utilizing water extracts of allelopathic plants namely rice (Oryza sativa L.), Parthenium hysterophorus L., Phragmites australis Cav., and Datura alba L. with reduced rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA to control weeds. Application of Phragmites australis and Parthenium hysterophorus along with lower rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA showed promising results by controlling weeds and improving yield. Parthenium hysterophorus extract with half of the recommended dose of fenoxaprop-p-ethyl and bromoxynil plus MCPA reduced weed density by 51 and 50% during year 1 and year 2, respectively, compared with the control. Phragmites australis extract with half of the recommended dose of fenoxaprop-p-ethyl produced grain yield (5.7 and 6.1 t ha⁻¹ during year 1 and 2, respectively) in wheat. However, these results were also at par with Parthenium hysterophorus and Datura alba extracts in combinations with half the recommended doses of the above mentioned herbicides. The study of microbial activity showed higher amount of mineralizable carbon in D. alba with half the recommended dose of fenoxaprop-p-ethyl treated plots (0.073 g during both the years). The lowest amount of mineralizable carbon (0.035 and 0.030 g during year 1 and 2, respectively) was observed in the control plots. The presence of allelopathic plants in field crops and subsequent mixing in soil by tillage may create problems in crop production. Therefore, further studies are suggested to fully explore all the possible interactions among allelochemicals and herbicides.     

Identifying genetic markers of wheat (Triticum aestivum) associated with flavor preference using a laboratory mouse model

Whole wheat products provide critical nutrients for human health, but flavor of whole wheat products may hinder consumer acceptance. However, flavor differences among wheat varieties are not well understood. Using a mouse model system, flavor of whole wheat grain was examined using a two-choice feeding system. A bi-parental recombinant inbred line (RIL) population derived from Clark's Cream x NY6432-18 was used for mapping flavor preference. Clark's Cream is a hard white, and NY6432-18 is a soft white wheat. “Yummy” (cv. Diva soft white) and “yucky” (cv. Macon hard white) varieties were used as ‘checks’ for evaluating each RIL. Marker-trait association was performed using the Student's t as a preference phenotype from each check-RIL comparison. Twenty-two significant marker associations were found. Because mice prefer softer kernel texture, the effect of the Puroindoline b haplotype and phenotypic kernel texture were used as covariates in analyses. Twenty-eight markers exhibited significant associations in the two covariate analyses, with an additional five having significant associations in both covariate analyses. The results indicate that there is an identifiable genetic basis for flavor preference independent of kernel texture. Identifying flavor genes in wheat grain may help facilitate the development of varieties with greater palatability for whole-wheat products.     

Chemical control of weeds in wheat (Triticum aestivum L.) in Iran

Experiments were conducted in 2006–2007 at six research stations of the Iranian Plant Protection Research Institute to study the efficacy of different herbicides to control weeds in wheat. Treatments included mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (WG) at 45 + 45 + 135 g a.i./ha, respectively, sulfosulfuron at 21, 31.5, 42 and 51 g a.i./ha, chlorsulfuron at 15 g a.i./ha, bromoxynil plus MCPA at 600 g a.i./ha with clodinafop propargyl at 64 g a.i./ha, sulfosulfuron plus metsulfuron-methyl at 36 g a.i./ha, mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (OD) at 15 + 3 + 45 g a.i./ha, respectively, and a full season weed-free control. Herbicides were applied at wheat tillering. Results showed that sulfosulfuron plus metsulfuron-methyl, and bromoxynil plus MCPA with clodinafop propargyl resulted in satisfactory weed control and wheat grain yield at most locations. Weed control efficacy of both formulations of mesosulfuron-methyl plus iodosulfuron-methyl-sodium was variable across locations. Efficacy of the OD formulation appears to depend upon location, so that application of this herbicide at Shiraz and Gorgan resulted in better weed control compared to use of the WG. Satisfactory performance of the OD formulation at Gorgan and Shiraz could be attributed in part to the even pattern of rainfall distribution during the growing season and wheat cultivar used, respectively. With respect to grain yield, however, the OD formulation was better than WG formulation at most of the locations.     

小麦细胞质光敏雄性不育育性恢复的遗传研究

以核质杂种ＮＣ２１３４和Ｄ＾２－鉴２６（均带有Ｄ＾２细胞质）为细胞质供体,以筛选恢复系和转育不育系为目的,用６９个春小麦品种为核供体进行回交转育,观察不同核质组合后代的育性变化。初步结果表明,大约２８％的品种携带有Ｄ＾２细胞质长日光敏雄性不育的恢复基因,约３５％的品种通过回交可以转育成Ｄ＾２细胞质长日光敏雄性不育系。对其中一些组合Ｆ２群体单株育性的分布情况进行了调查和分析,结果表明,不同核质组合育     

不同冠温特征小麦的籽粒灌浆特性及内源激素的变化

为阐明小麦冠层温度与其籽粒灌浆特性、内源激素变化的关系,2001~2003年对黄淮麦区及河南省推广的30个小麦品种冠温特征、籽粒灌浆特性和籽粒发育过程中内源激素(玉米素ZR、赤霉素GA3、生长素IAA、脱落酸ABA)含量及比值的变化进行了研究。结果表明,豫麦50在灌浆后期冠层温度明显降低,表现为冷尾型;豫麦34和豫麦70在灌浆后期冠层温度有上升的趋势,表现为暖尾型。在灌浆末期冷尾型与暖尾型小麦冠层温度相差超过2.5℃。冷尾型豫麦50强、弱势粒的最大灌浆速率、平均灌浆速率和渐增期、快增期、缓增期的灌浆速率均大于暖尾型豫麦34、豫麦70;强势粒的激素含量变化及其比值变化规律性明显,弱势粒表现的规律性不如强势粒。冷尾型豫麦50强势粒ZR、IAA、GA3含量峰值均高于豫麦34、豫麦70,其ZR/ABA、GA3/ABA、IAA/ABA峰值亦高于暖尾型豫麦70和豫麦34,而ABA含量在灌浆中期上升快,且高峰值大于豫麦70和豫麦34,达到高峰后下降较快;在弱势粒中,豫麦50上述各种激素含量仍保持较高状态。     

Evaluation of post-emergence herbicides for the control of wild oat (Avena fatua L.) in wheat and barley in Argentina

Wild oat (Avena fatua L.) is the most troublesome weed in cereal crops in Argentina. With the aim of studying the effects of different herbicides, doses, and wild oat growth stage at application on weed control and crop yield, field experiments were conducted in wheat and barley crops during three growing seasons in the south of Buenos Aires Province, Argentina. Treatments were post-emergence applications of new herbicide, pinoxaden + cloquintocet mexyl (5%-1.25%), at doses that ranged from 20 g to 60 g a.i. pinoxaden ha⁻¹, applied at two to three leaves and the beginning of tillering of wild oat. In addition, standard treatments were included and applied at the same wild oat growth stages. Diclofop methyl at 511 g a.i. ha⁻¹ and fenoxaprop-p-ethyl at 55 g a.i. ha⁻¹ were applied in barley. In wheat, diclofop methyl was replaced by clodinafop-propargyl + cloquintocet mexyl (24%-6%) at 36 g a.i. clodinafop-propargyl + 9 g cloquintocet mexyl ha⁻¹ and in 2008/09 wheat experiments, iodosulfuron plus metsulfuron methyl (5%-60%) at 3.75 g a.i. ha⁻¹ + 3 g a.i. ha⁻¹ also was included. In both crops, pinoxaden at 30 g a.i. ha⁻¹ and at higher rates, fenoxaprop-p-ethyl and clodinafop-propargyl gave the best control of wild oat. In 2006/07 wheat crops, treatments applied at tiller initiation provided better control than the early timing averaged across herbicides. However, wheat yield generally was greater with early application. In barley, wild oat control and crop yield were similar regarding time of application. Variations in crop yield were correlated with grain number m⁻² both in wheat and barley, but relationships between both grain number and spikes m⁻² and with grains per spike were identified only in wheat.     

Integration of soil-applied herbicides at the reduced rates with physical control for weed management in fennel (Foeniculum vulgare Mill.)

Fennel has been widely used in traditional medicine for their antimicrobial effects. Since fennel is long duration crop and have slow initial growth, it protection from weed is essential. Experiments were conducted for two consecutive seasons to evaluate the efficacy of soil-applied herbicides at the reduced rates in combination with physical control for weed management and optimizing the yield of fennel. Treatments were type of herbicide (trifluralin and pendimethalin), application dose (recommend dose (R), 75% R, 50% R, and 0% R) and physical weed control (none, one hand-weeding at 50 day after planting (DAP), wheat straw mulch). Weed-free control treatment was also included in each year. The results showed that the use of soil-applied herbicides resulted in reduced weed biomass but did not provide season long weed control without an additional physical control. In both seasons, pendimethalin provided better weeds control than trifluralin. Reduced herbicide rates were found to be more effective when herbicides application followed by hand-weeding than when were used alone or combined with mulch. Experimental results also showed that one time increasing in herbicide rates increased seed yield by 17.5 and 7.5% in 2012 and 16.5 and 6.3% in 2013, when one hand-weeding and mulching were used as supplemental control, respectively. Overall, the 75% of the labeled recommended rate of herbicides followed by one hand-weeding at 50 DAP produced consistently high yields and less weed biomass, reflecting both superior weed control and crop safety.     

Evaluation of potential biocides for control of the earthworm Eukerria saltensis (Oligochaeta: Ocnerodrilidae), a pest of rice in southern Australia

The earthworm Eukerria saltensis can cause severe crop establishment problems in aerially sown rice grown on heavy clay soils in southern Australia. Damage occurs indirectly through destabilization of the topsoil, increased water turbidity, and mobilization of soil nutrients into the water column which leads to increased algal growth. We investigated the possibilities for chemical control of E. saltensis using laboratory bioassays and a series of field trials involving either the use of enclosures in flooded crops or soil incorporation of pesticides into rice fields during fallow periods or shortly before flooding. The four most toxic compounds in 7 day soil/water laboratory bioassays were carbofuran, acetamiprid, bendiocarb and lambda-cyhalothrin which provided corrected mortalities of 86–100% at 2 mg a.i. L⁻¹. Other compounds that showed some level of efficacy (corrected mortality >20% at one or more rates) were imidacloprid, esfenvalerate, thiacloprid, niclosamide and alpha-cypermethrin. Twenty-six of the 38 pesticides evaluated failed to produce mean corrected mortalities >6% at application rates of up to 2 mg a.i. L⁻¹. Eight trials were conducted in flooded rice crops using small stainless steel enclosures and carbofuran, thiodicarb, niclosamide and bendiocarb at rates of 1 and 2 kg a.i. ha⁻¹. Trials were assessed 8–14 days after chemical application. None of these treatments produced a statistically significant decrease in Eukerria biomass, although consistent downward trends in response to higher treatment rates were evident in 2 trials (one with carbofuran and one with bendiocarb). Three trials with liquid pesticides watered into fallow rice fields were conducted with carbofuran (0.5, 1.0 and 5.0 kg a.i. ha⁻¹) and thiodicarb (0.94 and 1.87 kg a.i. ha⁻¹) however only the 5.0 kg a.i. ha⁻¹ carbofuran treatment provided significant (P < 0.05) levels of control. Preflood soil applications of liquid carbofuran, thiodicarb and niclosamide (2 kg a.i. ha⁻¹), granular carbofuran and granular ethoprophos (0.5–2 kg a.i. ha⁻¹) also did not provide statistically significant levels of control, although the 2 kg a.i. ha⁻¹ liquid and granular carbofuran treatments did provide moderate levels of suppression (49–84%). Although further field trials with compounds such as acetamiprid and lambda-cyhalothrin may prove valuable, our results suggest chemical control of E. saltensis may be difficult to achieve with environmentally acceptable pesticides applied at economically viable rates. Cultural approaches such as appropriate crop rotations and landforming to ensure uniformly shallow water should continue to form the basis of Eukerria management programs.     

Detection of mutations in the 7A allele of wheat (Triticum aestivum) granule-bound starch synthase (Wx-7A) with a monoclonal antibody produced by targeted peptide immunisation

A peptide sequence unique for the granule-bound starch synthase (GBSS1) of hexaploid wheat (Triticum aestivum) was identified by sequence alignment of the three isoforms. Multiple antigenic peptides (MAP) of different length (16 and 20 AA) were synthesised against the selected sequence. The assessment of the immune response in mice against differently presented forms (resin-bound, free) and two types of adjuvants indicated that the free MAP with the longer peptide is more immunogenic. A 20AA MAP that elicited a strong immune response was used to produce a monoclonal antibody for the 7A isoform of GBSS 1. Epitope mapping of the selected Mab (F5-1F2) revealed that a 12mer partial sequence of the immunising peptide was specifically detected. Based on this Mab, a simple high throughput ELISA was developed that allows the quick identification of wheat lines carrying the 7A allele of GBSS 1 with minute amounts of sample.     

Efficacy of aluminum phosphide tablets to control Richardson’s ground squirrel (Spermophilus richardsonii) populations in southern Saskatchewan, Canada

The objective of this study was to assess, using a capture-recapture program, the effectiveness of aluminum phosphide tablets for control of Richardson’s ground squirrels (Spermophilus richardsonii) in southern Saskatchewan grasslands, from April to July 2007-2009. Aluminum phosphide tablets were tested in study plots in moist or dry soil conditions, where burrow openings had either been marked with a flag (to ensure that all openings would be found and treated) before treatment or left unmarked. In five study plots with moist soil conditions and flagged burrow openings, the mean control level was 80.9 (SD = 6.3) %. In two study plots with dry soil conditions and flagged burrow openings, and one study with moist soil conditions and unflagged burrow openings, control levels were < 60%. It is recommended that aluminum phosphide tablets be used to control Richardson’s ground squirrels in relatively small areas (i.e., < 5 ha) with moist soil conditions and flagged burrow openings, or in specific sites where there are still high concentrations of ground squirrels after an initial treatment with poison food baits.     

Aerial treatment of the migratory locust, Locusta migratoria (L.) (Orthoptera: Acrididae) with Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) in Australia

Between November 1998 and March 1999, bands of nymphs of Locusta migratoria were aerially treated using a ULV oil formulation of strain FI-985 of Metarhizium anisopliae var. acridum. At a dose of 3–4×10¹² conidia/ha, there was <10% survival of locusts in treated sorghum crops, open grassland or open woodland with grass. Decline was less at lower doses or in dense woodland. During the first week after treatment, bands showed little change in numbers, but then rapidly declined in size and rate of movement. The decline was slower where vegetation was tall or dense, or where bands were large and moved out of the treated area a few days after spraying. In areas where bands were treated with Metarhizium, populations were suppressed in that few adult swarms formed. Adjacent untreated areas had many adult swarms which had to be controlled using chemical insecticides. Preventive locust control, as currently practised in Australia, involves beginning treatment when areas of band and swarm are small and the potential for direct damage limited. The clear demonstration that Metarhizium can suppress small local populations of L. migratoria indicate that it could be a valuable component of preventive control programmes against this species. The delay in mortality when treating with Metarhizium would be no impediment to its use in such programmes.     

Effectiveness of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. for control of the stem borer Chilo partellus (Swinhoe) in maize in Kenya

The fungus Beauveria bassiana (Bals.) Vuill. and insecticide trichlorfon were compared for the control of stem borer, Chilo partellus (Swinhoe) in field experiments at different times of infestation. Egg masses of C. partellus at the blackhead stage were pinned to the undersurface of the maize leaves. Two fungal formulations, conidial aqueous suspensions and a granular formulation, were applied. Compared with the untreated checks, the numbers of surviving C. partellus larvae were significantly reduced in treatments where B. bassiana was applied at a concentration of 10¹³ conidia ha⁻¹ as granules and as two aqueous spray formulations. No significant difference in numbers of stem borer larvae was found between trichlorfon and the untreated check. Fungus granules persisted longer in the field than did one spray of the fungus inoculum at the same concentration, or trichlorfon. A major increase in grain yield was obtained with two fungal sprays and with fungus granules both applied at a concentration of 10¹³ conidia ha⁻¹. A granular formulation of B. bassiana should be considered for the control of the stem borer C. partellus.     

Investigation into the apparent failure of chemical control for management of western flower thrips, Frankliniella occidentalis (Pergande), on plums in the Western Cape Province of South Africa

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), causes russetting, pansy spot and silvering damage on plums. Despite routine insecticide applications for thrips control, some plum producers report economic losses due to pansy spot damage, pits and holes that render fruit unfit for export. Six commercial plum orchards in two climatic regions in the Western Cape Province, South Africa, were monitored to determine (1) why current management practices based on monitoring and insecticide applications failed to prevent damage in some orchards, and (2) whether WFT is responsible for pitting damage. Western flower thrips was the dominant thrips species in all orchards, though low numbers of Frankliniella schultzei Trybom also occurred. Blue sticky traps were more efficient for monitoring WFT and F. schultzei than yellow traps. Insecticide applications early in bloom and unfavourable weather conditions for thrips flight contributed to very low numbers of WFT on sticky traps during the flowering and fruit set periods. Flower dissections, however, revealed varying levels of oviposition damage to ovaries and fruitlets. Dissections confirmed that WFT enter flowers to lay eggs in the ovaries and other flower parts before petals are fully open. No consistent significant relationship between sticky trap counts and WFT oviposition damage to plums were found, therefore no treatment threshold level could be recommended. Insecticide applications during bloom limited thrips feeding damage, but were too late to prevent oviposition damage. Some oviposition sites developed into typical pansy spots, whilst others formed holes or pits that increased in size as the fruit matured. After insecticide applications ended, and as air temperature increased, WFT populations increased. Weeds and wild vegetation in and around orchards provide a continuous source of potential infestation for as long as the fruit remains attractive and vulnerable to WFT. As oviposition damage by WFT can occur before flowers open, and because of the risk to pollinators when insecticides are applied during flowering, a purely chemical control strategy does not appear to be feasible. A new approach to WFT management is required.