Phylogenetic Analysis of Sugarcane Rusts Based on Sequences of ITS, 5.8 S rDNA and D1/D2 Regions of LSU rDNA

Phylogenetic analysis of sugarcane rusts based on sequences of ITS and the 5.8 S rDNA revealed two highly divergent ITS groups among isolates of Puccinia sp. sensu Muta, 1987 and P. kuehnii specimens. Although there is sufficient divergence (exceeding normal intraspecific variation) between the ITS regions of the two groups to support separation into different species, unusually high homology of the ITS group I sequences with those of members of Cronartium and identical sequences of the D1/D2 regions of the LSU rDNA for all the isolates of “Puccinia sp.” and P. kuehnii that otherwise exhibited different ITS sequences, suggest that the two highly divergent sequences may have resulted from abnormal genetic events leading to non-orthologous, intraspeciflc polymorphisms. The other sugarcane rust, P. melanocephala and the grass rusts, P. miscanthi and P. rufipes, were separated from “Puccinia sp.” and P. kuehnii and from each other in D1/D2 region analyses, indicating that D1/D2 region sequences may more correctly reflect phylogenetic relationships in these rusts than do the ITS regions. Further studies to examine differences in patho-genicity or finer morphological features within P. kuehnii that may be correlated with the high divergence in ITS sequences and experiments to determine if these two sequence types represent intraspeciflc polymorphism are necessary. Received 11 October 2000/ Accepted in revised form 24 November 2000     

Long-term tillage and crop rotation effects on weed seedbank size and composition

Size and composition of the weed seedbank was assessed after 12 years of application of four tillage systems in two crop rotations. Mouldboard and chisel ploughing at 45 cm, minimum tillage at 15 cm and no tillage were compared in continuous winter wheat and a pigeon bean/winter wheat 2-year rotation. Weed control was based upon post-emergence herbicide application. Weed seedling emergence from soil samples taken at 0–15, 15–30 and 30–45 cm depths was assessed in a non-heated glasshouse for 12 months. The tillage system influenced weed seedbank size and composition to a much greater extent than crop rotation. Total weed seedling density was higher in no tillage, minimum tillage and chisel ploughing plots in the 0–15, 15–30 and 30–45 cm layers respectively. Density in the whole (0–45 cm) layer did not differ significantly among tillage systems. With no tillage, more than 60% of the total seedlings emerged from the surface layer, compared with an average 43% in the other tillage systems. Crop rotation did not influence either weed seedbank size or seedling distribution among soil layers, and only had a small influence on major species abundance. The weed seedbank was dominated (>66%) by Conyza canadensis (L.) Cronq. and Amaranthus retroflexus (L.), which thrived in chisel ploughing and no tillage respectively. Results suggested that crop rotation and substitution of mouldboard ploughing by non-inversion tillage (especially by minimum tillage) would not result in increased weed problems, whereas use of no tillage might increase weed infestations because of higher seedling recruitment from the topsoil.     

苔藓植物生态学研究的数量分析方法

植被数量分析方法在苔藓植被中的应用起步较晚，仅有20多年的研究历史，但发展却十分迅速。这里介绍了目前苔藓植物生态学研究中应用较为普遍的数量分析方法，并探讨了各自的优缺点。     

新疆哈纳斯自然保护区地衣群落的聚类分析

我们根据多年的实地调查结果并采用聚类分析方法对分布在哈纳斯国家级自然保护区的地衣群落进行了研究。结果表明分布在该地区的地衣种类有 10 3种 ,他们分别属于 2 0科 ,4 0属。地衣物种形成了 6种群落。同时发现该地区地衣对基物形成专一性 ,它们的基物包括 :树皮、藓丛、藓土、草地、石面、地面、土层、石浮土等。     

三唑酮种衣剂对小麦白粉菌侵染和非侵染位点硅等元素含量的影响

 借助扫描电子显微镜-X射线能谱分析方法从超微结构和元素水平观测了三唑酮种衣剂包衣处理和空白对照的小麦幼苗上白粉病菌侵染及非侵染位点硅等元素含量的变化。结果表明,接种后20~36 h内三唑酮种衣剂处理的麦苗侵染位点细胞内元素硅含量由5.204%上升为42.064%,非侵染位点由5.821%上升为12.342%;空白对照中侵染位点元素硅含量由低于检测水平上升为17.388%,非侵染位点接种后36 h时为19.460%。在处理和空白对照的麦苗上侵染和非侵染位点均检测到了含量不等的磷、硫、氯等元素存在。     

超临界流体萃取技术在农药残留分析中的应用进展

从萃取过程控制的角度，综述了近几年来国外超临界流体技术不同形态的基体的农药残留分析中的应用情况、研究现状及前景。     

小麦禾缢管蚜种群动态的研究

本文采用平均密度（X），聚块性指标（m/m）和有蚜株率（F）对小麦禾缢管蚜种群动态进行模糊聚类分析。找出了其种群消长的4个时期：点片发生期，始盛期，猖獗期和衰退期；防治重点应在始盛期，即瓢虫卵期，以达到经济有效，充分保护利用天敌的目的。     

N-(pyrid-3-yl)thioureas and derivatives as acaricides. II. Quantitative structure-activity relationships and chemodynamic behaviour

The biological activity of a series of N-(pyrid-3-yl)thioureas and -carbodiimides, analogues of the insecticide/acaricide diafenthiuron, towards the carmine spider mite (Tetranychus cinnabarinus Boisd.) and the two-spotted spider mite (T. urticae Koch) was analysed using QSAR methodology. A canonical correlation analysis allowed for the establishment of a prediction model and the identification of outliers within that model. The chemodynamic behaviour of certain compounds in the two series, including these outliers, determined by using photochemical experiments in the laboratory as well as in the glasshouse, was shown to be responsible for anomalous results obtained in the biological tests. It was found from the above study that the biological activity towards both spider mite species is extremely sensitive to the kinetics of formation of the carbodiimides from the corresponding thioureas and to the photostability of the former. The results obtained with a thiourea which underwent no appreciable photochemical transformation into the corresponding carbodiimide supported the hypothesis that the thioureas are also in-vivo propesticides of the acaricidal carbodiimides.     

The 1997-1998 classical swine fever epidemic in The Netherlands--a survival analysis

The aim of this analysis was to characterise the temporal pattern of infection during the 1997/98 classical swine fever (CSF) epidemic in The Netherlands and hence identify and quantify risk factors for infection in different enterprise types and areas. Survival analysis and Cox proportional hazards regression were used to describe the epidemic. Substantial differences in temporal survival patterns (herd breakdown rate) were found between areas where different control policies operated. Factors with a significant influence on the infection hazard of individual herds included: sow numbers as a percentage of total sows and fatteners (HR = 3.38 for mixed herds (0.1–60% sows) vs. fattening herds (0% sows) and HR = 2.74 for breeding herds (60–100% sows) vs. fattening herds), the number of ‘transport contacts per month’ (>0.3 vs. <0.3; HR = 4.11), pig density (pigs/km²) in the area (HR_{1000 pigs} 1.48) and herd size (HR_{100 pigs} = 1.01).

Pre-emptive slaughter in an area appeared to be associated with lower subsequent disease levels. Higher frequency of transport contacts for welfare slaughter during the epidemic, however, well regulated and controlled, was associated with a substantially higher risk of becoming infected. The positive association of a higher pig density with CSF indicates the potential importance of local spread as a factor in disease transmission and emphasizes that dilution of the pig population can contribute to reduction in CSF occurrence. This analysis suggests however, that if pre-emptive slaughter can promptly be applied effectively in an area after initial diagnosis, pig density is then not a significant factor. Mixed and breeding herds had a higher probability of becoming infected than fattening herds, possibly due to different types and frequencies of inter-herd contacts. These contacts continue to some extent during the epidemic, despite the standstill of animal movements.     

安哥拉山羊与建昌黑山羊及其杂种后代的DNA指纹分析

以 (CA/GATA/TCC) 5探针 ,HinfI酶切 ,研究安哥拉山羊和建昌黑山羊及安哥拉山羊与建昌黑山羊级进杂交的F2 、F3的DNA指纹图谱。结果 ,在供试山羊中 ,个体平均检出 1 8.2± 0 .4条谱带 ,安哥拉山羊、F2 、F3的鉴别机率分别为 1 .38× 1 0 - 12 ,1 .1 8× 1 0 - 13,0 .50× 1 0 - 10 ;群体内相似系数安哥拉山羊为0 .4 539,F2 为 0 .4 0 77,F3为 0 .61 1 1 ;亲子鉴定的父权概率W =0 .9889;安哥拉山羊与建昌黑山羊比较 ,2 .3kb和 8.6kb谱带为安哥拉山羊的特异谱带