不同烟草品种对云南烟草野火病菌的抗性鉴定

采用采自云南省不同地点、不同生理小种的24株烟草野火病菌对24个不同烟草品种及两个野生种黄花烟和长花烟进行抗病性鉴定分析。结果表明，不同抗性品种对不同生理小种的抗性反应差异显著，根据接种后不同烟草品种的形成的病斑直径，将其划分为4个等级：高抗、中抗、中感、高感。辽烟15，G28对于烟草野火病菌0，1号生理小种均表现为高感，而云南省大面积栽培的K326、红花大金元、云烟87等对于两个生理小种均表现为中感，而两个野生种黄花烟和长花烟均表现为高抗，可以作为烟草野火病抗性育种优先利用的种质资源。     

烟草野火病土壤颉颃细菌的筛选和鉴定

从植物根系的土壤中分离到127个细菌分离物,皿内实验筛选出对烟草野火病有抑制作用的菌株6个,盆栽试验表明,菌株S1对烟草野火病兼有保护和治疗作用,防效分别为85.98%和76.95%,同时菌株S1对植株还具有明显的促生作用。经鉴定菌株S1为芽孢杆菌属枯草芽孢杆菌。     

烟草野火菌毒素致病作用的研究进展

 烟草野火病是一种世界普遍发生的病害。烟草野火病菌毒素是一种重要的致病因子，从该毒素的结构，合成，致病机制及研究现状等方面概述了其在致病过程中的作用。     

Fall-Grazing and Grazing-Exclusion Effects on Cheatgrass (Bromus tectorum) Seed Bank Assays in Nevada,United States

Cheatgrass (Bromus tectorum L.) seedlings suffer mortality if they do not occupy safe sites that provide establishment requirements. Previous research demonstrated that fall cattle grazing has strong potential for reducing invasive annual grass species dominance in winter-dominated precipitation areas of the Intermountain West. Fall cattle grazing reduces the volume of safe sites through the removal of standing dead biomass in the fall and early winter, when cheatgrass can actively germinate. This study continued an assessment of cheatgrass seed bank characteristics under fall-grazing and grazing exclusion treatments initiated by a previous study. A seed bank assay was organized into a randomized complete block, repeated measure design to assess cheatgrass seed bank characteristics from 2014 to 2017 in central Nevada. Across years, fall-grazed areas had about half the assayed seed bank levels (3 432 ± 2 513 seeds ∙ m⁻²) of ungrazed areas (7 187 ± 1 569), (P <0.0001). There was also a difference among years with 2015 producing higher assayed numbers in both grazing treatments. Combined plotted data from this and the previous study indicated that after several years of fall-grazing treatments, removal of fall cattle grazing for only 1 yr can result in significant increases in cheatgrass seed bank size. Conversely, reapplication of fall cattle grazing can quickly decrease cheatgrass seed bank potential.     

Inheritance of resistance to wildfire and angular leaf spot derived from Nicotiana rustica var. Brasilea

Summary The introgression of wildfire (races 0 and 1) and angular leaf spot (ALS) resistance from N. rustica var. Brasilea into N. tabacum has proved economically useful in Zimbabwe although the mode of inheritance of, and genetic relationships between the resistance are unknown. This study was undertaken to (1) examine the mode of inheritance of the resistance to races 0 and 1 of wildfire, and ALS, (2) determine the genetic relationship between the resistances and (3) establish whether the N. rustica-derived wildfire race 0 resistance is allelic to that obtained from N. longiflora. Inheritance was examined under greenhouse and field conditions by studying disease reactions in the parental, F1, F2 and backcross generations derived from crosses of three susceptible lines to a resistant line Nr-7. Three-point backcrosses to the susceptible parent were examined for linkage and segregating generations from a cross of Nr-7 to Burley 21 which carries the N. longiflora race 0 resistance were used to test for allelism. In general, we observed that all resistances are determined by a single dominant gene although some incosistent ratios were obtained likely due to misclassification of disease reactions and erratic transmission. All resistances showed linkage although pleiotropism cannot be ruled out. Allelism tests demonstrated that the N. rustica race 0 resistance is not allelic to that obtained from N. longiflora. Our findings are examined in relation to the efficacy of indirect selection for resistance.     

烟草野火病重要流行环节的初步定量研究Ⅱ.病原菌侵染、潜育显症和病斑扩展

应用系统分析及定量流行学方法对烟草野火病的重要流行环节进行了初步定量研究。结果表明 :野火病菌只要一接触伤口 ,就完成侵入过程。野火病发病数量与接种体数量的 2 / 3次方成正比。野火病菌的侵染概率 (Y)与露温 (x)的关系为一单峰曲线 ,其回归式为Y =sin(- 2 1x +0 32x2 - 0 0 36x3 )。侵染概率 (Y)与叶表湿润时间 (t)、风速 (v)、空气相对湿度 (h)的关系 ,均为直线关系 ,其回归方程式分别为Y =1 6 4+0 .19t ,Y =1.0 5 8+0 .0 46v ,Y =- 3.8481+0 .0 86 9h。在吉林省生态条件下野火病潜育期为 3～ 5d ,其逐日显症率 (Y)与显症后顺序日数 (d)的关系为“S”型曲线 ,其回归方程为Y =1/ (1+0 .414e-1.3 1d)。野火病斑日龄(d)与野火病斑面积 (S)之间的关系为一倒“J”型曲线 ,其回归方程为S =sin(6 5 3d - 0 2 0d2 +0 0 0 12 6d3 )。     

吉林省烟草野火病药剂防治指标研究

研究了在吉林省生产条件下烟草野火病药剂防治指标。结果表明：在吉林省烟区，6月上旬即开始对烟草野火病情进行田间监测，如果病情指数达到1，且在此前后几天天气较有利于野火病发展（天气经常有雨，无连续高温天气），应马上施药防治。结果天气特别有利于野火病发生流行（连续几天有较大风雨），当病情指数达到0.5时即应进行药剂防治。如果天气条件不利于野火病发展，则可在病情指数达到2时进行药剂防治。     

Growth and Development Responses of Three Acacia Species to Long-Term Light Regimes

Abstract

Three species of Acacia which are used in various forestry systems in Micronesia are the Acacia confusa Merr., A. mangium Willd., and A. auriculiformis Cunn. ex Benth. The responses of these species to limited light have not been established. The objective of this study was to determine the growth responses of these three species to light ranging from 19% to 100% sunlight transmission in order to determine the relative tolerance of these species to shade. Several common adaptations to low light occurred with all three species, such as increased leaf surface area in relation to mass of supportive tissue and reduced leaf mass per unit leaf area. However, other adaptations to low light were not evident. Numerous indicators of growth were decreased at low levels of sunlight transmission. The relative reduction in growth at 19% transmission compared with 100% transmission was similar for each species. The results indicate that these Acacia species exhibit some adaptations to development in limited light, but they are not tolerant of shade. All three species are thus classified as shade avoiders, and have limited application under shaded conditions in any Pacific island forestry system.     

The shadow of the Balbina dam: A synthesis of over 35 years of downstream impacts on floodplain forests in Central Amazonia

1. The Balbina hydropower dam in the Central Amazon basin, established in the Uatumã River in the 1980s, is emblematic for its socio-environmental disaster. Its environmental impacts go far beyond the reservoir and dam, however, affecting the floodplain forests (igapó) in the downstream area (dam shadow), which have been assessed using a transdisciplinary research approach, synthesized in this review.
2. Floodplain tree species are adapted to a regular and predictable flood pulse, with high- and low-water periods occurring during the year. This was severely affected by the operation of the Balbina dam, which caused the suppression of both the aquatic phase at higher floodplain elevations and the terrestrial phase at lower floodplain elevations (termed the ‘sandwich effect’).
3. During the period of construction and reservoir fill, large-scale mortality already occurred in the floodplains of the dam shadow as a result of reduced stream flow, in synergy with severe drought conditions induced by El Niño events, causing hydraulic failure and making floodplains vulnerable to wildfires.
4. During the operational period of the dam, permanent flooding conditions at low topographical elevations resulted in massive tree mortality. So far, 12% of the igapó forests have died along a downstream river stretch of more than 125 km. As a result of flood suppression at the highest elevations, an encroachment of secondary tree species from upland (terra firme) forests occurred.
5. More than 35 years after the implementation of the Balbina dam, the downstream impacts caused massive losses of macrohabitats, ecosystem services, and diversity of flood-adapted tree species, probably cascading down to the entire food web, which must be considered in conservation management.
6. These findings are discussed critically, emphasizing the urgent need for the Brazilian environmental regulatory agencies to incorporate downstream impacts in the environmental assessments of several dam projects planned for the Amazon region.

     

Cattle Grazing Fails to Control Shrub Encroachment in Mediterranean Landscapes

The Common Agricultural Policy supports the use of free-ranging cattle herds to control woody encroachment and fire hazards in Europe. There is, however, little empirical evidence about the effectiveness of extensive grazing to preserve open landscapes in the Mediterranean Basin. In this work, we evaluated the effects of extensive beef cattle grazing on the vegetation structure in a Mediterranean ecosystem using a twofold framework: 1) analyzing temporal changes in the forest, shrub, and grassland cover in areas under different grazing pressures for 16 yr (1993 ? 2009) and 2) studying diet selection to assess the impact of cattle on the local Mediterranean vegetation. Our landscape structure analyses revealed a remarkable change in land cover over the study period. However, woody community dynamics seemed to be more related to natural vegetation succession than to cattle effects. Extensive grazing seemed to preserve grasslands but only at high stocking rates. On the other hand, the diet analyses supported the lack of a role for cattle in encroachment control. Beef cattle diets were based on herbaceous plants (59%) with lower contribution of woody ones (41%). Cattle only showed a significant preference (P < 0.05) for few woody species (Erica multiflora, Olea europaea, Quercus ilex, and Rosmarinus officinalis), mostly at high-density stocking rates. Hence, our results support the idea that extensive cattle grazing alone exerts a negligible effect on shrub encroachment and thus on the risk of fire in the studied Mediterranean area. We urge a redesign of current research to truly integrate extensive cattle grazing as High Nature Value farming in European policies to successfully meet its putative goals, such as shrub encroachment control and wildfire risk prevention.