Mechanisms involved in the biological control ofBotrytis cinerea incited diseases

Mechanisms involved in the biological suppression of infection and inoculum potential ofBotrytis cinerea are numerous and variable and the involvement of two or more mechanisms has been demonstrated in several systems. Reported combinations include antibiosis with enzyme degradation ofB. cinerea cell walls; competition for nutrients followed by interference with pathogenicity enzymes of the pathogen or with induced resistance; and alteration of plant surface wettability combined with antibiosis. Since germinatingB. cinerea conidia are dependent on the presence of nutrients, competition for nutrients is regarded as important in systems where biocontrol is involved. Conidial viability and germination capacity are also potentially affected by the presence of antibiotics produced by biocontrol agents and present in the phyllosphere. Slower in action are mechanisms involving induced resistance in the host plant and production of hydrolytic enzymes that degradeB. cinerea cell walls. The latter has been demonstrated much more convincinglyin vitro than in the phyllosphere. Biocontrol in established lesions and reduction of sporulation on necrotic plant tissues is a means to minimize the pathogen inoculum.Abbreviations BCA bio-control agent - Bc Botrytis cinerea - PG polygalacturonase - PL Pectin lyase - PME Pectin methyl esterase - PR pathogenesis related - VPD vapour pressure deficit     

Synthetic Analogue of Butenolide as an Antifouling Agent

Butenolide derivatives have the potential to be effective and environmentally friendly antifouling agents. In the present study, a butenolide derivative was structurally modified into Boc-butenolide to increase its melting point and remove its foul smell. The structurally modified Boc-butenolide demonstrated similar antifouling capabilities to butenolide in larval settlement bioassays but with significantly lower toxicity at high concentrations. Release-rate measurements demonstrated that the antifouling compound Boc-butenolide could be released from polycaprolactone-polyurethane (PCL-PU)-based coatings to inhibit the attachment of foulers. The coating matrix was easily degraded in the marine environment. The performance of the Boc-butenolide antifouling coatings was further examined through a marine field test. The coverage of biofouler on the Boc-butenolide coatings was low after 2 months, indicating the antifouling potential of Boc-butenolide.     

Host-parasite soil communities and environmental constraints: Modelling of soil functions involved in interactions between plant-parasitic nematodes and Pasteuria penetrans

Nematodes belonging to the genus Meloidogyne are the most ubiquitous and widespread plant-parasitic nematodes. They occur worldwide, are polyphagous and can parasitize most cultivated plants leading to reduced crop yields. They are especially harmful in developing countries because of the lack of suitable and feasible management strategies. Among all the control practices (chemicals, physical techniques, cultural practices, resistance), the use of natural enemies as biological control agents is the most recently developed. Pasteuria penetrans which is an obligate Gram-positive, endospore-forming bacterium, is perhaps the most promising plant-parasitic nematode biocontrol agent. Despite much research conducted on prey-predator interactions (host-parasite specificity, mechanisms of attachment, field efficacy), the influence of the soil environment on host-parasite interactions is poorly understood even when the soil appears to be the key factor. Beyond common studies on the influence of climatic conditions on the attachment of endospores of P. penetrans to nematodes, more knowledge about the systemic interactions between plants, soil water dynamics, soil texture and structure, and other biota on the parasitism of nematodes by P. penetrans would improve their utilization as biological control agents. The aim of this review is to analyze the literature dealing with the influence of the soil on nematode - P. penetrans interactions in order to suggest a helpful conceptual model based on partitioning the Pasteuria population in sub-populations according to their soil habitat (dispersible and non-dispersible aggregates, microporosity, macroporosity), not all of them being available for attachment and infection on nematodes. Such concerns should be taken into account by epidemiologists for improving biological management strategies based on the use of this bacterium.     

杂色鲍幼体附着基藻际细菌群落的PCR-DGGE分析

附着基是苗期杂色鲍(Haliotis diversicolor Reeve)生活的主要场所, 其表面藻际细菌对幼体的生长有重要的影响, 然而对附着基藻际细菌多样性的研究较为少见。本研究在杂色鲍育苗期间定期采集附着基样品, 再利用PCR-DGGE技术对藻际细菌群落进行多样性及变化规律分析。相似性和UPGMA聚类结果表明, 藻际细菌群落结构随时间变迁呈现出连续性变化, 相邻两天细菌群落的戴斯相似性系数C_s高达80.9%~96.1%, 但育苗前期与育苗后期的藻际细菌群落组成差异较大。多样性指数分析显示, 育苗前期藻际细菌多样性随时间变化趋于丰富, 之后多样性稍有下降但仍维持较高水平。受附着基上藻类生长状况及鲍摄食活动等因素的影响, 细菌多样性指数出现一定波动。本研究旨为鲍的科学育苗与健康养殖提供理论参考, 为进一步深入研究环境变化与鲍苗期细菌性病害的关系打下良好基础。

     

Induction of root-mat symptoms on cucumber plants by Rhizobium, but not by Ochrobactrum or Sinorhizobium, harbouring a cucumopine Ri plasmid

Ochrobactrum CSL 2573, Rhizobium CSL 2411 and Sinorhizobium CSL 2611 strains harbouring the Agrobacterium cucumopine Ri plasmid (pRi), previously were shown to induce root-mat symptoms in an in vitro cucumber cotyledon assay. In whole-plant, rockwool-grown cucumber host tests Rhizobium CSL 2411 was shown to be as efficient an inducer of root-mat symptoms as the virulent Agrobacterium radiobacter strain NCPPB 4042, which also harbours a cucumopine pRi. Conjugal transfer of pRi to ingressing, avirulent Agrobacterium isolates was observed within root tissues with symptoms. Ochrobactrum CSL 2573 and Sinorhizobium CSL 2611 were not able to induce root-mat symptoms on plants. Rhizobium CSL 2411 and Ochrobactrum CSL 2573 were reisolated from inoculated plants, but Sinorhizobium CSL 2611 was not detected or isolated from inoculated plants 68 days after inoculation. It was postulated that the differences in pathogenicity observed between the in vitro and in situ host tests were caused by a lack of proper attachment to inoculated root tissues by pRi-harbouring Ochrobactrum and Sinorhizobium in the whole-plant host tests.     

核基质结合区对马铃薯Y病毒全长非翻译CP基因介导抗病性的影响

 为探索核基质结合区(matrix attachment regions,MARs)对RNA介导的病毒抗性的影响,我们将从烟草中克隆到的核基质结合区TM2构建在包含马铃薯Y病毒全长非翻译CP基因的植物表达载体pRPVYCPN的表达盒的两侧,构建了植物表达载体pRTM2CPNTM2。采用农杆菌介导基因转化法,将表达载体pRPVYCPN和pRTM2CPNTM2转入烟草品种NC89中,分别获得了144株和344株转基因烟草。抗病性检测发现,核基质结合区的存在能明显提高RNA介导抗性的产生效率。在含MARs转基因植株中,抗病植株的比率为15.1%,而不含核基质结合区的转基因植株的抗病比率则为8.3%。这一研究结果对抗病毒植物的分子育种和转基因表达调控有指导意义。     

Pathogenesis by fungi and by parasitic plants: Similarities and differences

The processes by which fungi and parasitic plants infect their plant host are compared. The steps considered are: location of the host by the pathogen, the concept of the haustorium, attachment of the pathogen to the host, mechanism of penetration into the host, responses of the host to infection by fungi and by parasitic plants, and the suppression of the host response by the pathogen. Although superficially similarities between fungal infection and infection by parasitic plants exist, the underlying mechanisms appear to be different and only in the penetration step are similar strategies used, including the use of lytic enzymes. These differences are important when seeking ways of combating the parasitic plants. The strategies used against the parasitic plants must be different from those used to combat fungal infections and should not be based only on analogies with host resistance to fungal pathogens. http://www.phytoparasitica.org posting Nov. 2, 2005.     

从业本到人本——“重农”新解

自古四业以农为本。但历代王朝"重农"而农民负担益重。以重农为名抑商,不只是打击民间工商业,而且窒碍农业发展。为了避免"重农而农益轻",王夫之等曾力主"轻自耕之赋"甚至"有田者必自耕,……不为农则无田",对于借口重农而抑商,叶适也曾提出尖锐批评。今日中国仍需重农。维护家庭农民的各项合法权益并积极扶持务农人走向富裕,是在农业和农村落实"以人为本"的不二选择。     

农杆菌对蕉柑(Citrusreticulata var.tankan Hayata)胚性细胞的附着研究

农杆菌能够附着蕉柑的胚性细胞。农杆菌对蕉柑胚性细胞的附着曲线表明 ,农杆菌与蕉柑胚性细胞之间的附着是一个动态过程。农杆菌在蕉柑胚性细胞上的附着量受共培养介质中乙酰丁香酮 (As)和表面活性物质影响较小 ,而与共培养介质中的农杆菌浓度呈正相关     

Agriculture and biodiversity: Finding our place in this world

Agriculture has been recently viewed as the primary destructive force of biodiversity, but the places that produce our food and fiber may also hold the key to saving the richness of life on earth. This argument is based on three fundamental positions. First, it is argued that to value and thereby preserve and restore biodiversity we must begin by employing anthropocentric ethics. While changing our understanding of intrinsic values (i.e., the unconditional values of biodiversity as a state and process in-and-of-itself, without reference to human interests) is often advocated as the means by which our behavior will reflect the importance of biodiversity, a change in how we perceive and conditionally value biodiversity is proposed as a more effective and compelling approach. Second, I suggest that anthropocentric values can be linked to a sense of Place, with agriculture playing a vital role in this context. Agriculture forms a powerful basis for personal, experiential development of a profound meaning and connection to a setting or landscape. The agricultural setting has tremendous potential for arational (emotional, aesthetic, and spiritual) values that ultimately compel our actions. The constancy of relationship and mutuality of dependency between humans and agricultural lands, particularly extensive agroecosystems, fosters an intensity of association that transcends our recent affinity to wildlands. Third, a mature understanding of places and their biodiversity must include those organisms that account for many of the ecological processes and the majority of the species richness -- the insects. The importance of these insects in structuring the landscape and the effects of habitat destruction on these organisms both suggest a vital, intimate, and reciprocal link between insects and Places. Finally, it is argued that the most important avenue for future efforts to protect and restore biodiversity on the part of agricultural and other scientists is educational -- the presentation of our research to the public in terms that provoke emotional, aesthetic, and spiritual meaning which lies at the core of human values and actions.