ACUTE DIE-BACK OF CLOVE TREES IN THE ZANZIBAR PROTECTORATE

The most widespread die-back of clove trees ( Eugenia aromatica) in the Zanzibar Protectorate is caused by Cryptosporella eugeniae sp.nov. The most noticeable symptom is the death of a branch or a portion of a branch, or, in young saplings, of the entire tree; in mature trees infection eventually leads to the semi-moribund trees now common in almost every clove plantation. The fungus invariably enters through a wound, most often one resulting from harvest damage. Pycnidia, and later perithecia, develop near the point of entry. Internally the infected wood is clearly distinguishable from the healthy by a dark red-brown stain.
Experimental infections that reproduce typical symptoms can rarely be caused in plants aged 18 to 36 months, and not at all in young seedlings. Experimental infection of older plants becomes more certain with increasing age, and with saplings of 7–10 years old failure is rare.
The prevalence of Cryptosporella die-back is almost entirely attributable to the destructive methods of harvesting now practised, combined with the presence of much infected material present in the plantations. Suggested control measures are based on the removal of old sources of infection and prevention of future damage, combined with remedial treatment where possible.     

STUDIES IN THE BACTERIAL DIE-BACK AND CANKER DISEASE OF POPLAR

The bacterial die-back and canker of poplar is characterized by dark necrotic areas in the leaves, die-back accompanied by cracks in the bark of 1–4-year-old branches, and by cankers on the trunk and branches of different ages. The cankers may be 'closed' or 'open' and when moist exude slime containing bacteria.
The disease is caused by Pseudomonas syringae f. sp. populea , a new forma specialis closely resembling Ps. syringae in bacteriological characters but differing from it in parasitism. The association of the slime with the bacteria is essential for the production of typical lesions.
Inoculations with the pathogen alone, or in association with other organisms produce atypical symptoms.
The bacteria attack the cortical parenchyma and occasionally invade the xylem vessels.     

Bacterial canker of poplars in Britain: The cause of the disease and the role of leaf-scars in infection

Bacterial canker and die-back of poplars in Britain is caused by Aplano-bacterium populi Ridé. Pseudomonas syringae (van Hall), which has been suggested as the causal agent, plays at most only a minor role in canker lesions. It may cause a shoot blight in spring, a distinct pathological condition frequently associated with bacterial canker. Marked variation in infectivity of bacterial slime between seasons and at different dates of collection within one year appears to be the main cause for situations in which varieties, resistant in trials to inoculation with slime, have proved susceptible in the field. Leaf scars afford the main avenues for infection but their infectibility declines rapidly during October. The implications of the temporal separation of availability of natural inoculum and available infection sites are discussed.     

Tree regeneration after bamboo die-back in Chinese Abies-Betula forests

Abstract. Gaps created by disturbance in the forest canopy are important sites for tree regeneration from seed but plants already established in gaps may slow gap-filling. This study deals with consequences of bamboo die-back for tree regeneration and the dynamics of Abies-Betula forests in southwest China. Bamboo dominates the forest understory impeding tree regeneration when in its vegetative phase. Populations of tree seedlings were sampled in 1984–85 and 1990 in two sets of permanent plots where bamboo had died back in 1983. Both Abies and Betula density increased after bamboo die-back, Betula more so than Abies, especially in gaps. Before bamboo die-back, seedlings were established on raised surfaces such as logs but afterwards seedlings became common on the forest floor. This reduced the intensity of clumping of seedling populations between 1984 and 1990. A tree by tree replacement model predicts an increase in Abies and a decrease in Betula after bamboo die-back. Life histories of tree species, gap characteristics, and the bamboo growth cycle (mature/die-back/building) interact to promote fluctuating dominance of Abies and Betula in old-growth forests.     

Central Die-back of Monoclonal Stands of Reynoutria japonica in an Early Stage of Primary Succession on Mount Fuji

Reynoutria japonica is a common perennial pioneer species onJapanese volcanoes. In a volcanic desert (1500m above sea level)on Mount Fuji (3776m), central Japan, this species forms circularstands (patches). As a patch develops, shoot density decreasesin its centre (‘central die-back’). The centraldie-back has been considered a key process in the early stagesof primary succession, though its mechanism has been unknown. The pattern of patch development, population dynamics of aerialshoots, and growth patterns of below-ground organs were analysedin order to investigate the mechanism of die-back, and the followingtraits are clarified: (1) central die-back areas occur in mostsmall patches (approx. 1m²) without later successional species;(2) shoot characteristics are dependent both on their positionwithin a patch and on patch size; (3) despite the large differencesin shoot density, neither time course of shoot growth nor theirmortality differs between the centre and periphery of patches;and (4) rhizomes ofR. japonicagrow outwards with regular sympodialbranching. From these results, it is concluded that neither interspecificnor intraspecific competition is likely to be a primary causeof the die-back phenomenon, but that central die-back is broughtabout intrinsically by the growth pattern of the rhizome systems.We also discuss the importance of the central die-back in facilitatingestablishment of later successional species in the early stagesof primary succession. Clonal plant; central die-back; competition; facilitation; Japanese knotweed; Mount Fuji; primary succession;Reynoutria japonica ; rhizome growth; volcanic desert     

A survey of die-back disease of neem in Tamil Nadu,India and PCR-based confirmation of the isolates

A survey of die-back disease of neem was done in different agro climatic regions of Tamil Nadu, India using Global Positioning System (GARMIN 12). Twigs of Azadirachta indica (Neem) infected with die-back were collected from different regions of Tamil Nadu, India and they were further analyzed to determine the pathogen. Phomopsis azadirachtae the causal organism was isolated on malt extract agar from die-back infected neem twigs. They were identified by conventional and molecular methods. Phomopsis genus specific primers (5.8S r-DNA) were then used for the confirmation of P. azadirachtae – the causative agent of die-back of neem by Polymerase chain reaction (PCR). Studies revealed the amplification of expected 141bp DNA in P. azadirachtae isolated from the diseased trees of different regions of Tamil Nadu confirming the causal organism of die-back of neem. Studies revealed a very high incidence of die-back in most of the places of Tamil Nadu. Hand held GPS was used in the study which would help in continuous monitoring of the diseased trees.     

Mechanisms of Central Die-back of Reynoutria japonica in the Volcanic Desert on Mt. Fuji. A Stochastic Model Analysis of Rhizome Growth

Reynoutria japonica (Polygonaceae) is a pioneer clonal herbcolonising the volcanic desert on Mt. Fuji (height 3776 m),central Japan; establishment of secondary successional speciesoccurs only in the central die-back parts of the clonal standsofR. japonica. Clonal stands were excavated and the morphologyand growth pattern of the rhizomes were investigated with specialreference to the mechanisms of central die-back. Four morphologicalparameters, length of mother rhizomes, and number, branchingpositions and branching angle of daughter rhizomes on respectivemother rhizomes were measured or counted, and their roles inrhizome growth were examined employing a stochastic computersimulation model of the whole stand development. The simulationsclarified that, of these four parameters, the branching anglewas the most influential determinant of the whole pattern ofshoot distribution and that the central die-back was producedwhen the mean branching angle was 40° or smaller. Theseresults strongly infer that the onset of central die-back iscaused intrinsically byR. japonica itself by having the meanbranching angle of 40°. The adaptive significance of thegrowth pattern is discussed in relation to resource acquiringand habitat exploitation strategies of this species. Below-ground morphology; branching angle; central die-back; clonal plant; computer simulation; Japanese knotweed;Reynoutria japonica Houttuyn; rhizome growth pattern     

Diverse sources of infection and cryptic recombination revealed in South African Diplodia pinea populations

This study considers the population diversity and structure of Diplodia pinea in South Africa at different spatial scales from single trees to plantations, as well as comparing infections on healthy and diseased trees. A total of 236 isolates were characterized using 13 microsatellite markers. Analysis of these markers confirmed previous results that D. pinea has a high level of gene and genotypic diversity in South Africa, with the latter values ranging from 6% to 68% for the different plantations. The data also reflect a fungus with randomly associated alleles in populations at local plantation scales and for the population as a whole. These results suggest that recombination is occurring in D. pinea and that it most likely has a cryptic sexual state. The study also reveals the sources of endophytic infection and stress related disease out-breaks as diverse infections that have occurred over a long time period. In contrast, wound-associated die-back appears to be caused by clones of the pathogen occurring in narrow time frames.     

Seedling development of the miombo woodland tree Julbernardia globiflora

Abstract. The development of seedlings of the miombo tree (Julbernardia globiflora) was studied for 28 months (December 1987 - April 1990) at a Zambian grassland site from which fire has been excluded for many years. Germination occurred 10–25 days after seed planting and germination rates under laboratory and field conditions did not differ significantly. Seed germinability after one year of storage declined to 38 %. Leaf production occurred between December and April with peaks in January each year. Leaf fall occurred steadily throughout the dry season but leafless seedlings were first observed in August of each year. All seedlings had shed all their leaves by the end of November during the first year while 10% of the seedlings remained leafy throughout the second year. Annual seedling mortality was about 60 % during the first year and declined to 3 6 % during the second year. Survivorship appeared to stabilise at 3 8 % when seedlings were 5 5 - 5 9 weeks old. Every seedling experienced shoot die-back during the first hot dry season (September - November) when open-pan evaporation rates averaged 5–10 mm / day. However, shoot mortality did not necessarily result in plant mortality. Because of recurrent shoot die-back there was little increase in shoot biomass and height at the end of the second and third growing seasons. Seedlings that survived shoot die-back sprouted from roots which showed a steady annual accumulation of biomass. Early shoot die-back in seedlings of Julbernardia globiflora as documented in this study was not causedby fire but most probably by drought and / or nutritional stress.     

Comparison between biomass and C,N, P,S contents of vigorous and die-back reed stands of Lake Fertő/Neusiedler See

The production of vigorous and die-back sites of the same reed belt and nutrient content of reed were studied to detect possible causes of reed die-back. Shoot density, total aboveground and belowground biomass and their C, N, P and S contents were also determined.     

An overview of the effects of phytotoxins on Phragmites australis in relation to die-back

The accumulation in sediments of the low molecular weight, volatile, monocarboxylic acids and/or sulphide, generated by the decay of (i) the underground parts of the reed and/or (ii) organic deposits produced under eutrophic conditions, may play a crucial part in Phragmites die-back. In the field high levels of some of these phytotoxins have been detected at certain die-back sites and in sediments containing the rotting underground parts of the plant.Symptoms of die-back include a clumped habit, stunting and death of roots and shoots, bud death, premature senescence of shoots, weakened stems, impeded aeration of the underground parts of the plant due to callus development, blockages within the vascular systems, lignification and suberisation of laterals and apical regions of adventitious roots and lower levels of starch in rhizomes. Poor convective aeration of the rhizome system has also been associated with higher proportions of alanine, γ-amino butyric acid and serine in culm bases, indicating hypoxic metabolism in the underground system.In laboratory experiments plants developed almost all of the growth, morphological and anatomical symptoms of die-back when treated with various single phytotoxins, e.g. acetic, propionic, n- and iso-butyric and n-caproic acids and sulphide at concentrations reported for die-back sites and/or associated with the decaying underground parts of the plant. For each acid alone, a concentration of ca. 1 mM, was highly toxic at pH 4.5, but relatively non-toxic at pH 6.0. However, when a cocktail of the five acids was applied (where each acid was 1 mM) the mixture proved to be toxic even at pH 6.     

果树盲蝽的发生与防控技术

近年来,盲蝽在我国果树上大量发生,刺吸危害枣、葡萄、苹果、梨、樱桃、桃树等果树,造成嫩芽皱缩,落蕾落花,叶片穿孔,水果畸形脱落,导致严重的经济损失。本文介绍了我国果树上盲蝽的种类、危害和发生规律,综述了果树盲蝽防治策略和防治措施,提出了果树盲蝽的防控对策和建议。     

Effects of Extreme Weather Events on Plant Productivity and Tissue Die-Back are Modified by Community Composition

Extreme weather events are expected to increase in frequency and magnitude due to climate change. Their effects on vegetation are widely unknown. Here, experimental grassland and heath communities in Central Europe were exposed either to a simulated single drought or to a prolonged heavy rainfall event. The magnitude of manipulations imitated the local 100-year weather extreme according to extreme value statistics. Overall productivity of both plant communities remained stable in the face of drought and heavy rainfall, despite significant effects on tissue die-back. Grassland communities were more resistant against the extreme weather events than heath communities. Furthermore, effects of extreme weather events on community tissue die-back were modified by functional diversity, even though conclusiveness in this part is limited by the fact that only one species composition was available per diversity level within this case study. More diverse grassland communities exhibited less tissue die-back than less complex grassland communities. On the other side, more diverse heath communities were more vulnerable to extreme weather events compared to less complex heath communities. Furthermore, legumes did not effectively contribute to the buffering against extreme weather events in both vegetation types. Tissue die-back proved a strong stress response in plant communities exposed to 100-year extreme weather events, even though one important ecosystem function, namely productivity, remained surprisingly stable in this experiment. Theories and concepts on biodiversity and ecosystem functioning (insurance hypothesis, redundancy hypothesis) may have to be revisited when extreme weather conditions are considered.     

Branch sacrifice: cavitation-associated drought adaptation of riparian cottonwoods

In their native riparian zones (floodplains), Populus deltoides (prairie cottonwood) and P. fremontii (Fremont cottonwood) commonly experience substantial branch die-back. These trees occur in semi-arid areas of North America and unexpectedly given the dry regions, they are exceptionally vulnerable to xylem cavitation, drought-induced air embolism of xylem vessels. We propose that the vulnerability to cavitation and branch die-back are physiologically linked; drought-induced cavitation underlies branch die-back that reduces transpirational demand enabling the remaining shoot to maintain a favorable water balance. This proposal follows field observation along various western North American rivers as precocious branch senescence, the yellowing and death of leaves on particular branches during mid- to late summer, was common for P. deltoides and P. fremontii during hot and dry periods of low stream-flow. Branches displaying precocious senescence were subsequently dead the following year. The proposed association between cavitation, precocious senescence and branch die-back is also supported by experiments involving external pressurization of branches to about 2.5 MPa with a branch collar or through an adjacent cut-branch. The treatments induced xylem cavitation and increased leaf diffusive resistance (stomatal closure) that was followed by leaf senescence and branch death of P. deltoides. P. trichocarpa (black cottonwood) appeared to be less affected by the pressurization treatment and this species as well P. angustifolia (narrowleaf cottonwood) and P. balsamifera (balsam poplar) seldom display the patchy summer branch senescence typical of P. deltoides and P. fremontii. ’Branch sacrifice’ describes this cavitation-associated senescence and branch die-back that may provide a drought adaptation for the prairie and Fremont cottonwoods. Received: 13 May 1999 / Accepted: 4 November 1999     

Seedling ecology of two miombo woodland trees

The development of seedlings of two miombo trees, Brachystegia spiciformis Benth. and Julbernardia paniculata (Benth.) Troupin, was studied during two growing seasons (December 1989–April 1991) at a Zambian grassland site. Seed germination rates under laboratory and field conditions were not significantly different although germination in the field was delayed by 1–2 weeks due to insufficient rainfall. After one year of storage J. paniculata seed germination had declined from 67% to 17% while germination of B. spiciformis seeds remained at about 83%.Leaf production was confined to the rainy season. Leaf fall occurred during the dry season and in J. paniculata this was followed by shoot die-back during the hot dry period (August–November). Two-thirds of B. spiciformis seedlings experienced shoot die-back but shoot die-back did not necessarily result in seedling mortality. Seedling deaths occurred during the germination period (6–10 weeks after planting) and in the hot dry period (40–50 weeks after planting) during September–November. Survivorship of B. spiciformis seedlings was 74% at the end of the second growing season while this was 46% for J. paniculata.Shoot growth was negligible during the second growing season. In fact mean maximum leaf area of B. spiciformis decreased significantly from 19.7 cm² (SD=5.7) per plant at the end of the first growing season to 13.3 cm² (SD=5.8) at the end of the second growing season (t=3.31, P<0.01). However, root biomass of B. spiciformis seedlings increased 2.8 times during the second growing season.These results suggest that shoot die-back in seedlings of miombo trees is caused by drought and that the slow shoot growth is the result of allocating most of the biomass to root growth during seedling development.     

Genetic survey on a reed-bed in Central Italy showing early die-back symptoms

Phragmites australis die-back is a well known phenomenon in Central Europe and rather recently observed also in some Mediterranean wetlands. In this study we analyze the genetic structure of a reed-bed in a protected wetland in N-W Tuscany (Italy) recently showing some clear symptoms of die-back, in particular the clumped growth-form, searching for any possible relationships with the ecological condition or the health status of common reed stands. After a diachronic analysis of vegetation maps (from 1988 to 2013) and a field survey, we have sampled four temporarily emerged and four permanent submerged reed stands, being the submersion regime a crucial trigger of reed die-back. Aquatic plots showed two clear conditions, with the presence of clumped and non-clumped stands. Emerged stands have been sampled in areas showing temporarily stable, increasing and decreasing reed-bed surface. In order to investigate the genetic structure of the population, the AFLP technique was applied on 69 individuals. The total reedbed surface showed a decrease in the observed time, partly due to the human activities and partly attributable to the RDBS. In several areas of the Lake the reed-bed appeared clumped and fragmented. The genetic analysis put in evidence a rather high level of genetic diversity, compared to the results of previous international studies on other populations of the same species. No significant differences between temporarily and permanently submerged stands were found. The major portion of genetic variation appeared within sampling sites rather than between sampling sites, indicating the absence of isolation between the different reed stands of the lake and a negligible role of genetic diversity in the occurrence of die-back symptoms.     

铁皮石斛疫病及其病原菌

铁皮石斛疫病2001年发现在浙江义乌栽培田间,是由疫霉菌引起的。在田间,疫霉菌侵染茎基部,引起当年移植苗根腐、植株枯萎和死亡,但侵染2-3年植株幼嫩顶部仅引起顶枯症状。通过对病原菌形态学、交配型的观察,以及核糖体DNAITS序列分析,侵染铁皮石斛的5个分离菌株被鉴定为烟草疫霉菌Phytophthora nicotianae。致病性试验表明,铁皮石斛是烟草疫霉菌的寄主。     

Phragmites die-back: toxic effects of propionic, butyric and caproic acids in relation to pH

Symptoms which are associated with die-back in Phragmites : growth inhibition, root and bud death, premature shoot senescence, blocked aeration and vascular systems, especially in rhizomes and roots, and abnormal surface and internal cell-wall lignification and suberization of roots were induced by each of three of the lower volatile organic acids, propionic, butyric and caproic. These acids were applied in nutrient media in concentrations similar to those previously associated with die-back sites and/or in sediments containing rotting rhizomes and roots of the plant. At concentrations of 1.4 and 0.56 mM, respectively, butyric and caproic acids were each found to be highly toxic at pH 4.5, but relatively innocuous at pH 6. Propionic acid, applied at a much higher concentration of 10.4 mM, was highly toxic at both pH 4.5 and 6. The results support previous findings that the undissociated forms of the organic acids are the more toxic. Rhizomes and roots, rotting in water or waterlogged sand, released cocktails of acids and produced pH in the range 4.8–5.4. Phragmites seedlings planted in these media died within 12 h. Overall, the results support the theory that die-back in Phragmites can be induced and/or perpetuated by organic acids released from the decaying underground parts of the plant or other sources of organic matter.     

Effect of Multiple Freezing/Thawing Cycles on the Structural and Functional Properties of Waxy Rice Starch

The structural and functional properties of non-gelatinized waxy rice starch were investigated after 1, 3, 7, and 10 freezing/thawing cycles. Freezing caused an increasing damaged starch from 1.36% in native waxy rice starch to 5.77% in 10 freezing/thawing-treated starch (FTS), as evidenced by the cracking surface on starch granules. More dry matter concentration was leached, which was characterized by high amylopectin concentration (4.34 mg/mL). The leaching was accompanied by a decrease in relative crystallinity from 35.19% in native starch to 31.34% in 10 FTS. Freezing treatment also led to significant deviations in the functional characteristics, for instance decreased gelatinization temperature range, enthalpy, and pasting viscosities. The resistant starch content of 10FTS significantly decreased from 58.9% to 19%, whereas the slowly digested starch content greatly increased from 23.8% in native starch to 50.3%. The increase in susceptibility to enzyme hydrolysis may be attributed to porous granular surface, amylopectin leaching, and the decrease in the relative crystallinity caused by freezing water.     

The effect of different preservation methods on the carbon content of megacyclops gigas

The effect of various preservation methods on the carbon content of the copepod Megacyclops gigas was studied using the carbon content of living animals as a control. No differences were found between animals dried at –20, +60, or +105°C, but in all cases the carbon content was slightly lower than that found in living animals. Chemical preservation with formaldehyde and acid Lugol's solution rapidly resulted in about 35% loss of carbon. Freezing at –20°C in water caused less marked but significant loss of carbon, whereas freezing in dilute formaldehyde yielded values agreeing with those of living animals.