Morphological characterization of seeds of three Australian wild Citrus species (Rutaceae): Citrus australasica F. Muell., C. inodora F.M. Bailey and C. garrawayi F.M. Bailey

The comparative morphology of the seeds of three Australian Citrus species, C. australasica C. inodora and C. garrawayi, was studied. Their seed characteristics were broadly similar to those of the cultivated species of the genus, when observed under light and scanning electron microscopy. Citrus garrawayi differed in seed shape (rounded to triangular) and seed coat morphology (i.e., thicker with longer epidermal protrusions) from C. australasica and C. inodora (rounded surface with flat underside in shape). The well-developed minute epidermal protrusions on the seed coat of C. garrawayi were more similar to those in the cultivated species, C. × sinensis and C. × aurantium. In contrast, the surface topography of C. australasica and C. inodora seeds was more like that of the cultivated species, C. × aurantifolia and C. × limon. Seed morphology, especially surface topography, was found to be a useful tool for taxonomic identification in Australian wild citrus.     

Diversity, distribution and management of yam landraces (Dioscorea spp.) in Southern Ethiopia

Yam (Dioscorea spp.) is widely grown in many parts of Ethiopia and plays a vital role in local subsistence. Nevertheless, its diversity has not been studied in detail. A survey covering 339 farm households and eight districts was conducted in the major yam growing regions of Southern Ethiopia to investigate the diversity and distribution of yam landraces using structured and semi-structured questionnaires. A total of 37 named landraces were recorded, with a range from one to six (mean 2.9) on individual farms. Farmers’ decisions regarding the number and type of landraces maintained was influenced by tolerance of the landraces to drought, their maturity time and market demand. Most landraces had limited abundance and distribution, and only a few dominant landraces were widely grown. There was also variation amongst districts with respect to diversity, distribution and abundance of the landraces found. In the majority of the localities surveyed, farmers reported a decreasing trend in the number of landraces maintained on individual farms and in the overall yam production. Besides, in those limited areas where yam production is expanding, farmers are increasingly relying on a few selected landraces that mature early. Findings of this study suggest that local farmers in Wolayita and Gamo-Gofa zones maintain considerable yam diversity that remains to be further explored for sustainable utilization and conservation of the available genetic resources.     

Isozyme polymorphism and genetic differentiation in natural populations of an endemic tetraploid species <Emphasis Type="Italic">Avena maroccana</Emphasis> in Morocco

A wild tetraploid oat Avena maroccana Gdgr. was collected from the 11 populations in the periphery of Rommani and Casablanca geographic groups of Morocco. Genetic diversity of the species was investigated using six allozyme systems. Allelic frequencies were scored representing eight polymorphic and five monomorphic loci. Coefficient of gene differentiation (Gst) was 0.3019, which indicated great genetic differentiation. The number of alleles per locus was 2.6154, the percentage of polymorphic loci was 61.54, and the expected heterozygosity was 0.2462 in all populations. Genetic diversity in A. maroccana was high in comparison to self-pollinated species. In total, nine heterozygotes resulting from outcrossing were found in the progeny from M1, M3, M4, M22 and M26. The population of M7 had peculiar alleles Pgd–2SS and Pgd-1SS in high frequency. M9 had the lowest level of diversity out of the 11 populations. Geographic and genetic distances between all the populations were not significantly correlated with each other (r = 0.0996). Cluster analysis showed that two groups, (M1, M22, M2 and M4) and (M3, M23, M8, M5 and M26) were apparently differentiated. Two populations of the Casablanca group, M7 and M9 were independent from each other, and were separated distinctly from the other populations. Genetic diversity of the Rommani and Casablanca groups was almost the same in all the parameters. This was due to the similar man-made habitat such as roadside or rich fertile soil and brown clay soils. The population size of A. maroccana was small and restricted to the narrow central Morocco with great genetic differentiation so that genetic diversity may be reflected from the results of genetic drift and outcrossing heterozygote segregation.     

基于Landsat TM的西安地区土地利用变化与图谱研究

利用两期TM影像,通过遥感与GIS技术．结合景观生态学理论和地学信息图谱理论,深入分析了10a来西安地区土地利用变化的数量和空间特征以及由此所引起的一系列生态环境效应。研究区城镇建设用地面积显著增加．水体、耕地、林地面积呈减少趋势。城镇建设用地的增加是以侵占大量农田为代价的。景观破碎度变大,形状趋于复杂．优势度降低,多样性和均匀性增大,景观类型有向多样性或均衡化方向发展的趋势。景观的匀质化发展降低了景观抗干扰的能力,同时导致景观稳定性降低。分析表明,研究区内土地利用变化以各类型转化为城镇建设用地的趋势最强,在一定程度上显示了研究区正处于城市化的快速阶段。     

血液细胞图像分割方法综述

图像分割是图像处理的基础,是图像工程技术中的一个重要问题。本文简单介绍了图像分割的原理,系统地回顾了血液细胞图像分割的方法并进行了讨论。近年来,人们越来越重视血液细胞图像的分割算法,并期望寻求一种实时性、鲁棒性较好的算法。     

多作物收割机割台的设计与试验

针对作物收获时农机具利用率低且存在因振动造成割台损失大、工作稳定性差等问题,以4LZ–3.2型水稻联合收割机为研究对象,设计一种面向水稻、玉米、大豆联合收割的多作物割台,确定割台伸缩、接穗板及连杆机构的具体参数,开展割台振动试验和田间收获试验。通过增设液压缸伸缩机构和基于连杆联动的接穗板变换机构来满足多作物收割要求,理论分析确定玉米收获时割台伸缩长度为200 mm;接穗板的折角为15°、总长为300 mm、宽度为30 mm、折起长度为135 mm、厚度为5 mm;连杆Ⅰ长度为330 mm,连杆Ⅱ长度为70 mm,拉杆长度为530mm,转动杆长度为510mm;部件所用材料均为Q235钢板。振动试验结果表明：在发动机低转速(1800 r/min)时割台振动以收割机共振为主;高转速(2600 r/min)时以振源影响为主,其中切割器的往复运动是主要振源;物料流的喂入对割台不同位置的振动强度受挠度影响很大,而喂入量的变化对割台振动影响不大。可见,所设计割台损失较通用收割机割台变化不大。田间收获试验表明：收割机行驶速度为0.6～1.4 m/s时,收割机收获水稻、玉米、大豆时的割台损失率平均值分别...     

宁夏春小麦品种农艺性状遗传多样性 调查试验

本试验通过对宁夏近40年选育的63个春小麦品种（品系）试验材料进行调查分析,结果表明,在生长正常情况下,春小麦品种（品系）间遗传变异系数和遗传多样性指数都相对较低,宁夏育成春小麦品种（品系）农艺性状遗传多样性与外省份相比,水平偏低。     

玉米根系对玉米抗倒伏性影响的研究进展

【目的】研究玉米根系对玉米抗倒伏性的影响,为筛选出抗倒伏性优良、产量高的玉米品种提供理论依据。【方法】本文通过国内外玉米根系对玉米抗倒伏性的影响研究专题进行了归纳总结,从玉米根系的三维图像构建、生长发育质量、延伸形态、抗倒伏指标和遗传性状,对影响玉米抗倒伏重要因素之一的根系性状进行系统的综述。【结果】随着技术的进步构建玉米根系三维模型正逐步应用到实际操作当中,为研究人员提供便利;玉米初生根、次生根、气生根生长发育优良的品种,极大提升了玉米抗倒伏性;横展型根系是玉米理想的抗倒伏根系延伸形态;根干重、根系开张角度、入土次生根条数、根体积、根直径、根层数是大多数学者选用的根系抗倒伏指标;目前常用QTL与GWAS技术对根系基因进行分析,定位了初生根直径、初生根长度、总根长、根尖数等一些根系相关的QTL,筛选出气生根直径、气生根角度等气生根性状相关联的SNP位点。【结论】明确玉米抗倒伏根系的优良性状并用现有的技术对其加强表达,是增产的重要手段。