Pear Branches Research Articles

Biocontrol activity and action mechanism of Paenibacillus polymyxa strain Nl4 against pear Valsa canker caused by Valsa pyri.

Pear Valsa canker caused by Valsa pyri is among the most destructive diseases of pear, which causes significant economic loss. The present study was developed to explore the biocontrol efficiency and underlying antagonistic mechanism of Paenibacillus polymyxa strain Nl4 against V. pyri. P. polymyxa strain Nl4, one of the 120 different endophytic bacterial strains from pear branches, exhibited strong inhibitory effects against the mycelial growth of V. pyri and caused hyphal malformation. Culture filtrate derived from strain Nl4 was able to effectively suppress mycelial growth of V. pyri, and was found to exhibit strong protease, cellulase and β-1, 3-glucanase activity. Through re-isolation assay, strain Nl4 was confirmed to be capable of colonizing and surviving in pear branch. Treatment with strain NI4 effectively protected against pear Valsa canker symptoms on detached pear twigs inoculated with V. pyri. Moreover, strain Nl4 promoted enhanced plant growth probably through the solubilization of phosphorus. Comparative transcriptomic analyses revealed that strain NI4 was able to suppress V. pyri growth in large part through the regulation of the expression of membrane- and energy metabolism-related genes in this pathogen. Further transcriptomic analyses of pear trees indicated that strain NI4 inoculation was associated with changes in the expression of genes associated with secondary metabolite biosynthesis, signal transduction, and cutin, suberine, and wax biosynthesis. Together, these data highlighted P. polymyxa strain Nl4 as a promising biocontrol agent against pear Valsa canker and investigated the possible mechanisms of strain Nl4 on control of this devastating disease.

Effect of the Pyrolysis Process Applied to Waste Branches Biomass from Fruit Trees on the Calorific Value of the Biochar and Dust Explosivity

The article discusses the findings related to the calorific value as well as the explosion and combustion parameters of dust from the raw biomass of fruit trees, i.e., apple, cherry, and pear branches, and from biochars produced using this type of biomass during pyrolysis processes conducted under various conditions. The plant biomass was thermally processed at 400, 450, or 500 °C for a duration of 5, 10, or 15 min. The study aimed to identify the calorific value of the biomass obtained from waste produced in orchards and to estimate the explosion hazard during the processing of such materials and during the storage of the resulting solid fuels. Tests were conducted to assess the total contents of carbon, ash, nitrogen, hydrogen, and volatile substances as well as the calorific value. The findings show a significant effect of the thermal transformation of fruit tree branches on the calorific value of the biochars that were produced. It was found that the mean calorific value of all of the biochars was increased by 62.24% compared to the non-processed biomass. More specifically, the mean calorific values of the biochars produced from apple, cherry, and pear branches amounted to 27.90, 28.75, and 26.84 MJ kg−1, respectively. The maximum explosion pressure Pmax measured for the dust from the biomass and for the biochars was in the range 7.56–7.8 and 7.95–11.72 bar, respectively. The maximum rate of pressure rose over time (dp/dt)max in the case of the dust from the biomass, which was in the range of 274.77–284.97 bar s−1, and the dust from biochar amounted to 282.05–353.41 bar s−1. The explosion index Kst max measured for non-processed biomass and biochars was found to range from 74.46 to 77.23 and from 76.447 to 95.77 bar s−1, respectively. It was also shown that a change in the temperature and duration of the pyrolysis process affected the quality of the biochars that were obtained. The findings show that pyrolysis, as a method of plant biomass processing, positively affects the calorific value of the products and does not lead to an increased risk of explosion during the treatment and storage of such materials. It is necessary, however, to continue research on biomass processing in order to develop practices that adequately ensure safety during the production of novel fuels.

Biological Control of Pear Valsa Canker Caused by Valsa pyri Using Penicillium citrinum

Valsa canker caused by Valsa pyri is one of the most destructive diseases of commercial pear. For the present analysis, 29 different endophytic fungal strains were isolated from the branches of a healthy pear tree. In dual culture assays, strain ZZ1 exhibited robust antifungal activity against all tested pathogens including Valsa pyri. Microscopic analyses suggested that following co-culture with ZZ1, the hyphae of V. pyri were ragged, thin, and ruptured. ZZ1 also induced significant decreases in lesion length and disease incidence on detached pear branches inoculated with V. pyri. ZZ1 isolate-derived culture filtrates also exhibited antifungal activity against V. pyri, decreasing mycelial growth and conidium germination and inhibiting V. pyri-associated lesion development on pear branches. These results suggest that the ZZ1 isolate has the potential for use as a biological control agent against V. pyri. The strain was further identified as Penicillium citrinum based on its morphological characteristics and molecular analyses. Overall, these data highlight a potentially valuable new biocontrol resource for combating pear Valsa canker.

Pectobacterium carotovorum subsp. actinidiae associated with canker on pear trees in Brazil

In summer of 2016, cankers were observed on 8-year-old pear trees (Pyrus communis L.) cv. Yali grafted on the Caleriana rootstock, in a commercial orchard in Monte Castelo, SC. Eight hundred out of 1200 trees died and the rest of the orchard was eradicated. Affected plants showed cankers on trunks and twigs with exudation; the branches turned brown and slowly died. Bacterial colonies were isolated on King’s B medium from infected tissues. Pathogenicity, biochemical tests were conducted and some isolates selected for whole genome sequencing using Ion Personal Genome Machine™ (PGM™) System (ThermoFisher Scientific). PCR with Y1/Y2 and PcaF/PcaR primers, specific for Pectobacterium carotovorum and Pectobacterium carotovorum subsp. actinidiae, respectively, were also carried out. The section of inoculated apple and pear branches showed longitudinal darkening, with wilt and leaf blight. Shoots of kiwifruit Actinidia deliciosa cv. Hayward inoculated with the bacterium showed no symptoms. The bacterium was re-isolated from all symptomatic tissues, satisfying Koch’s postulates. Selected isolates were gram-negative, facultative anaerobic, rod-shaped and exhibited a strong pectolytic activity in potato and carrot disks, and showed similar biochemical profile using a BIOLOG GEN III MicroPlate. The pathogen of the symptoms observed on pear trees in Brazil show highest genome (87.1%; DDH analysis) and proteome identity (99.8%; Patric analysis) with P. carotovorum subsp. actinidiae. A product of the expected size was obtained in both specific PCR (Y1/Y2 (434 bp) and PcaF/PcaR (343 bp) primer pairs). Results from the present study clearly show that P. carotovorum subsp. actinidiae was associated with canker on pear trees in Santa Catarina, Brazil.

Steam explosion treatment for ethanol production from branches pruned from pear trees by simultaneous saccharification and fermentation.

This study investigated the production of ethanol from unutilized branches pruned from pear trees by steam explosion pretreatment. Steam pressures of 25, 35, and 45 atm were applied for 5 min, followed by enzymatic saccharification of the extracted residues with cellulase (Cellic CTec2). High glucose recoveries, of 93.3, 99.7, and 87.1%, of the total sugar derived from the cellulose were obtained from water- and methanol-extracted residues after steam explosion at 25, 35, and 45 tm, respectively. These values corresponded to 34.9, 34.3, and 27.1 g of glucose per 100 g of dry steam-exploded branches. Simultaneous saccharification and fermentation experiments were done on water-extracted residues and water- and methanol-extracted residues by Kluyveromyces marxianus NBRC 1777. An overall highest theoretical ethanol yield of 76% of the total sugar derived from cellulose was achieved when 100 g/L of water- and methanol-washed residues from 35 atm-exploded pear branches was used as substrate.

FIREBLIGHT SURVEY AND FIRST CHARACTERIZATION OF ERWINIA AMYLOVORA ISOLATES FROM ALGERIA

During field surveys conducted in Spring and Summer 2010-2011, typical fire blight symptoms were observed on twigs and branches of pear (Pyrus communis) and apple (Malus domestica) in Algerian commercial orchards located in the areas of Algiers, Blida, Tipaza and Boumerdes. The disease was observed in 284 orchards, mainly on pear cv. Santa Maria and on apple cvs Royal gala and Golden delicious. Bacterial colonies were isolated on King’s medium B (KB) and the semi-selective medium CCT (cycloheximide, cristal violet and thallium nitrate). Bacterial isolates displayed biochemical patterns typical of Erwinia amylovora and reacted positively in a serological slide agglutination test. Pathogenicity of bacterial isolates was confirmed by inoculating immature pear fruits of cv. Conference. The identity of the isolates was further confirmed by nested-PCR, and rep-PCR. A sequenced DNA fragment (713 bp) of the recA gene (accession No. JN812979) matched with 100% identity all E. amylovora recA DNA sequences available in GeneBank.

Phylogenetic and Pathogenic Analyses Show That the Causal Agent of Apple Ring Rot in China Is Botryosphaeria dothidea.

Apple ring rot and Botryosphaeria canker are severe diseases affecting apple production in China, but there is confusion regarding which pathogens cause these diseases and their similarity to other diseases, such as white rot of apple, and ring rot and Botryosphaeria canker of pear. In this study, the pathogen of apple ring rot in China was compared with the pathogen of apple ring rot in Japan and Korea, the pathogen of Botryosphaeria canker of apple and pear in China, the pathogen of pear ring rot in China, and the pathogen of white rot of apple in the United States. Comparisons were based on morphology, pathogenicity on branches and fruit, and sequences of rDNA in the internal transcribed spacer region and of the β-tubulin and actin genes. Results showed that the causal agent of apple ring rot and Botryosphaeria canker of apple in China was Botryosphaeria dothidea, which has also been reported to be the pathogen of apple ring rot in Korea and Japan. Pathogenicity tests showed that B. dothidea infection on apple and pear branches may induce wart or canker symptoms depending on the conditions. These results are consistent with the hypothesis that the same pathogen causes the wart symptom of apple ring rot and the Botryosphaeria canker symptom on apple branches in China. The results also suggest that apple ring rot and white rot are the same disease and are caused by B. dothidea. Finally, B. dothidea isolates from pear and other fruit or forest trees may serve as inoculum for apple ring rot.

Effects of regulators on the respiratory enzyme of pear branches during dormant period

The effects of regulators on the respiratory enzymes of Qiyuesu’s pear branches during dormant period were studied. The results showed that enzyme activities of SDH, G-6-PDH and 6-PGDH were increased by 0.02 mmol/L SA and 120 mg/L GA3. The enzyme activities of phosphohexoisomerase were reduced by 0.02 mmol/L SA and 120 mg/L GA3. Compared with the control, the PGI activity was reduced by 20.5% and 13.6% using 0.02mmol/L SA and 120mg/L GA3. Similarly, the SDH activity was increased by 6.1% and 29.2%, respectively. Likewise, the activity of G-6-PDH and 6-PGDH was increased by 93.9% and 24.8%. Changes of respiratory enzymes were consistent with respiratory pathway of regulators, which indicated that SA and GA3 were helpful to break the dormancy by enhancing activities of SDH, G-6-PDH and 6-PGDH.

The Influence of the Export of Japanese Pear Branches to Pear Farmers in Japan

The Influence of the Export of Japanese Pear Branches to Pear Farmers in Japan

Detection of three pear viruses by multiplex RT-PCR assays with co-amplification of an internal control

Apple stem pitting virus, Apple chlorotic leaf spot virus and Apple stem grooving virus are economically important and common pathogens of pear and apple cultivars. All are symptomless in commercial pear and apple cultivars. Two multiplex RT-PCR methods with co-amplification of an internal control from a plant mRNA sequence were used to detect these three viruses simultaneously. The approaches, including what materials were to be selected and how to extract nucleic acids, were designed to improve detection efficiency. Detection assays, using bark chips of 1- or 2-year-old pear branches, could be performed both in the growing season and in dormant trees. A specific internal RNA control, which could be amplified from total nucleic acids, was co-amplified with the target viruses. Therefore, purified RNA as an amplification template was not necessary. Isolation of nucleic acids from bark chips was more successful than isolation from leaves. Three virus-specific primer pairs were designed to allow two multiplex RT-PCR amplifications accompanied by one pair of primers of the mitochondrial nad5 gene. Four amplification products including three viruses and an internal control were sequenced to prove the specificity of all primer pairs. By using a nad5 gene in mitochondrial mRNA of the apple as an internal control of co-amplification, these methods reduced the risk of false negative results that may occur with routine RT-PCR assays.

Branch Strength of Bradford Pear ( Pyrus calleryanavar. ‘Bradford’)

Previously planted extensively as a street tree, Bradford pear (Pyrus calleryana var. ‘Bradford’) has fallen out of favor because of its reputation for branch breakage. Despite this reputation, Bradford pear branch strength has never been tested. Prior studies on branch breaking have discounted the influence of branch attachment angle, suggesting that the ratio of branch to trunk diameter, or aspect ratio, is a better predictor of branch attachment strength. Twenty-six Bradford pear branches from 10 trees were broken by pulling them with a winch. To assess the effect of branch cross-sectional dimensions, breaking stress was calculated considering the branch cross-section as either an ellipse or a circle. Breaking stress was normalized by dividing it by the modulus of rupture measured on wood samples from each broken branch. The location of failure, either in the branch itself or at the branch/trunk attachment, did not affect breaking stress. Aspect ratio was a better predictor of branch attachment strength than branch attachment angle. Breaking stress calculated considering the branch cross-section as an ellipse was greater than when stress was calculated assuming the branch cross-section was a circle. Results are compared with previous studies and the importance of measuring branch cross-sectional dimensions is discussed.

Induction of Cankers on Pear Tree Branches by Neofabraea alba and N. perennans, and Fungicide Effects on Conidial Production on Cankers.

Cankers formed on pear branches after inoculations with mycelia of Neofabraea alba or N. perennans, causal agents of bull's eye rot of pear fruit. The highest proportions of successful infections followed inoculations made in fall and winter. Cankers induced by N. perennans were larger than those induced by N. alba. Small, superficial cankers were obtained after inoculations with conidia of N. perennans on wounded branches of pear trees. Sporulation of both pathogens on mycelial-induced cankers occurred throughout the year, with the largest amount of conidia produced at the end of summer and during fall. Sporulation on cankers induced by N. perennans spanned at least 2 years. Copper sulfate reduced sporulation on cankers induced by N. alba, while copper sulfate, trifloxystrobin, and ziram applied to sporulating cankers reduced germination of conidia of N. perennans.

AN ARCHITECTURAL ANALYSIS OF PEAR CULTIVARS GROWN UNDER SOUTH AFRICAN CONDITIONS AND THE RELEVANCE TO LOCAL MAINTENANCE PRUNING STRATEGIES

To quantify the growth habit of locally important pear varieties, initially, 2-year-old pear branches were classified into groups based on the length and position of lateral shoots. Four groups were formed that ranged from cultivars with a spurred growth habit and strong apical control, to cultivars with a spreading growth habit and weak apical control. Secondly, the development of fruiting branches was observed for up to five years by observing the five developmental alternatives of the terminal buds of laterals, i.e., dormant, vegetative, reproductive without fruit, reproductive with fruit, and abortion. Under local conditions two general problems were observed. A large proportion of buds remain vegetative giving rise to poor flowering, and many buds remain dormant, probably due to the use of vigorous rootstocks and inadequate winter chilling. Local training systems address these shortcomings through the use of rest-breaking agents, girdling, and winter pruning techniques. Winter pruning strategies for locally important cultivars can be split into two broad approaches. In one approach spurs are renewed within spur systems primarily via bourse shoots. In the other approach spurs are renewed via year-old shoots. The motivation for the use of these systems is discussed in light of the above architectural findings.

The Role of Autumn Infections in the Progression of Fire Blight Symptoms in Perennial Pear Branches.

The role of autumn infections in the progression of fire blight (caused by Erwinia amylovora) symptoms in perennial pear branches was studied in orchard-grown trees in Israel. The extent of symptom progression and the final length of fire blight cankers in perennial branches were variably affected by the vigor of the trees and the season of infection. Following spring infections, when all trees supported active shoot growth, fire blight symptoms progressed more rapidly and to longer distances in trees that exhibited high vigor (i.e., with numerous annual shoots on most terminal branches) than in low-vigor trees (i.e., few or no annual shoots on terminal branches). Irrespective of the vigor of the trees, the progression of fire blight symptoms in perennial branches ceased between mid-May and mid-July, and only a small proportion (0 to 14.2%) of the infections had invaded main limbs or trunks of trees. Progression of fire blight symptoms following autumn infections was related to the preceding summer (August to No-vember) shoot regrowth: in trees in which the shoots did not restore their growth in the summer, the rate of symptom progression in perennial branches was higher in trees with a low vigor than in those with a high vigor, whereas for those with summer regrowth the relationship between rates of symptom expression was reversed. Irrespective of the vigor group and of whether there was summer regrowth, symptoms in perennial branches continued to progress through the winter until the following spring. Most of the autumn infections (50 to 78.5%) that developed in susceptible trees had invaded main limbs or trunks of trees. The results of this study indicate that factors related to host phenology and physiology, rather than factors related to environmental influences (such as temperature), govern the extent, rate, and duration of fire blight progression in perennial pear branches. Furthermore, it turned out that autumn infections play a substantial role in fire blight epidemiology in Israel.

Branching habit of 2-year-old pear branches classified on the basis of length and position of 1-year-old laterals

Two-year-old branches of Pyrus communis L. were classified into groups according to the proleptic (from dormant buds) branching habit, indirectly quantifying the degree of apical control. In winter 1998 upright and flat, 2-year-old branches were randomly sampled from trees of seven pear cultivars, i.e., Forelle (on Quince A and BP1 rootstocks), Abaté Fetel, Flamingo, Packham’s Triumph, Golden Russet Bosc, Rosemarie and Beurre D’Anjou on BP1 rootstock. For each branch the length and position of the 1-year-old shoots on the 2-year-old axis was determined. Laterals were classified according to length (<1, 1–5, 5–20 and >20 cm) and position (distal to proximal quadrants on the 2-year-old axis); 16 classes in total. The number of shoots per length class per cm quadrant length for each cultivar was subjected to a cluster analysis, then a canonical and a stepwise discriminant analysis. The cultivars were grouped into four groups from group 1 (‘Flamingo’), which resembles a spurred growth habit with strong apical control, to group 4 (‘Packham’s Triumph’ and ‘Golden Russet Bosc’), which resembles a spreading growth habit and weak apical control. Groups 2 and 3 were intermediate. The gravimorphic influences on the branching habit were investigated.

Duration times of the immature stages of Cacopsylla pyri L. (Hom., Psyllidae), estimated under field conditions, and their relationship to ambient temperature

The duration of the immature stages of Cacopsylla pyri L. was studied under field conditions by artificially infesting pear branches on several dates during the year. The duration of the egg stage decreased from winter to summer, as the season progresses and temperature rises, and slightly increased in September. It ranged from 27.4 to 6.7 days. The same trend was observed in the duration of the first three larval stages (L1−3) which ranged from 18.8 to 10.3 days. For eggs deposited during the period February–August the duration of the last two larval stages (L4−5) ranged from 17.5 to 12.1 days. However, the duration of L4−5 developed from eggs deposited in September and which give rise to winter‐form adults were the longest observed. The rate of egg development was related to average ambient temperature with a highly significant linear relationship. This relationship indicates that the egg stage requires a constant number of 158.9 (SD = 5.0) of day‐degrees above an average temperature of 2.31°C to complete development. The rate of development both of L1−3 and L4−5 were related to average ambient temperature with curvilinear relationships. These relationships indicate a proportional increase in the developmental rate as temperature rises between 10–22°C. At the higher average temperatures that occurred in the summer experiments (24–27°C) the acceleration of development of L1−3 is reduced and the developmental rate of L4−5 decreases. The developmental rates of L4−5 developed from eggs deposited in September did not follow the established relationship with temperature and they were lower than those in the other periods of the year with the same average temperature.

Characterization of theErwinia amylovora population in Israel

A collection of 205 strains ofErwinia amylovora isolated in Israel over a period of 12 years has been established. The strains were isolated from different varieties of pear, apple, loquat and quince grown in Israel, and collected from different locations in the country. They were characterized in respect to degree of virulence on several hosts and serological and molecular characters. Pathogenicity tests carried out on flowering branches of pear and apple, shoots of pears, and on trees of pear and loquat grown in containers outdoors, revealed no significant differences in the severity of blossom blight or shoot blight among the various strains. ELISA and immunofluorescence assays revealed no serotypic groups among the Israeli strains. Genomic diversity was studied by random amplified polymorphic DNA (RAPD) analysis using 24 arbitrary 10-base primers. All the strains examined (45 Israeli and 11 from Egypt, Cyprus and Greece) produced the same RAPD patterns with each of the primers used. Amplification patterns were indistinguishable from those produced by strains isolated from the neighboring countries. Results presented in this study suggest that the population ofE. amylovora in Israel is homogenous.

Degree-Day Model for Predicting Emergence of Pear Rust Mite (Acari: Eriophyidae) Deutogynes from Overwintering Sites

Emergence times of deutogynes of the pear rust mite, Epitrimerus pyri Nalepa, from overwintering sites on branches of pear, Pyrus communis L., were compared between laboratory-stored (constant 1°C)and field-wintered branches at 2–4-wk intervals over 20 wk. Until wk 16, which corresponded to 1 March, 1992, the mean time to 50% emergence of mites declined steadily and was not significantly different between the two groups of branches. After wk 16, the mean time to median emergence of mites from field-wintered branches continued to decline, but there was no further decline in the emergence time of mites from laboratory-stored branches, resulting in a significant difference between the two groups. This divergence of the emergence times of mites from laboratory-stored and field-wintered branches after wk 16 indicated that Reid-wintered mites had begun “post-diapause” development or reactivation after ≍ 1 March. Emergence rates of individual mites from branches held at 1°C for 20 wk were compared at seven constant temperatures: 5.3, 7.8, 10.6, 13.3, 15.5, 17.6, and 20.8°C. Weighted, least squares linear regression was used to describe the relationship between emergence rate and temperature (rate = −0.1008 + 0.0162[temp]) for prediction of emergence in the field.The base threshold temperature for emergence was 6.2°C, as determined by extrapolation of the regression line to the x -axis. The relationship predicted that median (50%) emergence of mites requires 62 ± 1 degree-days (±SE) above the base temperature. The degree-day model was validated using field phenology data collected at one and four sites in 1991 and 1992, respectively. Using a 6.0°C threshold temperature for emergence, and daily minimum-maximum air temperatures beginning 1 March, the model accurately (±2 d) predicted the 50% emergence point. This article discusses the use of the degree-day model to improve current pear rust mite management practices in British Columbia.

Monitoring the Emergence and Behavior of Pear Rust Mite (Acarina: Eriophyidae) Deutogynes Using Sticky-Band Traps

Deutogynes of pear rust mite, Epitrimerus pyri (Nalepa), emerging from overwintering sites on branches of pear, Pyrus communis L., were captured in the laboratory and field using sticky-band traps. On branches in the laboratory, mite emergence was stimulated by light, and active mites were positively phototactic. Emergence was not affected by bud development. The rate of mite emergence at 15°C was significantly less than at 20°C. In the orchard, the same trends of emergence and activity were recorded from traps on fruit spurs and on 2-yr-old branches. In 1991, emergence began slowly in late March, peaked sharply in mid-April, then declined to near zero by early May. The results are discussed in relation to the potential for the development of a predictive model of pear rust mite emergence upon which growers could base the timing of acaricide applications.

Effect of Prebloom Oil Applications on Pear Fruit Set and the Possible Mode of Action1

Abstract Dilute sprays of 4, 8 and 16% Volck Supreme oil at dormant and repeated at delayed dormant to mask pear trees against psylla, Psylla pyricola (Foerster), oviposition delayed bloom slightly, while 2% applications in the Meld advanced bloom less than 1 day. Dormant pear branches dipped under laboratory conditions in oil at concentrations of 8% and higher caused injury to vegetative buds and slight injury to flowering buds. Single and repeat field applications of oil at 2, 4 and 8% caused no reduction of fruit set or cropping of ‘Anjou’, ‘Bartlett’, ‘Cornice’, ‘Bose’, and ‘Seckel’ pear trees, and in some cases increased fruit set on ‘Anjou’ trees. Hormonal analysis of oil-treated buds indicated a slight increase of gibberellin (GA) and a reduction of abscisic acid (ABA) levels.