Effect of slash removal on Gremmeniella abietina incidence on Pinus sylvestris after clear-cutting in northern Sweden

The Gremmeniella abietina outbreak in Sweden in 2001-2003 forced forest owners to sanitary clear-cut large areas of middle-aged Pinus sylvestris stands. There is, however, little knowledge of effective reforestation of P. sylvestris on G. abietina-infected sites. Gremmeniella abietina disease incidence on P. sylvestris seedlings planted in 2003 was studied with and without (control) removal of infected P. sylvestris slash. Removed slash was piled in stacks around the regeneration plots. The seedlings were planted within 1 year after sanitation felling on three sites in northern Sweden. One year after planting, G. abietina pycnidia were found on 32% of the control seedlings and total infection, including stem cankers, reached 44%. Total and G. abietina-induced mortality was 15 and 10%, respectively. The method of removing and piling the infected slash reduced the number of infected seedlings by 50% and seedling mortality by 27% 1 year after planting, compared with control. Consequently, even if there is a clear sanitation effect of removing infected slash to the sides of the regeneration area, it does not eradicate the infection source from the stands. Postponed planting, slash burning or complete removal of the infected slash is needed to minimize the infection risk. The positive correlation found between slash coverage and infection rate indicates that clear-cuts with large amounts of infected slash should be given priority for slash treatment.     

杨树烂皮病的研究防治

杨树烂皮病是杨树的常见病和多发病,该病对杨属和柳、榆等树种危害极大。本文对杨树烂皮病的病原和症状及发生规律进行了分析研究,在研究的基础上提出了综合防治的方法。     

基于高光谱成像技术检测脐橙溃疡

为了研究从带有不同缺陷的柑橘类水果中快速识别出溃疡果的有效方法,基于高光谱成像技术,该文提出特征波段主成分分析法及波段比算法。以脐橙为研究对象,选取包括溃疡在内常见的10类脐橙果皮缺陷果及正常果。首先,提取并分析11类果皮感兴趣区域（ROI）光谱曲线并结合主成分分析法确定5个最佳波段（630、685、720、810和 875 nm）;然后基于特征波段做主成分分析,选取第5主成分（PC-5）作为分类识别图像,识别率达到80%。为了进一步提高溃疡识别率,该文又提出采用特征波段主成分分析法与波段比算法相结合的方法,基于此算法溃疡正确识别率提高到95.4%。试验结果表明,基于高光谱成像技术可以有效地对带有溃疡病斑的脐橙分类识别。     

柑桔溃疡病菌基因组DNA的微波法抽提及快速检测

利用微波热震惊提取固体表面柑桔溃疡病基因组DNA并加以优化,所得到的基因组DNA可作为PCR反应的模板进行16SrDNA基因有效扩增。与柑桔溃疡病基因组DNA其他抽提方法相比较,微波法更适用于该病的快速检测,具有快速、简便、费用低廉等特点,且对设备的要求不高,用特异性引物XCF/XCR可实现柑桔溃疡病菌的快速鉴定。     

Influence of selected bactericides on biofilm formation and viability of Xanthomonas citri subsp. citri

Citrus Bacterial Canker (CBC) is a serious disease that affects production of almost all commercial citrus cultivars in subtropical citrus growing regions worldwide. The causal agent, Xanthomonas citri subsp. citri (Xcc), is classified as a quarantine pathogen in European Union (EU) which necessitates treatment of citrus fruit before entry into the EU marketing zone. In this study, the effectiveness of selected bactericides for leaf and fruit disinfection was evaluated. Bacterial aggregation and viability were assayed on abiotic or biotic surfaces in vitro and in planta after treatments with NaCl, CuSO₄, NaClO, sodium orthophenylphenate and two hydrogen peroxide based compounds. Most of the bactericides at higher concentrations reduced biofilm formation and Xcc viability compared to the non-treated control, but did not completely prevent or remove biofilms or eradicate Xcc from either biotic or abiotic surfaces. Some of the bactericides at sub-lethal concentrations increased aggregates in which Xcc was viable. Based on these results, we conclude that exposure to the bactericides is variable depending on biofilm formation and that plant and fruit disinfection will not only require treatment with an effective bactericide to kill the bacterium but also include the biofilm disruption.     

Detection to Pathogens of Poplar Cankers by Multiplex PCR Technique

Fungal pathogens causing poplar canker diseases are cosmopolitan in species,and have a wide range of hosts.These pathogens have diverse anamorphs and their morphology overlaps with each other;Their teleomorphs are hardly discovered in nature.Furthermore,the identification of these pathogens is usually limited by the geography,host and taxonomic knowledge.Therefore,a culture-independent method used to identify determine pathogens is expected to be developed for field diagnostics.Through amplifying,sequencing and analyzing multiplex nucleic acid templates and genetic marked target sequences,a multiplex PCR technique has been established and used to directly detect various environmental samples.In this study, four pathogen strains and environmental samples were amplified using fungal universal primers ITS1/ ITS4 and EF1-728F/EF1-986R by general PCR and multiplex PCR.The amplicons were sequenced,and then aligned in GenBank.The result showed that the multiplex PCR was able to successfully amplify the target gene and identify the pathogens from environmental samples in the condition of an annealing temperature of 55.6℃and primers final concentration of 0.2μmol·L^-1.The multiplex PCR could amplify the target at the concentration level of approximately lng of genomic DNA.This method would provide a useful tool for the identification of canker pathogens by the multiplex PCR and the high-throughput DNA microarray detection of environmental samples.     

Ceratocystis species infecting stem wounds on Eucalyptus grandis in South Africa

Reports of Ceratocystis spp. causing disease of exotic plantation hardwood species have increased in recent years. Ceratocystis fimbriata causes wilt and canker on Eucalyptus spp. in Africa and South America, and C. albofundus results in wilt and death of Acacia mearnsii in Africa. Ceratocystis spp. generally infect wounds on trees, and artificial stem wounding can thus be used to determine the presence of these fungi. The aim of this study was to identify Ceratocystis spp. infecting wounds on Eucalyptus grandis in South Africa. Isolated Ceratocystis spp. were identified using morphological characteristics and comparisons of DNA sequence data for the ITS and 5·8S regions of the rRNA operon. Pathogenicity trials were conducted in the greenhouse to determine the possible role that these Ceratocystis spp. could have in disease development. These trials were also conducted under field conditions. Three Ceratocystis spp. were collected: C. fimbriata , C. moniliformis and C. pirilliformis . This is the first report of C. fimbriata and C. pirilliformis from Eucalyptus spp. in South Africa, and the first report of the latter fungus outside Australia. Both C. fimbriata and C. pirilliformis caused significant lesions on inoculated E. grandis trees. This is the first evidence that C. pirilliformis is a pathogen of Eucalyptus spp. From the results of both greenhouse and field trials, it has the potential to cause serious disease problems in Eucalyptus plantations.     

Interactions Between the Potato Cyst Nematode Globodera rostochiensis and Diseases Caused by Rhizoctonia solani AG3 in Potatoes Under Field Conditions

Findings from 2 years of field experiments investigating the relationship between Globodera rostochiensis and Rhizoctonia solani on unique field sites are reported. In 2000, a field experiment was positioned on land that had previously been used for experimental work investigating integrated potato cyst nematode (PCN) management methods. This study had produced an ‘untypical’ mosaic of PCN population densities ranging from 5 to 221 eggs g⁻¹ soil. In 2001, the field experiment was conducted on a different field site and overlaid on a focus of G. rostochiensis population densities ranging from 11 to 108 eggs g⁻¹ soil. In each experiment, potatoes (cv. Désirée) were grown in plots with similar population densities of G. rostochiensis that were either uninoculated or inoculated with R. solani. A series of potato plant harvests were undertaken to investigate the effects of nematode infestation on the incidence and severity of R. solani diseases and the associated development of plants. In both experiments, a clear relationship was found between the density of G. rostochiensis juveniles present in potato roots and the incidence of stolons infected by R. solani, 6 weeks after planting. For the first time this interaction has been determined under field conditions. The results of the study suggest that the interaction between nematode and fungus is indirect and possible mechanisms are discussed.     

树皮内酚类物质的含量及苯丙氨酸解氨酶的活性与杨树抗溃疡病的关系

本文通过不同含水量盆栽苗的接种试验,结果表明,水分亏缺是杨树溃疡病发生发展的诱因。在树皮含水量高的植株中,苯丙氨酸解氨酶(PAL)的活性强,邻苯二酚和对-羟基苯甲酸等酚类物质的含量高,且它们的活性(或含量)随着树皮含水量的降低而降低。室内抑菌试验及盆栽苗的注射试验证明了邻苯二酚是寄主活体内的重要抑菌物质。     

应用PCR技术快速检测柑桔溃疡病的研究

应用PCR检测柑桔溃疡病，所用引物为5′TTGGTG TCGTCGCTTGTAT 3′和5′CACGGGTGCAAAAAATCT 3′。从病样的叶片、果皮和枝皮抽提溃疡病菌核酸进行PCR扩增，其产物经琼脂糖凝胶电泳，产生大约220bp的特征条带，与纯培养溃疡病菌的PCR产物一致。试验比较两种核酸抽提方法，微量快速抽提法的灵敏度明显高于高盐抽提法。有症状病样品的不同部位均能检测到溃疡病；病株的无症状叶片、果皮、枝皮有部分检测到病菌。病果园健康植株大多数检测不到病菌，少数植株PCR产物电泳条带较弱。取样量以10～20mg为宜。该PCR技术可用于快速检测柑桔溃疡病。