Induction of pear blossom blast caused by Pseudomonas syringae pv. syringae

Conditions were established for inducing pear blossom blast caused by Pseudomonas syringae pv. syringae on both attached and detached shoots. The incidence of blossom blast was proportional to the logarithm of the P.s. pv. syringae population under optimal temperature, moisture, and bloom developmental stage. Highest incidence of blossom infection followed occurrence of a major exotherm (an increase in temperature caused by the heat of fusion from ice formation within blossom tissue) in the presence of P. s. pv. syringae. The exotherm was detected inside ovary tissue at temperatures ranging from –1.8 to –3.5 C. Wetness duration following the thawing process was less important than wetness during and immediately after the freeze event. Blossoms inoculated, then air-dried or removed from low-temperature treatment prior to occurrence of an exotherm, had a low incidence of infection, The full bloom stage of blossom development was more susceptible to blossom blast than either the open cluster or tight cluster stages of development.     

The problem of bacterial canker of hazelnut in Greece caused by Pseudomonas syringae pv. avellanae1

The present situation of the disease in Greece and its main aspects, causal agent, symptomatology, epidemiology and control measures are described. The characteristics differentiating the pathogen from some other Pseudomonas species are also reported.     

猕猴桃溃疡病菌的分子检测技术研究

 猕猴桃溃疡病是猕猴桃生产上的主要病害,为建立该病的快速诊断技术,本实验通过RAPD分析获得一条1 300 bp左右的致病菌的特异片段,对该片段进行克隆测序,在测序的基础上设计并合成一对特异引物F7/R7,优化特异引物扩增条件,并验证引物的特异性和灵敏性。利用该特异引物对包括猕猴桃溃疡病菌在内的14个菌株基因组DNA进行PCR扩增表明,只有猕猴桃溃疡病菌能扩增出1条约为950 bp的特异条带,其他菌株及对照均未扩增出特异条带。对采自果园的染病枝干组织和接种致病菌的枝干组织的检测表明,该特异引物能特异性地检测到猕猴桃溃疡病菌的存在,其在组织中的检测灵敏度为100 fg/μL。因此,利用设计合成的特异引物F7/R7,参考优化的体系和程序,结合简单的试剂盒法提取猕猴桃溃疡病菌或植物组织DNA,可以在短时间内完成对该病原菌的分子检测。     

Genetic diversity of Pseudomonas syringae pv. actinidiae,pathogen of kiwifruit bacterial canker

Bacterial canker disease of kiwifruit currently occurs in at least 15 countries, causing serious damage. The causative agent of the disease is Pseudomonas syringae pv. actinidiae (Psa), which is genetically diverse and is currently classified into five biovars, namely, biovars 1, 2, 3, 5 and 6. In Japan, four biovars except biovar 2 have been found so far. These biovars have been confirmed to have differences in the virulence and composition of pathogenicity-related genes, such as toxin biosynthesis and type III effector genes. Biovars 1 and 6 possess the tox island, a genomic island of approximately 38 kb, which contains phaseolotoxin biosynthesis genes (argK-tox cluster) and is confirmed to have been acquired from other bacteria through horizontal transfers. Also, on the megaplasmid possessed by biovar 6, there exist coronatine biosynthesis genes, and biovar 6 has the ability to produce two phytotoxins, phaseolotoxin and coronatine. In 2014, biovar 3, considered to be of foreign origin, was confirmed for the first time in Japan. Biovar 5, whose virulence is relatively weak, is distributed only in a limited area. In addition to the tox island and various plasmids, a large number of mobile genetic elements are confirmed to be present on the Psa genomes, which might have played a major role in helping Psa to acquire new features. In order to understand how Psa acquired the ability to infect kiwifruit systemically, it is important to make polyphasic comparisons with related pathovars, such as P. syringae pv. theae and pv. actinidifoliorum.     

Genetic variability of Iranian strains of Pseudomonas syringae pv. syringae causing bacterial canker disease of stone fruits

Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from healthy and diseased stone fruits tissues sampled from 38 stone fruits orchard sites in Iran in 2010 and 2011. These strains were tested for pathogenicity and the presence of the syrB gene and were genetically characterized by using ERIC (enterobacterial repetitive intergenic consensus), REP (repetitive extragenic palindromes), and BOXAIR and IS50 (insertion sequences) primers and PCR. All 78 strains of Pss tested were moderately to highly pathogenic on Loring peach seedlings. A total of 78 isolates of the Pss amplified a 752-bp fragment with the syrB primers. To assess genetic diversity among the strains, genomic DNA was extracted from strains and used in rep-PCR and IS50-PCR analysis. Cluster analysis was performed using UPGMA. The strains of Pss were separated into nine distinguishable genotypic groups by the combination data set of both rep-PCR and IS50-PCR at 73 % similarity level. There was no significant correlation between genetic diversity and geographical origin of the isolates. These results indicate that a combination of rep-PCR and IS50-PCR fingerprinting can be used as a high resolution genomic fingerprinting method for elucidating intrapathovar diversity among strains of Pss. The results of this study demonstrated the existence of a considerable genetic diversity among Pss strains causing canker of stone fruit trees in Iran. In this study, genetic variability in Iranian strains of Pss were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.     

Potential spread of kiwifruit bacterial canker (Pseudomonas syringae pv. actinidiae) in Europe

Pest risk analyses (PRAs) are conducted to determine whether an organism is a pest and whether and how it should be regulated. Estimation of the potential area of establishment and pest spread are key factors of this analysis. Tools for modelling and mapping of these key factors have to be quick and easily applicable for a wide variety of organisms with limited data for parameterization. For this purpose, a dispersal kernel model based on a 2Dt‐distribution had been developed in a European Union project (PRATIQUE). The aim of the present study was the evaluation of this spread model hitherto tested on insects, plants, fungi and nematodes in order to determine its applicability to bacterial pests. Therefore, the potential distribution and spread of kiwifruit bacterial canker Pseudomonas syringae pv. actinidiae in Europe was investigated based on climatic suitability and host plant availability. The results of the modelling were compared with the spread history of the pest in Europe. It is shown that this generic spread model can also be applied to a bacterial pest.     

Bacterial inflorescence rot of grapevine caused by Pseudomonas syringae pv. syringae

Molecular sequencing (rpoB) and standard pathological and microbiological methods identified Pseudomonas syringae pv. syringae (Pss) as the causal agent of bacterial inflorescence rot of grapevines (Vitis vinifera) in three vineyards in Tumbarumba, NSW, Australia in 2006 and 2007. Pss strains from shrivelled berries and necrotic inflorescences of diseased grapevines were used to inoculate leaves and inflorescences of potted cv. Semillon grapevines. Pss caused disease symptoms similar to those experienced in the field, including angular leaf lesions, longitudinal lesions in shoot tissues and rotting of inflorescences from before flowering until shortly after fruit set. High humidity promoted symptom severity. The necrotic bunch stem and leaf lesions were susceptible to the development of Botrytis cinerea infections. Cryo‐scanning electron microscopy (cryoSEM) indicated that Pss entered leaves and inflorescence tissues via distorted, open, raised stomata surrounded by folds of tissue that appeared as ‘star‐shaped’ callose‐rich complexes when viewed by UV light microscopy. In necrotic tissues, cryoSEM revealed Pss within petiole parenchyma cells and air‐filled rachis xylem vessels. This is the first report of inflorescence and hence fruit loss caused by Pss in grapevines. The disease is described as ‘bacterial inflorescence rot’ and regarded as one that expands the previously reported pathology of grapevines caused by P. syringae. This study also indicated that infection by Pss might promote destructive B. cinerea infections when the fungus is already present but latent, although further experimentation is needed to prove such an interaction.     

Identifying resistance in wild and ornamental cherry towards bacterial canker caused by Pseudomonas syringae

Bacterial canker is a major disease of stone fruits and is a critical limiting factor to sweet cherry (Prunus avium) production worldwide. One important strategy for disease control is the development of resistant varieties. Partial varietal resistance in sweet cherry is discernible using shoot or whole tree inoculations; however, these quantitative differences in resistance are not evident in detached leaf assays. To identify novel sources of resistance to canker, we used a rapid leaf pathogenicity test to screen a range of wild cherry, ornamental Prunus species and sweet cherry × ornamental cherry hybrids with the canker pathogens, Pseudomonas syringae pvs syringae, morsprunorum races 1 and 2, and avii. Several Prunus accessions exhibited limited symptom development following inoculation with each of the pathogens, and this resistance extended to 16 P. syringae strains pathogenic on sweet cherry and plum. Resistance was associated with reduced bacterial multiplication after inoculation, a phenotype similar to that of commercial sweet cherry towards nonhost strains of P. syringae. Progeny resulting from a cross of a resistant ornamental species Prunus incisa with susceptible sweet cherry (P. avium) exhibited resistance indicating it is an inherited trait. Identification of accessions with resistance to the major bacterial canker pathogens is the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.     

不同猕猴桃品种对细菌性溃疡病的抗病性及其聚类分析

通过田间定点抗病性调查,结合前人的研究结果得出:不同猕猴桃品种对细菌性溃疡病的抗性存在明显差异。金魁和两种雄株中华软、美味硬最为抗病,早鲜次之,魁蜜稍抗。华美2号、海沃德中感。秦美、金丰最感病。用最长距离法对安徽省9个猕猴桃品种进行抗细菌性溃疡病系统聚类,可以将9个品种划分为5类。在谱系图上,抗病性相同的品种大致划分在同一个类中,第1类中华软、美味硬(8、9)为免疫品种;第2类早鲜、金魁(6、7)为高抗品种;第3类魁蜜(5)为中抗品种;第4类为中感品种,华美2号(4)为偏抗病,海沃德(3)为感病品种;第5类则为感病品种,金丰(1)为高感品种,秦美(2)为感病品种。其结果与实际抗性调查情况基本相符。     

Influence of rootstock on the susceptibility of sweet cherry scions to bacterial canker, caused by Pseudomonas syringae pvs morsprunorum and syringae

In a field trial to determine whether the rootstock influenced the susceptibility of cherry cultivars to bacterial canker three cultivars (Napoleon, Roundel and JI 14039), each grafted on two rootstocks (F 12/1 and Colt), were subjected to natural infectionand to inoculation with three bacterial canker pathogens (Pseudomonas syringae pv. morsprunorum races 1 and 2 and P. syringae pv. syringae). Inoculations were made through leaf scars and through wounds. The high susceptibility of Napoleon and high resistance of JI 14039 were confirmed. Napoleon was more susceptible to inoculation through branches when on F12/1 than when on Colt but the reverse was true for leaf scar inoculations. JI14039 was more susceptible to race 1 inoculated through leaf scars when grown on F12/1 than when on Colt. No rootstock/scion interaction was detected with Roundel.
The complexity of the relationships between the pseudomonad pathogens and their cherry hosts is briefly discussed.     

Identification of Pseudomonas syringae pv. syringae causing bacterial leaf blight of Miscanthus sinensis

Journal of Plant Diseases and Protection - In the late summer of 2015, severe leaf blight occurred on Miscanthus sinensis grown on natural riverside lands of the Han River in Seoul, South Korea....     

Occurrence of specific reactions induced by Pseudomonas syringae pv. syringae on bean pods, lilac and pear plants

A study on the pathogenicity of 81 strains of Pseudomonas syringae pv. syringae (PSS) isolated from 16 different hosts was conducted on lilac plants, bean pods and pear seedlings, using artificial inoculation.
Only 55 among the 81 strains induced a necrotic lesion when inoculated on lilac leaves. On bean pods, all but one of the bean isolates, and only eight strains among the 52 strains isolated from other hosts, induced typical green water-soaked lesions. On pear leaves, only pear isolates incited a typical progressive necrotic reaction, the isolates from other origins inducing no symptoms or a weak reaction limited to the inoculation point. This study indicates that in addition to the large variability observed in aggressiveness of PSS strains, host specificity occurred on bean and pear.     

Field evaluation of treatments for the control of the bacterial apical necrosis of mango (Mangifera indica) caused by Pseudomonas syringae pv. syringae

Bacterial apical necrosis is a critical disease in the main production area of mango in Europe. It is caused by Pseudomonas syringae pv. syringae, and produces necrotic lesions on mango buds and leaves, causing severe yield losses due to a decrease of flowering and fruit set. A field study to evaluate control treatments against bacterial apical necrosis was carried out during three seasons on mango trees cv. Tommy Atkins in Huelva (Spain). Experimental treatments included Bordeaux mixture, fosetyl-Al, acibenzolar-s-methyl, gibberelic acid, silicon gel, a mixture between acibenzolar-S-methyl and Bordeaux mixture, and combined applications of fosetyl-Al with Bordeaux mixture or silicon gel. The treatments which caused a consistent reduction in bacterial apical necrosis symptoms at similar levels to the conventional treatment with Bordeaux mixture, were the plant resistance activator acibenzolar-S-methyl and the phosphonate derivative fosetyl-Al applied singly or in combination with other compounds, which could be alternative treatments. These treatments showed a significant decrease in the necrotic buds and/or leaves numbers; however, minor differences in P. syringae-like population levels were observed. The analysis of the inhibitory and bactericidal concentrations of cupric compounds against P. syringae strains isolated from mango tissues suggests that the commercial copper-based treatments with Bordeaux mixture used in the management of mango crops do not work in a bactericidal mode of action.     

Pseudomonas syringae pv. avellanae pathovar nov., the bacterium causing canker disease on Corylus avellana

The results of an extensive study of 170 morphological, physiological, biochemical, serological and pathological characters of 18 representative isolates from the filbert canker pathogen are presented. These indicate that the bacterium responsible for the disease of filberts ( Corylus avellana ) in Greece is properly characterized as a typical member of the species Pseudomonas syringae. It is placed in group Ia according to the LOPAT tests. The differences in some characters between Pseudomonas syringae pv. syringae and the filbert Pseudomonas , as well as its host specificity, justify its classification as a new pathovar of Pseudomonas syringae and the name of Pseudomonas syringae pv. avellanae pv.nov. is proposed for the bacterium causing the disease 'bacterial canker' of Corylus avellana.     

Susceptibility of European pear cultivars to Pseudomonas syringae pv. syringae using immature fruit and detached leaf assays

The susceptibility of thirty-three pear cultivars and two pear rootstocks to four virulent strains of Pseudomonas syringae pv. syringae was evaluated by inoculating detached immature fruits and young leaves. The four strains were similarly virulent and did not show cultivar specificity although they were isolated from different pear cultivars and exhibited different biochemical profiles. The most frequently planted pear cultivars, Conference, Abate Fetel, General Leclerc, Williams, D. Comice, El Dorado, Alexandrine, B. Anjou, Passe Crassane and the rootstock OHxF 333 were susceptible to P. syringae pv. syringae. Maximal severity values were obtained on 'Preguystar' leaves (about 90%). The rootstock Winter Nelis was less susceptible. Results with immature fruit and detached leaf assays agreed with field observations on cultivar susceptibility to bacterial blast. However, the detached leaf test gave a more accurate prediction and has the advantages that symptoms develop quickly (48 h), and leaves are available for a longer period of time than fruits. This method is proposed as a rapid and reproducible screening system of cultivar susceptibility to bacterial blast of pear.     

Bacterial brown spot on Avena storigosa Schereb. caused by Pseudomonas syringae pv. alisalensis

Avena storigosa Schereb. (bristle oat) is used as a green manure in crop rotations and as an antagonist of nematodes in Nagano Prefecture, Japan. In 2011, necrotic, brown, water-soaked lesions were observed on young bristle oat plants. A pathogenic bacterium was isolated from symptomatic leaves of infected plants and produced the same symptoms after inoculation. Bacteriological properties of the bacterial isolates from bristle oat matched those of Pseudomonas syringae pathovars. The host range of the bristle oat isolates was identical to that of P. syringae pv. alisalensis. This is the first report of bristle oat disease caused by P. syringae pv. alisalensis.     

Evaluation of drench treatments with phosphonate derivatives against Pseudomonas syringae pv. syringae on pear under controlled environment conditions

Several phosphonate derivatives including theoomycetic antifungal agents phosphonate andtris-o-ethylphosphonate (fosetyl), theethylene-releasing compound 2-chloroethylphosphonate(ethephon), and the antibiotic2-epoxypropylphosphonate (phosphomycin) were evaluatedfor in vitro and in planta activityagainst Pseudomonas syringae pv. syringae.Inhibition of colony growth in CYE agar byphosphonate, fosetyl and etephon was very slight(minimal inhibitory concentrations MIC= 0.31–;0.62 gHP /l). Also, survival of P. syringae pv. syringae in aqueous solutions ofphosphonate or fosetyl was high. Only phosphomycinshowed significant antibacterial activity invitro (MIC=10-20 µg HP /ml) comparedto streptomycin (1-2 µg a.i./ml). Potted pearplants irrigated with these chemicals and inoculatedwith Pseudomonas syringae pv. syringae had significantly less disease than non-treatedcontrols ( P<0.001). Phosphomycin was the mostactive compound with a median effective dose(ED₅₀) of less than 0.62 g HP /l.Activities of the other phosphonates were weak butconsistent between experiments. The ED₅₀s on wholeplants were 2.1, 3.3, and 6.9 g HP /l for ethephon, phosphonate and fosetyl, respectively. TheED₅₀of P. syringae pv. syringaeincreased from 6.5 in non-treated controls to 7.7-8.8log₁₀ cfu/ml on plants treated with phosphonatesat 1.86 g HP /l. It was concluded thatdrench treatment with fosetyl is not a practicaloption for control of P. syringae pv. syringae on pear.     

Role of phaseolotoxin production by Pseudomonas syringae pv. actinidiae in the formation of halo lesions of kiwifruit canker disease

Pseudomonas syringae pv. actinidiae, the causal bacterium of kiwifruit canker, induces the formation of chlorotic halo lesions on infected leaves and inhibits the growth of Escherichia coli. The inhibition ofE. coli growth was shown to be reversed by L -arginine or L -citrulline, but not by L -glutamine, suggesting that the pathogen produces a toxin similar to phaseolotoxin, which inhibits ornithine carbamoyltransferase. The toxin was purified from culture broth of P. syringae pv. actinidiae strain Kw11, and was shown by nuclear magnetic resonance to be identical to phaseolotoxin. Assays based on inhibition of E. coli growth and on amplification of a phaseolotoxin fatty acid desaturase gene (ptx) fragment revealed that, among the plant pathogenic bacteria examined, the production of phaseolotoxin is restricted to strains of P. syringae pv. phaseolicola and pv.actinidiae . A non-toxigenic mutant of strain Kw11 generated by disruption of the ptx gene induced the formation of necrotic lesions on kiwifruit leaves; however, the lesions were not surrounded by a chlorotic halo as were those induced by the parent strain. The growth rate of the non-toxigenic mutant in leaf tissue was similar to that of the parent strain. These results suggest that phaseolotoxin production contributes to the formation of chlorotic halo lesions in kiwifruit canker but is not required for multiplication of the pathogenic bacterium during infection.