Effect of selection under cultivation on morphological traits and yield of Ladino white clover landraces

One reason for the relatively low genetic advance realized in forage legumes may be the possible selection, under the severe intraspecific competition occurring naturally during cultivation, of a few high-yielding genotypes that would be of similar value in a broadly-based landrace or old cultivar and a narrowly-based, modern variety. The effect of selection under cultivation was assessed in two Ladino white clover farm landraces. Genotypes collected from each farm after a three-year crop cycle (survivor populations), or obtained from the seed used to establish each meadow (original populations), were multiplied clonally and evaluated in isolation and monoculture conditions for one year. The occurrence of directional selection was observed only in the landrace featured by greater intra-population variation in favour of genotypes with longer petioles (+11%), larger leaf size (+13%), less stolons (–14%) and lower production of heads (–16%). Selection for the first two traits would imply an increase of competitive ability, whilst that for the fourth trait appeared mainly as a correlated response. The trade-off between leaf gigantism and head production could act as a buffering mechanism against rapid change in genotype frequencies following random mating. A slight trend towards directional selection for higher yield (+6%) in the same landrace was not statistically significant. No disruptive or stabilizing selection was observed for any trait in either landrace.     

用基于遗传算法的BP神经网络识别牛肉肌肉与脂肪

利用遗传算法的全局搜索能力,改进标准BP算法随机选取初始权重的不足,并构建了3-12-1的三层遗传BP神经网络,进行了3次牛肉肌肉与脂肪像素的分类试验,研究用BP网络对牛肉肌肉与脂肪两类像素点进行识别的可行性。以像素点的RGB值作为BP网络输入向量,每次训练集样本数62,测试集样本数43。测试的最终结果为：训练集的样本识别率分别为100%、100%、98.3871%;对应测试集的样本识别率分别为97.6744%、97.6744%、100%。试验结果表明,尽管基于遗传算法的BP神经网络对训练样本集以及测试样本集的肌肉和脂肪的识别率均在97%以上,但由于牛肉图像像素值在颜色空间中比较分散,有利于聚类的规律性不明显,因而是否可用BP网络来完成肌肉与脂肪的识别,还需要在网络拓扑结构、训练样本集等方面进一步研究。     

Sulphur speciation and turnover in soils: evidence from sulphur K-edge XANES spectroscopy and isotope dilution studies

Sulphur K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to quantify S species in humic substance extracts from ten soils from the UK, China and New Zealand, which differ in land use and agricultural management. XANES spectroscopy showed the presence of most reduced (sulphides, disulphides, thiols and thiophenes), intermediate (sulphoxides and sulphonates) and highly oxidised S (ester sulphates) forms, with the three groups representing 14-32%, 33-50% and 22-53% of the organic S in the humic substance extracts, respectively. Land use had a profound influence on the relative proportions of S species. Well-drained arable soils generally had a higher proportion of organic S present in the most oxidised form than the grassland soils collected nearby, whereas paddy soils showed a more reduced profile due to episodic flooding. In the Broadbalk Classical Experiment at Rothamsted, reversion of an arable system to grassland or woodland in the 1880s resulted in an increase of the most reduced and intermediate S species at the expense of the most oxidised S species. Long-term applications of farmyard manure to an arable plot also shifted S species from the most oxidised to the intermediate and the most reduced species. Sulphur immobilisation and gross mineralisation were determined in seven soils using the ³⁵S isotope dilution method. Gross mineralisation during a 53-day incubation correlated more closely with the amounts of the most reduced and intermediate S species than with the most oxidised S species, suggesting that the former (C-bonded S) were the main source of organic S for mineralisation in the short-term.     

地下滴灌专用滴头的研制及初步应用

介绍一种既具有防负压堵塞性能又具备较佳压力补偿性能的地下滴灌专用滴头的设计思路和结构，通过室内试验，对滴头的防负压性、出流均匀性及压力—流量补偿关系等进行测试，并在田间进行实际应用考核。结果表明，这种滴头的结构不仅可以有效地防止因系统负压引起的滴头流道堵塞，同时滴头自身还具有良好的水力学性能。与传统的枣树穴灌方法对比，采用地下滴灌技术可节水约42%，增产26%，节水增产效果显著。     

Effects on some clay soil qualities following the passage of rubber-tracked and wheeled tractors in central Italy

There is increased use of rubber-tracked tractors for ploughing on clay soil (Vertic Cambisol) in central, south and insular Italy instead of metal-tracked tractors, because they allow travel on public roads. Field tests were carried out on arable soil previously ploughed and harrowed to compare two types of tractors, one rubber-tracked (CAT Challenger Ch 45) and one wheeled (New Holland 8770) in order to establish the compacting effects resulting from 1 and 4 passes of the tractors in the same track. The following parameters were studied: soil penetration resistance, bulk density and its increment ratio, soil shear strength, soil macroporosity and hydraulic conductivity. Multiple passes made by the two tractors induced very similar effects on the soil in regards to soil penetration resistance. Mean values of penetration resistance (0–0.20 m depth) were 1.15 MPa for the rubber-tracked tractor and 1.11 MPa for the wheeled tractor; mean values of penetration resistance (0.21–0.40 m depth) were 1.07 MPa for the rubber-tracked tractor and 1.17 MPa for the wheeled tractor. The decrease in macroporosity, in particular that of elongated pores in the soil surface layer (0–0.10 m depth) was greater in treatments involving the rubber-tracked tractor (from 20.2 to 2.7%) than for the wheeled tractor (from 20.2 to 10.3%). Following traffic of the two tractors, hydraulic conductivity decreased and the following values were found for the five treatments: control, 18.48 mm h⁻¹; wheeled tractor 1 and 4 passes, 11.15 and 7.45 mm h⁻¹, respectively; rubber-tracked tractor 1 and 4 passes, 3.25 and 1.1 mm h⁻¹, respectively. Highly significant correlations between shear strength and dry bulk density, and between hydraulic conductivity and elongated pores and total macroporosity were found. Significant linear relationships between macroporosity and penetration resistance for 1 and 4 passes of both tractors were found in the soil layers (0–0.10 m). A significant difference was found between tractors and for correlations of penetration resistance values above control values. However, in the soil layer (0–0.20 m depth), with respect to the higher degree of macroporosity and low values of penetration resistance, treatments involving wheeled tractor (1 pass) showed a lower degree of soil compaction than was observed after 1 pass of the rubber-tracked tractor.     

Replant diseases: Bacterial community structure and diversity in peach rhizosphere as determined by metabolic and genetic fingerprinting

Peach tree replant disease, though reported on in the literature for more than two centuries, has yet to have its causes clearly defined. Decline in peach productivity has been attributed to toxic agents, insects, nutritional disturbances, spray residues, fungi and nematodes. Bacteria has also been indicated as a contributing factor.Peach replant disease was reproduced by using two successive cultures on the same soil. Bacterial communities were isolated and characterized from healthy and diseased peach trees. The potential role of cyanide production by rhizobacteria in the replant problem of peaches was studied. Culture-dependent (evaluation of the number of culturable bacteria, metabolic activities, Biolog^® GN2) and independent (ribosomal intergenic spacer analysis, RISA) methods were used, in order to compare bacterial community structure and diversity in healthy and sick soils and to evaluate the possible role of cyanide.Bacterial densities were significantly increased in sick soils. Metabolic activities (Biolog^® GN2) and genetic structure, observed through RISA, were also significantly modified in sick soils. Changes in the composition of individual microbial groups in the rhizosphere of peach trees excavated from healthy or sick soil indicated the involvement of rhizobacteria in the etiology of the replant sickness of peach soil. More than 60% of the strains isolated from healthy soils corresponded to Pseudomonas sp. and 58% of the isolates from sick soils were Bacillus sp. This study determined that Bacillus were able to produce in vitro HCN. It also appeared that in sick soil, there was a shift in the structure of bacterial communities with an increase noted in phytotoxic microorganisms capable of producing HCN compounds.     

速生型刺槐遗传转化体系的建立

为获得稳定的转基因刺槐植株,以速生型刺槐叶轴为转化受体,对转化过程中的一些影响因素进行了探究,建立了较为完善的遗传转化体系。结果表明:继代20~35d之间刺槐叶轴最适宜转化;卡那霉素的筛选浓度为30mg/L;头孢霉素的抑菌浓度为200mg/L;合适的侵染时间是20min;30mg/L的乙酰丁香酮有利于抗性芽的发生;共培养2d对转化适宜;抑菌7d后再加选择压有利于抗性芽的产生。最后得到的抗性植株经PCR检测,初步证明外源目的基因OsDREB1已整合到刺槐基因组中。     

合成大豆异黄酮的植物基因工程研究进展

异黄酮主要存在于豆科植物中,是一种具有广谱抗菌活性的黄酮类物质。结合本课题组的工作,综述以基因工程的方法在植物内合成异黄酮的研究历史与进展,重点深入分析和讨论异黄酮生物合成所受到的分子调控。     

分形理论在土壤肥力研究中的应用与前景

分形理论的提出对于定量描述复杂的、高度不规则的系统特征与机理提供了方法.本文从土壤腐殖质、土壤微生物、土壤团聚体等方面回顾了分形理论在土壤肥力研究中的主要结果:土壤腐殖质胶体在不同条件下形成不同分形特征的聚合物;同一种微生物可能形成具有不同分形特征的结构;土壤中的有机无机胶体在不同条件下凝聚成不同的团聚体,从而形成不同的土壤结构并对其肥力功能产生影响.我们认为分形理论在探索土壤的形成过程和肥力功能上将具有重要的应用前景:如团粒结构体的形成可能是由土壤胶体分形凝聚而成;土壤中的活性有机质有逐渐老化的现象,可能和腐殖质胶体由结构疏松的分形结构向普通团聚体过渡的过程有关;土壤微生物在不同微环境下具有不同的分形特征,可以推测在各种土壤过程(包括物理、化学以及生物化学过程)中它们的功能也可能是不一样的.此外,土壤结构的开放程度决定孔隙、水分以及空气的分布,从而决定了微生物的生存空间.所以土壤结构体对微生物空间分布的影响也是将来该领域值得研究的内容之一.     

有机化工废弃物的土地处理研究

本文对三种供试工业废弃物，经土地处理后表明，发光细菌毒性明显降低，有的废渣处理物毒性已消除；Ａｍｅｓ试验和发光细菌自发暗变种的遗传毒减弱，由阳性下降为阴性，或阳性程度明显减弱。