Girdled Branches Research Articles

Water restriction, girdling and paclobutrazol on flowering and production of olive cultivars

Information about reproductive behavior of the olive trees (Olea europaea L.) in regions with lower occurrence of cold is fundamental to the expansion of its economic cultivation. Researches studding the adequacy of management techniques in order to promote flowering in these regions are important. Thus, this research was conducted to evaluated water restriction, girdling and paclobutrazol on flowering and production of olive cultivars. Three experiments were conducted in Federal University of the Jequitinhonha and Mucuri Valleys in Diamantina, Minas Gerais, Brazil. In the first experiment, ‘Arbequina’ olive trees were subjected to water restriction and two environmental conditions. In the second experiment, the girdled branches in different times on flowering and nutritional behavior of ‘Grappolo 541’ and ‘Barnea’ olive trees were evaluated. And in the third experiment, the application of paclobutrazol (PBZ) and the water restriction were studied in the vegetative growth and flowering of ‘Ascolana’ olive trees. The flowering of ‘Arbequina’ olive tree occurred with the averages of minimum temperatures varied from 8.4 to 11.7°C, in autumn and winter. The girdling at different times did not influence the production of olive trees ‘Barnea’ and ‘Grappolo 541’. The girdled branches had a higher nutrient levels in leaves.The application of paclobutrazol in the soil promoted the reduction in vegetative growth of ‘Ascolana’ olive trees, with increase of flowering and fruiting. The water restriction did not favor the flowering of ‘Arbequina’ and ‘Ascolana’ olive trees and it reduced the effect of PBZ in ‘Ascolana’.

NOTES ON THE BIOLOGY OF Oncideres bouchardii BATES (Coleóptera: Cerambycidae), A TRUPILLO TWIG GIRDTER FROM SANTA MARTA, COLOMBIA

Aspects of the biology of Oncideres bouchardii Bates from Santa Marta, Colombia are described. Imagines of this twig girdler appear shortly after the rainy season during the months of November to February, ringing twigs and branches of trupillo trees, Prosopis juliflora (L.) and aromo bushes, Acacia fameÿiana Willd. Observations showed that this activity is only performed by the females, which commonly copulate at the same time. After girdling the twig, the females lay their white eggs one by one into especially prepared egg cavities that are sealed after oviposition. There is evidence that locating the entrance to the future egg chamber with the ovipositor is greatly facilitated by means of a marking on the bark made with the ovipositor while making the entrance with the mandibles. The eggs are deposited by means of the telescopic and inflatable ovipositor which is inserted deeply under the bark through hemolymph pressure and acts to force open the egg chamber between bark and wood. After approximately a week the larvae hatch and soon dig into the drying twig. The lifecycle of Oncideres bouchardii lasts one year, the longest part of it belonging to the larval stage. Most imagines live less than a week or two, although a few survive as long as 45 days. In places where much destruction of the trees is caused by this twig girdler, it is recommended to collect and burn the girdled twigs or branches that contain the woodboring larvae or eggs of the species.

English

Abscission of flowers and fruit in Citrus latifolia cultivars is more intense than in seeded Citrus ones. The purpose of this study was to evaluate the effect of different levels of branch girdling in C. latifolia fruit fixation. The work was carried out in an orchard of C. latifolia grafted onto three-year-old Citrus limonia spaced 3x1, located in the Goiás State University experimental field. The experiment was set up according to the randomized block design with four treatments (girdling of 0, 25, 50 and 100% of the branches existing in the plant), five replications, parcels of four usable plants and total of 20 plants. Girdling was accomplished on 29/08/2014 and full flowering occurred on 13/09/2014. The plants that had 100% of their branches girdled presented high productivity of fruit with low juice volume. Those with 50% of branches girdled showed higher productivity and good juice yield per fruit. Results indicate that total blocking of transportation of assimilation from the canopy to the root system has negative impact on the volume of fruit juice.   Key words: Tahiti lime, carbohydrates, citrus culture, photoassimilates.

Alternative technique for lychee flowering

The experiment was conducted in the municipality of Colatina -ES, Brazil, aiming at evaluating the flowering of lychee ( Litchi chinensis Sonn.) in response to the girdling of branches of different diameters, located in different parts of the plant canopy and in two seasons, October 2010 and March 2011. The girdling was also carried out in October, as an attempt to extemporaneous production of litchi. As the girdling in October produced no induction of flowering, the final analysis of the experiment outlined in randomized blocks was done in 4 x 4 factorial (quadrants x branches), with four replications and one tree as experimental plot. The girdling in isolated plants consisted of: girdling branches or main branches (8.0 to 10.0 cm in diameter), girdling branches from 6.0 to 7.9 cm in diameter, girdling branches with diameters of 4.0 to 5.9 cm, and without girdling (control), located in the southeast, southwest, northeast and northwest quadrants of the plant’s canopy. The amount and the length of the inflorescences and the percentage of flowering of lychee were evaluated in light of the girdling of branches and of the location of the quadrants in the canopy of the plants. It was observed that there was a difference between the amount of girdling in the variables for length and amount of inflores­cences, while the girdling of branches with 8 to 10 and from 6 cm to 7.9 cm in diameter were superior to the control in girdling of branches of 4 to 5.9 cm diameter. Concerning the position of the branches in the canopy (quadrants) it was discovered that the quadrants receiving less light (southeast and southwest) had more flowers and flowering percentages, but there was no significant difference for the variable length of the inflo­rescence according to the quadrants. The girdling of the branches can be an alternative to the insertion of hot climates in the production of lychee.

Regulation of correlative inhibition of axillary bud outgrowth by basal branches varies with growth stage in Trifolium repens.

In Trifolium repens the decline in bud outgrowth that occurs with distance from basal root systems is due to correlative inhibition by the first-formed basal branches. The apical and axillary buds on these basal branches are the source of the inhibitory effect, but their mode of action is unclear. Inhibition might occur via basal branches being a sink for xylem-transported branching stimulants or alternatively by providing a source of inhibitory signals, or by both mechanisms. To distinguish between these mechanisms, four experiments were conducted on plants varying in initial growth stage from 10 to 19 nodes along their main stems to determine any variation in the relative importance of the operative mechanisms of correlative inhibition. Inhibitory signal exported into the main stem, detected as a branching response to girdling of basal branches, was relatively more significant in smaller (initially with 10-15 nodes on the main stem) than in larger (>19 nodes on main stem) plants. This signal was shown not to involve auxin fluxes, and is unidentified. However, across all stages of growth, the predominant mechanism driving correlative inhibition was the action of axillary and apical buds of basal branches as sinks for the stimulatory signal. This study indicates that the relative importance of the mechanisms regulating bud outgrowth in T. repens varies with growth stage and that, during intermediate stages, regulation has some similarity to that in Pisum.

Carbohydrate regulation of photosynthesis and respiration from branch girdling in four species of wet tropical rain forest trees.

How trees sense source-sink carbon balance remains unclear. One potential mechanism is a feedback from non-structural carbohydrates regulating photosynthesis and removing excess as waste respiration when the balance of photosynthesis against growth and metabolic activity changes. We tested this carbohydrate regulation of photosynthesis and respiration using branch girdling in four tree species in a wet tropical rainforest in Costa Rica. Because girdling severs phloem to stop carbohydrate export while leaving xylem intact to allow photosynthesis, we expected carbohydrates to accumulate in leaves to simulate a carbon imbalance. We varied girdling intensity by removing phloem in increments of one-quarter of the circumference (zero, one--quarter, half, three-quarters, full) and surrounded a target branch with fully girdled ones to create a gradient in leaf carbohydrate content. Light saturated photosynthesis rate was measured in situ, and foliar respiration rate and leaf carbohydrate content were measured after destructive harvest at the end of the treatment. Girdling intensity created no consistent or strong responses in leaf carbohydrates. Glucose and fructose slightly increased in all species by 3.4% per one-quarter girdle, total carbon content and leaf mass per area increased only in one species by 5.4 and 5.5% per one-quarter girdle, and starch did not change. Only full girdling lowered photosynthesis in three of four species by 59-69%, but the decrease in photosynthesis was unrelated to the increase in glucose and fructose content. Girdling did not affect respiration. The results suggest that leaf carbohydrate content remains relatively constant under carbon imbalance, and any changes are unlikely to regulate photosynthesis or respiration. Because girdling also stops the export of hormones and reactive oxygen species, girdling may induce physiological changes unrelated to carbohydrate accumulation and may not be an effective method to study carbohydrate feedback in leaves. In three species, removal of three-quarters of phloem area did not cause leaf carbohydrates to accumulate nor did it change photosynthesis or respiration, suggesting that phloem transport is flexible and transport rate per unit phloem can rapidly increase under an increase in carbohydrate supply relative to phloem area. Leaf carbohydrate content thus may be decoupled from whole plant carbon balance by phloem transport in some species, and carbohydrate regulation of photosynthesis and respiration may not be as common in trees as previous girdling studies suggest. Further studies in carbohydrate regulation should avoid using girdling as girdling can decrease photosynthesis through unintended means without the tested mechanisms of accumulating leaf carbohydrates.

Cerambycidae and other Coleoptera Associated with Branches Girdled byOncideres sagaDalman (Coleoptera: Cerambycidae: Lamiinae: Onciderini)

Species of Oncideres Serville, often referred to as twig girdlers, girdle tree branches prior to oviposition to promote larval development. The behavior creates a unique niche that is utilized by other beetle species. The objective of this study was to compare emergence of insects from branches girdled by Oncideres saga Dalman in an intercropping system and a monoculture of Acacia mangium Willd. in the Atlantic Rainforest of Minas Gerais, Brazil. Twenty-four Coleoptera species emerged from the branches: 17 Cerambycidae; three Cleridae; and one individual each from Cantharidae, Cucujidae, Elateridae, and Trogossitidae. Although branches from the intercropping system yielded more individuals, branches from the monoculture had higher species richness, including almost all of the cerambycid species and all of the potential predators. The use of girdled twigs may confer a reproductive advantage to subsequent cerambycid colonists, which are probably attracted to the volatiles released by the girdled branch. Beetles belonging to other families may prey on the Cerambycidae dwelling inside the branches. Potential predators may be ecologically important, contributing to the natural biological control of O. saga. Collecting and burning the infested branches is the technique most extensively used to control the twig girdlers. However, this also destroys beneficial organisms as well as the subsequent colonists that depend upon these branches.

Application of GA3 and girdling of branches on the production of extemporaneous fruits of 'Tahiti' acid lime

The objective of this study was to evaluate the effect of girdling of branches and the application of GA3, still in the main crop flowering on the formation of reproductive structures, the fruit set of the following extemporaneous flowering of 'Tahiti' acid lime. This work used a randomized block design with five replications in a 4x3 factorial design. The first factor was the foliar application of GA3, 88 days before extemporaneous flowering at five concentrations (0, 7, 14 and 21 mg.L-1). The second factor was the girdling times, 108 days before flowering onset (A108AF), 78 days before flowering (A78AF) plus no-girdling control (NG). In extemporaneous flowering, the proportion of buds, flowers and fruits that abscised was 38.75, 31.25 and 18.64% respectively and 11.34% of all reproductive structures formed were collected. GA3 did not affect fruit set. Girdling increased fruit set by 229 and 256% at A108DAF and A78DAF respectively, in relation to NG plants. The GA3 reduced the formation of floral structures, which resulted in a quadratic increase in field production by reducing the competition for photoassimilates among fruits. The concentration of 21 mg.L-1 was the most productive, with 15.97 fruit.plant-1.

DOWN-REGULATION OF PHOTOSYNTHESIS VIA SINK LIMITATION IS LINKED TO FOLIAR SOLUBLE SUGAR CONTENT IN HIGH- AND LOW-YIELDING VARIETIES OF SWEET CHERRY

The objective of this study was to investigate the basis for yield differences between ‘Kordia’ and ‘Sylvia’, low- and high-crop load carrying sweet cherry cultivars, respectively. Branch girdling was effected on ‘Kordia’ and ‘Sylvia’ set up as Spanish Bush at Old Beach in the Derwent Valley, near Hobart, Tasmania, Australia. Photosynthesis was measured with a Li-Cor 6400 four times pre- and once post-harvest. Fruit set was 42% and 56% and fruitlet abscission was 69% and 34% in ‘Kordia’ and ‘Sylvia’, respectively. Maximum photosynthetic rate ( A sat ) increased from a low or around 12 µmol m -2 s -1 in early Spring to a maximum of around 18 µmol m -2 s -1 early Summer and was similar between cultivars pre-harvest. However, post-harvest, A sat of ‘Kordia’ was significantly lower at around 8 µmol m -2 s -1 relative to that of ‘Sylvia’ at around 16 µmol m -2 s -1 . Girdling had a stronger effect on A sat in the low-yielding ‘Kordia’ than in the high-yielding ‘Sylvia’ (-13% vs. -11%, respectively), and there was a greater increase in foliar soluble sugar (SS) content in ‘Kordia’ than ‘Sylvia’ (+18% vs. +13%), averaged across the season. There was a strong negative correlation between SS and A sat in leaves, across the season, cultivars and treatments. There were no girdling or cultivar effects on foliar starch content. The results suggest that girdling-induced sink-limitation leads to down-regulation of photosynthesis that is linked to the accumulation of SS content in the leaves. Despite minor differences in A sat between varieties, our results imply that the low-yielding ‘Kordia’ variety is not limited by source-supply potential during the growing season, but that low A sat post-harvest could be linked to the subsequent season’s fruitlet abscission that limits potential yields. Further investigation is warranted regarding carbohydrate storage as a factor in the relatively high fruitlet abscission in ‘Kordia’, and other low-yielding varieties of sweet cherry.

Girdling and tree death: lessons fromChamaecyparis pisifera

To investigate the effects of girdling on the water relation of trees, we measured a number of water-status parameters and morphological features following trunk and branch girdling of Chamaecyparis pisifera Siebold & Zucc. Girdling caused a marked reduction in the water-conduction area of the trunk cross section at the girdled part. Some girdled trees generated intense acoustic emissions (AE), simultaneously decreased leaf water potentials (LWP), and then died within 1 year. However, others lived for more than 2 years after girdling. In these survivors, the water-conduction area of the trunk cross section was reduced but not entirely blocked, and LWP decreases did not occur. Consequently, we conclude that girdling affects xylem water conductivity and sometimes causes short-term (within 1 year) tree death by blocking water uptake from soil to leaves. The results of this study on whether tree death from girdling occurs sooner or later could be important in the use of girdling for thinning management.

Starch Content of Citrus Leaves Permits Diagnosis of Huanglongbing in the Warm Season but Not Cool Season

One of the most prominent characteristics of huanglongbing (HLB or citrus greening)-affected citrus trees is the abundant starch accumulation in photosynthetic cells and all other remaining parenchyma cells of aerial parts. Under natural conditions, citrus leaves store very low levels of starch and detectable amounts are only seen as a result of zinc deficiency or accidental girdling of branches. Therefore, leaf starch concentrations over a threshold level should indicate the presence of HLB. In this report, we detailed a comprehensive statistical analysis of starch levels in citrus leaves and compared them with real-time polymerase chain reaction (PCR) detection of the presumptive causal agent Candidatus Liberibacter asiaticus. Starch content was found to reliably predict the PCR results (the proxy for HLB presence) during the “warm season” (June through November) but not in the “cool season” (December through May). During the cool season, starch levels for HLB-positive trees tend to be lower, and 43% of samples were incorrectly classified using Linear Discriminant Analysis (LDA). In contrast, during the warm season, only 8% were misclassified. Furthermore, assuming PCR possibly has error, the total probability of misclassification for HLB status could be controlled using an “uncertain” classification. The temporal pattern of leaf starch is consistent with our understanding of seasonal changes in plant development and bacterial titer.

Twig morphology effects on the number of egg incisions and reproductive success of Oncideres ocularis (Coleoptera: Cerambycidae)

The objective of this study was to analyze whether the morphology of girdled twigs has an effect on the number of incisions and the reproductive success of Oncideres ocularis (Coleoptera: Cerambycidae). Eight parameters of girdled branches were evaluated. Surface area showed the highest coefficient of determination for the number of eggs laid per branch and for the number of hatched larvae. Surface area, volume and length of girdled branches correlated significantly with the number of laid eggs and hatched larvae, as has been reported for similar insects.

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The objective of this study was to characterize the damage caused by Oncideres saga in plantations of Acacia mearnsii . The percentage of trees attacked was evaluated and the diameter and length of the branches were measured. It was observed that 34.3 % of the trees of A. mearnsii presented branches cut by O. saga . The average diameter and length of the cut branches were 5.75 cm and 4.95 m, respectively. The lower third of the girdled branches showed 64.23% of the posture incisions.

Down-regulation of photosynthesis following girdling, but contrasting effects on fruit set and retention, in two sweet cherry cultivars

Sweet cherry (Prunus avium) trees were manipulated to analyse the contribution of soluble sugars to sink feedback down-regulation of leaf net CO2 assimilation rate (Anet) and fruit set and quality attributes. Total soluble sugar concentration and Anet were measured in the morning on fully expanded leaves of girdled branches in two sweet cherry cultivars, ‘Kordia’ and ‘Sylvia’ characterised typically by low and high crop load, respectively. Leaves on girdled trees had higher soluble sugar concentrations and reduced Anet than leaves on non-girdled trees. Moreover, RuBP carboxylation capacity of Rubisco (Vcmax) and triose-phosphate utilisation (TPU) were repressed in the girdled treatments, despite Jmax remaining unchanged; suggesting an impairment of photosynthetic capacity in response to the girdling treatment. Leaf Anet was negatively correlated to soluble sugars, suggesting a sink feedback regulatory control of photosynthesis. Although there were significantly less fruit set and retained in ‘Kordia’ than ‘Sylvia’; girdling had contrasting effects in each cultivar. Girdling significantly increased fruit set and fruitlet retention in ‘Sylvia’ cultivar, but had no effect in ‘Kordia’ cultivar. We propose that low inherent sink demand for photoassimilates of ‘Kordia’ fruit could have contributed to the low fruit retention rate, since both non-girdled and girdled trees exhibited similar retention rate and that increases in foliar carbohydrates was observed above the girdle. In ‘Sylvia’ cultivar, the carbohydrate status may be a limiting factor for ‘Sylvia’ fruit, since girdling improved both fruit set and retention, and leaf soluble solids accumulation.

Bioecology of Oncideres ocularis Thomson (Coleoptera: Cerambycidae) on Acacia mangium Willd. (Fabaceae)

Twig girdlers are beetles that girdle branches and trunks of living trees so that they can deposit their eggs in incisions made by their mandibles. There are few studies about the biology and ecology of the girdler Oncideres ocularis Thomson, which is considered a potential pest of forest plantations that can cause injuries to tree species of the family Fabaceae. The objective of this study was to increase knowledge related to the biological phases and the ecological patterns of girdling and oviposition of O. ocularis. Field studies were conducted at four plantations of Acacia mangium Willd located in the cities of Coimbra and Viçosa, State of Minas Gerais, Brazil. The incubation period of eggs was 12.1 ± 0.2 (SE) days and viability was 61% (n = 70). The number of egg incisions per girdled branch was 17.27 ± 1.0. The great number of eggs was laid in the mid-basal and middle sections of branch with a mean of 5.80 ± 0.38 and 4.97 ± 0.3 eggs on these portions. The base diameter of the girdled branches was 9.88 mm ± 0.18 and the mean length was 99.21 cm ± 2.23. A girdled branch by O. ocularis led to an average loss of leaf area of 4233.05 cm2 per tree that corresponds to 0.46% of total leaf area. Other beetles that emerged from the girdled branches were Engyum quadrinotatum (Thomson), Orthostema abdominale (Gyllenhal), Nesozineus bucki (Breuning) and Lepturges sp.

Branch girdling at fruit green mature stage affects fruit ascorbic acid contents and expression of genes involved in l-galactose pathway in citrus

Although citrus is an important source of ascorbic acid (AA), and even though girdling is an important agronomic practice in citrus production, the effect of girdling on ascorbate (ASC) accumulation has rarely been studied. In the present study, branch girdling (BG) was carried out on trees of Citrus unshiu cv. ‘Guoqing No. 1’ at 40 days before harvest to investigate its effect on fruit ASC accumulation and on the expression of genes involved in the AA l-galactose biosynthetic pathway. BG increased total ASC and AA contents in fruit peel and pulp. In parallel, soluble sugars in the fruit pulp increased. Moreover, the expression of all genes, except for l-galactose-1-P phosphatase (GPP), in the l-galactose pathway were induced in fruit pulp at least during the first 20 days of treatment while their expression (except for GPP) in fruit peel was reduced by BG treatment. Taken together, the expression profiles of six l-galactose biosynthetic genes did not coincide closely with the changes in fruit ASC content following BG. ASC content may respond to girdling via other biosynthetic, catabolic or recycling pathways.

Impact of phloem girdling on leaf gas exchange and hydraulic conductance in hybrid aspen

We investigated phloem-xylem interactions in relation to leaf hydraulic capacity in hybrid aspen (Populus tremula L. × P. tremuloides Michx.) by using phloem girdling method. Removal of bark tissues (phloem girdling) at the branch base resulted in a substantial decline in stomatal conductance (gS), net photosynthetic rate (PN), and leaf hydraulic efficiency, and in increase of leaf water potential (ΨL). Although gS declined more than PN (83 versus 78 %), the ratio of intercellular to ambient CO2 concentrations (ci/ca) increased from 0.67 to 0.87 in three days after girdling. Girdling induced a decrease in leaf hydraulic conductance (KL) on average by 43 % (P = 0.006). The changes in gS and leaf conductance to water vapour were co-ordinated with KL only in girdled branches whereas intrinsic water-use efficiency was invariant to KL. The declines in KL with girdling were not accompanied by changes in potassium ion concentration ([K+]), electrical conductivity, or pH of xylem sap. The results suggest that phloem girdling at the branch base does not influence the recirculation of ions between the phloem and xylem in hybrid aspen and the decrease of KL in response to the manipulation is not related to changes in [K+] and total ionic content of xylem sap.

Severe Outbreak of Bacterial Blight Caused by Xanthomonas arboricola pv. corylina on Hazelnut cv. Tonda di Giffoni in Central Italy.

Hazelnut (Corylus avellana L.) is one of the most economically important tree crops in Italy. Xanthomonas arboricola pv. corylina (Xac) causes bacterial blight of hazelnut (4). During early summer 2010, a survey of three orchards (5 ha total) containing 4-year-old hazelnut trees (cv. Tonda di Giffoni) in Viterbo Province, Latium region, Italy, showed an 80 to 100% incidence of bacterial blight. Initially, water-soaked, necrotic spots were visible on leaves, fruit involucres, and shells, followed by lateral shoot dieback and development of cankers as longitudinal bark cracks on twigs, branches, and main trunks. Brown necrosis of the cambium was observed when bark tissue was removed. By late summer, necrosis had extended down main branches to the trunk, causing complete girdling of branches. Symptomatic tissues were collected from leaves, branches, and trunks, sections were surface-sterilized in 1% NaOCl for 1 min followed by two rinses in sterile distilled water (SDW, each for 1 min), and each section was then crushed in SDW. A loopful of the suspension was streaked onto yeast extract-dextrose-calcium carbonate agar medium (YDCA). Thirty six (12 from each type of tissue) yellow-mucoid, shiny, round bacterial colonies, each approximately 2 mm in diameter, were subcultured on YDCA. All strains were gram-negative and aerobic; negative for indole, lecithinase, urease, tyrosinase, and nitrate reduction; and positive for catalase, growth in 2% NaCl in nutrient broth, and growth at 35°C. All strains produced dark green pigment on succinate-quinate (SQ) medium. Inoculum of each of 15 isolates was prepared in nutrient broth, and washed cells from late log-phase cultures used to prepare a bacterial suspension of each isolate for inoculation of 2-year-old potted hazelnut plants cv. Tonda di Giffoni. A suspension of 106 CFU/ml for each isolate was sprayed onto leaves (10 ml/plant), and drops of inoculum were placed on wounds made on twigs with a sterile scalpel (0.10 μl/wound). For each isolate, three plants were inoculated per inoculation method. Inoculations with two reference strains of Xac (Xaco 1 from central Italy (3) and NCPPB 2896 from England) and SDW were performed on the same number of plants for positive and negative control treatments, respectively. Inoculated plants were maintained at 26 ± 1°C in a greenhouse. After 21 days, all inoculated plants had developed symptoms on leaves, while cankers developed on twigs after 40 days. Positive control plants developed the same symptoms, while negative control plants remained asymptomatic. Bacteria recovered from lesions on plants inoculated with the test strains or positive control strains had the same morphological and physiological characteristics as the original strains. No bacteria were recovered from negative control plants. Total DNA was extracted from bacterial suspensions and 16S rDNA amplified using universal primers (2). Sequences (GenBank Accession Nos. JQ861273, JQ861274, and JQ861275 for strains Xaco VT3 to VT5) had 99 to 100% identity with 16S rDNA sequences of Xac strains in GenBank. In Italy, Xac was reported by Petri in 1932 in Latium, and later in other regions on several hazelnut cultivars (1). However, to our knowledge, this is the first report of the disease causing severe damage in Italy.

Characterization of leaf starch from HLB-affected and unaffected-girdled citrus trees

Starch content in leaves of HLB (Huanglongbing or citrus greening)-affected branches increases sharply compared to those from non-HLB trees. Starch not only over-accumulates in photosynthetic cells, but starch grains become prominent in vascular parenchyma and sieve elements as well. These observations imply strong disturbances in starch metabolism and photoassimilate partitioning in HLB-affected trees. Based on the elevated starch content, appearance of starch granules in phloem elements, and previous reports of the pathogen effect on starch properties, we hypothesized that starch from HLB-affected citrus trees may differ morphologically, physically and/or chemically from starch accumulated in otherwise healthy leaves. To obtain starch granules from healthy trees of comparable size to those of HLB-affected trees, we girdled 2-year-old branches and allowed starch to accumulate for 3 months. Starch morphology was investigated under brightfield, polarized light and SEM. HLB-induced starch grains were not morphologically different in size, shape and overall appearance from those of girdled branches. When reacted with 2% I2, no significant difference was observed in the absorption spectra of whole starch fractions (λmax for HLB = 604.1 and girdled 606.2 nm, respectively; n = 6; p ≤ 0.05) nor in their amylose/amylopectin ratio (HLB = 1.4 ± 0.17 and girdled = 1.16 ± 0.07, p ≤ 0.05) after chromatographic separation. However, λmax for individual fractions of HLB-affected leaves increased between 11 and 14 nm indicating a significant increase in the degree of polymerization of chain lengths of 12–45 glucose units. The increase in amylopectin chain length was confirmed by the rise in gelatinization temperature of approximately 10 °C observed by polarized light microscopy. Our results indicate that starch grains from leaves affected by HLB were morphologically similar but differed biochemically from those formed by healthy trees after phloem blockage caused by mechanical injury.

Teores de carboidratos nas folhas e produção de limeiras ácida 'tahiti' aneladas e tratadas com ácido giberélico

O objetivo do trabalho foi avaliar o efeito do ácido giberélico (GA3) e anelamento de ramos sobre os teores de carboidratos nas folhas, a produção e o peso de frutos de limeira ácida 'Tahiti'. O delineamento experimental foi em blocos casualizados, com cinco repetições, em esquema fatorial 4x3. O primeiro fator foi a aplicação de GA3 em quatro concentrações (0; 7; 14 e 21 mg/L-1), e o segundo, duas épocas de anelamento, no início e um mês após o florescimento, mais a testemunha sem anelamento. Verificou-se que o GA3 não teve efeito sobre a produção e o anelamento de ramos, independentemente da época em que foi realizado, aumentaram a produção das plantas e os teores de carboidratos nas folhas. A maior produção e relação frutos/m-3 de copa causou redução no peso médio dos frutos de limeira ácida 'Tahiti'.