Perspectives and challenges from the 20th century

ABSTRACT The magnitude of change in our understanding of tree diseases during the past century is almost incomprehensible. This does not mean to imply that we know everything, but the science of forest pathology has come a long way in the past 100 years. This remarkable progress was driven by three events: (i) an investment in the early 1900s in federal and state experiment stations, which established the need for, and benefits of, research in tree diseases; (ii) veterans acquiring an education under the GI Bill, which created a pool of forest pathologists and students eager to solve the devastation caused by diseases such as chestnut blight, white pine blister rust, Dutch elm disease, and oak wilt; and (iii) the McIntire-Stennis Cooperative Forestry Program, which established a strategy for the federal government to assist the financing of forestry research in the universities. Although all three of these events are being drastically modified by a discontented tax-paying public, the threats of changing land use patterns, population pressures, and exotic pests on fragile forested ecosystems will certainly force a renaissance in our field that will dwarf progress of the past century and help assure an acceptable quality of life in the new century. The magnitude of what forest pathologists will accomplish, to a great extent, depends on what the public is willing to pay for.     

Dominating north american forest pathology issues of the 20th century

ABSTRACT The profession of forest pathology evolved in the early decades of the 20th century from a science describing microorganisms that infect trees to a discipline that was required to deal with numerous disease outbreaks. The foundations of the science were carried from Europe to the "New World" and initially dealt with decay and the resource losses it caused. The profession was forced to shift direction quickly because it was called upon to address major diseases caused by the introduction of pathogens from other continents; notably organisms inciting chestnut blight, Dutch elm disease, and white pine blister rust. Changes in natural ecosystems that resulted from a legacy of poor forest practice, land abuse, and an increase in plantation monocultures gave rise to other disease problems when host-pathogen balances in natural ecosystems were disturbed. Further, the need for large numbers of tree seedlings resulted in numerous nursery disease problems. Although many of the principles of general plant pathology had application to the study of forest diseases, the long-term nature of forests requires varied approaches to their study and management. Today, the science continues to evolve as the complexities of forest ecosystems unfold.     

Evidence for presence of the founder Ia mtDNA haplotype of Phytophthora infestans in 19th century potato tubers from the Rothamsted archives

Late blight remained a significant disease for potato growers in Europe long after the famine of the 1840s. Of the four mitochondrial haplotypes of Phytophthora infestans, only the Ia mitochondrial DNA (mtDNA) haplotype has been identified previously in infected potato leaves from famine‐era herbarium specimens collected in England, Ireland and Europe in the 19th century. Long‐term soil fertility experiments were conducted on potato between 1876 and 1901 in Rothamsted to investigate effects of combinations of organic manures and mineral fertilizers on disease and yield. This report identifies for the first time the same Ia mtDNA haplotype of P. infestans in three diseased tubers from 1877 from the long‐term Rothamsted trials, thus providing the earliest evidence of the presence of the founder Ia mtDNA haplotype of P. infestans in potato tubers in England. Soil amendments had a significant impact on disease and yield. A real‐time PCR assay was used to detect and quantify P. infestans in tubers. The level of pathogen DNA was greatest in tubers from highest yielding plots that received combinations of inorganic nitrogenous and mineral fertilizers and least in tubers from plots with organic farmyard manures or non‐nitrogenous mineral fertilizers. The Ia mtDNA haplotype was also confirmed from diseased potato leaves during the same time period. Thus, the founder Ia mtDNA haplotype survived in potato tubers after 1846 and was present over 30 years later in the UK.     

Rainfall patterns of Algerian steppes and the impacts on natural vegetation in the 20~(th) century

Since 1960, the steppe regions of North Africa have been subject to an increasing desertification, including the degradation of traditional pastures. The initially dominant species(Artemisia herba-alba, Lygeum spartum and Stipa tenacissima) declined and were progressively replaced by other species(Atractylis serratuloides and Salsola vermiculata) that are more tolerant to the new conditions. It is not clear whether these changes are due to anthropogenic reasons or climatic determinism. We have carried out a statistical analysis of the climate to detect putative rainfall changes during the 20~(th) century in the Algerian steppes based on data from 9 meteorological stations, including 2 Saharan stations(El Oued and Touggourt), 3 pre-Saharan stations(Biskra, Laghouat and Ain Sefra) and 4 steppe stations(Djelfa, Saida, Méchéria and El-Bayadh) located in the arid high plains, which represent the bioclimate diversities of the region. Previous studies suggested that significant rainfall changes for the 20~(th) century only had records in the south of the Oran region. Most of the studies, however, looked at restricted territories over limited periods, and did not integrate the rainiest period 2004–2014. Our work is designed to integrate all the longest time series of meteorological data available for the steppe regions of Algeria. Our results confirm the spatial rainfall distribution(significant rainfall changes only recorded in the southwestern region) evidenced by previous studies, and reveal a decreasing rainfall gradient from northeastern to southwestern Algeria. Moreover, the results reveal a trend of significant decrease of rainfall in the southern Oran region, marked by two drought periods in 1980–1985 and 1999–2003. However, with the exception of the southwestern region, rainfall overall has not declined since the beginning of the 20~(th) century. While less marked in other regions, the drought appear to have affected all territories of the Algerian steppe. Consequently, our study implies that the climate was not a leading influence in the on-going degradation of the vegetation cover of steppe landscapes. Such a vegetation evolution thus appears to be have been determined more by human activities than by climate forcing.     

20世纪天水干旱气候演变对农业影响及对策分析

通过对20世纪60年代以前，天水干旱气候的历史演变和有气象资料记录以来的近40a主要气象要素变化分析，得出了天水20世纪百年干旱气候自90年代以来显著加重的演变规律及对农业生产的影响。同时，提出了相应的农业对策与建议，为加快农业结构调整、生态环境建设提供科学依据。     

Variation in resistance to Orobanche crenata in species of Cicer

Crenate broomrape (Orobanche crenata) is a major constraint for legume cultivation in Mediterranean agriculture. Field trials, pot and in vitro experiments demonstrated that resistance to O. crenata is present in chickpea and wild species of Cicer. The resistance is the result of the combination of several mechanisms, including low induction of parasite seed germination and in some accessions, either a darkening at the infection site on the host root that prevents establishment, or a reduced development of established parasite tubercles.     

Gene expression profiling of Medicago truncatula roots in response to the parasitic plant Orobanche crenata

Orobanche crenata is a root parasitic weed that is a major constraint for grain and forage legume cultivation in Mediterranean and West Asia. Only moderate to low levels of incomplete resistance of complex inheritance has been identified so far in legume crops, which has hampered genetic and genomic analysis. In the present study, we provide a gene expression profile of roots of the model legume Medicago truncatula in response to infection by O. crenata . M. truncatula accessions SA27774 (complete resistance acting at early penetration stages) and SA4087 (incomplete late acting resistance mediated by necrosis of parasite tubercle) were inoculated with O. crenata seeds in a semi-sterile dish system. Roots were harvested at 15 (first contacts of the parasitism structures with the host roots), 21 (initial stage of parasite tubercle formation on SA4087) and 35 (prior necrosis of well-developed parasite tubercle of on SA4087) days post-inoculation. Array hybridisations revealed several hundred genes up-regulated in response to O. crenata infection. Gene expression patterns suggest that resistance mechanisms activated in both genotypes are temporally and spatially different and resemble those associated with plant resistance to microbial pathogens. Regulated genes identified here represent a comprehensive resource that can be used as a support to breeding strategies for resistance.     

中国20世纪干旱化趋势分析

采用东安格利亚大学气候研究中心的时间序列2.0气象数据集,利用Holdridge可能蒸散率干燥度计算方法,分析20世纪我国干燥度的动态变化。用GIS软件对其结果进行插值计算,并做出干燥度分布的数字化地图。分析结果表明：20世纪我国的湿润气候区面积减少严重,半湿润气候区面积有较大增加,干旱气候区面积增加也较显著,干旱化趋势明显。温度升高和降水量的减少导致了地表水分收支减小,不利于陆地表面的水分累积,是产生和加剧干旱的一个重要因素。     

20世纪塔克拉玛干沙漠环境及其变迁

20世纪,塔克拉玛干沙漠环境的变迁,出现了由自然因素影响为主到人为因素影响为主的转变,表现为生物种群,分布和数量的急剧减少;水系空间分布格局的全面改变;河流下游区雏形沙丘的迅速发育和局部区域小气候环境的恶化等。环境恶化的趋势仍在继续发展。增强人类对大自然的改造作用,减少人类对大自然的破坏影响,是对沙漠环境进行调节控制的有效途径。     

18世纪中叶至20世纪中叶乌鲁木齐城市与区域意象研究

意象是人们对城市与区域环境的感知,空间环境具有辩证性,人们通过经验和价值观主观接受环境的刺激,并对其进行简化、分割、歪曲等处理,形成空间认知。通过梳理18世纪中叶至20世纪中叶对乌鲁木齐相关记载的游记、笔记、日记、诗文等资料,研究了二百年间乌鲁木齐城市意象的变化。     

21世纪初黑龙江省粮食生产的区域差异及成因分析

以县域为基本空间单元,运用塞尔指数和GIS方法分析了黑龙江省粮食生产的空间格局及其区域差异,并基于2000～2007年42个典型县域粮食生产的面板数据建立多元回归评估模型,探讨该省粮食生产区域差异的成因.研究结果表明:(1) 黑龙江省粮食生产主要集中于省域东部、南部和西部,三大片区行政面积约占全省的46%,粮食总产量约占全省的80%.(2) 2000年以来,全省及三大片区内部各县域粮食生产的区域差异逐渐由波动趋于相对稳定.(3) 化肥使用量、农村用电量、耕地面积比重、农村居民人均纯收入、除涝面积是黑龙江省粮食生产区域差异扩大的主要原因,而耕地面积、水库容量则在一定程度上缩小了区域差异.     

Rph20: adult plant resistance gene to barley leaf rust can be detected at early growth stages

Rph20 is the only designated gene conferring adult plant resistance to leaf rust in barley, and to date, it has not displayed race specificity. It is not known at what particular growth stage the onset of Rph20 resistance occurs, or if the expression of the gene could be observed in controlled greenhouse assays. The present studies demonstrated that Rph20 can be identified reliably under greenhouse conditions in 5-week-old seedlings under normal temperature conditions (22?±?2 °C), although the resistance becomes effective at 4 weeks in certain genetic backgrounds. The resistance conferred by Rph20 was strongest and best expressed at cooler temperatures (18?±?2 °C). The effectiveness of Rph20 at cooler temperatures may have important implications in the epidemiology of barley leaf rust under field conditions, by preventing the carryover of inoculum through winter and early spring, leading to a delayed onset of rusting and subsequently lower, if any, yield losses. The detection of Rph20 in early growth stages could help simplifying the selection of the gene in breeding programs and in monitoring Puccinia hordei populations for pathogenicity.     

Impact of land use/land cover types on surface humidity in northern China in the early 21st century

In the context of global change, it is essential to promote the rational development and utilization of land resources, improve the quality of regional ecological environment, and promote the harmonious development of human and nature for the regional sustainability. We identified land use/land cover types in northern China from 2001 to 2018 with ENVI images and ArcGIS software. Meteorological data were selected from 292 stations in northern China, the potential evapotranspiration was calculated with the Penman-Monteith formula, and reanalysis humidity and observed humidity data were obtained. The reanalysis minus observation (RMO, i.e., the difference between reanalysis humidity and observed humidity) can effectively characterize the impact of different land use/land cover types (forestland, grassland, cultivated land, construction land, water body and unused land) on surface humidity in northern China in the early 21^st century. The results showed that from 2001 to 2018, the area of forestland expanded (increasing by approximately 1.80×10⁴ km²), while that of unused land reduced (decreasing by approximately 5.15×10⁴ km²), and the regional ecological environment was improved. Consequently, land surface in most areas of northern China tended to be wetter. The contributions of land use/land cover types to surface humidity changes were related to the quality of the regional ecological environment. The contributions of the six land use/land cover types to surface humidity were the highest in northeastern region of northern China, with a better ecological environment, and the lowest in northwestern region, with a fragile ecological environment. Surface humidity was closely related to the variation in regional vegetation coverage; when the regional vegetation coverage with positive (negative) contributions expanded (reduced), the land surface became wetter. The positive contributions of forestland and water body to surface humidity were the greatest. Unused land and construction land were associated with the most serious negative contributions to surface humidity. Affected by the regional distribution pattern of vegetation, surface humidity in different seasons decreased from east to west in northern China. The seasonal variation in surface humidity was closely related to the growth of vegetation: surface humidity was the highest in summer, followed by autumn and spring, and the lowest in winter. According to the results, surface humidity is expected to increase in northeastern region of northern China, decrease in northern region, and likely increase in northwestern region.     

Identification of sources of resistance to crenate broomrape (Orobanche crenata) in Spanish lentil (Lens culinaris) germplasm

The weedy root parasite Orobanche crenata constitutes a serious threat to lentils and other legumes grown in the Mediterranean and western Asia. Control strategies have centred on agronomic practices and the use of herbicides. Resistance breeding is hampered by scarcity of proper sources of resistance and of a reliable and practical screening procedure. A stepwise procedure was used here. A Spanish germplasm collection of 234 accessions of lentils (Lens culinaris) was screened for resistance to crenate broomrape under field conditions. A wide range of responses was observed, however, complete resistance was not detected. Some accessions exhibited a substantial reduction in broomrape infection. Thirty‐five lentil accessions with reduced broomrape infection were selected for further screening in the field and to determine the components of resistance in pot and in mini‐rhizotron experiments. Low infection seemed to be based on a combination of various escape and resistance mechanisms: (i) a lower root density, (ii) a lower induction of Orobanche seed germination, (iii) the reduced establishment of broomrape radicles and (iv) a limited development of established tubercles. In addition, necrosis of tubercles was observed in some accessions. This study shows how complementary in vitro screening methods may be used to rank and identify lentil accessions with potential broomrape resistance, based on different resistance mechanisms which may in the future be combined into a single cultivar by breeding.     

Variation Among and Within Populations of the Parasitic Weed Orobanche crenata from Spain and Israel Revealed by Inter Simple Sequence Repeat Markers

ABSTRACT The patterns of genetic variation among Orobanche crenata populations from Spain and Israel were studied using radiolabeled inter simple sequence repeat amplification products that were separated in sequencing polyacrylamide gels. The analysis of molecular variance indicated that most of the genetic diversity was attributable to differences among individuals within a population although significant divergences were found between regions. The Jaccard's similarity matrix was analyzed by unweighted pair-group method with arithmetic average and the resultant dendrogram clearly divided six populations by region, with the Spanish populations being more similar to each other than the Israeli populations. These results are consistent with the predominantly allogamous behavior of O. crenata and the extremely efficient dispersal of its seeds.     

Using the age shift method to determine gains from weed management for Pinus radiata in New Zealand

Understanding the effects of interspecific competition on long‐term growth of plantation forestry crops is critical to forest management decisions around methods used for weed control. A series of permanent sample plots (31) incorporating trees maintained either weedy or weed‐free until canopy closure were established across New Zealand between 2000 and 2002. We used the age shift method to characterise growth responses of Pinus radiata, in New Zealand, to interspecific competition over the first third of a typical rotation. Eight years after planting, age shifts between treatments ranged between ?0.60 years and +3.07 years. On average, the age shift due to weed control increased from 0.62 to 0.96 years between 4 and 8 years of age. This was due to divergent tree growth between weedy and weed‐free plots at 55% of the sites, while at 32% and 13% of sites, respectively, differences between treatments remained constant or decreased beyond age 4 years. The magnitude of the age shift was found to be related to the type of weed dominating early interspecific competition, with woody weeds associated with significantly greater age shifts. Continued divergence in tree growth between weedy and weed‐free treatments up to 8 years after planting at the majority of sites was an unexpected result and contrasts with previous literature. In situations where growth divergence continues beyond 2 years, managers should consider continued treatment of weeds to mitigate the detrimental impacts of on‐going competition.     

Orobanche crenata resistance and avoidance in pea (Pisum spp.) operate at different developmental stages of the parasite

Orobanche crenata (broomrape) is an important constraint to pea (Pisum sativum) cultivation in the Mediterranean area, because little resistance is available in commercial crop varieties. Field experiments have demonstrated that some resistance is present in a number of P. sativum and P. fulvum accessions. The goal of this work was to characterize such resistance. The Pisum–O. crenata interaction and the resistance symptoms were studied under controlled conditions by using Petri dish and polyethylene bag assays. The content of phenolics and peroxidase activity in host tissue from infected and non-infected plants were also measured. Resistance and avoidance mechanisms, acting at different developmental stages of the parasite, have been identified, including low stimulation of O. crenata seed germination, unsuccessful penetration of host roots, delay in post-attachment tubercle development and necrosis of the attached tubercles. Infection caused an increase in the content of total soluble phenolics in some Pisum genotypes. Peroxidase activity was higher in resistant than in susceptible accessions. Results obtained with different Pisum genotypes showed that resistance is the result of several mechanisms acting at different stages of the infection process. Resistance is also related to increased levels of peroxidase activity in host roots.     

我国苹果主要病害研究进展与病害防治中的问题

苹果是重要的经济作物,2012年中国的栽培面积已超过200万hm2。在苹果的高产优质栽培中,病害成为制约产业发展的重要因子。腐烂病仍是苹果树上的第一大病害,目前正面临第5次大流行的威胁;苹果实施套袋栽培措施后,枝干轮纹病逐年加重,在环渤海湾和黄河故道苹果产区部分果园的危害已超过腐烂病;褐斑病在西北黄土高原苹果产区每年都造成严重落叶;随着城市和道路的绿化,苹果锈病的危害逐年加重,成为部分果园每年必防的病害;病毒病有进一步扩展蔓延的趋势,正严重威胁着新建果园;“黑点病”是自苹果套袋后新出现的一种病害,每年造成的产量损失约为5%~30%;炭疽叶枯病是2011年在我国新发现病害,正威胁着‘嘎啦’、‘金冠’、‘秦冠’等品种的栽培;苹果疫腐病、炭疽病、霉心病、斑点落叶病、白粉病、褐腐病等病害偶有暴发,生产中不可忽视。本文从病害管理角度出发,回顾了近年来,尤其是成立农业产业体系以后,苹果病害研究方面的进展,分析了病害管理中存在的问题,以促苹果病害管理水平的提高。