Effects of the estrogen mimic genistein as a dietary component on sex differentiation and ethoxyresorufin-O-deethylase (EROD) activity in channel catfish (<Emphasis Type="Italic">Ictalurus punctatus</Emphasis>)

A number of aquaculture species, including channel catfish Ictalurus punctatus, are fed high proportions of soybean meal in their diet. We have investigated the potential for the most common phytoestrogen in soybean meal to alter phenotypic sex during sexual differentiation in channel catfish. Channel catfish were fed four dietary concentrations of the phytoestrogen genistein (0, 2, 4, and 8 mg g⁻¹) to determine its effect on gonadal sex differentiation. The four treatment diets were fed to sexually undifferentiated channel catfish between 5 and 140 days post hatch (dph) and between 60 and 150 dph. Phenotypic sex was determined by histological examination of the gonads. Ethoxyresorufin-O-deethylase activity was not significantly different among the treatment and control groups. Phenotypic sex was significantly dependant on dietary phytoestrogen concentration (P = 0.01). Additionally, logistic regression showed a significant relation between genistein concentration in the diet and gonadal sex (P = 0.02). Intersex individuals were present at all treatment concentrations, with increasing proportions of intersex fish as the genistein concentration increased for individuals fed treated diets between 5 and 140 dph. Increased proportions of phenotypically male individuals resulted from chronic dietary exposure to the estrogen mimic genistein. There were no significant differences in the proportions of males and females between feed treatment durations. These findings establish that dietary concentrations of genistein can alter sex ratios in cultured channel catfish populations and demonstrates the need to further understand the actions of this and other prominent phytoestrogens in aquaculture species.     

Biochemical markers for cabbage seedpod weevil (<Emphasis Type="Italic">Ceutorhynchus obstrictus</Emphasis> (Marsham)) resistance in canola (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

In the last decade, the cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham)) has become a major insect pest of canola (Brassica napus L.) in Canada reducing seed yields up to 35%. Therefore, the benefits of developing weevil resistant germplasm to canola breeders and the industry would reduce input costs, pesticide use, environmental degradation and increase yield. Yellow mustard (Sinapis alba L.) is resistant to C. obstrictus (CSPW), although the exact mechanism is not known (McCaffrey et al. 1999). A unique canola population was generated at the University of Guelph from a cross between B. napus and S. alba through embryo rescue and backcrossed to canola several times prior to double haploid (DH) production. Approximately one-half of this DH population had canola quality glucosinolate concentration (<16 μmol/g) and was used for further breeding. The hypothesis was that some DH progeny from this cross inherited resistance to CSPW from S. alba. Weevil infestation levels were assessed for the B. napus × S. alba BC2 and BC3 DH populations in the field over 7 years in Alberta where weevil pressure is strong to establish the resistant or susceptible status of these lines. The basic objectives for this study were to confirm field resistance in the B. napus × S. alba germplasm in Ontario and to identify any biochemical markers associated with resistance/susceptibility. Canola doubled haploid lines derived from BC2 or BC3 families were field screened for resistance (R) followed by chemical analysis of glucosinolates to detect biochemical polymorphisms correlated with CSPW resistance using High Performance Liquid Chromatography (HPLC). Two polymorphic peaks were found, one each, from extracts of upper cauline leaves and Stage 3 pod seed, with retention times of ~23 and 19 min, respectively. These HPLC peaks consistently correlated with larval infestation data and the peak differences between R and S DH lines were significant. Therefore, these two peaks can be considered as biochemical markers in this breeding germplasm and may play a role in rapid and early detection of CSPW resistance.     

Sensitivity of Uncinula necator to quinoxyfen: evaluation of isolates selected using a discriminatory dose screen

Quinoxyfen is a protectant fungicide that provides excellent control of many powdery mildew diseases. Prior to the launch of quinoxyfen in vines in 1998, a leaf disc sporulation assay was developed to assess the sensitivity of Uncinula necator (Schw) Burr to quinoxyfen. The distribution of EC(50) values from 56 monoconidial U. necator isolates collected from six countries between 1993 and 1996 was found to range from less than 0.03 to 2.6 mg litre(-1). Although this range of EC(50) values was quite broad, the inability to establish a minimum inhibitory concentration (MIC) for the majority of these isolates, including some of the most sensitive isolates, was unexpected and suggested that the leaf disc sporulation assay may not reflect the true activity of quinoxyfen in the field. In 2002, following the detection of isolates resistant to quinoxyfen in Blumeria graminis Speer f. sp. tritici Marchal, a discriminatory dose screen was developed to test large populations of U. necator for rare individuals with significantly decreased sensitivity to quinoxyfen. The individual isolates selected by this method were tested with the leaf disc sporulation assay. Although a significant proportion were found to have EC(50) values within the original distribution, a number of isolates with apparent reduced sensitivity to quinoxyfen were also detected. However, further examination of a subset of these isolates in a more quantitative germination/germ tube elongation inhibition assay suggested that the magnitude of the reduction in sensitivity for some of these isolates was much less than predicted by the sporulation assay. Thus, for an exclusively protectant fungicide such as quinoxyfen, a leaf disc sporulation assay may overestimate the frequency of isolates with significantly reduced sensitivity and the threat of decreased performance due to resistance.     

白芦笋花药愈伤组织诱导及绿芽分化

为建立芦笋单倍体育种技术体系以解决国内芦笋新品种资源贫乏问题,笔者以白芦笋花药为外植体进行了愈伤组织的诱导及绿芽分化研究。试验结果表明,芦笋花药经过4d的冷藏(4℃)处理后,接种于含有NAA2.0 mg/L、6-BA1.0mg/L及6%蔗糖的1/2MS培养基上,可产生愈伤组织;每年的4月份接种花药的愈伤组织诱导率最高,8月份次之,11月份最低。品种间、同一品种不同单株间花药的愈伤组织诱导率不同,以‘UC155’品种(18.9%)最高,显著高于其他三个品种‘UC142’(11.6%)、‘Gijnlim’(10.3%)、‘Thielim’(5.8%),所有试验株系中以‘UC155’-8的愈伤组织诱导率最高,达83.5%;每日补充光照强度为1000 lx的光照,比全暗培养更有利于芦笋花药愈伤组织的形成;花药接种前进行离心处理(4000 r/min)30 min,不能提高愈伤组织诱导率;愈伤组织转瓶培养于NAA 0.5 mg/L、6-BA 1.0 mg/L及3%蔗糖的MS培养基上,能分化出无根绿芽;不同品种间绿芽分化率有差别,以‘Gijnlim’品种最高(67.2%),‘UC142’品种最低(14.1%);未分化绿芽的愈伤组织再转入于不含植物生长调节剂的MS培养基上培养,部分愈伤组织能分化出绿芽     

Use of goats as biological agents for the renovation of pastures in the Appalachian region of the United States

Much of hill-land pasture in the Appalachian region of the United States is dominated by herbaceous weeds and brush. Low cost, low input and environmentally acceptable reclamation procedures are needed to maintain the productivity of these pastures. This experiment evaluated the effectiveness of using goats (Capra hircus hircus) alone (30 mature, brush does/ha) or cattle (Bos taurus) with goats (17 mature, brush does/ha + two to three steers/ha -- 225 kg average live weight) to reclaim a pasture from an abandoned, overgrown 5.9 ha orchard left untouched for 15 years. Over four grazing seasons, managed defoliation resulted in a substantial increase in herbaceous vegetative cover in plots grazed by goats alone (65 to 86%) and by goats with cattle (65 to 80%) while vegetative cover decreased from 70 to 22% in the control plot. Similarly, the cover by grass species increased in the grazed plots (goats: 16 to 63%; goats + cattle: 13 to 54%) while averaging 10% in the control plot. Multiflora rose (Rosa multiflora Thumb.) bushes were practically eliminated after four grazing seasons as quantified by an average reduction in height from 2.1 m to 0.6 m, and by the number of dead canes (stems) in both the goat (100%) or goat + cattle (92%) treatments. Results indicated that the foraging habits of goats resulted in the elimination of multiflora rose bushes and in a significant increase in desirable forage species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Monitoring and modeling temperature variations inside silage stacks using novel wireless sensor networks

By monitoring silage temperature at different locations inside silage stacks, it is possible to detect any significant increases in temperature occurring during silage decomposition. The objectives of this study were: (1) to develop novel noninvasive wireless sensor nodes for measuring the temperature inside silage stacks; (2) to design a suitable sensor protection housing that prevents physical and chemical damage to the sensor; and (3) to mathematically model temperature variations inside a silage stack, using system identification techniques. The designed wireless nodes were used to monitor temperatures in a full-sized silage stack over 53 days. Results showed that the wireless sensor nodes accurately monitored the temperature inside the silage stack at depths of 25 and 50 cm and reliably transmitted the measured data through the network; between 98.9% and 99.4% of the packets disseminated from the sensor nodes were successfully delivered to the gateway. The reliable performance of the network confirmed the correct choice of network characteristics (i.e., frequency range of 433 MHz, a handshaking communication protocol, and 10 mW transmission power). The designed sensor housings were capable of withstanding the high loads that occurred during ensiling, storage, and feed-out. Mathematical models estimating the relations between the silage temperatures (at depths of 25 and 50 cm) and air and soil temperatures were obtained. Black-box modeling using the prediction error method (PEM) was selected as the identification method. Among different black-box models such as ARX, ARMAX, output-error (OE), and Box–Jenkins (BJ), with different model orders, a third-order Box–Jenkins model structure gave the best performance in terms of prediction accuracy. The success rate of the models proposed for silage temperature prediction ranged between 90.0% and 94.3%. Furthermore, there was no significant autocorrelation remaining in the residuals. The results of this study indicate that the designed wireless sensor nodes could potentially be used for detecting silage decomposition processes and improving the efficacy of silage conservation systems.     

Effects of solids removal on water quality and channel catfish production in a biofloc technology production system

Total suspended solids control was evaluated in a channel catfish (Ictalurus punctatus) biofloc technology production system. Settling chamber flow rates were 0.9 (LO) or 2.9 (HI) L/min to reduce total suspended solids to 300 mg/L; solids were not removed from control tanks. Channel catfish yields (7.6–8.7 kg/m³) were not affected significantly, but control fish were skewed toward smaller size classes. Control treatment channel catfish tolerated 1,410 mg/L total suspended solids without adverse effects. LO- and HI-treatment fillet geosmin concentrations were high enough to be designated as off-flavor. Water quality results suggested that nitrification was affected by solids removal.     

New multiple-herbicide crop resistance and formulation technology to augment the utility of glyphosate

Glyphosate has performed long and well, but now some weed communities are shifting to populations that survive glyphosate, and growers need new weed management technologies to augment glyphosate performance in glyphosate-resistant crops. Unfortunately, most companies are not developing any new selective herbicides with new modes of action to fill this need. Fortunately, companies are developing new herbicide-resistant crop technologies to combine with glyphosate resistance and expand the utility of existing herbicides. One of the first multiple-herbicide-resistant crops will have a molecular stack of a new metabolically based glyphosate resistance mechanism with an active-site-based resistance to a broad spectrum of ALS-inhibiting herbicides. Additionally, new formulation technology called homogeneous blends will be used in conjunction with glyphosate and ALS-resistant crops. This formulation technology satisfies governmental regulations, so that new herbicide mixture offerings with diverse modes of action can be commercialized more rapidly and less expensively. Together, homogeneous blends and multiple-herbicide-resistant crops can offer growers a wider choice of herbicide mixtures at rates and ratios to augment glyphosate and satisfy changing weed management needs.