Can pruning help maintain vitality of ash trees affected by ash dieback in urban landscapes?

Hymenoscyphus fraxineus causes a destructive invasive tree disease known as ash dieback threatening the survival of common ash not only in the forests, but also in urban and landscape settings. Pruning is a potential management practice that could help maintain tree vitality and aesthetics in parks, gardens, alleys and recreation areas, as well as maintaining veteran trees having high heritage or cultural value, or trees with high genetic importance (e.g. located in clonal seed orchards). In this study we investigated the maximum distance proximal to the lesion margin at which H. fraxineus can be detected on individual branches infected by the fungus in order to provide recommendations for pruning. Pruning of branches was carried out on 38 trees in southern Sweden. Tissue samples including bark and wood were collected from the margin of the lesion and at 5 cm intervals proximal to the lesion. Molecular analysis revealed presence of H. fraxineus in 91.3% of the investigated lesions. The proportion of lesions at which H. fraxineus could be detected declined with increasing distance from the lesion margin, with a significant reduction in the number of positive samples at 10 cm proximal to the margin. At 30 cm from the lesion edge the pathogen was never detected. Our results suggest that routine pruning may help maintain the vitality of younger trees. Pruning branches at least 35 cm from visible, active lesions in the bark should exclude the fungus and therefore reduce the probability of stem infection by H. fraxineus, however this cultural control tactic may only be economically feasible for high value amenity trees.     

Urban salt contamination impact on tree health and the prevalence of fungi agent in cities of the central Lithuania

An analysis of tree health in urban greeneries exposed to winter road salt contamination was carried out in the cities of Alytus and Kaunas, Lithuania, during spring and summer 2009–2014. Trees were assessed for crown dieback, crown defoliation and foliage discolouration. In addition, the prevalence of saprotrophic pathogenic fungi that cause sooty mold disease was assessed in street and recreational plantings. Tilia cordata Mill. (small-leaved lime) was found to be the most common tree species among urban deciduous trees. Summarising the tree foliage results, saprotrophic fungi were detected on 16 species plants belonging to 13 genera. Three species of fungal pathogens belonging to two genera, two families, two classes, and two divisions, and 12 species of anamorphic fungi from nine genera were isolated and identified from Tilia cordata leaves. The most frequent sooty mold disease agents were Aspergillus brasiliensis and Cladosporium herbarum. Nonetheless, a weak correlation between salt contamination and lime tree damage by sooty mold was found.     

Biology and control of the apple canker fungus Neonectria ditissima (syn. N. galligena) from a Northwestern European perspective

A review of apple canker caused by Neonectria ditissima is presented for Northwestern Europe with a focus on the Lower Elbe region (Northern Germany). Whereas conidia released by rainsplash are produced mainly from spring to autumn, the liberation of wind-borne ascospores peaks in autumn and/or early spring. Infection occurs via natural as well as pruning-induced wounds, some of which are present throughout the year. Autumnal leaf scars are the most frequent entry point for N. ditissima. Wounds on tree trunks, especially bark cracks in the crotch regions, are potentially even more serious because cankers on trunks and leader shoots commonly cause the total loss of a tree. Surface moisture is a prerequisite for leaf scar infections but possibly not for an entry through other wounds. Irrespective of the entry route, successful infection of a wound requires a mass inoculum of at least 50–100 conidia or ascospores. Infections of trees originating in nurseries may enter a state of latency from which they can break out up to 3 years after the trees have been explanted into the production orchard. Streaks of brown wood discolourations can be caused both by systemic colonisation of the xylem by N. ditissima and by winter frost damage. Apple varieties may show pronounced differences in their sensitivity to canker. For highly susceptible varieties, this disease can be a major production-limiting factor. Flower infections by N. ditissima commonly lead to a pre-harvest rot at the blossom end of the fruit, whereas infections of the growing fruit before harvest lead to a storage rot. Rigorous pruning is an essential canker control measure. Chemical control during the growing season is achieved by apple scab fungicides such as dithianone, captan or dodine. At leaf fall and in winter, copper fungicides are indispensible for controlling canker on highly susceptible varieties in Northern Germany.     

Pruning Trials With Worcester Pearmain Apple

Three pruning treatments were compared on Worcester Pearmain on M.IV rootstock, viz.: open-centre tree, established-spur pruned; delayed open-centre tree, established-spur pruned; regulated pruned tree. In the fifteenth year secondary treatments were begun, the trees being pruned either annually or in alternate years, with and without fruit thinning by hand. The trees were grubbed after 21 years and scion weights were obtained.

There were no important differences in growth and cropping between open-centre and delayed open-centre trees. Regulated trees had an 11% smaller area of branch spread than established-spur pruned trees at 21 years. At 15 years there was no significant difference between treatments in total weight of prunings, but three times as much old wood as new had been removed from regulated trees compared with two and a half times as much new wood as old from established-spur pruned trees. During a 6-year period, the same weight of wood was removed from alternate-year pruned trees as from those pruned annually.

During the first 10 years regulated trees yielded twice as much fruit as did established-spur pruned ones, and 49% more during the second 10-year period. In many years, in the absence of fruit thinning, regulated trees bore smaller fruits than did established-spur pruned trees. Regulated trees had more red colour on the fruits than established-spur pruned trees, and alternate-year pruning, whether regulated or established-spur, gave more red colour on the fruits than did annual pruning, especially in seasons following no pruning. Alternate-year pruning had no harmful effect upon fruit size. Fruit thinning had no important effect upon red colour but it increased the percentage crop weight in the larger size grades, especially on established-spur pruned trees. The regulated method is well suited to the growth habit of Worcester provided that the fruit is thinned by hand or chemical spray in years of heavy setting.

The relative ratios between total crop : scion weight and crop 15–21 years : scion weight, were similar; scion weights were twice as heavy as weights of prunings.     

Effects of roads on fruit crop and removal rate from rowanberry trees (Sorbus aucuparia) by birds in urban areas of Finland

Roads destroy natural habitats. To reduce erosion, support wildlife and decorate surroundings, ornamental trees are planted near the roadside. However, it is inadequately understood how roads influence fruit production of trees and birds that consume their fruits, within urban landscapes. During the autumn and winter of 2012–2013, we studied the extent to which birds used the fruit from rowanberry trees (Sorbus aucuparia), in two cities along a 700 km latitudinal gradient in Finland. In matched pair design (total of 35 pairs), we compared roadside trees (approximately 8 m from main roads) with trees grown away from roads (control trees; approximately >80 m from the roads). During the autumn, each rowanberry tree pair was photographed, and frugivorous birds were surveyed twice per month until all of the rowanberry fruit-crop was consumed. There was no difference in fruit crop size between roadside trees and control trees. A total of eight frugivorous bird species and 960 individuals were observed foraging in roadside trees. The three most abundant species were Bohemian waxwing (Bombycilla garrulus, 56.4%), Pine Grosbeak (Pinicola enucleator, 28.9%) and Fieldfare (Turdus pilaris, 10.5%). Total abundance and species richness of frugivorous birds were lower around roadside trees than control trees during most of the study period. Fruits were consumed later from roadside trees than from control trees, probably due to human-caused disturbance. Therefore, roadside rowanberry trees extended the period when frugivorous birds stayed in urban habitats. Later consumption of fruits in northern areas than in southern areas was related to earlier peak abundance of frugivorous birds in south than in north. Our results indicated that rowanberry is a suitable ornamental tree for urban and roadside landscaping and may additionally benefit birds and other frugivorous wildlife.     

Urban London plane tree dieback linked to fungi in the Botryosphaeriaceae

Since the first report of the stain canker agent Ceratocystis platani in 2001 in Geneva, dieback of London plane trees (Platanus × acerifolia) has focused greater attention and an epidemiological monitoring has been implemented, as part of a compelling state directive for stain canker management. Genetic identification was carried out in order to ascertain the presence or absence of C. platani. We report here observations recorded between 2011 and 2013, of samplings from a total of 6 plane trees in 4 locations. Identification of bacteria and fungi was performed by sequencing of the rDNA ITS region for fungi, and of the 16S rRNA gene for bacteria. Fungi belonging to the Botryosphaeriaceae species occurred in almost every sampling, whereas Ceratocystis platani was only isolated in 2 trees. The 4 botryosphaeriaceous species, Diplodia mutila, Dothiorella sp., Diplodia seratia and Neofusicoccum parvum, could be responsible for the observed plane cankers, while other fungi could participate in the dieback symptoms. Since these species have been reported as canker agents on other tree species in Europe, artificial infections were carried out with pure cultures of Dothiorella sp., Diplodia mutila and Neofusicoccum parvum on young plane trees. Only Neofusicoccum parvum managed to provoke cork canker symptoms after a few months, but D. mutila and N. parvum were found in internal necrotic tissues. This is the first report of Dothiorella sp., Diplodia mutila and Neofusicoccum parvum associated with plane tree dieback in Switzerland and the first report of pathogenicity of Neofusicoccum parvum in plane trees. This survey showed that most cases of plane tree dieback in the Geneva region were not caused by C. platani and that other fungi could be responsible for similar symptoms.     

An Experiment in Pruning Cox’s Orange Pippin Apple Trees in Alternate Years

Five pruning treatments were compared on Cox’s Orange Pippin on M.II rootstock, viz.

1. Open-centre tree, established-spur pruned

2. Open-centre tree, renewal-pruned

3. Delayed open-centre tree, established-spur pruned

4. Delayed open-centre tree, renewal-pruned

5. Regulated-pruned tree.

At 15 years, secondary pruning treatments were begun and carried on for a further 7-year period, the trees being pruned by the same methods but either annually or in alternate years. Differences in growth and cropping between trees pruned to open-centre and delayed open-centre shapes were small, but open-centre trees cropped more heavily than did delayed open-centre trees when renewal-pruned, probably on account of their greater branch spread. The method used in pruning the laterals had an effect upon cropping during the first 10 years. At the end of the trial there was no effect of either primary or secondary treatments upon trunk girth, neither was there a significant difference in girth increment between the secondary treatments. Almost the same amount of wood was removed from trees pruned in alternate years as from those pruned annually, but a greater proportion of old to new wood was removed from trees pruned in alternate years. Pruning in alternate years increased the cropping of established-spur pruned trees but not with regulated or renewal-pruned trees. There was no consistently adverse effect upon fruit size but, when a year of heavy setting followed a winter when the trees were left unpruned, fruit size was reduced and early fruit thinning would have been necessary to lessen the proportion of fruit in the two smallest size grades. With this variety fruit colour was unaffected by pruning in alternate years.     

Allergenic pollen of ornamental plane trees in a Mediterranean environment and urban planning as a prevention tool

Green spaces and urban green infrastructure are new concepts in urban planning, and lately, the influence of green spaces in cities and how this presence affects local climate change have been taken into account. Moreover, some of the ornamental trees most used in cities provoke allergic symptoms in sensitized people. Due to the importance the plane trees in our parks and cities have as ornamental trees, this article assesses the urban Platanus airborne pollen concentration in the air of five cities of the SW Iberian Peninsula and tries to determine the differential factors that its distribution has by means of combining continuous monitoring of the air using volumetric spore traps and the geolocation of plane trees. They were counted separately according to the direction (Q1 NE, Q2 SE, Q3 SW, Q4 NW) around the spore trap location in circles of 100, 200, 300, 400, 500, 1000, 1500, 2000 and 2500 m in diameter. Pollen sums were distributed according to the predominant wind direction for each day. The highest concentrations for Platanus pollen were recorded in Don Benito. Differences amongst pollen stations were found and were mainly related to their degree of maturity and their proximity to spore traps, and finally, with the number of plane trees. Furthermore, other factors, as the pruning, which is different in each city and even in a more local way, affects pollination and is frequently unknown to aerobiological studies. The geolocation of ornamental trees can be a useful tool for providing summarized information about their behavioral differences amongst cities, which can be used to create healthy itineraries, minimizing the natural hazards in human health (allergic diseases) and could be implemented into a model to help policy-makers to create measures to improve green urban development.     

Mechanical injury and occlusion: An urban,tropical perspective

Eight common tree species used for urban landscaping were examined in this study for the effect of branch pruning on the rate and extent of wound closure (occlusion) and internal discolouration in the stem. Rate of wound closure when branches were removed with stem or branch of origin (flush cut pruning) and cuts made away from the branch collar (natural target pruning) were compared on all species over a 3-year period. Understanding the effects of pruning will benefit urban foresters in tree selection and potentially prevent downstream challenges associated with mechanical injury. The findings for all eight species supported the recommended guidelines of retaining the branch collar during pruning which has shown to facilitate effective wound closure. The exposed wood diameter (exposed) for all species were significantly reduced after the second growing season for injuries derived through natural target pruning but for the same period, injuries derived through flush cut pruning, only six species showed significant reductions in exposed wood diameter. Two other species (Mimusops elengi and Lagerstroemia speciosa) were observed to have no further reduction in exposed wood following the first growing season. Both wound inducing techniques (flush cut pruning and natural target pruning) resulted in no significant change in healing tissue production following the second growing season. Correlation analysis showed a strong positive relationship (r = 0.8–0.9) between the width of the wound and the length of discolouration in the stem, suggesting that smaller cuts were better suited to avoid extensive wound induced discolouration. This finding was further reinforced through visual observations of numerous pruning wounds of all eight species which showed that smaller cuts were better able to close over as opposed to larger wounds.     

Variation in modulus of elasticity (E) along Acer platanoides L. (Aceraceae) branches

Arborists and managers of amenity trees could benefit from an improved understanding of how tree canopies withstand loading events such as wind, snow or ice. Knowledge of how material properties change along tree branches is important in understanding how a branch tips can bend in the wind yet resist displacement at the base which could lead to branch failure. Limited knowledge of modulus of elasticity (E or stiffness) in branch wood is available in the literature and is typically measured at only one location on a branch. This study investigated variation of E and density-specific E (E/ρ) at five locations along the axis of 20 branches from seven trees. E and E/ρ were found to be 70% lower at the branch tips than in the proximal locations. The variation in E was negatively correlated with the percentage of tissue area composed of vessels and positively correlated with mean fiber cell wall size, suggesting a balance between the two principle functions of hydraulics and mechanics. Reaction wood was observed in the form of gelatinous layers in fibers along the branch tops, but did not result in a difference in E between the top and bottoms at each branch location. It is proposed that differences in material properties are probably related to wood development type, as juvenile wood is considered to have lower stiffness than mature wood.     

Effects of pruning intensity on the biochemical status of shoot buds in three mango (Mangifera indica L.) cultivars planted at high density

Summary

Mango (Mangifera indica L.) trees grown at high density show a decline in flowering and fruiting after good fruiting years as a result of various factors. Annual pruning can restore production and productivity in such trees. Chlorophyll, total sugars (TS), total phenolics (TP), and proline contents as well as polyphenol oxidase (PPO) activities, were measured in the 2005–2006 and 2006–2007 seasons in shoot buds with a few leaves in three mango cultivars (‘Amrapali’, ‘Mallika’, and ‘Dashehari’). Trees were grown at high density in an orchard and the aforesaid parameters were measured 1 month after different degrees of pruning (Stage I) and after subsequent fruit bud differentiation (FBD; Stage II). Severely-pruned mango trees had the highest contents of chlorophyll a, while chlorophyll b and total chlorophyll contents were found to be highest in moderately-pruned trees. Lightly-pruned trees had the highest contents of reducing sugars (RS), whereas TS contents were highest in severely-pruned trees. The contents of RS and TS increased in shoot buds during the FBD stage. A moderate intensity of pruning significantly increased TP contents, while the lowest TP contents were recorded in non-pruned trees. ‘Off’-year shoots had higher TP contents than ‘on’-year shoots. Irrespective of pruning intensity, shoot buds of ‘Mallika’ trees had the highest PPO activities, with lower levels in ‘Amrapali’ and ‘Dashehari’ shoot buds. PPO activities were reduced at the FBD stage in ‘on’-year shoots. Severely-pruned trees had the highest PPO activities, while the lowest PPO activities were recorded in lightly-pruned trees. Shoot bud proline contents were found to be highest in non-pruned trees, and decreased with increasing pruning intensity. Thus moderate pruning can be adopted in high density orchards to obtain sustainable production with improved maintenance of canopy architecture.     

Both native and invasive bark beetles threaten exotic conifers within the spa towns in the Czech part of “The Great Spas of Europe”

Exotic coniferous trees in forests adjacent to spa towns and in parks within spa towns are increasingly being attacked by outbreak populations of native bark beetles in western Bohemia (Central Europe). In the 12 localities in western Czech Republic the current study, we detected a total of 19 native bark beetle species infesting more than 10 % of exotic tree species in the genera Abies, Picea, Pinus, and Pseudotsuga in 1 year. Several exotic tree species were identified as new hosts for native European bark beetles. We also identified three non-native bark beetles, including Phloeosinus aubei, a species that transmits the pathogens that cause cypress canker disease.The numbers of infested trees in the localities were not correlated with the distance from surrounding bark beetle outbreak sites in commercial forests, because all forests adjacent to spas and all forests in spa towns (i.e., “urban forests”) are close to commercial forests with infested trees. Infestations were greater in spa towns than in the forests adjacent to spa towns. We therefore assume that trees within spa towns will be further attacked due to the increasing abundance of native bark beetles.     

Carbohydrate dynamics in roots,stems, and branches after maintenance pruning in two common urban tree species of North America

The ability of plants to tolerate stress is determined in part by the carbon allocated to their reserves. We studied two common urban tree species in northeastern North America, Acer saccharinum (Silver maple, native) and Acer platanoides (Norway maple, exotic), to assess the dynamics of non-structural carbohydrate (NSC) concentrations immediately following a maintenance pruning of 30% of the tree crown. NSC concentrations were measured by high-performance liquid chromatography in branches, main stems, and root tissues for both pruned and un-pruned trees at three intervals during the growing season. NSC concentrations in tree organs of A. platanoides were 75% higher than in A. saccharinum. Maintenance pruning did not have any significant depletion effect on carbohydrate concentrations in the tissues of either species. Yet, there was a significant increase in the NSC concentrations in un-pruned branches of pruned trees of A. platanoides at the end of the growing season, but no effect was observed in A. saccharinum. Higher levels of carbohydrates after pruning in woody plant tissues suggested that A. platanoides may have compensatory mechanisms that allow this species to respond better to maintenance pruning than A. saccharinum.     

A citywide survey of the pine processionary moth Thaumetopoea pityocampa spatial distribution in Orléans (France)

There is a growing recognition that urban trees provide various valuable benefits and services such as enhanced human wellbeing. However, they also have a cost in terms of public health either directly (allergies) or by harboring species representing health risk for humans. This paper focuses on such a forest insect species, the pine processionary moth Thaumetopoea pityocampa. Its caterpillars develop gregariously during winter in a conspicuous silk nest in coniferous hosts. When disturbed, the larvae release urticating hairs that cause human or animal serious health problems. The purpose of our survey was to (1) inventory all individual trees belonging to potential host species and estimate the density of T. pityocampa (2) assess the spatial pattern of the insect population at the city scale. We conducted an exhaustive inventory of potential coniferous host trees in five municipalities (ca. 5000 ha) in the north of Orléans, France. Each tree was identified, geo-referenced and the number of moth nests it hosted was counted. A total of 9321 urban trees representing 11 coniferous taxonomic units were investigated. The distribution of T. pityocampa exhibited a marked spatial structure citywide. Geostatistics allowed to draw risk maps revealing strong patchiness. We provide the first estimate of T. pityocampa host tree preference in an urban context and found that Pinus nigra, P. pinaster and P. sylvestris were the most attacked trees. We also report numerous cases of T. pityocampa occurrence on the exotic ornamental Himalayan cedar Cedrus deodara. The management implications of our findings are two-fold: (1) risk maps constitute a useful framework for communication and public information, and can help developing control strategies; (2) some species frequently used for ornamental purposes are poor quality hosts regarding T. pityocampa and should therefore be preferred in public place usually frequented by vulnerable people (schools, nurseries, hospitals).     

Two new planting systems for early ripening peaches (Prunus persica L. Batsch): Yield and fruit quality in four low-chill cultivars

Summary

Trees of peach cvs Flordastar, Flordaprince, Flordacrest and Maravilha, low in chill requirement (Flordaprince 150; Flordacrest 350 C.U.), with a short fruit development period (Flordaprince 90; Flordacrest 110 d) and a very early ripening time (Flordastar mid May; Flordacrest first week of June), were planted in Sicily (37° 30′ Lat. N) both in a medium (667 trees per ha) and a high density (2000 trees per ha) plantation system. In the medium density planting system, the trees were trained to a Fusetto, and in the high density to a Y-shape. Both in the Fusetto and Y, the size of the trees was controlled by severe pruning soon after harvest, consisting in the shortening of most of the one year old wood. From mid June to October, the trees of all four cultivars were able to recover a “fruiting canopy”; flower bud density, flower fertility, fruit set, fruit quality and crop efficiency were not affected by the severe summer pruning. Due to the planting density and the pruning, the tree growth was restricted: no platforms or ladders were required to perform the cultivation techniques at the top of the Fusetto nor was the wire-trellis necessary to sustain the Y-shaped trees. To distinguish these training systems from the original ones, Fusetto and Tatura trellis, we called them “dwarfed Fusetto” (dF) and “free standing Tatura” (fsT), respectively. Although production per tree was higher in the dF, due to planting density fsT yielded more per hectare.     

The Hamburg Tree Pruning System – A framework for pruning of individual trees

Trees in urban areas are pruned for several reasons. Each pruning cut causes a wound, which leads at least in the exposed wood at the wound surface to discoloration and decay. The extension of the resulting defect depends on wound diameter, tree species, time of wounding, wound treatment, and last but not least the attachment of the branch to the stem. The effects of different pruning cuts on urban trees has been investigated in Hamburg, Germany, since 1985. The study of 750 different pruning wounds on typical urban tree species lead to the Hamburg Tree Pruning System (Hamburger Schnittmethode). The system is described in this paper and answers the following questions: How should branches with and without a branch collar be removed? How should dead branches be removed? How should branches with included bark or codominant stems be removed? What are the differences between tree species in wound response? What is the maximum wound size which will be effectively compartmentalised by the tree?     

Dimensional and genetic characterization of the last oriental plane trees (Platanus orientalis L.) of historical sites in Lazio (central Italy)

In central Italy, Platanus orientalis L. specimens characterize many gardens in urban and suburban villas. In this research, centuries-old oriental plane trees were studied in different historical sites of Lazio according to the COVE (COnservation of VEteran trees) multidisciplinary model. Historical sources, morphological and dendrometric aspects, crown quality, genetic traits of each specimen, as well as their susceptibility to the canker stain disease, were investigated. Platanus orientalis was clearly distinguished from P. occidentalis and their hybrid P. acerifolia through molecular tools. UPGMA analysis based on SSR and ISSR molecular markers clustered the plane trees in different sub-groups, probably according to the different sites of sampling. These findings, supported by historical and morphological data collected in the considered sites, showed that almost all the trees studied are a small remnant of those planted in the period running from the second half of XVI century to the first decades of XVII century. Plant health conditions diverge within and among the sites inspected. Past-prolonged severe pruning treatments of trees located near the main monuments affected their growth, causing faster and premature senescence. However, the management of historical gardens has so far led to an efficient prevention of Ceratocystis platani introduction, spread and establishment. This study highlights the importance of a multidisciplinary approach to interpret the present status of the ancient tree asset within historical sites and let the past become a lesson for the future in a broader scenario of conservation and management of cultural heritage.     

Dispersal limitation at the expanding range margin of an evergreen tree in urban habitats?

Dispersal limitations contribute to shaping plant distribution patterns and thus are significant for biodiversity conservation and urban ecology. In fleshy-fruited plants, for example, any preference of frugivorous birds affects dispersal capacities of certain fruit species. We conducted a removal experiment with fruits of Ilex aquifolium, a species that is currently expanding its range margin in northern Europe in response to climate change. The species is also a popular ornamental tree and naturalization has been observed in many parts of its range. Fruits of native I. aquifolium and of three cultivars were offered to birds at the expanding range margin in urban habitats in eastern Denmark. The four fruit types were removed at different rates and red fruits were preferred over a yellow cultivar. Small fruit diameter was positively related to fruit removal, and removal was faster under tree canopies compared with open habitats. The preference for red cultivars compared with native I. aquifolium may contribute to naturalization and potential invasion of garden escapes. Preferential foraging under closed canopies indicates trees and shrubs as recruitment foci for fleshy-fruited plants in urban landscapes. The results should be included in urban forestry and planting of potentially invasive ornamental species.     

Protein and isozyme electrophoresis and isoelectric focusing for the characterization of apple clones

To identify apple (Malus domestica Borkh.) clones, electrophoretic and isoelectric focusing of protein and isozyme pattern differences were investigated. Existing electrophoretic methods were adapted to obtain satisfactory separation and reproducibility of patterns. Several protein extraction buffers and procedures were evaluated to optimize protein recovery and enzyme activity from shoot bark tissue and other organs and to counteract the interference of other cell components. Sodium dodecyl sulfate—polyacrylamide gel electrophoresis (SDS-PAGE) did not reveal useful differences among cultivars, nor did total native protein patterns (non-denaturing PAGE). Peroxidase, esterase, acid phosphatase and indoleacetic acid oxidase extracted from shoot bark tissue did, however, show isozymic differences useful for identification. These enzymes expressed constant isozyme patterns at different times of the year and from trees growing under different conditions, and patterns were independent of wood age and rootstock influence.     

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees: Part I. Low temperature and potassium chlorate effects on FI and hormonal changes exerted in terminal buds and sub-apical tissue

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees was achieved in controlled greenhouse experiments by low temperature (LT) and by the application of potassium chlorate at high temperature (HT + KClO₃) during two consecutive seasons. The latter treatment was successful also at temperatures above 20 °C. The present experiment was conducted to investigate possible alterations in the concentrations of plant hormones exerted by these two methods and to relate them to the floral induction process. The following hormones were examined by radioimmunoassay in the shoot apical buds (SAB), and in sub-apical bark and wood: the auxin indole-3-acetic acid (IAA); gibberellins (GAs); and the cytokinins zeatin/zeatin riboside (Z/ZR) and isopentenyl-adenine/isopentenyl-adenosine (iP/iPA).