Two in vitro assays to evaluate resistance in Linum usitatissimum to Fusarium wilt disease

Two types of in vitro seedling tests were developed to evaluate resistance in flax (Linum usitatissimum) against Fusarium oxysporum f.sp. lini. In the first test a solid medium was used. The second test was based on a liquid medium. Disease severity was assessed after three weeks, using the observed reduction of plant length as a scale. Both methods proved to be useful for screening for resistance, for evaluating race specificity of resistance and for studying symptomatology. The solid medium method proved to be the more accurate for the screening, but the liquid medium method was much less time- and labour-consuming. The results of the tests were significantly correlated with observations under field conditions.     

Inoculation of cucumber roots with zoospores of mycoparasitic and plant pathogenic Pythium species: Differential zoospore accumulation, colonization ability and plant growth response

Hydroponically grown cucumber (Cucumis sativus) seedlings were inoculated with zoospores of 1 mycoparasitic (Pythium oligandrum) and 2 pathogenic (Pythium aphanidermatum and Pythium group F) Pythium spp. During the first 2 days after inoculation, all the Pythium spp. caused reduction in the root length. However, roots treated with Pythium oligandrum quickly reached the length of the control and on the 8th day, and for the rest of the experimental period, stimulation of root elongation was noted. Pythium oligandrum was not pathogenic on cucumber and no differences in the fresh weights of control and Pythium oligandrum inoculated plants were observed in the course of the experiment. Pythium group F and Pythium aphanidermatum were pathogenic on cucumber seedlings, but their pathogenicities differed. Thus, while Pythium group F had a constant, negative influence on root length and plant growth, measured as fresh weight, Pythium aphanidermatum caused generalized necroses of the root system, inhibiting consistently root elongation and plant growth and finally causing plant death. Moreover, the zoospores of 2 mycoparasitic species, Pythium oligandrum and Pythium periplocum, were not attracted to roots of cucumber and accumulated on the roots in very low numbers compared to those of the pathogenic species, Pythium aphanidermatum, which were strongly attracted and accumulated in large numbers. Finally, it was also found that Pythium oligandrum colonized the roots very poorly, while Pythium group F and Pythium aphanidermatum were significantly better root colonizers. The significance of these findings is discussed in relation to the ecology of Pythium species and biocontrol.     

罗布泊南部野双峰驼的分布与环境

在１９９５－１９９６年两年调查的基础上,我们又利用家驼队深入荒漠腹地,考察了罗布泊南部野双峰驼的分布和栖息环境,结果表明在罗布泊南部的湖岸区,阿尔金山北麓及山前丘陵地带均有野驼分布,库姆塔沙漠中部无野驼进入,但其西侧戈壁及丘间谷地为野驼南北迁徒的通道,冬季野驼主要集中活动在科什兰孜等罗布泊南岸及阿奇克谷地;夏季主要在山区北麓活动,所以应将该区域与上述分布区同归于一个分布区整体,即南北配置的景观复合     

塔克拉玛干沙漠腹地纵向沙垅表面沙物质粒度特征

本文对塔克拉玛干沙漠腹地纵向沙垅表面沙粒、丘间地沙粒进行了粒度分析。结果表明,沙垅以极细沙为主,平均粒径３．０６Φ,沙粒从沙垅迎风侧到背风侧逐渐变细。沙丘沙比丘间地沙分选好,沙垅背风侧比迎风侧分选好。沙粒属极负偏,偏度－０．２２,丘间地沙比沙丘沙更趋向负偏。峰度１．３８,属尖峰态。粒径与偏度和峰度成正相关,分选和偏度成良好负相关。沙丘沙以单峰态为主,累积频率曲线为２～３段式,丘间地以双峰态为主,累积频率曲线为３～４段。大尺度地形对沙粒段式没有影响,对各段组分含量相对大小有影响。     

西北地区沙尘暴的危害及对策

该文以大量的例证,详实的数据介绍了西北地区沙尘暴的危害,并综合分析了沙尘暴产生形成原因、危害方式,为保护生态环境提出了治沙防沙的基本对策。     

TM影像VI提取植被信息技术研究

应用规一化植被指数（ＮＤＶＩ）、土壤调节植被指数（ＳＡＶＩ）和修正后的土壤调节植被指数（ＭＳＡＶＩ）,研究了ＴＭ影像植被信息的提取技术。结果表明,ＳＡＶＩ较之ＮＤＶＩ和ＭＳＡＶＩ,消除土壤背景影响和适应植被密度变化的能力更强,是植被信息提取效果较好的植被指数。使用ＳＡＶＩ,关键是要确定一个合适的土壤调节参数Ｌ,以最大限度地消除土壤背景的影响,ＳＡＶＩ提出时推荐的最佳Ｌ值（０．５）应用于卫片处理有很大局限性;基于研究结果,本文给出了适于不同植被条件卫片处理的最佳Ｌ取值。     

地学空间数据聚类方法研究

本文介绍了地学空间数据迭代聚类的算法原理。根据类别分离度在线性映射变换下的不变性,用Ｋ－Ｌ变换进行地学空间数据的特征提取。在特征空间上两类分布的分离度只依赖于特征值最大和最小的两个特征向量,且其大小依赖于上述两个特征值与某个定值的偏差。据此可设计一个迭代过程,使分类后样本集的特征值都尽可能趋近某个定值,从而达到最佳分类结果。用该算法对乌鲁木齐河流域土壤类型进行了分类研究,取得了较好的效果。     

柴达木盆地资源开发与经济社会发展

柴达木盆地是中国著名的“聚宝盆”,以盐湖资源、石油天然气、有色金属和多种非金属为主体的矿产资源十分丰富,水土资源开发潜力亦较大。本文分析了柴达木盆地的资源优势,论述了资源开发利用方向,指出了资源开发同盆地经济和社会发展的关系。     

柴达木盆地水资源与合理开发利用研究

本文通过对柴达木盆地水资源量、农业水资源开发利用现状分析,结合盆地水土资源匹配情况与经济发展方向,提出了实现盆地水资源合理开发利用的基本途径,并指出在实施水资源开发利用中所要注意的具体问题,为盆地可持续发展提供依据。     

河西人口与绿洲资源、环境、经济发展研究

本文在考察了河西绿洲人口与绿洲发展历史演变的基础上,重点分析了当前河西绿洲人口的数量与质量压力及其掠夺式开发利用资源所伴随的土地承载力负荷过大,人口与水土资源矛盾突出、人口与绿洲环境、人口与社会经济发展之间的负反馈等危及河西绿洲可持续发展的重大问题,并提出了处理好当前河西人口与绿洲资源开发利用、环境保护、社会经济协调发展的几项具体措施。