Infected Orchards Research Articles

RECORDS OF PSEUDOMONAS SYRINGAE pv. ACTINIDIAE ON ACTINIDIA spp. IN TRENTINO (NORTH-EAST ITALY)

During 2012-2015, extensive field surveys were performed in new and old kiwifruit orchards located in the province of Trento (North-East of Italy). Symptoms resembling those incited by Pseudomonas syringae pv. actinidiae (Psa) (i.e, leaf spotting, twig wilting) were observed mainly on Actinidia deliciosa cv. Hayward and in a new orchard planted with A. chinensis cv. Soreli. The incidence of the disease ranged from 1% to 80%, and some old Hayward orchards (i.e., 35 years old) resulted severely damaged. From all infected orchards, samples were collected and, subsequently, processed in the laboratory for isolation by following routinely procedures (Ferrante and Scortichini, 2009). Bacterial isolates were obtained from all infected kiwifruit orchards; they were identified according to the techniques described by Ferrante and Scortichini (2010). Upon repetitive-sequence PCR using BOX, ERIC and REP primer sets, their fingerprint pattern perfectly matched that shown by the pandemic Psa 3 strain CRA-FRU 8.43. In addition, with isolates representative of all the sites from where the samplings were obtained, pathogenicity tests were carried out by artificially inoculating one-year-old, pot-cultivated A. deliciosa cv. Hayward plants according to the techniques described by Ferrante and Scortichini (2009, 2010). All the isolates induced, upon 10-15 days from the inoculation, the leaf spot and wilting symptoms. On the basis of these results, we conclude that P. s. pv. actinidiae was the causal agent of the field symptoms observed in green-fleshed and yellow-fleshed kiwifruit orchards located in Trentino. This is the first record of the disease in this region.

Effect of bacterial canker caused by Pseudomonas syringae pv. actinidiae on postharvest quality and rots of kiwifruit ‘Hayward’

Kiwifruits produced from plants infected by Pseudomonas syringae pv actinidiae (Psa), the agent of bacterial canker, do not show visible disease symptoms and can be commercialized. Firmness, total soluble solids (TSS), and titratable acidity (TA) of Actinidia deliciosa ‘Hayward’ fruit, infected or not by Psa, were quantified, for two years, at harvest, at 90 days storage, and during shelf life. Analysis of dry matter (DM) and calcium at harvest, and postharvest rots, caused by Botrytis cinerea, during shelf life were also assessed. DM was higher and calcium content was lower in the kiwifruit from orchards infected by bacterial canker. During storage, firmness decreased and TSS increased rapidly in fruit from infected orchards. These parameters, together with the lower TA, favoured the higher susceptibility to grey mould rots. Besides the incidence of bacterial canker, climate conditions throughout the cropping seasons greatly affected the postharvest quality of fruit. Also the storage conditions modified the fruit quality: controlled atmosphere (CA) and 1-MCP treatment delayed fruit softening compared to normal atmosphere. TSS on fruit from healthy orchards was not influenced by the storage conditions. Fruit from Psa diseased orchards showed significantly lower TSS in CA storage and after 1-MCP treatment, compared with normal atmosphere storage. In this work, we showed that the presence of bacterial canker affects postharvest quality, shelf life, and susceptibility to postharvest rots of fruit.

USE OF BENEFICIAL MICROORGANISMS AND ELICITORS FOR CONTROL OF PSEUDOMONAS SYRINGAE PV. ACTINIDIAE IN KIWIFRUIT (ACTINIDIA SPP.)

The kiwifruit pathogen Pseudomonas syringae pv. actinidiae (Psa-V or biovar 3) was first identified in New Zealand in 2010 and currently affects over 75% of the country’s kiwifruit orchards. Our research focused on the use of root endophytic Trichoderma isolates for control of this disease. These fungi have the potential to limit damage from pathogens by colonising root surfaces, penetrating roots, releasing metabolic compounds and inducing plant systemic resistance, thereby improving general plant health and growth. To identify promising Trichoderma isolates for the control of Psa-V, we obtained root endophytic Trichoderma from healthy kiwifruit vines and a wide variety of other healthy plant species in areas with high Psa incidence. In laboratory screening assays, young kiwifruit seedlings of different cultivars were inoculated with selected isolates. Challenging seedlings with Psa-V by stab inoculation allowed the identification of several promising Trichoderma mixtures and single isolates. Field trials in Psa-V infected orchards using container-grown kiwifruit also confirmed the efficacy of the best treatments (both alone and in combination with a plant elicitor and other microorganisms) to reduce Psa-V symptoms. When re-isolating Trichoderma at the end of the orchard trial from the roots of plants that had or had not received a combination of Trichoderma and other treatments before being exposed to Psa-V in the field, we found significantly higher numbers of Trichoderma isolates in the roots of Trichoderma-treated plants compared to the untreated controls. Our results indicate that a single Trichoderma inoculation early during plant development has a significant effect on kiwifruit plant health and survival and promotes the establishment of a strong root endophytic Trichoderma community, which contributes to the control of Psa-V on kiwifruit, even when older plants are treated.

First report of citrus bacterial blast and citrus black pit caused by Pseudomonas syringe pv. syringae in Tunisia

During recent years (2013-2015) a disease similar to citrus bacterial blast of orange (Citrus sinensis) and citrus black pit of lemon (Citrus limon) has been observed in Tunisian citrus orchards. In a recent survey 35 infected orchards were located in almost all known citrus-growing regions in Tunisia (with a concentration in the Cap Bon region, North Tunisia). Symptoms were blasted flowers and buds, spotted and blistered fruits, stem cankers, leaf blights and plant dieback in both orange and lemon (Figs. 1, 2). Leaf symptoms were black discolored areas, often at the junction of leaf blade and petiole wings. Spotted orange fruits were rarely found, but blasted lemon plants were frequently observed and the latter symptom was not previously reported. Eighty bacterial isolates were obtained, producing fluorescent pigment on King's B medium and white, glistening, convex colonies on nutrient sucrose agar (NSA). Isolates produced a hypersensitive reaction on tobacco (Nicotiana tabacum). Fourteen isolates were selected for further study using methods described by Lelliot & Stead (3). They were all Gram negative, and belonged to LOPAT group Ia. Strains GBBC1158 (P. viridiflava, Veronica austriaca, Belgium), GBBC748 (P. syringae, Malus, Belgium) and IO527 (P.s. pv. morsprunorum race1, Prunus avium, Poland) were included as references. Identity was further confirmed by PCR using primers Ps-for and Ps-rev (Widmer et al., 6) specific to the Pseudomonas genus. Also presence of genes encoding synthesis of the toxin syringomycin was confirmed (Bultreys & Gheysen, 1). Strain LMG1247 (P.s. pv. syringae, Syringa vulgaris, UK) was used as reference. Twelve isolates were positive with PCR. All of them possessed the syrB gene and eleven the syrD gene. Partial 16S rRNA sequences for seven isolates (LN876273-LN876279) showed highest similarity (97-99%) to P.s. pv. syringae strains KFB 93 (JQ071937), XJLX-2-2 (KC816630), XJLX-8-3 (KC816627), HH-02 (KF500097), XJLX-2-2 (KC816630), IZB228 (KP099979) and XJLX-8-3(KC816627). Additionally, rpoD sequence analysis (LN876268-LN876272), according to Sawada et al. (5), showed that our isolates belong to P.s. pv. syringae. Pathogenicity was tested on citrus fruits, twigs and plantlets (cvs. Eurêka, Washington Navel, Maltaise and Cassar) which were inoculated with a 108 cfu/ml bacterial suspension. Sterile distilled water was used as control. Seven days after inoculation on fruits small black areas about 2 to 5 mm in diameter, surrounded by a greenish zone were formed. Twigs and plantlets showed typical blast symptoms. To fulfill Koch's postulates, bacteria were re-isolated from plant tissue with symptoms, and identity was confirmed based on colony morphology on King's B and NAS media. Identity was validated as well by LOPAT, GATTa tests and ERIC, REP and BOX PCR (according to Louws et al., 4). The re-isolated bacteria were HR positive. A phylogenetic based on rep-PCR data showed them similar to originally inoculated isolates and most closely related to P.s. pv. syringae strain LMG 5496, isolated from citrus. To our knowledge, this is the first report of the occurrence of citrus bacterial blast/citrus black pit and their causal agent P.s. pv. syringae in Tunisia. The authors thank Dr. Samir Chebil and Ms Synda Chenenaoui from the Biotechnology Center of Borj-cedria for their much appreciated assistance.

Statement in response to the comments submitted by the US phytosanitary authorities on a previous EFSA opinion (EFSA Journal 2011;9(12):2461) regarding the export of Florida citrus fruit to the EU

The European Food Safety Authority (EFSA) has been asked to address the comments submitted in April 2012 by the US phytosanitary authorities on the EFSA scientific opinion on the US request related to the export of Florida citrus fruit. The EFSA Panel on Plant Health acknowledges the responses provided by the United States Department of Agriculture (USDA) and considers that the USDA misinterpreted the conclusions made by the Panel in its previous opinion (EFSA Panel on Plant Health (PLH), 2011). The Panel considers that the extrapolations of the data provided by Shiotani et al. (2009) and Gottwald et al. (2009) were not supported by sound evidence. The Panel considers that both the responses provided by Dr Shiotani and by Dr Gottwald and colleagues do not lead to any major change in the set of scientifically sound information related to citrus canker and Xanthomonas citri pv. citri. The Panel, after evaluating the response provided by the USDA regarding the previous EFSA scientific opinion on citrus canker, considers that the removal of mandatory mitigation measures in field and packinghouse facilities increases the risk of contamination of fruit during the growing season and thus the bacterial load and frequency of infected fruit in consignments. Permitting the trade of citrus fruit originating from infected orchards increases the probability of the presence of X.citri pv. citri on fruit in consignments from those sites. The Panel considers that citrus fruit is a pathway for introduction of X.citri pv. citri into the European Union and the related risk is being evaluated in a separate EFSA opinion under preparation on the plant health risk of citrus canker for the EU.

Biological Control of Apple Ring Rot on Fruit by Bacillus amyloliquefaciens 9001.

Apple ring rot disease, caused by Botryosphaeria dothidea (Moug. ex. Fr) Ces. et de Not., is one of the most important diseases on apple fruits. In this study, strain 9001 isolated from healthy apple fruits from an infested orchard was evaluated for its biocontrol activity against apple ring rot in vitro and in vivo. Strain 9001 showed obvious antagonistic activity to B. dothidea YL-1 when plated on potato dextrose agar. Soaking healthy apples in the bacterial suspensions of strain 9001 prior to artificial inoculation of fungal pathogen resulted in a dramatic decrease in disease incidence when compared to the control. Moreover, either field application in the growth season or postharvest treatment of apples from infected orchards with bacterial suspensions of strain 9001 resulted in significantly reduced disease incidence within the storage period for 4 months at room temperature. Based on the phylogenetic analysis of 16S rRNA and the gyrA gene, strain 9001 was identified as Bacillus amyloliquefaciens. These results indicated that B. amyloliquefaciens 9001 could be a promising agent in biocontrol of apple ring rot on fruit, which might help to minimize the yield loss of apple fruit during the long postharvest period.

Pseudomonas syringae pv. actinidiae: chemical control, resistance mechanisms and possible alternatives

Pseudomonas syringae pv. actinidiae (Psa) is a Gram‐negative bacterium that causes the bacterial canker of both green (Actinidia deliciosa) and yellow (Actinidia chinensis) fleshed kiwifruit. Since the emergence of an economically devastating Psa outbreak in Japan in the 1980s, the disease took a contagious turn causing severe economic loss to kiwifruit industries in Italy, South Korea, Spain, New Zealand and other countries. Research shows that the pathogenic strains isolated from different infected orchards vary in their virulence characteristics and have distinct genes coding for the production of different toxins. The global Psa outbreak has activated research around the world on developing efficient strategies to contain the pandemic and minimize loss to the kiwifruit industry. Chemical and biological control options, orchard management and breeding programmes are being employed in this global effort. Synergy between different disease control strategies has been recognized as important. Phytotoxicity, resistance development and regulatory measures in certain countries restrict the use of copper compounds and antibiotics, which are otherwise the mainstay chemicals against bacterial plant diseases. Therefore, because of the limitations of existing chemicals, it is important to develop novel chemical controls against Psa. Antimicrobial peptides, which are attractive alternatives to conventional antibiotics, have found promising applications in plant disease control and could contribute to expanding the chemical control tool box against Psa. This review summarizes all chemical compounds trialled so far against Psa and provides thoughts on the development of antimicrobial peptides as potential solutions for the future.

Anthracnose Caused by Colletotrichum horii on Sweet Persimmon in Korea: Dissemination of Conidia and Disease Development

AbstractAnthracnose disease caused by Colletotrichum horii (C. gloeosporioides), results in considerable economic damage to sweet persimmon in southern Korea yearly. This study deals with the life cycle of the pathogen in terms of seasonal fluctuations of spore dispersal and the development of disease based on field surveys, spore potential and fungal isolation. Anthracnose disease was observed first on twigs in the last week of May and reached an incidence of 1.2%. Subsequently, the disease increased rapidly and reached an incidence of 86% by the end of July. Infection of fruits started in mid‐June (2.8%) and increased gradually to 64.4% by the end of July. In severely infected orchards, 46.2% of diseased fruits were dropped. The pathogen began releasing conidia in the first week of May and continued until the end of September. The maximum release of spores was observed in mid‐July. To determine the optimal use of chemicals for control of anthracnose, the following spray programme was evaluated. Spraying two or three times resulted in 89.4 and 93% control, respectively, whereas spraying more than four times led to 100% control. In comparison, the disease rate of unsprayed trees was 89.8%. To control anthracnose effectively, it is recommended to take steps to eliminate inoculum sources in sweet persimmon orchards before spraying chemicals.

GNOMONIOPSIS CASTANEA sp. nov. (GNOMONIACEAE, DIAPORTHALES) AS THE CAUSAL AGENT OF NUT ROT IN SWEET CHESTNUT

The genus Gnomoniopsis (Gnomoniaceae, Diaporthales) is currently composed of 13 species which are endophytic and/or parasitic to plants in the families Fagaceae, Onagraceae and Rosaceae. Species definition is based on a combination of morphological traits, association with specific plant hosts, and phylogeny. In this paper a new species, Gnomoniopsis castanea sp. nov., is described based on the association with Castanea sativa (a plant species never reported to be infected by fungi the genus Gnomoniopsis), morphology and phylogenetic analysis of the ITS region of ribosomal DNA and on the EF1-a locus. The fungus is consistently associated with nut rot and caused the disease when artificially inoculated to fruits or flowers. Infection incidence varied depending on the orchard and the year and attained up to 83% of the nuts in some areas of north-western Italy. The fungus was also consistently isolated from the bark of symptomless branches in naturally infected chestnut orchards.

A Destructive New Disease of Citrus in China Caused by Cryptosporiopsis citricarpa sp. nov.

Defoliation, dieback and mortality of Satsuma mandarin (Citrus unshiu), as well as kumquat (Fortunella margarita), in Chenggu County, Shaanxi Province, China was first noticed in 2006 and caused substantial economic losses to citrus production. The incidence of leaves infected approached 100% in some badly infected orchards. The disease prevailed only in late winter and early spring, where early symptoms were rounded and target-like spots on leaves. The disease was named target spot. Black conidiomata were observed on the upper surface of the leaves. A Cryptosporiopsis species was consistently recovered from the infected leaves, shoots, and branches. Koch's postulates were fulfilled by inoculating the conidial suspension of Cryptosporiopsis sp. onto the leaves of Satsuma mandarin. Phylogenetic analysis based on LSU sequence data indicated that this taxon clustered in Cryptosporiopsis (teleomorph: Neofabraea, Dermateaceae). Phylogenetic analysis based on ITS, SSU, and TUB indicated that the isolates of Cryptosporiopsis sp. constituted a distinct clade. Further study also demonstrated that this taxon was morphologically distinct from other species of Cryptosporiopsis, thus suggesting it might belong to an undescribed species. The name Cryptosporiopsis citricarpa sp. nov. is given to accommodate the fungal pathogen in this study.

Xanthomonas aboricola pv. pruni에 의한 자두 검은점무늬병의 발생과 핵과류 과수 품종에 대한 병원성

자두 검은점무늬병에 걸린 식물체로부터 순수분리된 X. arboricola pv. pruni 균을 NA배지에서 배양한 후 국내재배 핵과류에 분무접종한 결과 자두, 매실, 살구에 있어서는 과실에 뚜렷한 병원성을 나타내었으나 복숭아 과실은 저항성을 나타내었다. 특히 매실과 살구에서는 극심한 초기 과민성반응이 나타났는데 과실의 50% 정도가 생장 정지되어 낙과되는 현상을 보였으며 병반의 크기는 자두와는 달리 크게 진행되지 않고 많은 점무늬를 형성하는 병반형태를 나타내었고 복숭아에서는 과실병징이 나타나지 않았다. 접종된 여름철 신초가지에서 자두 포모사품종에서는 도관부까지 궤양조직이 형성되었으나 살구 그리고 매실에서는 체관부일부에서만 궤양조직이 형성되어 분리된 병원균은 자두 포모사품종에 특이적인 감염조직을 형성함을 알 수 있었다. Xanthomonas arboricola pv. pruni is the causal agent of bacterial black spot disease on some stone fruits, e.g. peach, plum and apricot. To evaluate pathogenicity of Xanthomonas arboricola pv. pruni strain from plum, inoculum of the isolated strain was spray inoculated to fruits and leaves of apricot, Japanese apricot and plum. Apricot and Japanese apricot showed severe black spot symptoms on fruits and shot hole symptoms on leaves. In case of apricot, about fifty percent of fruits did not grow and dropped by hypersensitive reaction to spray infection. Plum, cv. Formosa was very susceptible, showing severe black injury lesions on fruits and cankers on leaves and new twigs. On the other hand, plum cv. Daesukjosaeng, was highly resistant. Fruits of several plum cultivars such as Formosa and Chuhee were severely infected at natural infected orchards by X. arboricola pv. pruni. Where as those of Daesukjosaeng, Taeyang, Soldam and Hongrogen were moderately infected.

Molecular characterization of Pseudomonas syringae isolates from fruit trees and raspberry in Serbia

Infection of fruit trees by Pseudomonas syringae is a potentially serious problem that may limit the establishment and sustained productivity of pome and stone fruit orchards in Serbia. To estimate possible diversity of Pseudomonas syringae fruit trees strains, we collected a set of strains in several areas of Serbia. The samples were taken from infected orchards with raspberry, plum, cherry, sour cherry, peach, pear and apple trees. Genetic diversity of P. syringae strains isolated from fruit trees was determined by using SpeI macrorestriction analysis of genomic DNAs by pulsed-field gel electrophoresis (PFGE) and REP-PCR. Molecular analysis showed that most of isolates had unique profiles, with the exception of isolates from plum and cherry that displayed profiles identical to each other and similar to P. syringae pv. morsprunorum. The study presented here clearly demonstrates the discriminative power of molecular techniques in enabling a detailed analysis of the genetic variations between strains of P. syringae from different pome and stone fruit hosts in Serbia.

Molecular characterization of two distinct strains of blueberry scorch virus (BlScV) in northern Italy

During blueberry scorch virus (BlScV) surveys of highbush blueberries in Italy between 2005 and 2010, we initially discovered infected orchards only in Piedmont. Since 2009, however, three infected orchards have also been found in Trentino, where a new host species, Vaccinium ashei, was found to be infected by BlScV. Molecular characterization of isolates during the study period suggests that two very distinct epidemics are now present in Italy: the Piedmont isolates belong to a new BlScV strain, whereas the Trentino isolates are almost identical to the Washington State strain.

Dissemination of Pseudomonas syringae pv. actinidiae through pollen and its epiphytic life on leaves and fruits

The role of pollen in disseminating Pseudomonas syringae pv. actinidiae ( Psa ) in kiwifruit orchards was investigated and the survival of the pathogen as an epiphyte on leaves and fruits was followed, from pollination time until the pre-harvest season. Pollen with natural inoculum was obtained from an infected orchard and pollen harvested without any contamination by Psa was experimentally inoculated at approximately the same contamination level. Two pollination techniques were used in glasshouse experiments: dusting and spraying. In parallel, field trials in commercial orchards were carried out: two plots were designed in two orchards, where bacterial canker was present at low incidence. From petal fall to 3 weeks before harvesting, leaf and fruit samples were taken and analysed for the presence of Psa , using two different PCR protocols and direct isolation. Results confirmed the dissemination of Psa through pollen, especially when using the aqueous suspensions. Both in glasshouse experiments and in the orchards Psa was found as an epiphyte for several weeks after pollination. Pathogen populations on leaves were, initially, 10 to 100 times less than on fruitlets. As the summer continued, the epiphytic contamination levels of fruits decreased constantly, being no more detectable from early August, whereas Psa was present at detectable levels on leaves until early October, approx. 20 days before harvesting time. Our results confirmed the role of pollen in disseminating Psa , the long epiphytic survival of the pathogen on kiwifruit leaves and the increasing unsuit­ability of fruits to harbour detectable, epiphytic populations of the bacterium through the summer season in commercial orchards with low disease incidence, when they are reaching the final development stage. Thus, kiwifruit surfaces do not appear to be a suitable niche for a long term survival of Psa as an epiphyte and, therefore, kiwifruits should not represent a pathway for Psa dissemination and pose a negligible risk for the introduction of the pathogen into new areas.

CONTROL OF SHARKA BY BREEDING

PPV is the most dangerous virus in stone fruit growing and is spread worldwide. In infected areas it is recommended that only tolerant or resistant cultivars are cultivated. From the plum breeding programme at Hohenheim 6 tolerant or resistant cultivars have been produced, which are successful in production in Germany. Some promising clones will be introduced. Tolerant or resistant cultivars can be infected by PPV and will continue to be a source of infection. The first absolute virus resistant cultivar worldwide is 'Jojo' introduced in 1999. 'Jojo' reacts hypersensitivly to PPV and has continued to grow healthily for more than 20 years in totally infected orchards. In the breeding programme quantitative and hypersensitive resistance were combined. The heredity of hypersensitivity depends upon the chosen parents. Using donors from Hohenheim the hypersensitivity index has been much higher than that achieved by using the K 4 hybrid or its progenies. Forty-three promising clones with different size and ripening times have been selected for tests in different regions. By pyramiding of the genes responsible for quantitative and hypersensitive PPV resistance we hope to get cultivars with a durable absolute PPV resistance and high fruit quality.

STUDY OF XANTHOMONAS ARBORICOLA PV. JUGLANDIS POPULATION DYNAMICS IN FRENCH WALNUT ORCHARDS OVER THREE YEARS

Walnut blight, caused by Xanthomonas arboricola pv. juglandis is a major disease of Walnut in France, mainly responsible for necrosis on fruits and early nut drop before harvest. The population dynamics were studied over three years in orchards in the South-West of France, with comparison among orchards with different infestation levels. Samples of buds, leaves, flowers, pollen and fruits were collected from the beginning of April till the end of August, and the epiphytic population size of X. a. pv. juglandis was measured by plating dilutions of water extract on Tween Modified Medium. Population size broadly varies during the year from 10 3 to 10 7 cfu/g, increasing from budbreak, and remains stable after flowering. The level is a little lower in less infected orchards, suggesting that the expression of disease is more affected by pedo-climatic conditions than bacterial population level.

CONTROL OF WALNUT HUSK FLY USING ALTERNATIVE METHODS

The walnut husk fly (Rhagoletis completa Cresson) was observed for the first time in the South-East of France in 2007. In highly infected orchards, this quarantine organism can damage up to 80% of the annual production. In 2008, a network of orchards was monitored and experiments were set up in order to; (1) follow spatial propagation and (2) assess husk fly management techniques. Six different substances were tested, focusing on non chemical products. Four of them are in accordance with the specifications of organic farming. Two commercial products composed of kaolin have been tested. Treatment consists of a suspension of clay in water, sprayed on the whole canopy. This method has been successfully used to control cherry and olive fruit flies. The clay deposited on the walnut husk forms a physical barrier which should prevent oviposition. Two plant protection products containing Spinosad have also been tested: one in the form of bait, the other sprayed as a classic insecticide. Moreover, five kinds of traps have been tested and the most efficient could be studied in order to validate a massive trapping programme in low fly density situations. The results concerning the efficacy of the different control methods and the spatial propagation of the walnut husk fly in 2008 are presented and discussed.

First report of the quarantine pathogen Xanthomonas arboricola pv. pruni on apricot and plum in Switzerland

Xanthomonas arboricola pv. pruni (Xap), cause of stone fruit bacterial spot on many Prunus species, is a European and Mediterranean Plant Protection Organisation (EPPO) A2-list quarantine pathogen (Anonymous, 2006). It can cause significant yield loss and tree death. In Europe, Xap occurs in France, Italy, Bulgaria, Romania and Ukraine, but appears to be spreading due to changes in trade patterns, climate, host range and/or pathogen genotype. This is the first report of the bacterial pathogen in Switzerland, occurring with very limited distribution. Xap was first detected on apricot trees and fruit (Prunus armeniaca) showing symptoms in 2005 in four orchards located in canton Valais, the primary Swiss production region. It was detected in 2009 on Japanese apricot (P. mume) inter-cropped with apricot in two of these orchards. Isolation from symptom-bearing fruit, leaf and canker samples using YCDA medium confirmed recovered colonies to be Xap based on colony morphology, quinate metabolism, serology (Neogen Europe, EXPRESS™), gyrB sequencing (Parkinson et al., 2009; GenBank Accession No. FJ719771–FJ719773) and pathogenicity bioassays with detached peach leaves. Direct detection in symptom-bearing fruit, leaves and cankers was achieved in 100% of samples using Xap-specific PCR primers (Pagani, 2004) and in 40% using X. fragariae/arboricola primers (Weller et al., 2007). These primer sets gave 100 and 93% agreement, respectively, with standard identification methods when applied to Xap isolates. All Swiss isolates were copper sensitive. During intensive surveys between 2006 and 2009 throughout the region where the bacterium was first detected (208 ha), no incidence of disease has been observed outside the four original infected orchards. In three of these orchards Xap is considered eradicated, with all symptom-bearing trees removed in the fourth. This suggests probable introduction via planting material rather than fruit or aerosols. Xap is considered present with limited distribution but not eradicated. This work was funded by the Swiss Secretariat for Education and Research within COST Action 873.

Determination of the Presence of Huanglongbing in Seeds and Movement of the Pathogen in Citrus reticulata

Problem statement: Huanglongbing (HLB) also known as citrus greening disease is a fastidious phloem-inhabiting bacterium in the genus Candidatus Liberibacter. Using universal primers, the 16S ribosomal DNA sequence of three strains of the bacterium were obtained by PCR. However there is very little information on seed transmission and HLB pathogen movement to find a way for control or reduce the severity of HLB on the field. The study was conducted to detect HLB pathogen in seeds of Citrus, to determine pathogen movement in citrus seedling after infection and to detect the HLB pathogen in citrus roots. Approach: Seeds of Citrus reticulata cv. Limau Madu were collected from infected orchard and were germinated in screenhouse condition. The seeds of Citrus reticlata cv. L. Madu were planted in screenhouse too for HLB pathogen movement and HLB detection in roots. The seedlings were inoculated using infected grafting methods. Results: HLB was not amplified in new seedlings after germination. HLB moved slowly reaching up to 1.5 cm after 2 weeks, 1.5-4.5 cm after eight weeks and detected on 4.5-9 cm after 14 weeks below the grafting area. HLB was also detected up to 9-15 cm after 16 weeks, 15-24 cm after twenty weeks, 24-28.5 cm after 22 weeks and 28.5-30 cm after 24 weeks below the grafting area. Conclusion: Base on conventional PCR test, HLB disease in citrus is not seed borne and it can reach to the roots 26 weeks after inoculation.

Infection Dynamics of Fusarium mangiferae, Causal Agent of Mango Malformation Disease

Conditions affecting germination and growth of Fusarium mangiferae, causal agent of mango malformation disease, were studied in vitro. Both conidial germination and colony growth required temperatures >5 degrees C and reached a peak at 28 and 25 degrees C, respectively. A minimum 2-h wetness period was required for conidial germination, reaching a peak after 8 h of wetness. High incidence of fungal colonization in buds, predominantly the apical buds, was detected compared with inoculated leaves. The pathogen was detected in the roots of inoculated soil 19 weeks postinoculation but not in aboveground parts of the plants, and symptoms of the disease were not observed, either. Dry, malformed inflorescence debris serving as a source of inoculum caused significantly higher colonization (52 and 20%) of inoculated buds, compared with that (0%) of the untreated controls. Incidence of sampled leaf disks bearing propagules of F. mangiferae from an infected orchard peaked in June and July and decreased during the following months, whereas airborne infections on 1-month-old branches was the highest in May and June, corresponding with inoculum availability released from infected inflorescences. Colonization pattern, determined in naturally infected vegetative and woody branches, was significantly higher in node sections than in the internode sections. This study sheds light on infection dynamics, colonization patters, and the disease cycle of F. mangiferae in mango.