Effects and side effects of penicillin injection in huanglongbing affected grapefruit trees

Trunk injection with penicillin has been tested to control citrus huanglongbing (HLB), but side effects and environmental safety must be assured before approval of penicillin injection can be considered. We investigated effects of penicillin injection on densities of Candidatus Liberibacter asiaticus (Las) in leaves, as well as culturable bacterial populations in rhizospheres and petioles of grapefruit trees in field and greenhouse experiments. Trees were injected with penicillin G, and leaf and root concentrations were assessed in bioassays with Bacillus subtilis. Las densities were determined by qPCR, and bacteria were isolated on a low carbon medium from roots plus rhizosphere and surface-sterilized petioles at various times after penicillin injection. Selected bacterial isolates were tested for penicillin resistance (20 μg/mL) and glyphosate resistance (7000 μg/mL), because glyphosate is widely used and cross-resistance against antibiotics had been documented. One month after penicillin injection half of the greenhouse trees were inoculated with Phytophthora nicotianae. Cycle threshold (Ct) values of Las in old and young leaves significantly increased 90 days after trunk injection with penicillin. Bacterial populations in petioles and root-rhizospheres initially increased after penicillin injections, probably due to nutrient release, then returned to control levels after one week. Penicillin resistance was common in isolates from penicillin-injected and control trees (30–94%). Significantly more glyphosate resistant than sensitive isolates were penicillin resistant (81% versus 52%). Phytophthora root rot was not increased after penicillin injection. Thus, side effects of penicillin injection tested here were minimal, while Las titers were reduced after three months.     

Limitations of colony morphology and antibiotic resistance in the identification of a Bradyrhizobium sp. (Lotus) strain in soil

Summary We investigated the reliability of antibiotic resistance and colony morphology of clones of a Bradyrhizobium sp. (Lotus) strain for strain identification in nodulation competitiveness experiments in soil. There was no difference in nodulation competitiveness between the wild type strain and each of five mutants resistant to streptomycin and spectinomycin at the time of their isolation from antibiotic-containing media. However, these mutants were significantly less competitive when tested 4 months later. The apparent instability of the newly isolated mutants and their subsequently decreased nodulation competitiveness show that mutants must be examined carefully after being allowed time to stabilize. Two clones of the Bradyrhizobium sp. (Lotus) strain that differed in colony morphology on yeast mannitol medium did not differ in antigenic properties, whole cell protein electrophoresis profiles, mean cell generation times in yeast mannitol medium, N₂-fixing ability, nodulation of Lotus pedunculatus in growth pouches, or in nodulation competitiveness. Both clones retained their colony morphology after numerous transfers on yeast mannitol agar over 3 years and after at least 6 months in soil. A limiting factor, which may restrict the use of colony morphology as a marker for strain identification in competition experiments, is the problem of detecting double-infected nodules when the small colony type comprises a relatively small portion of the total nodule population.     

夏棉高产优质栽培措施优化决策及生育模型研究

试验选用播期(x_1)、密度(x_2)、追纯氮(x_3)打顶留果枝数(x_4)、去蕾果枝数(x_5)五因素五水平二次正交旋转回归设计,对夏棉农艺组合措施、群体动态、成铃分布及产量结构进行研究,通过对建立起皮棉产量、霜前花两个目标性状的回归模型进行分析,结果表明,筛选出兼顾高产、优质的综合农艺措施决策方案是合理的。同时研究了夏棉高产优质的群体生育动态,找出了看苗促控的管理指标及成铃分布状况和产量构成因素相互影响彼此消长的互变关系,进而模拟出不同产量水平的产量结构,明确了夺取夏棉高产优质的主攻方向,实现夏棉高产优质。达到667m2产皮棉60kg,霜前籽棉200kg以上的综合农艺措施决策方案为5月20～23日播种,密度7.3～7.5千株,追纯氮11.04～12.0kg,打顶留果枝数8.4～8.7个,去下部1个果枝的早蕾。     

绿色农业产业集群评价指标体系及应用研究 ――以陕西省渭北绿色果品产业集群为例

在提出绿色农业产业集群的概念的基础上,以陕西省渭北的绿色果品产业集群为研究对象,为其设计科学合理的指标体系。同时,根据设计的指标体系,利用非货币评价方法和层次分析法分别对该集群在2001-2005年所产生的集群效应进行综合评价。这种方法旨在通过对绿色农业产业集群的评价,客观认识整个集群的发展现状和发展过程中存在的问题,全面了解整个集群的可持续发展能力,从而为政府部门制定该集群的可持续发展战略和规划提供客观依据,使集群产业链上的企业了解自身的宏观发展环境,以便及时调整自身的发展战略和长期的营销策略。     

基于多种优化SVM的林木冠层图像分割

针对林木冠层图像,采用多种优化支持向量机(SVM)进行图像分割,提取树干分割图。采用模拟退火法(SA)、差分进化法算法(DE)、人工蜂群算法(ABC)等寻找最优惩罚系数(C)和高斯核函数中参数,然后运用SVM方法对训练样本综合训练建立最佳分类模型,并对林木冠层图像分割测试。结果表明:SA-SVM,DE-SVM,ABCSVM等3种方法对樟树、马褂木、杨树的林木冠层图像做树干图像分割,SA-SVM的分割效果最佳。     

Grouping of soil bacteria by analysis of colony formation on agar plates

Summary The colony formation of soil bacteria was studied in relation to incubation time. The process was simulated by a colony-forming curve (CFC) which was a superposition of several component curves (cCFC) given theoretically by the first-order reaction (FOR) model. This model had been previously proposed to define the colony formation of cells of a single culture. Soil bacteria were divided into several groups by these cCFC, as different types of bacteria produced their own colonies. Bacteria belonging to a single group grew at a similar rate on the plating medium and each group was characterized by a different growth rate. Most copiotrophic bacteria were fast growers and most oligotrophic bacteria slow growers.     

紫外线对4个Bt亚种活性的影响

用培养24h的苏云金杆菌,经稀释处理,显微计数,然后将定量的菌液涂布于平板上,用紫外线对4个Bt亚种(Bt-1.897,Bt-1.903,Bt-1.905,Bt-1.959)进行不同照射时间处理后,再于平板上培养24h,结果表明:Bt-1.897在紫外线处理15min仍然还有活性,Bt-1.903在紫外线处理12min基本上全部失活,Bt-1.905和Bt-1.959这2个菌株在紫外线处理12min时还有活性,但在处理15min后全部失活。说明不同种的苏云金杆菌对紫外线的抗性有一定差异。经紫外线处理后Bt-1.897、Bt-1.903、Bt-1.905、Bt-1.959各自有部分菌落发生明显的变异,菌落大小明显小于原始菌落,并且发生变异的菌落呈现出新的颜色,经涂片后在油镜下观察发现,其菌体要比原始菌体小,为明显的变异菌株。     

基于GIS和气候、种群动态模型的红火蚁适生性分析

进行红火蚁Solenopsis invicta适生性分析，找出制约红火蚁种群发展因素及其潜在的地理分布是开展防控、监管工作的重要基础。利用气候模型和种群动态模型对红火蚁在中国可能的分布范围进行分析，并从地温和降雨两个方面探讨了其气候制约因素的地理分布特征。预测结果表明，红火蚁在我国广东、广西、福建、台湾、海南入侵定殖可能性很高，气候条件不能构成制约因素。云贵高原东南部、四川东部以及重庆、湖南、湖北、江西、浙江、安徽、江苏局部地区也存在被红火蚁入侵定殖的风险。两个模型预测相似的红火蚁分布北界为川西高原、陇南、关中、山西南部、河南北部、山东南部一线。当前红火蚁分布还远未达到其分布北界，且其分布范围还不大，仍然可通过执行严格防控、检疫策略以防止红火蚁进一步蔓延。     

乡镇企业集群与西部地区新农村建设

在我国当前着重解决"三农"问题,进行社会主义新农村建设这一新的历史时期,乡镇企业仍然在与时俱进,继续发挥着农村剩余劳动力就业和农民增收的主渠道作用。本文从企业集群理论探讨了西部地区社会主义新农村建设中大力发展乡镇企业集群的可行性,并就相关的发展措施和途径提出了建议。     

平川水地晋单27号高产群体结构浅析

依据晋单27号生理、生态特点，结合忻州平川水地土壤、气候特征，设计60000，67500，75000，82500，90000株／hm2等5个处理，通过对群体透光率、植株农艺性状、经济性状以及代表群体稳定性的弱小株、空秆株和倒折株的调查分析，总结出忻州平川水地晋单27号稳定的单作高产最低密度及群体、个体性状部分观测数据，为研究、生产提供依据。