Pear Rust Research Articles

Comparative transcriptome analysis and identification of candidate effectors in two related rust species (Gymnosporangium yamadae and Gymnosporangium asiaticum)

BackgroundRust fungi constitute the largest group of plant fungal pathogens. However, a paucity of data, including genomic sequences, transcriptome sequences, and associated molecular markers, hinders the development of inhibitory compounds and prevents their analysis from an evolutionary perspective. Gymnosporangium yamadae and G. asiaticum are two closely related rust fungal species, which are ecologically and economically important pathogens that cause apple rust and pear rust, respectively, proved to be devastating to orchards. In this study, we investigated the transcriptomes of these two Gymnosporangium species during the telial stage of their lifecycles. The aim of this study was to understand the evolutionary patterns of these two related fungi and to identify genes that developed by selection.ResultsThe transcriptomes of G. yamadae and G. asiaticum were generated from a mixture of RNA from three biological replicates of each species. We obtained 49,318 and 54,742 transcripts, with N50 values of 1957 and 1664, for G. yamadae and G. asiaticum, respectively. We also identified a repertoire of candidate effectors and other gene families associated with pathogenicity. A total of 4947 pairs of putative orthologues between the two species were identified. Estimation of the non-synonymous/synonymous substitution rate ratios for these orthologues identified 116 pairs with Ka/Ks values greater than1 that are under positive selection and 170 pairs with Ka/Ks values of 1 that are under neutral selection, whereas the remaining 4661 genes are subjected to purifying selection. We estimate that the divergence time between the two species is approximately 5.2 Mya.ConclusionThis study constitutes a de novo assembly and comparative analysis between the transcriptomes of the two rust species G. yamadae and G. asiaticum. The results identified several orthologous genes, and many expressed genes were identified by annotation. Our analysis of Ka/Ks ratios identified orthologous genes subjected to positive or purifying selection. An evolutionary analysis of these two species provided a relatively precise divergence time. Overall, the information obtained in this study increases the genetic resources available for research on the genetic diversity of the Gymnosporangium genus.

Gymnosporangium Species – An Important Issue of Plant Protection

Abstract Rusts (Fungi, Basidiomycota, Pucciniomycotina, Pucciniomycetes, Pucciniales) are one of the most important causal agents of diseases and they are infecting many plants including cereals and field crops, vegetables, trees and many ornamentals. They have been studied for a long time and have economic importance among the plant diseases caused by agents of different species of fungi. In Europe, thirteen rust genera have been reported, of which the genus Gymnosporangium is the second largest after genus Phragmidium. The most significant fruit tree rust pathogen is the genus Gymnosporangium. The literature review shows quite limited scientific information about this genus and its species. Studies have mainly focused on some stages of the pathogen development cycle, which are significant for the spread of diseases - uredo and teleito stages. Special attention of the review was paid to European pear rust (caused by G. sabinae (Dicks.) G. Winter), the distribution of which has increased during the last ten years, especially in organic pear orchards. Currently there is a limited number of scientific publications about European pear rust, and they are mainly based only on observations in vitro without trials in the field, despite the fact that it has become one of the most devastating diseases. Therefore, the presented review analyses the rust exploration history, diversity and distribution of species, life cycle, development biology and plant protection issues.

Evaluation of pear (Pyrus communis L.) cultivars in Latvia

Pears (Pyrus communis L.) are an important commercial crop in Latvia, ranked as a second most important fruit tree crop. The aim of this study was the choice of suitable new pear cultivars for growing in Latvia. The evaluation was carried out at the Latvia State Institute of Fruit-Growing. Eighteen cultivars were evaluated over six years. Flowering intensity, harvest date, average fruit weight, taste and chemical composition (total soluble solids, flesh firmness, titratable acidity (TA)) and resistance to diseases and pests were recorded. Flowering intensity showed significant differences among years: the highest was in 2009 and 2011, the lowest in 2007, but not among cultivars. The highest fruit weight (292 g) was detected for cv. Tavricheskaya, the high and stable fruit size for cv. Elektra. The best fruit qualities were produced by cvs Concorde, Condo and Conference. Stable and high content of soluble solids, high TA and fruit firmness were found in fruit of cv. Lyubimitsa Osennyaya. There were no cultivars resistant to European pear rust; the lowest susceptibility was detected for cv. Noyabrskaya (synonym Xenia), whereas cv. Talgarskaya Krasavitsa was resistant to sooty mould (caused by Leptoxyphium fumago) and cv. Smuglyanka - to pear leaf blister mite (Eriophyes pyri).

STIMULATION OF PEAR RUST MITE POPULATIONS DUE TO APPLICATION OF SPINETORAM IN SOUTHERN OREGON AND NORTHERN CALIFORNIA

Spinetoram is currently being used in pears for control of Lepidoptera and other pests. Over the last ten years, results of repeated trials in southern Oregon and northern California examining the effect of spinetoram use in pears have shown elevations in the population level of pear rust mite, Epitrimerus pyri. In both regions, the increase in pear rust mite populations due to the application of spinetoram has been statistically significant in multiple years. In 2013, an evaluation in northern California resulted in both significantly higher levels of pear rust mite throughout the sampling period and significantly higher levels of russet on the fruit at harvest. In the spinetoram treatment, 8.4% of the fruit sampled had greater than ¼ of the fruit surface with russet as compared to 0.2% of the fruit in the untreated check. Reduced levels of some natural enemies have been observed in southern Oregon trials, specifically parasitic hymenoptera, Encarsia sp., and the common earwig, Forficula auricularia. Whether the increase in pear rust mite resulting from spinetoram applications in pear is due to a reduction in natural enemies or to hormoligosis remains undetermined.

Increased content of phenolic compounds in pear leaves after infection by the pear rust pathogen

European pear rust induced by the fungus Gymnosporangium sabinae (Dicks) G. causes yellow to bright orange leaf spots on leaves of pear trees. The aim of this study is to identify and quantify polyphenolic compounds found in pear leaf extracts. Identified were: ten hydroxycinnamates, eight flavonols, nine flavan-3-ols and three arbutin derivatives. Polymeric procyanidins were additionally determined by UPLC-FL. The total content of phenolics in the control healthy green leaf extract was 11,889.98 mg but in the infected leaves it reached 28,573.89 mg in the samples with yellow spots and 11,480.06 mg/100 g dry matter (dm) in the green part of leaves. The yellow spots in pear rust leaves were characterized by increased content of flavanol (catechins and procyanidins) and arbutin compounds compared with the green part of the infected leaves and control healthy leaves.

FIRST REPORT OF GYMNOSPORANGIUM SABINAE ON CULTIVATED PEAR IN LEBANON

Gymnosporangium sabinae (Dickson) G. Winter (syn. G. fus- cum DC.), the causal agent of European pear rust disease, can se- verely reduce yield of cultivated pear (Pyrus communis). This fun- gus, an obligate parasite that alternates between species of Junipe- rus and Pyrus to complete its lifecycle, is heteroecious and causes perennial infections on juniper and annual infections on pear (Laundon, 1975). In October 2011, leaves of cultivated pear trees of cv. Coscia, heavily attacked by a rust were collected in two or- chards located, respectively, in Baskinta [Mount Lebanon (33°56’39’’ N, 35°47’15’’ E)] and in Basloukite [north Lebanon (34°18’28’’ N, 35°58’02’’ E)]. Based on morphologic features (Parmelee, 1971; Laundon, 1975), the pathogen was identified as Gymnosporangium sabinae. On the upper side of the leaf, there were irregular, bright orange-red spots, which contained compact conglomerations of spermogonia. These structures were dark- brown to black, hemispherical, protuberant, 3-4 mm in diameter, had many receptive hyphae and produced at maturity a large number of oblong hyaline spores (spermatia) measuring 5.1- 7.2×1.2-1.8 μm. On the lower side of the leaf, there were loose conglomerations of horn-like aecia located on protruding tissue outgrowths. From these aecia, pale-brown pseudo-peridia arose as small groups of 2-4 mm-long filaments, composed of irregular- ly prolate peridial cells with inner and lateral walls extremely thickened, ornamented with cylindrical warts, which produced 24-30×23-28 μm subgloboid, ellipsoid aeciospores, with 4-5.5 mm thick orange-brown walls. Symptoms on surrounding Junipe- rus spp. were not observed. To our knowledge, this is the first re- port of G. sabinae on cultivated pear in Lebanon.

Pome fruit health

The pome fruits, apple and pear, represent very important fruit crops in Europe. They are grown on 490,000 ha in 15 countries with a production of more than 11 million tons per year (FAO, 2003). This corresponds to an estimated annual value of €20 billion at consumer prices. European consumers are highly concerned about health and safety aspects of food. High quality fruits in sufficient amounts can only be produced on healthy plants. Thus, one of the most important tasks in crop production is an effective and sustainable management of plant diseases. Two of the most important diseases in European pome fruit growing are fire blight which is caused by the bacterium Erwinia amylovora, and the scab on apple and pear caused by the fungi Venturia inaequalis and V. pirina, respectively. Erwinia species cause not only severe losses in apple and pear but also attack numerous native wild species and popular ornamentals of the Rosaceae. Intensive investigations on these pome fruit diseases revealed new insights into the molecular aspects of the host–pathogen interactions, into possible mechanisms of defence by the host plants, into the genetic background of plant resistance and tolerance and into the molecular basis of virulence. Nowadays, nearly all European countries are facing similar problems regarding plant protection in pome fruit growing. Thus, co-operation at the international level is required and a network of more than 200 European scientists from 25 countries was established by the COST action 864 ‘Combining traditional and advanced strategies for plant protection in pome fruit growing’ (Acronym POME FRUIT HEALTH). The action focused on different aspects includes the (i) investigation of plant–pathogen interactions, (ii) germplasm resources and breeding, (iii) production methods and (iv) biotechnological resources. This special issue of Trees provides an overview of the fruitful yield of the interactions among European experts. A series of reviews and original articles cover actual research topics mainly in the fields of germplasm resources and breeding, host–pathogen interactions and fruit tree protection. For breeding, it is crucial to identify germplasm with heritable disease resistance. The development of efficient markers is essential for marker-assisted selection which is already used in breeding programs for scab resistance but is also attempted for fire blight resistance. Resource evaluation must include the susceptibility to fire blight (E. amylovora) and scab (V. inaequalis, V. pirina), but also to other diseases such as powdery mildew (Podosphaera leucotricha), pear rust (Gymnosporangium sabinae), brown spot of pear (Stemphylium vesicarium) and storage diseases (e.g. Penicillium expansum and Monilinia spec.). The knowledge of the genes behind a resistance and of its mode of action improves breeding success and offers prospects in gene technology. Recent advances are reviewed for the Vf resistance of apples against the scab. The possible involvement of secondary plant metabolites such as phenolic compounds in the defence of V. inaequalis is still debated. Various floral traits that may play a role in the onset and progression of E. amylovora infection are compared between susceptible and tolerant apple and pear varieties and the expression pattern of stress-related genes in E. amylovora-infected pear leaves is shown. It is not the core scope of Trees to deal with bacteria. However, it completes the examination of fire blight management. For progress in pome fruit protection against this bacterial D. Treutter (&) Unit Fruit Science, Technische Universitat Munchen, Durnast 2, 85354 Freising, Germany e-mail: dieter.treutter@wzw.tum.de

European pome fruit genetic resources evaluated for disease resistance

Pome fruit genetic resources collections constitute a highly valuable resource not only for fruit breeding but also for direct use by nurseries, growers, and home gardeners. In order to use these resources efficiently and sustainably, reliable evaluation data on fruit and tree characteristics must be generated. Here we focus on pome fruit genetic resources evaluated phenotypically and genotypically for susceptibility to apple scab (Venturiainaequalis), powdery mildew (Podosphaeraleucotricha), fire blight (Erwiniaamylovora), pear rust (Gymnosporangiumsabinae) and storage diseases (e.g., Penicilliumexpansum). Examples are presented of several ongoing projects throughout Europe, with the aim to evaluate fruit genetic resources for disease susceptibility and potential use in breeding and for commercial use. The COST action 864 has fostered international cooperation in the evaluation of pome fruit genetic resources, and some of these evaluations therefore involve research groups from several of the participating countries.

Basidiospore germination by repetition and saprotrophic mycelia in the gelatinous telial horns of Gymnosporangium sabinae

AbstractThe teliospores of Gymnosporangium sabinae facultatively germinate with basidia or with haploid hyphae. The germination of basidiospores is by means of secondary spores (by repetition) or with haploid hyphae. In the gelatinous telial horns a saprotrophic mycelium is developed, that infected probably the host of the dikaryophase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

First Report of Gymnosporangium sabinae, European Pear Rust, on Bradford Pear in Michigan.

Bradford pear, Pyrus calleryana Decne., is well known as an ornamental plant for its flowers, leaf color in fall, and disease resistance, making it desirable as a street tree. In August and October of 2008, the aecial stage of Gymnosporangium sabinae (Dicks.) G. Winter was collected from leaves of P. calleryana in Farmington, MI (Oakland County). The one tree had foliage that was severely affected by the rust fungus. Using published descriptions of G. sabinae as the synonym of G. fuscum, type of the genus Gymnosporangium (1-4), the Michigan specimen was identified and confirmed by comparison with previously reported European and U.S. specimens (BPI 118736 and BPI 856578). The diagnostic characteristics of G. sabinae include: spermagonia epiphyllous; aecia hypophyllous, roestelioid, 3 to 6 mm high; peridium balanoid (acorn shaped), becoming elongated at maturity, pale yellow, sides opening with lateral slits but remaining attached at light brown, pointed apex; peridial cells elongated, 51 to 68 μm long, outer walls smooth, inner walls and side walls sparsely echinulate; aeciospores globose to broadly ellipsoid, somewhat angular, surface slightly coronate, 22 to 32 × 22 to 36 μm, walls orange, 3.5 to 5.5 μm thick. This species is distinguished from other species of Gymnosporangium on Pyrus by the balanoid (acorn-shaped) peridium and the late season maturation of the aecial stage (4). Telia and teliospores of G. sabinae are produced on the alternate host, various species of Juniperus sect. Sabinae, but were not observed in Michigan. The specimen from Michigan is deposited in the U.S. National Fungus Collections (BPI 878928). G. sabinae is widely distributed in Europe, extending to Asia and North Africa, but is rarely reported in North America. It was accidentally introduced into California in the aecial stage on P. communis L. and the telial stage on Juniperus chinensis L. (2), as well as introduced into Canada (British Columbia) (3,4). The only previous report of G. sabinae on P. calleryana is in Germany (1). G. sabinae is known to attack commercial pear and ornamental juniper plants in Europe, thus it seems important to prevent the further spread of this fungus in North America.

European pear rust onJuniperus excelsaL. in south‐western Turkey

SummaryIn this study, the frequency of European pear rust (Gymnosporangium fuscum) lesions onJuniperus excelsawas investigated both on seedlings in a nursery and on forest trees in six juniper stands located in south‐western Turkey. In the nursery, lesions occurred on 0.7% of 5510 1‐year‐old seedlings and 29% of 200 2‐year‐old potted seedlings. In each of the juniper forests, 50 trees were chosen within a square of approximately 400 m2in size. In general, rust lesions were common on the trees. On average, 49.0% of the trees had lesions; on 17.3% of the trees, the lesions were located on the trunk, on 43.3% on the branches and on 11.7% on both. In lesion‐bearing trees, the average number of lesions was 1.47–3.59 and the maximum number of lesions per tree were six to 11. Most of the lesions (85.1%) were on branches. There were significant differences between the stands, which can be attributed to different age of the trees, site factors and the presence of alternate hosts. The rust identified from stem lesions in forest trees and from nursery seedlings was European pear rust (G. fuscum), but possible co‐occurrence of otherGymnosporangiumspp. cannot be excluded.

Gymnosporangium sabinae found in Norway

Gymnosporangium sabinae found in Norway

Gymnosporangium spp. (non‐European)

<i>Gymnosporangium</i> spp. (non‐European)

Effect of Environmental Conditions on Germination and Survival of Teliospores and Basidiospores of the Pear Rust Fungus (Gymnosporangium asiaticum)

Pear rust, caused by Gymnosporangium asiaticum, is an important disease of pear (Pyrus spp.) in China in areas where cypress (Juniperus spp. and Sabina spp.), the alternate host, is present. Controlled environment experiments were conducted to study the effects of temperature, relative humidity (RH) and duration of free water on germination of teliospores and basidiospores of G. asiaticum. Teliospores, sampled from Juniperus chinensis, germinated at temperatures ranging from 5 to 28 , with an optimum between 16 and 20 . For teliospores to germinate, telial horns required free water: soaking in water for 30 sec triggered teliospore germination. After initial wetting, RH had little effect on germination of teliospores except at extreme temperatures (5 and 30 ) where germination needed near-saturation moisture. The minimum time for telial horns to produce basidiospores was about 3 h at optimum temperatures. Teliospores in all telial horns germinated at 12--4 , but at 8 and 28 only those from a third of telial horns germinated. Basidiospores germinated at 5--0 with the optimum around 15 ; they needed free water or saturated moisture to germinate. Germination in free water was about eight times greater than at 100% RH. Logistic models described well the germination dynamics of basidiospores. Basidiospore survival declined exponentially with storage time, and linearly with increasing temperature and decreasing RH. Basidiospores survived for at least six days in dry conditions with RH as low as 45%.

The genus Epitrimerus Nalepa, 1898 and the pear rust mite, Epitrimerus pyri (Nalepa, 1891) (Prostigmata: Eriophyidae)

Confusion and many errors in the literature regarding the genus Epitrimerus and the pear rust mite Epitrimerus pyri (Nalepa, 189Id ), a vagrant eriophyid species sometimes injurious to the leaves of the common pear, Pyrus communis L. (Rosaceae), are discussed. The current taxonomic status is presented.

Occurrence and harmful effects of Gymnosporangium sabinae (Dicks.) Winter in Slovak Republc

The fungus Gymnosporangium sabinae (Dicks.) Winter was found only at three locations during the years 1965 to 1990 in Slovakia, they were the Arboretum at Mlyňany, Topoľčianky and Gbely (JUH&amp;Aacute;SOV&amp;Aacute; 1973, 1975, 1998). We noticed a more frequent occurrence of this fungus during recent years. The life cycle, range of woody host plants and degree of damage on pear leaves at selected locations inSlovakia are described.

Progress Toward Liquid Formulations of Particle Films for Insect and Disease Control in Pear

Particle film technology is aimed at controlling both arthropod pests and diseases of plants with a hydrophobic particle barrier primarily composed of kaolin. Field studies were conducted from 1996 to 1998 to compare the efficacy of dust and liquid applications, and hydrophobic and hydrophilic particle films, against key pests of pear. In addition, the effects of particle film applications on pear yield and quality were investigated in 1998. Dust and liquid applications of hydrophobic and hydrophilic particle films obtained high levels of early-season pear psylla control and prevented pear rust mite damage. We also found that prior seasonal applications of particle films in 1997 can carry over into the 1998 season to suppress early season pear psylla oviposition. A major concern in the shift from hydrophobic to hydrophilic particle films was the loss of disease control. We found that a water-repellant particle film was not required to control the fungal disease fabraea leaf spot. Pear yields were nearly doubled by liquid formulations of hydrophobic and hydrophilic particle films. Particle film deposits were measured using a spectrophotometer method we developed. Particle deposition differed among formulations for both leaf age and leaf surface (top or bottom). Yet, the particle formulations performed about the same against insects and fungal diseases, and in how they influenced the horticultural traits. None of the particle film formulations were found to be phytotoxic to pear foliage or fruit during the study period. A shift from hydrophobic to hydrophilic particles makes it possible to more easily formulate and disperse the particles in water so that conventional spray equipment can be used. The multifunctionality and low toxicity of particle films could make them an attractive alternative to conventional pesticides.

Pear, Early Season Control of Pear Psylla and Pear Rust Mite, 1996

Abstract Mature ‘Bartlett’ trees at the Trevor Nichols Research Complex in Fennville, MI (Pear 1 Block) were sprayed at a rate of 100 gpa with an FMC 1029 airblast sprayer. Trees were arranged in a CR design of single trees replicated 4 times. All materials were applied as indicated in the table on 4 Jun (IC) and 17 Jul (4C, PP Threshold of 0.3 nymphs per leaf). Streptomycin, Benlate, Penncozeb, Rubigan, Captan, and Funginex were applied to all treatments separately. Dates of PP and PRM evaluation were 19 Jun, 2 Jul, 15 Jul, and 8 Aug. At each evaluation, 50 leaves per replicate were picked, brushed in a mite-brushing machine and then examined under a stereo microscope for PRM adults. Twenty-five leaves per replicate were also evaluated under a stereomicroscope for PP nymphs and eggs. Mean data are reported as PRM adults per leaf, and PP nymphs or eggs per leaf. Harvest fruit evaluations were made on 27 Aug by picking 25 fruit randomly from the periphery of the tree from each replicate per treatment. They were examined for sooty mold from PP and PRM russetting. Sooty mold and russetting evaluations were based on visual inspection, with the scoring criteria listed in the table.

Pear, Control of Pear Psylla and Pear Rust Mite with Sankyo Products, 1996

Abstract Seven-year-old ‘Bartlett’ trees at the Trevor Nichols Research Complex in Fennville, MI (Pear 3 Block) were sprayed with an FMC 1029 airblast sprayed at a rate of 75 gpa. Trees were arranged in a CR design of single trees, replicated 4 times. Test materials were applied on 25 May (petal fall), 7 Jun (1C), and 31 Jul (PP threshold of 0.3 nymphs per leaf). Streptomycin, Benlate, Penncozeb, Rubigan, Funginex, Captan, and Guthion were applied to all treatments separately. Dates of PP and PRM evaluation were 10 Jun, 24 Jun, 8 Jul, 24 Jul and 14 Aug. At each evaluation, 50 leaves per replicate were picked, brushed in a mite brushing machine and examined under a stereomicroscope for PRM adults. Twenty-five leaves per replicate were also evaluated under a stereo microscope for PP nymphs and eggs. Mean data are reported as PRM adults power leaf, and PP nymphs or eggs per 25 leaves. Harvest fruit evaluations were made on 21 Aug by picking 25 fruit randomly from the periphery of the tree from each replicate and examining them for sooty mold from PP and PRM russetting. Sooty mold and russetting evaluations were based on visual inspection, with the scoring criteria listed in the table.

Pear Rust Mite (Acari: Eriophyidae) Fecundity and Development at Constant Temperatures

Longevity, preoviposition period, and fecundity of deutogynes of the pear rust mite, Epitrimerus pyri (Nalepa), were measured at three constant temperatures (10, 15, and 20°C), and compared between deutogyne and protogyne females at 20°C. Relationships between temperature (10, 15, 20, and 25°C) and the rate of development (days−1) of eggs, nymphs, and generations (egg to adult) were described using least-squares linear regression. Mean longevity and preoviposition period of deutogynes decreased with increasing temperature. The average rate of oviposition increased with temperature, but lifetime fecundity did not differ among temperatures. At 20°C, protogynes began ovipositing sooner than deutogynes and laid more eggs at a faster rate, but average longevity of the two morphs was the same. Significant linear relationships were found between temperature and the developmental rates of eggs, nymphs, and generations. Threshold base temperatures for development of eggs, nymphs, and generations were 2.2, 3.3, and 3.8°C, respectively. Degree-day (±SEM) requirements for median development of eggs, nymphs, and generations were 93.5 ± 2.5, 78.7 ± 3.4, and 144.9 ± 3.6 above their respective threshold temperatures. These results are compared with estimated developmental requirements calculated from Easterbrook (1978).