Quality versus quantity: spring wheat seed size and seeding rate effects on Avena fatua interference, economic returns and economic thresholds

A 3-year field experiment was conducted at Kalispell, Montana, USA, to investigate the effects of spring wheat seed size and seeding rate on wheat yield loss (YL), economic returns and economic thresholds (ETs), as a function of Avena fatua density. Crop competitive ability increased as wheat seeding rate and seed size increased, with the greatest differences among treatment factors being observed at low weed densities. Both treatment factors decreased spring wheat YL, increasing economic returns during all 3 years of the study despite the higher associated seed costs. Averaged over all other factors, adjusted gross returns (AGR) were 477 and 537$ ha⁻¹ for the low and high seeding rates, while values of 453, 521 and 547$ ha⁻¹ were obtained for the small, bulk and large seed size classes respectively. Weed-free yield potential varied yearly. As yield potential increased, A. fatua competitive effects were more evident and ETs decreased. Nonetheless, both treatment factors increased ETs in 2 of 3 years. These results demonstrate that the use of higher seeding rates and larger seed size classes both improve wheat competitive ability towards A. fatua while simultaneously increasing economic returns.     

Effectiveness of Coniothyrium minitans and Trichoderma atroviride in suppression of sclerotinia blossom blight of alfalfa

The effects of the mycoparasites Coniothyrium minitans and Trichoderma atroviride on the suppression of alfalfa blossom blight caused by Sclerotinia sclerotiorum were evaluated under indoor and field conditions. When T. atroviride (9·0 × 10⁴ conidia/floret) + S. sclerotiorum (6·0 × 10³ ascospores/floret) or C. minitans (9·0 × 10⁴ conidia/floret) + S. sclerotiorum (6·0 × 10³ ascospores/floret) were applied to detached young alfalfa florets, T. atroviride effectively inhibited saprophytic growth of S. sclerotiorum, whereas C. minitans showed no inhibition under the same conditions. When T. atroviride (6·9 × 10⁴ conidia/floret) + S. sclerotiorum (6·0 × 10³ ascospores/floret) or C. minitans (6·9 × 10⁴ conidia/floret) + S. sclerotiorum (6·0 × 10³ ascospores/floret) was applied to young alfalfa petals in vivo just after pollination, the percentage of pod formation was higher for T. atroviride+S. sclerotiorum than that for C. minitans+S. sclerotiorum, and the percentage of pod rot was lower for T. atroviride+S. sclerotiorum than that for C. minitans+S. sclerotiorum. However, when they were applied to senescent petals attached to developing pods of alfalfa at 9·2 × 10⁴ conidia/floret together with S. sclerotiorum at 4·5 × 10³ ascospores/floret at 14 days after pollination, C. minitans was more effective than T. atroviride in suppressing sclerotinia pod rot and seed rot of alfalfa. Field experiments showed that three applications of C. minitans (5·4 × 10⁶ conidia mL⁻¹) or T. atroviride (5·4 × 10⁶ conidia mL⁻¹) at a 7-day interval to blossoms of alfalfa effectively suppressed sclerotinia pod rot in two out of three annual trials. Coniothyrium minitans effectively suppressed sclerotinia seed rot in all three years, whereas T. atroviride was not effective against seed rot in any of the trial years. The efficacy of C. minitans was not significantly different (P > 0·05) from benomyl (250 µg ai mL⁻¹). This study suggests that C. minitans has potential as a biocontrol agent to control blossom blight of alfalfa caused by S. sclerotiorum.     

Effects of foliar- and root-applied silicon on the enhancement of induced resistance to powdery mildew in Cucumis sativus

Two cucumber ( Cucumis sativus ) cultivars differing in their resistance to powdery mildew, Ningfeng No. 3 (susceptible) and Jinchun No. 4 (resistant), were used to study the effects of foliar- and root-applied silicon on resistance to infection by Podosphaera xanthii (syn. Sphaerotheca fuliginea ) and the production of pathogenesis-related proteins (PRs). The results indicated that inoculation with P. xanthii significantly suppressed subsequent infection by powdery mildew compared with noninoculation, regardless of Si application. Root-applied Si significantly suppressed powdery mildew, the disease index being lower in Si-supplied than in Si-deprived plants, regardless of inoculation treatment. The resistant cultivar had a more constant lower disease index than the susceptible cultivar, irrespective of inoculation or Si treatment. Moreover, with root-applied Si, activities of PRs (for example peroxidase, polyphenoloxidase and chitinase) were significantly enhanced in inoculated lower leaves or noninoculated upper leaves in inoculated plants of both cultivars. Root-applied Si significantly decreased the activity of phenylalanine ammonia-lyase in inoculated leaves, but increased it in noninoculated upper leaves. However, Si treatment failed to change significantly the activity of PRs in plants without fungal attack. Compared to the control (no Si), foliar-applied Si had no effects either on the suppression of subsequent infection by P. xanthii or on the activity of PRs, irrespective of inoculation. Based on the findings in this study and previous reports, it was concluded that foliar-applied Si can effectively control infections by P. xanthii only via the physical barrier of Si deposited on leaf surfaces, and/or osmotic effect of the silicate applied, but cannot enhance systemic acquired resistance induced by inoculation, while continuously root-applied Si can enhance defence resistance in response to infection by P. xanthii in cucumber.     

基于分子遗传标记技术的实蝇种群遗传关系研究进展

分子遗传标记技术已用于分析实蝇的种群遗传关系,本文介绍了分子遗传标记技术在实蝇的起源、入侵、定殖、扩散及其他方面的研究进展,首次分析了我国实蝇种群遗传研究的现存问题并针对检疫性实蝇种群遗传关系研究提出了建议.     

简单、实用、高效的细胞培养技术

通过近几年的实践,笔者对我国兽医生物制品生产中传统的细胞培养工艺进行了一些改进,包括用洗洁精代替其他洗液,用自行研制的营养液代替常规营养液用于细胞培养,改变培养时的转速,改变细胞消化液,改进细胞的保存方法.这些方法均成功应用于生产,取得了良好的效果.     

Estimation of genetic parameters for lactational milk yields using two-dimensional random regressions on parities and days in milk in Chinese Simmental cattle

A two‐dimensional random regression model with regressions on days in milk (DIM) and parity number was applied to lactational milk yields in Chinese Simmental cattle. Random regressions were fitted for additive genetic and permanent environmental effects using a two‐dimensional polynomial on DIM and parity number. A total of 4340 lactational milk yields from Chinese Simmental cattle which calved between 1980 and early 2000 were used in this study. Variance components were estimated using Bayesian methodology via Gibbs sampling. Variances of random regression coefficients associated with all terms of the polynomials were significant. A covariance function showed that heritabilities of lactational milk yields between 200 and 400 DIM over parities varied between 0.25 and 0.45. Heritabilities of 305‐day milk yields from 1st to 6–8th parities were 0.28, 0.30, 0.32 0.32, 0.32, and 0.31, respectively. Ratios of permanent environment variances to total variances at each DIM were greater than corresponding heritabilities. Generally, genetic correlations were higher between lactational milk yields with similar DIM and parity number.     

犬顽固性咳嗽的中西兽医治疗方案探讨

日常动物医院门诊病例中,呼吸道病综合症在伴侣动物疾病临床上很常见,同行们称其为顽固性咳嗽。在新疆这个漫长的冬季当中,从每年的10月份至次年的4月份,呼吸道病综合症极为常见。这种病主要是由副流感病毒、腺病毒、犬瘟病毒、支原体、支气管败血波氏杆菌等病原和微生物单独或混合感染引起的高度接触性呼吸道传染病。对此病根据临床症状、X光检查、流行病学以及病理变化等不难做出初步诊断。对于犬呼吸道疾病的药物治疗方法值得研究与探讨。笔者采用中西兽医结合的治疗方案,从1998年至2002年共诊治犬顽固性咳嗽病例610例,疗效显著,总治愈…     

掘氏疫霉侵染甜瓜叶片的过程

 掘氏疫霉Phytophthora drechsleri为害甜瓜的苗、叶、蔓、瓜引起猝倒,烂叶,烂蔓,烂瓜。甜瓜种植区分布广泛,为害严重。     

棉花对硃砂叶螨抗性的鉴定和机制研究

1988-1991年进行的棉花抗硃砂叶螨试验表明,海岛棉和二倍体栽培棉(中棉和草棉)对硃砂叶螨具有较高水平的抗性,它们的抗螨性已通过远缘杂交技术转移到了感螨的陆地棉栽培品种中。来自四川省和河南省的一些品种以及来自美国的PD种质系对硃砂叶螨的抗性比湖北省当地品种要差。叶片有毛,无腺体和高含淀粉的棉花,硃砂叶螨为害较重;而叶片具有致密茸毛、棉酚、可溶性糖、叶绿素和类黄酮含量高以及叶片鲜重高的品种抗螨性较强。