荔枝霜疫霉中双组分信号转导系统的鉴定与表达分析

 荔枝霜疫霉(Peronophythora litchii)隶属于茸鞭生物界卵菌门疫霉属,由其引起的荔枝霜疫病是目前荔枝生产上一种最重要的病害,严重影响荔枝产量和鲜果品质。双组分信号途径在微生物中参与多种生命活动,但是在卵菌中尚未有相关研究。本研究通过生物信息学分析在荔枝霜疫霉中鉴定到2个杂合型组氨酸激酶(PlHK1、PlHK2)和1个响应调控蛋白(PlRR1)。其在卵菌中是保守存在的,并且与真菌在进化上相对独立。功能域分析表明,PlHK1和PlHK2的C端额外的融合了1个磷酸转移功能域(Hpt),这与真菌和植物的存在显著差异。转录分析表明3个基因在荔枝霜疫霉侵染阶段上调表达,并且响应渗透胁迫和氧化胁迫。以上结果揭示了双组分信号系统可能在疫霉致病过程中发挥重要作用。     

典型草原种群特征对放牧制度的响应

采用放牧形式研究典型草原不同放牧制度群落动态变化规律.结果表明,牧草生长季前期干旱年份(2001年),划区轮牧区月现存量、生长量、生产力都显著高于自由放牧区(P＜0.05),而在降雨充沛的年份(2002年),两放牧处理无显著差异(P＞0.05);划区轮牧区的优势种的密度、高度、盖度以及重要值在两年均高于自由放牧区(P＜0.05).     

Appraisal of the sustainability of dairy goat systems in Southern Spain according to their degree of intensification

This investigation aims to classify, describe and evaluate the sustainability of dairy goat production systems (GPS) in South Spain Sierra de Cadiz. The research took place throughout 25 goat farms during the 2001–2002 campaigns, with the method posed by Masera et al. (1999) [Masera, O., Astier, M., S., López-Ridaura. 1999. Sustentabilidad y manejo de recursos naturales. El marco de evaluación MESMIS (Sustainability and natural resource management. The MESMIS evaluation framework). Mundi-Prensa, S.A., Gira, IE-UNAM, México. 109 pp.] and adapted to animal production systems, as the guideline and framework to evaluate sustainability.

The principal component, namely energy input from grazing (eigenvalue 1.329) which comprises the indicators total area per goat (factorial value 0.664) together with net energy obtained from grazing (factorial value 0.903) allowed to differentiate significantly between semi extensive (SES), semi intensive (SIS) and intensive (IS) goat production systems.

Intensification of the GPS tends to be inefficient, especially in terms of net margin per litre of milk produced (p < 0.05). A higher degree of adaptability of IS (64.8%) derives from a higher investment on new production strategies. Likewise, higher self-management capacity of SES (60.9%) fosters standards of productivity (76.0%) and stability (42.9%). The SIS presented the highest equity values (67.8%).

On the whole, sustainability of GPS tends to decrease as the degree of intensification increases: SES = 57.3%; SIS = 55.7% and IS = 53.1%. The reduction of the dependency on external input alongside with the optimization of natural resources management would surely improve the standard of sustainability.     

Energy expenditure in Awassi sheep grazing wheat stubble in the northern Negev Desert of Israel

In semi-arid Mediterranean areas, small grain aftermath stubble represents an important summer source of food for grazing flocks of small ruminants. Wheat stubble is a mediocre source of forage and flocks are grazed in summer under harsh conditions of temperature and air dustiness. However, stubble grazing procedures are changing, water and shading are more frequently available between grazing sessions (“improved management”), and the biological soundness of this ancestral practice needs to be re-visited. The present study was aimed at evaluating the cost in energy of “improved” wheat stubble grazing, compared with feeding a similar diet indoors. The intake of stubble was first quantitatively and qualitatively evaluated in Awassi sheep. Ewes consumed daily 980 ± 100 g day^− 1 of wheat stubble. Ewes were then housed and fed diets consisting of wheat hay, straw and grain formulated to be iso-energetic and iso-nitrogenous to diets consumed from wheat stubble. The average intake of ME was similar during the confinement and the pasture periods (6.4 ± 0.5 and 7.6 ± 0.8 MJ day^− 1of ME, respectively). During 2 days of each period, animals were fitted with external electrodes and data loggers of heart rate and skin temperature. Energy expenditure (EE) was calculated from oxygen consumption estimated as the product of heart beats rate measured for the two days by the amount of oxygen delivered to body tissues at each heart beat (O₂ pulse). The O₂ pulse was determined by simultaneously measurement of oxygen consumption and HR twice daily on two occasions, while grazing stubble and indoors. Energy expenditure and energy balance were not different in sheep while grazing wheat stubble (11.1 and − 3.5 MJ day^− 1) or fed indoors (11.1 and − 4.8 MJ day^− 1). Our data show that stubble did not cover nitrogen and energy requirements for maintenance, and that the cost of summer stubble grazing carried out under conditions described here is less than thought before.     

Evaluation of the API 50CH and API ZYM systems for rapid characterization of Clavibacter michiganensis subsp. sepedonicus, causal agent of potato ring rot

API 50CH and API ZYM systems were used to characterize fifty-three strains of Clavibacter michiganensis subsp. sepedonicus from different geographic locations and several reference strains of the same and different species, including other potato pathogens. Clavibacter michiganensis subsp. sepedonicus strains displayed a high level of homogeneity, both in carbohydrate utilization and in enzymatic activity. Using API 50CH and API ZYM it was possible to differentiate C. michiganensis subsp. sepedonicus strains from the remaining taxa analysed in this study, which included representative strains of the other subspecies of C. michiganensis as well as other bacterial pathogens affecting potatoes. Therefore, these systems could be used as an effective method to characterize C. michiganensis subsp. sepedonicus. Such a procedure would constitute an alternative system to the conventional nutritional and physiological identification tests currently included in the official methods employed in the European Union to detect and identify this bacterium. The results obtained with the API systems agreed with the current taxonomic classification of C. michiganensis, clearly separating sepedonicus from the other subspecies belonging to this species.     

Landscape patterns and agriculture: modelling the long-term effects of human practices on Pinus sylvestris spatial dynamics (Causse Mejean, France)

This paper focuses on understanding human impact on landscape. Both ecological and human practices are analysed as interacting processes. An agent-based model integrating biological and historical knowledge is used to analyse the pattern of Scots Pine encroachment in a French Mediterranean upland. In the STIPA model, pine trees are autonomous agents and a cellular automaton simulates land-use. We test the effects of shifting cultivation on tree establishment at the landscape scale. This allows us to understand how agropastoral practices patterned this area from the 17th to 19th century: simulations show the importance of shifting cultivation in limiting woodland progression. Fallow duration linked to environmental heterogeneity is a significant factor for explaining pine dynamics and landscape patterning at the scale of the study region. We put this result in perspective with current rangeland management policies that often consider grazing as the most relevant tool for open landscape maintenance. Our results also show the importance of taking into account time-scale effects when linking landscape patterns to agricultural systems.     

Postcards from the past: charting the landscape-scale conversion of tropical Australian savanna to closed forest during the 20th century

Repeated sequences of digitised and geo-referenced historical aerial photography provide a powerful means of understanding landscape change. We use this method to demonstrate a landscape wide expansion of closed forest (42% increase in total coverage) in the Australian monsoon tropics over the past five decades. Retrospective habitat suitability models (HSI) of closed forest derived using four landscape measures (drainage distance, slope angle, aspect and elevation) for imagery taken in 1947 correctly forecast the subsequent spatial distribution of the expansion, with topographic fire protection primarily determining the closed-forest distribution. The dynamics of the closed forest-savanna boundary were predicted accurately by generalised linear models, with closed-forest expansion in fire-protected sites along forest edges and regression in the more fire-prone areas. Two factors may plausibly explain the expansion of closed forests. First, eco-ethnographic records stress the skilful use of fire by Aboriginal people in protecting isolated and locally resource-rich closed-forest patches. Second, the recent global increase in atmospheric CO₂ may be changing the competitive balance between savanna and forest by enabling C₃ trees to grow fast enough to escape the fire trap presented by flammable C₄ grasses.     

落叶果树无休眠栽培的原理与技术体系

无休眠栽培是指利用一定的措施使具有休眠特性的落叶果树避开休眠继续生长,进而开花结果的一种栽培模式。控制营养生长、保证花芽分化,使树体避开休眠,促进足够多的芽整齐萌发,避免二次休眠的发生是无休眠栽培成功的4项重要保证。温带地区无休眠栽培的研究重点是:自然休眠诱导因子的确定;花芽分化进程及自然休眠进程的精确界定;避免进入深度休眠及促芽整齐萌发的配套技术;无休眠栽培条件下树体的生长发育规律及树体综合管理技术;二次休眠现象发生的原因和克服措施;无休眠品种的选育。     

优质猪杂交繁育体系的构建与优化

选用杜洛克、长白、大白3个国外引进品种,冀合白猪专门化母系B1个国内培育品系,以及1个地方品种太湖猪,模拟杂交繁育体系的生物经济学过程,构建了优质猪的杂交繁育体系,并以每头后备母猪平均每年的利润、每头标准化商品猪的利润、每1000头标准商品猪相对应的母猪头数和商品代出栏猪肌内脂肪含量(肉质指标)4个评价指标对杂交繁育体系进行了优化选择,结果在4种杂交配套组合中,杜洛克×(大白×冀合白猪专门化母系B)经济效率和商品代猪肉质最优。     

Reduced inter-row distance improves yield and competition against weeds in a semi-dwarf durum wheat variety

Weed and nutrient management in cropping systems of semi-arid areas is a major constraint to cereal yield. Where the use of herbicides is banned or discouraged, the competitive ability of a crop is crucial to reduce weed growth and diffusion. Genotypic differences in the competitive abilities of crops are an important trait to reduce weeds, especially for plant height. However, there is contrasting information about the interactions of other management practices and genotypic traits on wheat yield and competitive ability against weeds and weed growth. The present study investigated yield and quality of durum wheat (Triticum durum Desf.) and weed growth and composition for two wheat cultivars with contrasting competitive abilities against weeds. Wheat was grown under three spatial arrangements (5-cm, 15-cm, 25-cm inter-row distance) and three sowing densities, and broadleaf weeds were either removed or not. The sowing rate did not affect the yield of these wheat cultivars or the weed growth. Reduced inter-row distance dramatically reduced weed biomass for both wheat cultivars, and increased wheat yield and nitrogen uptake in the low-competitive, high-yielding, semi-dwarf cv. ‘PR22D89’, when both weed free and with weeds. These results have direct implications for weed and nutrient management in low-input and organic cropping systems.