Using laser to measure stem thickness and cut weed stems

Summary Stem thickness of the weed Solanum nigrum and the crop sugarbeet was determined with a He–Ne laser using a novel non‐destructive technique measuring stem shadow. Thereafter, the stems were cut close to the soil surface with a CO₂ laser. Treatments were carried out on pot plants, grown in the greenhouse, at two different growth stages, and plant dry matter was measured 2–5 weeks after treatment. The relationship between plant dry weight and laser energy was analysed using two different non‐linear dose–response regression models; one model included stem thickness as a variable, the other did not. A binary model was also tested. The non‐linear model incorporating stem thickness described the data best, indicating that it would be possible to optimize laser cutting by measuring stem thickness before cutting. The general tendency was that more energy was needed the thicker the stem. Energy uses on a field scale are discussed.     

Identification of ALS inhibitor‐resistant Amaranthus biotypes using polymerase chain reaction amplification of specific alleles

Summary Polymerase chain reaction (PCR) amplification of specific alleles (PASA) was adapted as a molecular marker‐based method for the rapid detection of point mutations in Amaranthus retroflexus and Amaranthus rudis leading to ALS inhibitor resistance. Two pairs of primers were designed for the specific amplification of alleles of the ALS gene of susceptible and resistant biotypes. The allele‐specific primer matched the desired allele, but mismatched the different allele at its 3′ end. Differentiation was carried out by comparison of the amplified DNA fragments in gel electrophoresis after PASA‐PCR. In A. rudis, differentiation was possible with one PCR and genomic DNA as probe. A ‘nested’ PCR was necessary for the differentiation of sensitive and resistant A. retroflexus. PASA is useful for the identification of resistant weed biotypes and also as a monitoring tool to map resistance occurrence and distribution. Advantages include the fast and clear separation of those plants with and without mutations at an early stage of development, its easy and consistent performance and quick results compared with existing resistance detection tests. These advantages, when combined with management strategies, enable further activities to reduce herbicide resistance.     

A reactive pattern of ischemia-induced nestin protein in the rat brain

AIM:To explore the expressive profile of nestin protein in the focal ischemic brain and to study the recovery mechanism of brain focal infarct.METHODS:Cellular morphology,time-course and distribution pattern of nestin positive response were immunohistochemically examined in different brain regions of 36 adult male SD rats. RESULTS:Nestin positive response of different brain regions in sham operated rats was present in small- and micro-vasculartures and the third ventricle bottom and ependyma. A large number of nestin positive cells were detected in ischemic brain, and were more remarkable in the cortical areas of parietal lobe and preoptic area as well as ischemic caudoputamen. Stellate nestin positive cells were located in the deep layer of ischemic cortex, but fibrillary cells were located in the shallow layer. Nestin positive cells in the ischemic caudoputamen showed the same changes of morphology as those cells in the deep layer of ischemic cortex. Morphological and number alterations of nestin positive cells were the most remarkable at 1 weeks post-ischemia, which showed more hypertrophy and proliferation in morphology, and a marked increase in number was present in the ischemic cerebral cortex and the ischemic caudoputamen. These alterations of nestin positive cells persisted up to 6 weeks post-ischemia, and then, the nestin positive response in the ischemic brain decreased gradually.CONCLUSION:Focal cerebral ischemia induces nestin re-expression on reactive astrocytes, which may be very important to the self-recovery of cerebral infarct.     

松口蘑的研究热点

揭开松口蘑与松科植物的共生关系，开发松口蘑的人工栽培技术已成为国际性的松口蘑研究课题。近年来，日本、瑞典、美国、韩国和新西兰等国的研究人员为鉴别松口蘑及其近缘种提供了有效的分子生物学手段，从形态解剖学、生理学上验证了松口蘑是典型的外生菌根菌的理论，同时也提出了松口蘑-宿主是一个动态的共生关系。松口蘑快速人工菌根的合成体系已经建立，为松口蘑人工子实体的诱导奠定了不可缺少的基础。这一领域的研究必将与植物学、菌物学和土壤学的研究紧密地结合起来，以共同开发松口蘑的人工栽培技术。     

非自然越夏区小麦白粉病模拟鉴定病圃

作者于1990～1995年根据陕西省关中麦区小麦白粉病侵染循环特点,人工模拟自然发病条件,在非自然越夏区杨陵(省农科院试验地)成功地建立起白粉病菌可周年存活,且秋、春季均能充分诱发感染的混合菌系病圃,宜对小麦种质材料进行全生育期抗白粉病鉴定。利用该病圃已对陕西省1000余份小麦品种(系)及部分国内外抗源亲本材料做了抗病性鉴定和利用评价。     

丙硫磷控制稻瘟病的作用方式及应用技术

经１９９３－１９９５年生物测定和田间多点试验示范发现；１．丙硫磷对稻瘟菌孢子萌发和附着胞形成有显著的抑制活性，ＥＣ５０为１０３．３ｍｈ／Ｌ，５００ｍｇ／Ｌ的抑菌率达９６．２％；２．丙硫磷１０００ｍｇ／Ｌ对水稻苗叶瘟和穗瘟的预防效果分别为７９．４％和９０．７％，治疗效果分别为３９．３％和４１．８％；３丙硫磷６００－９００ｇ／ｈｍ＾２防治双季稻和瓜后稻穗瘟病的田间小区效果分别为７０．８％－８０．２％和     

Neurospora crassa对三唑醇的抗药性分子机制研究

 通过紫外光诱变获得Neurospora crassa对三唑醇杀菌剂抗性突变体"Nc70"。用2.5μg/ml三唑醇处理,突变体内甲基甾醇与脱甲基甾醇比例变化幅度远远小于亲本敏感菌株"STA"。突变体对三唑醇的吸收能力与敏感菌株相似,但药剂在体细胞内积累较少。三唑醇处理N.crassa 2 h后,药剂在菌体内的含量趋向稳定,突变体内的药量较敏感菌体低56.1%,而麦角甾醇合成量则高于敏感菌株53.7%。     

盐池半荒漠风沙区土地沙漠化发生发展规律的研究

本文耐盐池半荒漠风沙区土地沙漠化发生发展规律进行了探讨，主要分析了在土地沙漠化的过程中土壤和植被的变化过程及其成因。     

稀土对刺槐苗木生理特性影响的研究

稀土对刺槐苗木生理特性影响的研究赵兰勇，梁玉堂（山东农业大学林学院泰安２７１０１８）王九龄（北京林业大学北京１０００８３）关键词稀土，刺槐，光合速率，叶绿素含量，水分利用效率，矿质元素含量近年来，稀土元素在农业上的应用研究越来越受到人们的重视，并且已...     

山羊高床舍饲配套饲养技术探讨

山羊高床舍饲技术通过修建标准化山羊圈舍，实现山羊饲养过程中对山羊个体的有效控制和辅助，降低饲养劳动量和劳动强度；通过带动种草养羊、养羊与沼气结合，在实现山羊饲养的同时，促进了退耕还草、封山育林等生态建设项目的实施。