The histology of Hevea brasiliensis phloem necrosis

Phloem necrosis of rubber tree(hevea brasiliensis)is characterized by cel wall degradation, alteration of the middle lamella, the vesiculation of endomembranes, the formation of tylosoids and the internal coagulation of rubber.     

Statistical analysis of the spatio‐temporal dynamics of rubber tree (Hevea brasiliensis) trunk phloem necrosis: no evidence of pathogen transmission

Trunk phloem necrosis (TPN) of Hevea brasiliensis is an irreversible syndrome of the phloem that spreads from the collar towards the tapping cut. It is responsible for the cessation of latex production, the main constraint in rubber plantations worldwide. Numerous investigations have been undertaken to understand the mechanisms of this disease. The apparent linear spread of TPN supported the initial hypothesis of a biotic causal agent for TPN. However, previous and recent aetiological analyses remained inconclusive and the pathogen hypothesis is tending to be abandoned. In this paper we present a complementary statistical analysis of spatio‐temporal epidemiological data collected in a rubber plantation in Côte d'Ivoire. There, four study plots were surveyed each year from 2000 to 2003, with tree‐by‐tree disease assessment. In two plots, the tapping knife was systematically disinfected with sodium hypochlorite to stop any virus or viroid transmission. Based on permutation tests, our analysis confirmed the aetiological results: there was no evidence for spread by pathogen transmission. However, the spatial structure of the disease was clear. These results strengthen the current alternative scenario of a multi‐factor physiological disease caused by an accumulation of exogenous and endogenous stresses. Spatial heterogeneity of the risk factors probably results in the presence of areas of stress that can explain the spatial patterns observed among the TPN cases. The final contribution of this study was confirmation of the curative effect of sodium hypochlorite in the earliest stages of the disease, thus opening the way for control of this disease.     

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.     

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.     

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.     

Evaluation of unconstrained and constrained mathematical functions to model girth growth of rubber trees (Hevea brasiliensis) using young age measurements

No attempt has been made to date to model growth in girth of rubber tree (Hevea brasiliansis). We evaluated the few widely used growth functions to identify the most parsimonious and biologically reasonable model for describing the girth growth of young rubber trees based on an incomplete set of young age measurements. Monthly data for girth of immature trees (age 2 to 12 years) from two locations were subjected to modelling. Reparameterized, unconstrained and constrained growth functions of Richards (RM), Gompertz (GM) and the monomolecular model (MM) were fitted to data. Duration of growth was the constraint introduced. In the first stage, we attempted a population average (PA) model to capture the trend in growth. The best PA model wasfitted as a subject specific (SS) model. We used appropriate error variance-covariance structure to account for correlation due to repeated measurements over time. Unconstrained functions underestimated the asymptotic maximum that did not reflect the carrying capacity of the locations. Underestimations were attributed to the partial set of measurements made during the early growth phase of the trees. MM proved superior to RM and GM. In the random coefficient models, both Gf and G0 appeared to be influenced by tree level effects. Inclusion of diagonal definite positive matrix removed the correlation between random effects.The results were similar at both locations. In the overall assessment MM appeared as the candidate model for studying the girth-age relationships in Hevea trees. Based on the fitted model we conclude that, in Hevea trees, growth rate is maintained at maximum value at t0, then decreases until the final state at dG/dt ≥ 0, resulting in yield curve with no period of accelerating growth. One physiological explanation is that photosynthetic activity in Hevea trees decreases as girth increases and constructive metabolism is larger than destructive metabolism.     

Effect of tapping activity on the dynamics of radial growth of Hevea brasiliensis trees

Rubber tree (Hevea brasiliensis Müll. Arg.) radial growth dynamics were monitored with displacement sensors, together with latex production, to investigate three aspects of the dual production of latex and wood: (1) the usefulness of fine-scale dendrometric measurements as a physiological tool to detect water shortage through radial growth; (2) the dynamic aspects, both at the seasonal and at the multi-year scale, of the competition between latex and wood production; and (3) the spatial distribution of radial growth rates around the tapping cut. Radial growth of untapped control trees started with the onset of the rainy season and lasted until the onset of the dry season, ceasing completely during the driest period. Displacement sensors provided a sensitive means of detecting water shortage, with a clear correlation between diameter variations and changes in water availability (both daily evapotranspiration and monthly rainfall) over the whole annual cycle. However, the correlation was significantly disturbed in tapped trees. After resumption of tapping, the radial growth rate dropped sharply within two weeks and the effect persisted throughout the whole season, so that the cumulative growth of tapped trees was about half that of untapped trees, with the cumulative growth deficit reaching 80% for the period from mid-June to November. This long-known negative impact of tapping on growth was much stronger in the second year of tapping than in the first, whereas latex production increased significantly between the first and second year of tapping. The increased latex production, which could not be ascribed to climatic conditions, shows that the establishment of an artificial latex sink is a progressive, long-term process likely involving many aspects of metabolism. As expected, ethylene significantly increased latex production in both years; however, ethylene had no effect on the growth rates of tapped trees. Radial growth was differentially affected at different locations around the tapping cut, with growth rates significantly lower in the tapped panel than in the untapped panel, and higher above the cut than below the cut. Thus, caution is needed when deriving whole stem wood production from girth measurements at one location on the stem, especially from girth measurements made close to the tapping cut. This also provides new evidence for the location of the latex regeneration area in the tapped panel, below the cut.     

Growth,photosynthetic performance and shade adaptation of rubber (Hevea brasiliensis) grown in natural shade

We compared growth, photosynthetic performance and shade adaptation of rubber (Hevea brasiliensis Muell. Arg.) plants growing in natural shade (33, 55 and 77% reduction in incoming radiation) to control plants growing in full sunlight. Stem diameter and plant height, measured over a 15-month period, were greatest in plants grown in full sunlight, and both parameters decreased with increasing shade. At 7 and 14 months after planting (MAP), total plant dry mass was highest in control plants and lowest in plants in 77% shade. Expansion of the fourth leaf whorl, monitored at 5-6 MAP, was slowest in plants in 77% shade and fastest in unshaded plants, which had more leaves and higher leaf areas and inter-whorl shoot lengths. In response to increasing shade, specific leaf area increased, whereas leaf weight ratio and relative growth rate decreased. Chlorophyll a/b ratio decreased with increasing shade, indicating shade-induced partitioning of chlorophyll into light-harvesting complexes. Compared to the response in unshaded plants, CO2 assimilation saturated at lower photosynthetic photon flux densities in plants in 77% shade, with a lower upper-asymptote to the light response curve. Chlorophyll fluorescence revealed no evidence of sustained photoinhibitory damage in unshaded plants. Dynamic photoinhibition decreased with increasing shade, with the greatest depression in the ratio of variable to maximal fluorescence around midday. We conclude that shade adaptation and shade-induced reductions in dynamic photoinhibition account for the enhanced early growth of rubber in light shade.     

Tree species growth under a rubber (Hevea brasiliensis) plantation: native restoration via enrichment planting in southern Bahia,Brazil

Enrichment planting is a technique that is gaining recognition for its potential to restore native forests. Due to the steep economic trade-offs involved and dearth of silvicultural and ecological knowledge about native flora, however, it remains unclear whether it has promise for widespread application. Focusing on growth performance, this study explores the restoration potential of twenty-one native tree species 3 years after planting in the understory of a rubber plantation in southern Bahia, Brazil. We tested the effects of slope, aspect, successional guild and basal area of the overstory rubber trees on the enriched species’ height, root collar diameter, and diameter at breast height. Height was the growth parameter that most differentiated species, with Parkia pendula, Sloanea monosperma, and Tachigali densiflora being three of the most successful species. Pioneer species grew faster than the non-pioneer species. Overstory basal area was the most important variable influencing the performance of the planted tree seedlings, while aspect and slope were less important. For every additional unit of basal area per hectare of rubber, there was an incremental decrease in the growth rates of the enrichment species. This suggests that the tree species are likely limited by available light, and that there are distinct trade-offs between overstory rubber density and understory tree species growth that are important to consider when accelerating forest recovery by using enrichment planting techniques.     

Influence of sheep grazing on soil chemical properties and growth of rubber (Hevea brasiliensis) in Malaysia

In a rubber estate in Kelantan, Malaysia, sheep grazing increased N, P, Ca and Mg levels and soil pH. Foliar N, P, Ca, Mg and Na also increased with grazing, but K decreased. The girth of rubber trees under grazing had a higher increment than in the ungrazed areas.     

不同采收年限和月份对大丰95橡胶树产胶量的影响

为探讨不同采收年限和月份对大丰95橡胶树产胶量的影响,采用统收统测的方式对13个5~18 a中低割龄的大丰95无性系树位的5~12月份干胶产量进行测定分析。结果表明,不同割龄和不同采割月份的大丰95月株产干胶量和月公顷产干胶量差异均明显,其中,8个采割期中,株产干胶量和公顷产干胶量由高到低的月份均依次为11、7、6、8、9、10、12、5月。13个割龄中,11 a的年株产干胶量最高,达4.90 kg,16 a的年公顷产干胶量最高,达1 807.97 kg,18 a的年株产干胶量和年公顷产干胶量均最低,分别为2.59、373.82 kg,最高值与最低值间差异达极显著水平(P0.01)。13个割龄的月公顷产干胶量和年公顷产干胶量与月株产干胶量和年株产干胶量均呈极显著正相关(P0.01),而所有割龄与年株产干胶量和年公顷产干胶量的正相关均不显著。综上可见,大丰95中低割龄橡胶树的干胶产量显著受采收月份影响,而随采收年限变化则不明显。     

Radial variation of wood cell features under different stocking densities management of two new clones of rubberwood (Hevea brasiliensis)

Wood characteristics vary from pith to bark and this can influence the final use. These variations can be related to the effects of plantation management. The radial variation in fiber cells, vessel elements, and ray cells was investigated for a commercial and fast-grown species, the rubberwood (Hevea brasiliensis), at varying stocking densities. Nine-year-old trees of two new clones (RRIM 2020 and RRIM 2025) were categorized into four stocking densities of 500, 1000, 1500, and 2000 trees ha^?1. The sample blocks were anatomically analyzed to determine the changes in wood cells from pith to bark. The results generally showed a centrifugal increase in fiber features, vessel diameter, ray height, and ray area. Vessel density and ray density showed a decreasing trend. Vessel areas revealed a radial irregular variation. The ray area showed a striking relationship with ray density and ray height. Ray cell pattern indicated enough variation for visual approval to ensure within and between stocking density changes. Most radial variation was explained by the effect of cambial age. Owing to different stem width and growth rates, the mean cell features were not at the same radial distances from the pith.     

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。     

橡胶树冷应答转录组cDNA-AFLP分析

以橡胶树11个抗寒无性系和12个不抗寒无性系为研究对象,利用cDNA-AFLP技术对23个橡胶树无性系低温处理前后的基因表达谱进行差异分析。结果表明:通过100对引物组合的扩增筛选,共获得12条在2组材料中表现一致的差异片段(GenBank登录号:GO269543-GO269554);BLASTn和BLASTx比对分析显示,TDF7-8,TDF5-15,TDF16-103条片段分别与植物抗逆相关的ABC转运蛋白、3-脱氧-D-阿拉伯庚酮糖-7-磷酸合成酶(DAHPS)、WRKY基因有较高相似性,其余9条片段在GenBank未比对到同源序列。     

橡胶树优异种质的AFLP初步分析

通过AFLP方法,对15份特异种质及在云南植胶区选择的45份优良单株进行了基于遗传相似性系数的UPGMA聚类分析,得到60份优异种质的聚类图,并初步分析了60份种质间的遗传变异情况及AFLP方法对于分析橡胶树遗传变异的实用性,为橡胶树选育工作及该60份种质的进一步鉴定利用奠定基础。     

Biodegradation of Hevea brasiliensis wood by Rigidoporus lignosus and Phellinus noxius1

In vitro wood slats degradation assays reveal that both the white root rot fungus R. lignosus and the brown root rot fungus P. noxius cause a white rot of wood. In vivo (infected tap roots) they cause the same type of decay. Nevertheless lignin determination show the rubber-tree ability to react against the parasite aggression by increased lignification of tissues.     

用抑制消减杂交法分离巴西橡胶树胶乳特异表达基因

采用巴西橡胶树常割树胶乳的Poly(A )RNA为Tester,叶片Poly(A )RNA为Driver,通过抑制消减杂交法(suppressive subtractive hybridization,SSH)构建了一个胶乳特异表达基因差减文库,通过菌落PCR及反式Northern Dot-Blot筛选鉴定阳性差异片段,获得79个胶乳特异表达阳性克隆,部分阳性克隆还通过Northern Blot杂交及RT-PCR进一步验证.随机挑选部分阳性克隆序列比较分析,结果表明有部分克隆与巴西橡胶树中已知的基因相同,而多数克隆在巴西橡胶树中是新发现,它们与橡胶生物合成、物质代谢运输、信号传导和形态建成等相关.     

橡胶树PR107气刺微割排胶影响面胶乳生理分析

研究未刺激、乙烯利刺激、乙烯气体刺激胶树微割排胶影响面内不同高度部位胶乳的蔗糖、无机磷、总固形物含量和水势,并比较分析同种处理割胶前后及不同处理间割胶前后胶树胶乳中这些生理参数的差异变化,结果表明:乙烯气体刺激较其他2种处理能够较明显扩大胶树排胶影响面,有利于增加胶树胶乳产量.并提出用开割前和停排后的胶乳干含差来指导割胶生产.     

电导法配合叶片SPAD值鉴定橡胶树无性系的抗旱性

以田间鉴定为依据,选择橡胶树6个优树无性系为材料,对叶片的相对电导率、相对含水量、持水力及SPAD值进行测定。结果表明,在干旱胁迫期间,橡胶树不同无性系的叶片相对电导率和含水量存在极显著差异,表现出抗旱性强的无性系其相对电导率低,相对含水量高,测定的SPAD值也相对较高;相关性分析表明,SPAD值与胁迫后电导率上升幅度、相对含水量及胁迫21 h持水力间呈显著相关(P0.05)。运用电导法配合叶片SPAD值对橡胶树种质资源的抗旱性进行规模化筛选简便快捷,结果具有一定可靠性。