Modelling Plant Disease Epidemics

An epidemic is the progress of disease in time and space. Each epidemic has a structure whose temporal dynamics and spatial patterns are jointly determined by the pathosystem characteristics and environmental conditions. One of the important objectives in epidemiology is to understand such spatio-temporal dynamics via mathematical and statistical modelling. In this paper, we outline common methodologies that are used to quantify and model spatio-temporal dynamics of plant diseases, with emphasis on developing temporal forecast models and on quantifying spatial patterns. Several examples of epidemiological models in cereal crops are described, including one for Fusarium head blight.     

温湿度调控对番茄灰霉病菌产生的细胞壁降解酶的影响

 番茄灰霉病菌在致病过程中能够产生4种细胞壁降解酶,以PMG酶活性最高,其次是β-葡萄糖苷酶和PG酶,Cx最少。灰霉病菌在不同温度下侵染番茄叶片时产生的致病酶活性不同,4种酶在20℃时表现了最高的活性,15℃次之,当温度达到25℃时,各种酶的活性都急剧下降,随着温度的再升高,酶活更低。随着湿度的增高,病菌产生的细胞壁降解酶的活性也增加,当相对湿度达到90%以上时,4种酶的活性也达到最高。温湿度对番茄灰霉病菌产生细胞壁降解酶的影响趋势,与其对发病的影响趋势是一致的。     

桃品种需冷量评价模式的探讨

 通过1986～2001年对450余份桃品种需冷量的7．2℃模式、0～7．2℃模式(不包括0℃)和犹它模式比较分析，归纳出桃品种需冷量的评价模式为：以秋季日平均温度稳定低于7．2~C的日期为需冷量测定的起点，以0～7．2℃累积低温值作为需冷量的评价标准比较适宜；犹它模式在中需冷量和长需冷量范围内能有效预测休眠的结束，而不适宜低需冷量品种的测定；7．2℃模式不适宜作为需冷量的评价模式。品种的需冷量与叶芽开放和始花期的相关系数分别为0．52和0．58，均达到极显著水平。提出了桃品种需冷量评价的系列标准参照品种。     

新疆冬小麦农田蒸散估算模型的研究

本文在田间试验资料的基础上，综合考虑了影响冬小麦农田蒸散的气象、生物学特性和土壤水分等因素，选用蒸发力、冬小麦的叶面积指数和相对有效土壤湿度建立了新疆冬小麦农田蒸散估算模型，并且检验了该模型的计算效果。     

景观生态学原理与方法在荒漠化研究中应用的理论分析

荒漠化发生发展的过程实际上是指在自然和人为因素的作用下，生态系统结构遭受破坏、功能过程受阻和演变发生异化的过程，其防治的根本措施是恢复和重建健康的生态系统。所以，景观生态学理念在荒漠化的研究和防治中有着重要的意义。本文从荒漠化与生态系统结构、功能变化、荒漠化与生物多样性、荒漠化生态系统的物质循环和能量流动以及荒漠化生态系统的稳定性等方面论述了景观生态学理念在荒漠化研究中应用的可行性，并重点分析了景观生态学关于景观格局变化的评价指标与荒漠化土地动态变化之间的关系。     

有机修饰改性对旱地土壤吸附镉离子特性的影响

研究了以不同比例十六烷基三甲基溴化铵(CTMAB)单一修饰和十六烷基三甲基溴化铵 十二烷基磺酸钠(CTMAB SDS)混合修饰土娄土耕层对重金属镉离子吸附的影响,结果表明:吸附量顺序为耕层原土>50%CTMAB>100%CTMAB 20%SDS>100%CTMAB,温度升高,吸附量上升;最佳吸附等温线模型可以用BET模型描述,热力学参数的研究表明,吸附自发性与吸附量具有相同的变化规律,反应的焓变与熵变共同决定了反应的自发性。从热力学角度对修饰改性土娄土对Cd2 吸附的机理进行了探讨。     

Functional heterogeneity in resources within landscapes and herbivore population dynamics

Large mammalian herbivores are notorious for their propensity towards population irruptions and crashes, yet many herbivore populations remain relatively stable. I explore how resource heterogeneity within landscapes dampens population instability, using a metaphysiological modelling approach considering patch state distributions. Resource heterogeneity is functionally stabilizing through spreading consumption away from preferred resources before these become critically depleted. Lower-quality resources act as a buffer against starvation during critical periods of the seasonal cycle. Enriching resource quality is destabilizing, even if patch diversity is maintained, because food quantity then becomes the limitation. The potential consequences of landscape fragmentation are explored using the Serengeti ecosystem, characterised by broadscale resource gradients, as a hypothetical example. Further insights provided by the model are illustrated with specific examples concerning the effects of patch scales and waterpoint distribution. A metaphysiological modelling approach enables the basic consequences of landscape heterogeneity to be distinguished from further effects that may arise from specific patch scales and configurations, without the distracting detail of spatially explicit models.     

Using traffic flow theory to model traffic mortality in mammals

Traffic has a considerable effect on population and community dynamics through the disruption and fragmentation of habitat and traffic mortality. This paper deals with a systematic way to acquire knowledge about the probabilities of successful road crossing by mammals and what characteristics affect this traversability. We derive a model from traffic flow theory to estimate traffic mortality in mammals related to relevant road, traffic and species characteristics. The probability of successful road crossing is determined by the pavement width of the road, traffic volume, traversing speed of the mammals and their body length. We include the traversability model in a simple two-patch population model to explore the effects of these road, traffic and species characteristics on population dynamics. Analysis of the models show that, for our parameter ranges, traffic volume and traversing speed have the largest effect on traffic mortality. The population size is especially negatively affected when roads have to be crossed during the daily movements. These predictions could be useful to determine the expected effectiveness of mitigating measures relative to the current situation. Mitigating measures might alter the road and traffic characteristics. The effects of these changes on traffic mortality and population dynamics could be analysed by calculating the number of traffic victims before and after the mitigating measures. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of non-inversion tillage and light availability on dispersal and spatial growth of Cynodon dactylon

The invasive ability of Cynodon dactylon is dependent on self dispersal and on cultivation practices. Tillage can seriously change patch biomass and spatial structure, spreading vegetative propagules of the weed. The objectives of this study were: (i) to quantify the effect on non‐inversion tillage on dispersal, establishment and colonization of C. dactylon and (ii) to propose a simple model considering soil cultivation effects and light availability on spatial growth of weed patches. Two experiments were carried out, exploring different soils and environmental conditions. Spatial distribution of vegetative units differed when tillage was conducted with different non‐inversion implements and could be described by simple functions. A minimum patch biomass seems necessary before vegetative structures are vulnerable to movement by cultivation. Only a small proportion of the biomass dispersed from original patches was able to establish. However, simulation showed that the area colonized by C. dactylon mostly increased by means of tillage dispersal, both with and without crop competition, in one growing cycle. It appears sensible to consider changing cultivation practices to reduce weed dispersal and to use crop competition for light to create unsuitable habitats limiting weed colonization.     

Resistance to Botrytis cinerea in Solanum lycopersicoides is Dominant in Hybrids with Tomato, and Involves induced Hyphal Death

Botrytis cinerea causes gray mold disease and affects hundreds of plant species, including tomato (Lycopersicon esculentum). The wild nightshade, Solanum lycopersicoides, is cross compatible with tomato and is more resistant to B. cinerea, thus representing a potential source for crop improvement. Tests involving droplet inoculation of detached leaves and spray inoculation of entire seedlings demonstrated that resistance to B. cinerea varies among S. lycopersicoides accessions, with S. lycopersicoides LA2951 being the most resistant accession tested. Expression of resistance in the intergeneric hybrid (L. esculentum cv. 'VF36' × S. lycopersicoides LA2951) suggested that resistance is at least partially dominant in tomato. A green fluorescent protein-tagged B. cinerea strain was used for confocal microscopic comparison of infection in leaves of S. lycopersicoides and tomato. Even though S. lycopersicoides supported spore germination, there was evidence for hyphal lysis and death 3 days after inoculation, at a time when lesions were expanding on susceptible tomato plants. The reduced frequency of B. cinerea lesion spread on S. lycopersicoides explains why this fungus produced fewer spores in this wild nightshade than in tomato.