Rubber tree (Hevea brasiliensis) trunk phloem necrosis: aetiological investigations failed to confirm any biotic causal agent

Trunk phloem necrosis (TPN) is currently a main constraint in rubber (Hevea brasiliensis) plantations. The apparent spread of the disease, from tree to tree along the planting line, strongly supported the implication of a pathogen that could be transmitted mechanically via the tapping knife. In order to detect a causal agent of the disease, studies focusing on characterization of the known mechanically transmitted pathogens (e.g. viroids, cryptic viruses or phytoplasma) were initiated. RNA strands of low molecular weight (200–400 and >500 bp) displaying structural similarities with viroids and viral dsRNAs were observed in various tested samples. However, attempts to show the potential role of these RNA molecules in the spread of the disease failed. First of all, there was no significant or reproducible correlation between the health status of the rubber trees sampled and these RNA molecules. Moreover, no sequence homology with known pathogens could be found when randomly amplified cDNA fragments isolated from trees presenting the disease symptoms were sequenced. In conclusion, the aetiological investigations, in order to show the presence of a pathogen responsible of the TPN disease, were non‐conclusive, which tends to disprove the hypothesis of a biotic causal agent.     

Spatial distribution of Hevea brasiliensis trunk phloem necrosis within a plot: aggregation but no evidence of constraint on cumulated growth

Trunk phloem necrosis (TPN) is a major constraint in rubber (Hevea brasiliensis) plantations. Current knowledge supports a scenario of a multi‐factor physiological ‘disease’ caused by an accumulation of endogenous and exogenous stresses. Without evidence of a pathogen, the apparent spread of the syndrome from tree to tree along the planting line, strongly suggested the implication of a major local soil constraint. The objectives of the study were to address, within a plot, three points of the above scenario: the short‐distance aggregation of affected trees; their correspondence with local micro‐areas facing the highest environmental constraints; and the relative weakness of TPN trees that had accumulated several stresses since planting. The study was conducted in a young rubber tree stand (clone RRIM 600) of Northeast Thailand, where the number of TPN affected individuals was 8% after 3 years of tapping. Trunk girth and trunk basal area were used as indicators of local environmental constraints. Spatial patterns were analysed using the framework of marked point processes and K functions. The results confirmed the short‐distance aggregation of TPN affected trees. But, TPN trees were not located within micro‐areas where trees had a lower trunk basal area than average. Hence, the clusters of TPN do not occur in the most constraining environmental micro‐areas of the plot in terms of growth since planting. Moreover, from comparison of girth, current girth increment and height of bark consumption, we infer that TPN trees were not smaller and less vigorous than other trees before the syndrome outbreak. Finally, our conclusions mean the previous scenario driven by major soil constraints becomes a ‘more complex scenario’ in which specific soil conditions (not the most constraining in term of cumulated growth), possibly in interaction with inter‐individual competition, induce a late and subtle stress favouring a necrotic reaction against tapping stress.     

Biological activity of soils under rubber trees (Hevea brasiliensis) affected by trunk phloem necrosis

Trunk phloem necrosis (TPN) is currently one of the most economically important diseases of the rubber tree (Hevea brasiliensis). Investigations of the aetiology of the disorder have failed to identify any biotic causal agents but a multidisciplinary study has recently suggested that the disease may be caused by a combination of exogenous and endogenous stresses. These stresses can affect plant physiology and may also have an impact on soil biology and soil biochemistry. In this study, macrofauna diversity and soil enzyme activities were compared for the soils under trees affected by TPN and under healthy trees. Principal component analysis revealed associations between TPN and macrofauna diversity and soil enzyme activities. Groups of ants and termites were associated with the soil under healthy and trees affected by TPN respectively. Polysaccharidase (cellulase, xylanase and, particularly, amylase) activities were lower in the soil under trees affected by TPN whereas N‐acetylglucosaminidase activity was higher. These findings suggested that termite density and N‐acetylglucosaminidase activity are useful indicators of TPN, while lower values of polysaccharidases activities are the consequence of this disease. The impact of TPN on soil ecosystem was discussed.     

Spatial and temporal patterns at small scale in Austrocedrus chilensis diseased forests and their effect on disease progression

Austrocedrus chilensis is an endemic conifer of Patagonia that suffers a widespread mortality whose causes are a topic of discussion. Since Phytophthora austrocedrae is the most probable cause, we proposed that the spatial and temporal patterns of disease at small scale should reflect pathogen behavior. We aimed at characterizing the spatial and temporal patterns of diseased trees in different soil types and the effect of microsite variability on diseased trees spatial pattern. The spatial pattern of disease was influenced by soil type and tree density. In clay soils with low disease incidence (ca. 25%), the spatial pattern was random and not influenced by abiotic microsite conditions. When disease incidence increased (ca. 70%), concurring with denser plots, the spatial pattern was clustered, as a result of an infection process, and it was independent of microsite variability. In soils with better drainage conditions, that is, alluvial soils with volcanic ash input and coarse textured volcanic soils, the disease was clustered and associated with flat microtopographies. The progression of the disease at small scale was influenced by soil, precipitation and tree density. The spatial and temporal patterns of disease progression were associated with a contagion process and with environmental variables that affect drainage, coinciding with Phytophthora biology and requirements. Our results concur in pointing at Phytophthora as the cause of A. chilensis disease in the study area. Management practices should be urgently applied in order to minimize the spread of the inoculum.     

Optimizing Tapping-Tree Density of Rubber (<Emphasis Type="Italic">Hevea brasiliensis</Emphasis>) Plantations in South China

Tapping-tree density in rubber plantations affects the production of dry rubber. Farmers can estimate rubber productivity when they know with certainty the number of tapping trees within a plantation and can therefore increase productivity through optimized planting schematics. Historical data on planting distance between trees and between rows, planting density (trees/ha) and tapping-tree density (number of trees under tapping for latex harvest per hectare) from 1952 to 2014 have been collected for plantations in the Hainan, Yunnan and Guangdong provinces of South China. A plantation survey was conducted to collect more detailed data on current tapping tree and planting densities in various plantations in the three provinces. Planting density and row spacing are found to have increased with rubber tree planting time and plant spacing to have declined from 1952 to 2014. Tapping-tree density of rubber plantations from 1955 to 1995 in South China ranges from 270 to 345 tree/ha, averaging 300 trees/ha. Strong typhoons and cold snaps are important drivers of fluctuations in tapping-tree density. The factors driving tapping-tree density are similar across the three provinces but the degree of change differs between provinces. Tapping panel dryness (due to tapping beyond the natural limit of the rubber tree productivity), severe wind damage and cold damage are the major factors resulting in loss of tapping trees in plantations in South China. These results suggest that a combination of environmental management for extreme weather and targeted breeding could improve tapping-tree density in rubber plantation and therefore dry rubber yield per unit area.     

基于GIS的橡胶园信息管理系统的设计与实现

基于ArcEngine 10.0在Visual Studio 2015平台中设计和构建了云南农垦江城橡胶公司橡胶园信息管理系统。系统具备胶园基本情况查询、胶园生产管理、苗木管理、割胶管理、报表统计、橡胶树营养和胶园土壤养分空间查询分析和配方施肥自动决策等多种功能。     

东风橡胶分公司橡胶芽接树新割制生产情况调查

通过对橡胶树割胶树位调查,低于20割龄胶树实施新割制,一般表现干胶产量增产和年度间产量变化平稳,累计死皮病率低,而高于20割龄胶树实行新割制、老龄割制和强割制,虽然提高刺激剂使用浓度,仍不能表现干胶增产,同时4～5级死皮率明显增高;品系GT1表现比RRIM更耐刺激,增产幅度大,死皮率更低。     

乙烯利刺激对橡胶树热研7-33-97幼龄开割树的乳胶生理影响

通过对未开割胶树进行2％乙烯利刺激,在刺激后的6 h、12 h、24 h、48 h、72 h和CK （未用乙烯利刺激）割胶,分析对橡胶树无性系热研7-33-97幼龄开割树的乳胶生理影响。结果表明,乙烯利刺激稀释胶乳后72 h发生强烈稀释,蔗糖在刺激后48 h开始大量转运进入乳管;乙烯利刺激不同时间后割胶,与对照CK相比：随着割胶刀次递增,干胶含量递减,蔗糖、无机磷（除刺激24 h和72 h外）和硫醇含量在第2刀出现1个最低点,随后逐步升高。差异显著性分析表明,刺激72 h后割胶与短时间刺激干胶含量差异显著,长时间刺激（24 h）后割胶与短时间刺激（6～12 h）割胶蔗糖含量差异显著,72 h内刺激割胶无机磷含量差异不显著。故涂乙烯利刺激72 h后割胶较合适。     

云南橡胶树死皮病与立地环境关系调查

对云南植胶区不同橡胶宜林地、海拔高度、坡向的橡胶树死皮病进行调查,结果表明,死皮病发病率与不同等级宜林地、不同坡向有关:植胶环境条件最好的宜林地死皮病发病率最高,而次等宜林地则发病率随之降低;西坡橡胶树死皮病发病率显著高于其它坡向发病率,从宏观角度一定程度地证实橡胶树营养状态与死皮病的关系。     

茎点霉引起的橡胶幼树叶片病害的初步研究

报道西双版纳由茎点霉引起的一种橡胶幼树林叶片病害,及该病害病原菌的鉴定、防治药剂筛选的初步研究结果。     

Cellulose is degraded during phloem necrosis of Hevea brasiliensis

A cytochemical investigation was performed for studying cellulose alteration during phloem necrosis of the rubber tree. An exoglucanase-gold complex was used for localizing β-(1,4)-D-glucan linkages of non reducing ends of the polymer. Variation in cell wall labelling indicates that cellulose is degraded during this disease and suggests that cellulases are involved in this alteration. Wall appositions and periplasmic vesicles were also observed.     

低割面阴刀(由下往上割)新割胶技术综述及初探

综述了国内外橡胶树低割面阴刀割胶技术的研究结果.河口农场初试亦表明低割面阴刀割胶比常规割制有胶乳干含和产量提高、死皮明显降低的显著效果。     

Land tenure and farm management efficiency: The case of smallholder rubber production in customary land areas of Sumatra

This study assesses the impact of land tenure institutions on the efficiency of farm management based on a case study of rubber production in customary land areas of Sumatra, Indonesia. Using the modes of land acquisition as measures of land tenure institutions, we estimated tree planting, revenue, income, and short-run profit functions, and internal rates of return to tree planting on smallholder rubber fields. We find generally insignificant differences in the incidence of tree planting and management efficiency (defined as residual profits) of rubber production between newly emerging private ownership and customary ownership. This is consistent with our hypothesis that tree planting confers stronger individual rights, if land rights are initially weak (as in the case of family land under customary land tenure systems). On the other hand, short-term profits are higher on land that is rented through share tenancy. This result indicates that rubber trees are over-exploited under renting arrangements due partly to the short-run nature of the land tenancy contracts and partly to the difficulty landowners face in supervising tapping activities of tenants in spatially dispersed rubber fields. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mineral nutrition,resin flow and phloem phytochemistry in loblolly pine

Southern pine beetles and associated pathogenic fungi represent the largest biotic threat to pine forests in the southeastern USA. The two primary defensive mechanisms of the tree to the beetle-fungal complex are the primary oleoresin flow and the concentrations of preformed and induced secondary compounds. We compared oleoresin flow and concentrations of phloem nutrients, soluble sugars, starch, total phenolics and proanthocyanidins in Pinus taeda L. trees in fertilized and control plots in the Sandhills region of North Carolina. Four blocks of 10 trees per treatment were sampled on five dates from May to November 1995. Phloem nitrogen and potassium concentrations were elevated in trees on fertilized plots, whereas phloem calcium concentrations were decreased. Fertilization significantly enhanced (10-20%) concentrations of phloem phenolics and proanthocyanidins. In contrast, phloem soluble sugars and starch concentrations were up to 30% lower in fertilized trees than in control trees. Increased phenolic concentrations and lower nonstructural carbohydrates should correlate with reduced tissue palatability and decreased pathogen susceptibility in fertilized trees; however, resin flows were significantly lower (30-100%) in fertilized trees compared with control trees, which may facilitate pine bark beetle establishment. Furthermore, fertilization-induced increases in phloem nitrogen concentration may be more important than tissue carbohydrate or phenolic content in determining tissue palatability.     

Elm yellows: A phytoplasma disease of concern in forest and landscape ecosystems

Elm yellows (EY) is a lethal or decline phytoplasma disease that affects several Ulmus (elm) species and hybrids, which is widespread in North America and Europe. The symptoms vary among the elm species. In those native to North America, main symptoms include epinasty, chlorosis, premature casting of the leaves, yellow to brown discoloration of the phloem in the roots and stem and tree death that usually occurs within 1 or 2 years from the appearance of foliar symptoms. In contrast, affected trees of European and Asian species are primarily characterized by witches’ broom as a specific symptom, do not show phloem discoloration and are less prone to decline. The disease is caused by a relatively genetically homogeneous phytoplasma, the EY agent “Candidatus Phytoplasma ulmi,” a member of the EY phytoplasma group or 16SrV group, subgroup 16SrV‐A. In nature, this pathogen exhibits a high plant host specificity. The elm leafhopper Scaphoideus luteolus is the only confirmed vector of EY phytoplasma in North America, whereas Macropsis mendax has been reported as a natural vector in Northern Italy. However, other insect vectors are likely to be involved in its natural spread. Phytoplasmas of other taxonomic groups or 16SrV subgroups, which are known to infect a wide range of plant hosts, have been identified in naturally infected elm trees. However, the pathological relevance of these “non‐elm” phytoplasmas needs to be confirmed in many cases. Their detection is mainly based on the highly sensitive nested PCR assays, while pathological data are lacking. This study summarizes, within the framework of a single comprehensive review, the current knowledge of EY. Gaps in knowledge of this disease and prospects for future research are also critically discussed.     

对橡胶树不同品种实行新割制后存在状况的调查与思考

对云南景洪农场六作业区橡胶树RRIM600、PR107、GT1、云研1号等品种实行刺激割胶新割制后的存在状况进行调查,结果表明:胶树的病残株率随着割龄的增加而增高,在开割7年后现存株率、有效割株率及单位面积有效割株数随着树龄的增加而降低;RRIM600在所有割龄段中,相对于其它参试品种表现出较强的适应性,存株率、有效割株率及单位面积有效割株数明显较高、死皮明显较轻。研究提出应在更大范围去深入调查,再认识RRIM600的优良性状,作出新的评价,合理地应用于生产。     

Spatial estimation of the density and carbon content of host populations for Phytophthora ramorum in California and Oregon

Outbreak of the emerging infectious disease sudden oak death continues to threaten California and Oregon forests following introduction of the exotic plant pathogen Phytophthora ramorum. Identifying areas at risk and forecasting changes in forest carbon following disease outbreak requires an understanding of the geographical distribution of host populations, which is unknown. In this study, we quantify and map the population density and carbon contents of five key host species for P. ramorum in California and Oregon, including four hosts killed by the pathogen (Notholithocarpus densiflorus, Quercus agrifolia, Quercus kelloggii and Quercus chrysolepis) and the foliar host Umbellularia californica which supports high sporulation rates. We integrate multiple sources of vegetation data, assembled from sparsely distributed (regional-scale) forest inventory and analysis (FIA) plots and more densely distributed (landscape-scale) plots for monitoring sudden oak death, and develop spatial prediction models based on correlation with environmental variables and spatial dependencies in host abundance. We estimate that 1.8 billion N. densiflorus trees (68 Tg C) and 2.6 billion Quercus host trees (227 Tg C) occur across 3.9 and 17.7 million ha of their respective habitat. A total of 436 million U.californica trees (14 Tg C) occur across 4.2 million ha which frequently overlap with Quercus and N. densiflorus host populations. Combination of landscape-scale data with FIA data resulted in more accurate estimation of host populations and their carbon contents. Forests of northern California and southwest Oregon have the highest concentration of the most susceptible hosts along with climatic conditions that favor pathogen spread. This study represents the first spatially-explicit estimate of P. ramorum host populations and their carbon contents which exceed previously published estimates. Our results will inform landscape- to regional-scale models of disease dynamics and guide management decisions regarding ecosystem impacts including risk of C release following widespread tree mortality.     

巴西橡胶树胶乳生理诊断的研究与应用

橡胶树胶乳生理诊断法是一批法国学者于20世纪80年代发展起来的,用于判断胶树代谢与健康状况的方法。在研究了巴西橡胶树胶乳的各种成分在胶树中的生理功能及其变化规律,以及这些成分与胶树产量之间的相关性后,可以将无性系划分为不同的代谢类型,并根据不同的代谢类型,安排不同的采胶方法;同时也可以根据随机抽样理论找到这些成分的标准参考值,用来判断开割胶树的健康状况,以指导采胶生产。现在胶乳生理诊断主要用于无性系代谢类型判断与采胶强度判断。     

On-farm evaluation of the establishment of clonal rubber in multistrata agroforests in Jambi,Indonesia

Perennial tree crops are often grown in complex multistrata systems that incorporate natural vegetation. These systems contribute simultaneously to sustaining rural livelihoods and to the conservation of biodiversity, but their productivity is usually low. Introduction of high yielding germplasm, usually selected in monocultural plantations, is a potential way to increase productivity, but a critical requirement is that such plants can be established in a competitive multispecies environment. The establishment of clonal planting stock in the jungle rubber agroforests of Indonesia was explored through participatory on-farm research. The trial involved four farmers who grew clonal rubber trees in a total of 20 plots, constituting five replicate experimental blocks spread across four farms. Unexpectedly, vertebrate pest damage by monkeys (Presbytis melalophos nobilis) and wild pigs (Sus scrofa) was the most important influence on establishment, explaining almost 70% of the variation in rubber tree growth. The amount of labour invested in weeding was also positively correlated with rubber tree growth. Farmers generally decided to completely cut back vegetation between rows of rubber trees, including potentially valuable trees, rather than weeding within the rows and selectively pruning trees in the inter-row. Farmers thought that the inter-row vegetation would harbour vertebrate pests and compete with the clonal rubber, and they had access to fruits, firewood and other non-timber forest products from other land. Thus, contrary to expectations, when offered clonal germplasm, farmers opted to use plantation monoculture methods to protect what they considered a valuable asset, rather than maintain the traditional multispecies strategy they use with local germplasm. This revised version was published online in June 2006 with corrections to the Cover Date.     

河南省马尾松采脂量与树体因子关系的研究

通过设置１４块标准地进行采脂试验研究，结果表明，马尾松采脂量与采脂树木的胸径、树贞与树冠大小呈一元线性回归关系，其中采脂量与胸径相关关系极显著，在胸径为１６ｃｍ时，年采脂量为２．５６４ｋｇ；根据我省马尾松资源现状，、应贯彻以生产木材产品、生产松脂为副产品的经营原则；采脂树木胸径应不于１６ｃｍ，以下降式采脂方法为宜。