Some Physiological Aspects of Bacterial Wilt of Forage Grasses Caused by Xanthomonas campestris pv. graminis

The effect of host-plant age, environmental humidity and temperature on the development of the wilting disease of Lolium perenne L., caused by Xanthomonas campestris pv. graminis, was examined. Very young plants were more resistant than older ones. Dry and warm conditions favoured the development and expression of the disease symptoms. Losses in yield were observed under several environmental conditions.     

Prevention of Bacterial Wilt of Grasses by Phylloplane Bacteria

Various chromogenic bacteria were isolated from the mowing site in natural and sown meadows and in pastures. Their ability to protect young ryegrass plants from wilt by simultaneous inoculation with Xanthomonas campestris pv. graminis was tested under low concentrations of the parasite inoculum. From about 200 isolates tested 35% had a very high protective effect, 45% a moderate one, and only 20% had no significant effect. Mixtures of different species of phylloplane bacteria usually gave very good protection. Most of these bacteria live between the leaf-sheaths. In vitro antagonism of the phylloplane bacteria was not related to their protective effect. Avirulent mutant strains of X. c. pv. graminis and pathovars, of other grass species, e.g. pv. poae, pv. phlei, and pv. arrhenatheri, have the same protecting effect. Heat killed bacteria were no longer effective. These observations suggest an unspecific reaction of the plant, such as the induction of a general defense mechanism which results in resistance also to the parasite.     

Some Optical Properties of Leaves of Eight Temperate Forage Grasses

Two instruments are described for the measurement of the reflectionand transmission of radiation by grass leaves. The first ofthese was used to measure the spatial distribution of reflectedand transmitted light. It was demonstrated that reflection wasinfluenced by the epidermal structure of a leaf, and that theimportance of this layer increased with increasing angle ofincidence. The second instrument was used to compare the reflectance andtransmittance of leaves of different ages taken from eight temperategrasses. There were significant differences between the grassesin leaf transmittance, and generally the young emerging leafhad a greater transmittance than the fully-expanded leaves.The differences in leaf transmittance could be related to differencesin specific leaf weight. There were no significant differencesbetween the species and varieties in leaf reflectance.     

Sodium Absorption and Distribution in Forage Grasses of Different Potassium Status

The absorption and distribution of sodium were examined in threegrasses grown in flowing solution culture with different suppliesof potassium. There were marked differences between the speciesin the rate of absorption by their roots, timothy absorbingat a much slower rate than either ryegrass or cocksfoot. Inall species, the rate of Na absorption was greatest when therewas a maintained supply of K and/or when the K contents of theplants were high. Transport of Na from roots to shoots of timothywas restricted; it was less restricted in the other speciesand large proportions of the Na moved from roots to shoots whenK was not supplied to the plants. Sodium transported from theroots accumulated in old leaves and not in the younger leaves.When K was no longer supplied, the growth of ryegrass was maintainedin the plants previously grown with Na plus K; Na supplied insteadof K, however, did not maintain growth. Cocksfoot grown withNa grew less well than when grown without Na when plants wereno longer supplied with K; the growth of timothy was unaffectedby Na. Dactylis glomerata L., Lolium perenne L., Phleum pratense L., cocksfoot, ryegrass, timothy, absorption of ions, distribution of ions, potassium, sodium     

Canopy Photosynthesis and Crop Growth Rate of Eight Temperate Forage Grasses

The rates of canopy and individual leaf photosynthesis, ratesof growth of shoots and roots, and the extinction coefficientfor light of eight temperate forage grasses were determinedin the field during early autumn. Canopy gross photosynthesiswas calculated as net photosynthesis plus dark respiration adjustedfor temperature using a Q₁₀ = 2. The relationships between canopygross photosynthesis and light intensity were hyperbolic, andthe initial slopes of these curves indicated that light wasbeing utilized efficiently at low light intensities. The initialslope depended on the distribution of light in the canopy andthe quantum efficiency of the individual leaves. The maximumrate of canopy gross photosynthesis reflected the maximum rateof individual leaf photosynthesis. Although the maximum rateof canopy gross photosynthesis was correlated with crop growthrate, there was no significant relationship between daily grossphotosynthesis and crop growth rate. Indeed, daily gross photosynthesisvaried by only 22 per cent, whereas the daily growth of shootsand roots varied by 120 per cent. This poor correlation is influencedby a negative correlation (P < 0.01) between the maximumrate of canopy gross photosynthesis and the initial slope ofthe curve relating canopy gross photosynthesis and light intensity.Difficulties in the interpretation of measurements of dark respirationappeared to confound attempts to relate daily net photosynthesisto crop growth rate, individual leaf photosynthesis, and theextinction coefficient for light.     

The Effects of Temperature upon Seed Development in Three Species of Forage Grasses

The effects of three temperature regimes, 25°C day/20°Cnight, 20°C day/15°C night and 15°C day/10°Cnight upon seed development in S.22 Italian ryegrass, S.24 perennialryegrass, S.215 meadow fescue and a Swiss ecotype of meadowfescue were investigated. The largest ovaries and largest seedswere obtained from the 15/10°C environment and floret fertilitywas greatest at 20/15°C. The largest seed weight per inflorescencewas at 20/15°C, except for the Swiss ecotype of meadow fescuewhere it was greatest at 15/10°C. The percentage germinationwas highest from those seeds developed at 25/20°C and thiswas particularly marked at germination temperatures of 13–20°C.There was a low rate of germination of seeds from the 15/10°Ctreatment, but they produced seedlings with the largest dryweights. It is concluded that year to year temperature differenceswill affect the yield and quality of seed crops of forage grasses.     

A Mechanical Viewing Aid for Microscopical Examination of Convoluted Leaf Surfaces of Forage Grasses

An inexpensive instrument is described which allows all aspectsof the convoluted leaf surfaces of certain forage grasses tobe viewed and measured microscopically, using optic fibres.The instrument fits on a standard microscope stage and allowsup to x40 objectives to be used. Key words: Microscope, Leaf surface, Grasses     

Biological Control of Bacterial Wilt of Bean Using a Bacterial Endophyte, Pantoea agglomerans

Indoor studies were conducted to determine the potential use of Pantoea agglomerans isolate LRC 8311 as a biocontrol agent for control of bacterial wilt of bean caused by Curtobacterium flaccumfaciens pv. flaccumfaciens. Soaking seeds of great northern bean cv. US1140 in a suspension of 3 × 10⁸ cfu/ml P. agglomerans resulted in thorough endophytic colonization of the entire bean seedling from root to apical stem after 7 days, regardless of whether the inoculated seeds were hilum injured or not. Colonization of seedlings by P. agglomerans increased seedling height after 10 days, and had no negative effect on seedling emergence. Treatment of hilum‐injured bean seeds of great northern bean cv. US1140 or navy bean cv. Morden003 with a mixture of P. agglomerans + C. flaccumfaciens pv. flaccumfaciens resulted in a high rate of colonization of seedlings by P. agglomerans, reduced frequency of infection by C. flaccumfaciens pv. flaccumfaciens, improved seedling emergence and height, and reduced disease severity, compared with seeds treated with the wilt pathogen alone. Application of P. agglomerans as a soil drench 24 h after planting was also effective in suppressing bacterial wilt in some instances, but was generally not as effective as seed treatment. The study suggests that seed treatment with P. agglomerans may be an effective and practical method for control of bacterial wilt of bean.     

A Schedule Including Cold Treatment to Facilitate Somatic Chromosome Counts in Certain Forage Grasses

Pretreatment at low temperature of root tips of grass grown from tillers in small beakers was found to contract somatic chromosomes and thus facilitate determination of chromosome number. A modification of Randolph's infiltration and card technics has been adapted to working with root tips from large numbers of plants.     

Isolation and Characterization of Dinitrogen-Fixing Bacteria from the Rhizosphere of Temperate Cereals and Forage Grasses

N₂(C₂H₂)-fixing bacteria were isolated from the rhizosphere of various cereals and forage grasses grown in the greenhouse and from the rhizosphere of field-grown wheat in Sweden. All 46 isolates from the greenhouse plants lost their nitrogenase activity during purification. By imposing a stronger selection pressure, we obtained pure isolates with nitrogenase activity from field-grown wheat. Some isolates were identified as Enterobacter agglomerans and Bacillus polymyxa, but several bacteria of uncertain taxonomy also occurred. One of the isolates grew and reduced acetylene only in the presence of other bacteria or certain vitamins. Species of Azotobacter or Azospirillum could not be isolated from the rhizosphere of any of the cereals and forage grasses studied.     

子宫内膜与细菌L型感染

本文报道41例宫腔刮出物的病原微生物培养,其中子宫异常出血和早孕胎盘组织各15例,月经紊乱6例和不孕症5例。19例细菌培养为阳性(46.35),19例中之7例为细菌兼有 L 型感染,8例为单纯 L 型感染,3例为解脲脲原体和1例 G~ 厌氧球菌感染。L 型菌落呈典型“油煎蛋”样或颗粒样。子宫内膜和胎盘组织切片的细菌学检查发现大量 L 型巨形体、圆球体和长丝体。作者认为在妇产科范围内,细菌 L 型和解脲脲原体感染并非少见,可能是子宫异常出血、月经紊乱、不孕症和流产的重要原因之一。L 型的形成与抗生素治疗及体内因素的诱导有关。在治疗 L 型感染过程中,药物的选择很重要。     

植物青枯病菌环介导等温扩增快速检测技术研究

为实现植物青枯病的早期诊断,需要建立一种适于田间快速便捷检测青枯病菌的方法。以细胞色素C基因为靶标设计一套特异性引物,建立了植物青枯病的LAMP检测方法。此方法最低检测极限为1 pg,可在1 h内完成,不依赖昂贵复杂的仪器,结果可经肉眼观察。利用此方法,在人工接种发病的茄子、番茄、花生、芝麻和凹头苋茎部浸出液和马铃薯病薯块茎组织液中均检测出青枯病菌的存在,尤其适用于田间疑似罹病的芝麻、花生、番茄、马铃薯和甘薯等植株的检测,且LAMP法的检出率远高于PCR法。应用LAMP技术检测青枯病菌快速高效、特异性强、灵敏度高,操作简单,适于在基层推广运用。     

应用RAPD分析技术研究生姜青枯病的土壤防治

利用随机扩增多态性技术(RAPD)研究生姜连作地、施加有机肥后的生姜连作地及新开地中土壤微生物多样性与生姜青枯病的关系, 结果发现, 连作地的青枯病发病率为100%, 新开地没有发病, 而施加有机肥的连作地生姜青枯病发病率降至37%。发现施加有机肥连作地的真菌、放线菌数量增加, 平板上不同菌落形态的真菌、细菌、放线菌增加明显。多样性指数分析发现Shannon指数、Simpson指数等均显著增加。随机扩增条带出现连作地的条带丰富度较少、新开地的条带最多、施加有机肥连作地的RAPD条带明显多于连作地, 接近新开地, 并出现了一些连作地没有的特异条带。结果表明, 施加有机肥可以改善土壤微生物群落结构。     

辣椒种质资源抗青枯病的鉴定与评价

采用青枯菌FJC100301菌株对田间辣椒（Capsicum annuum）抗病品种76a和感病品种TW-1分别作了不同温度、不同接种量和不同接种方法的接种试验。结果表明,辣椒青枯病抗性的室内鉴定以接种温度28℃、浸根20 min和3×10^8cfu/mL接种浓度为宜;辣椒种质田间抗青枯病接种鉴定宜选择5月上旬进行,浸根20 min,接种浓度为3×10^8cfu/mL。采用田间抗性接种鉴定的方法,用青枯菌FJC100301菌株对106份辣椒材料进行了抗性鉴定。田间接种后每隔10 d统计病情指数,划分辣椒抗青枯病鉴定分级标准,获得了高抗材料14份、抗病材料8份、中抗材料23份、中感材料23份、感病材料20份、高感材料18份;采用离体叶片接种法对田间筛选得到的高抗和高感纯度较高品种进行抗性分析,结果与田间鉴定一致。     

不同品种(系)牧草镉修复能力综合评价

该研究选用3种高丹草、2种苏丹草、2种杂交狼尾草、一年生黑麦草和多年生黑麦草共9个牧草品系,采用盆栽试验,设置0(CK)、10(Cd10)、20 mg/kg(Cd20)镉胁迫处理,考察不同品系的生长指标、镉含量和富集指标,运用极差化法和主成分分析建立综合评价模型,通过计算各牧草在模型中的综合得分,筛选出最适宜实地修复的牧草,探究不同品种和不同品系牧草的镉修复能力差异,建立Cd污染土壤植物修复能力评价体系,发掘兼顾富集量和后处理的镉污染土壤植物修复资源。结果表明:(1)镉胁迫会不同程度降低牧草的株高和生物量,其中江苏苏丹草在Cd10和Cd20中的耐胁迫能力均较强;(2)在Cd10和Cd20处理下,一年生和多年生黑麦草均具有较高的地上部和地下部Cd含量,高丹草的3个品系在Cd含量和Cd积累量两方面存在较大差异;(3)在Cd10和Cd20处理下,高丹草和黑麦草的富集指标表现优异,且富集指标在高丹草品系间存在较大差异;(4)2个镉质量分数处理下综合评价得分最高的均是一年生黑麦草,其次为高丹草。研究表明,参试牧草对镉胁迫均有较强的耐受性,但耐受能力和富集能力在品系间存在明显差异,并以高丹草品系间差异最大;一年生黑麦草能耐受20 mg/kg以下镉胁迫,且生物量较小,对镉有较强的浓缩效应,可作为镉污染土壤实地修复的可靠材料;综合评价模型可作为镉污染修复植物资源筛选的可靠方法。     

细菌尿素酶的生化和分子生物学特点

尿素酶属于镍金属酶,能够分解尿素成氨和二氧化碳.细菌尿素酶在氮素循环和致病性方面有重要的作用.本文讨论了细菌尿素酶的生物化学和分子生物学性质,并就尿素酶的活化和调控方式以及生物学效应进行阐述.