Effects of Different Pathogen Sources of Watermelon Bacterial Fruit Blotch and Different Inoculated-pathogen Methods on Pathogenicity of Watermelon
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Using different over-wintering pathogen sources of watermelon bacterial fruit blotch and different inoculated-pathogen methods to test the pathogenicity of Xinong No.9.The results showed that the over-wintering pathogen sources of diseased fruit extract,dry diseased leaf,fresh diseased leaf and bacteria carrying soil all had pathogenicity,in which the over-wintering pathogen sources of bacteria carrying soil and dry diseased leaf had stronger pathogenicity;four different inoculated-pathogen methods(seed soaking,root drenching,needle inoculation and spraying) had a certain impact on pathogenicity of different over-wintering pathogen sources,in which the needle inoculation method had the strongest pathogenicity.Therefore,the results provide a scientific base for popularizing control measures,such as deep tillage,weed out diseased residues in filed,soil disinfection,reducing wounds caused by filed operation,etc..Cite
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Bacterial fruit blotch (BFB) is a devastating disease caused by Acidovorax citrulli, which was first observed in the United States in 1988 (3). A. citrulli can cause severe infection on a wide range of cucurbits, including watermelon, cantaloupe, and pumpkin. Cotyledon symptoms are brown, angular, necrotic spots or large necrotic lesions. The disease is seedborne, so seeds usually serve as the primary inoculum source for BFB outbreaks (2). In July 2012, seedling blight was observed by local farmers from Anhui province in China on watermelon seedlings grafted to pumpkin rootstocks; lesions were morphologically similar to those caused by A. citrulli. Presence of A. citrulli was detected in symptomatic samples by using species-specific primers BX-L1/BX-S-R2 (1). The seed company claimed seeds of watermelon (cv. Changfeng) were certified free of bacterial fruit blotch, but pumpkin seeds (cv. Kangkuxianfeng-1) had not been tested for A. citrulli. For investigating the inoculum source, the remaining seeds of watermelon (cv. Changfeng) and pumpkin (cv. Kangkuxianfeng-1) for seedling production were collected from the farmer and processed for pathogen extraction as described by Walcott and Gitaitis (2). Two microliters of seed wash was used as template for PCR using primers BX-L1/BX-S-R2 (1). The experiment was conducted three times. A 279-bp DNA fragment was consistently amplified by PCR from seed wash of pumpkin seeds, but not from the seed wash of watermelon seeds. Three Acidovorax-like strains (A1, A2, and A3) were isolated from pumpkin seed wash using TWZ semi-selective medium (0.5% peptone, 0.025% CaCl 2 , 1% Tween-80, 50 mg/liter berberine, 50 mg/liter cycloheximide, 50 mg/liter 2,3,5-triphenyltetrazolium chloride). PCR was performed on the 16S rDNA gene from isolate strain A1, A2, and A3 (1,492 bp; GenBank Accession Nos. JX875533, JX875534, and JX875535) with primers rp1/fd2 (4), and PCR products were sequenced. Results of sequence analysis showed the sequences of strains A1, A2, and A3 were 99% identical to that of the type strain of A. citrulli AAC00-1 (NC_008752). Pathogencity was confirmed by injection of pumpkin cotyledons with bacterial suspensions of each isolate. Collected pumpkin seeds (n = 100 seeds) and watermelon seeds (n = 100 seeds) were planted in plastic pots containing sterilized field soil at room temperature to detect A. citrulli by a wet chamber growing out test. Eight days later, brown, angular, necrotic spots or wilt developed in pumpkin seedlings, but no symptoms were noted on the watermelon seedlings. To our knowledge, this is the first report of A. citrulli causing watermelon seedling blight transmitted from pumpkin seeds by grafting in China. References: (1) O. Bahar et al. Plant Pathol. 57:754, 2008. (2) R. R. Walcott and R. D. Gitaitis. Plant Dis. 84:470, 2000. (3) G. C. Wall et al. Phytopathology 78:1605, 1988. (4) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991.
Citrullus lanatus
Pumpkin seed
Cucurbita
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The bacterial fruit blotch(BFB)caused by Acidovorax avenae ssp.citrulli(Aac)is a sort of devastating seed-borne quarantine disease of cucurbits.The impact of seed infection was investigated to the disease severity of cucurbit rootstock seedling and the infection process of Aac during seedling stage through artificially inculcating cucurbit seeds with Aac.In greenhouse condition,the relationship between different carrier amount of bacteria and the disease level of BFB was established.The results indicate that during the seed-borne infection process,the Aac infected the cotyledons firstly,then infected the hypocotyls and colonized in the xylem and phloem,caused the disease of the hypocotyls.Moreover,the higher amount of bacteria the seeds carried,and the higher disease rate and index the young seedling was.
Cotyledon
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In September of 2009,watermelons stored in low temperature conditions for 7 days were rotted and caused above 90% losses in Kaifeng.The fungus was isolated from diseased tissues and the morphological characteristics,pathogenicity and DNA sequence of 5.8S rDNA-ITS were studied.The fungus was identified as Colletotrichum orbiculare based on the morphological characteristics.DNA sequence of 5.8S rDNA-ITS of the isolate was 100% homologous with the other 5.8S rDNA-ITS sequences of C.orbiculare in GenBank.Inoculated watermelon with this isolate could produce the same symptoms as naturally infected plants.Reisolation of the fungus from lesions on inoculated fruit confirmed that the causal agent was C.orbiculare which caused watermelon rot during the storage period.
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A new leaf disease named as leaf blight of barbadosnut (Jatropha curcas), was first found in 2009 in Guizhou Province of China. The disease mainly infected leaves. The spots on diseased leaves were initially oval to irregular, then the spots gradually expanded and finally coalesced to form large leaf blight spots, and the seriously infected leaves easily defoliated earlier. Thirteen isolates were cultured from 16 leaf blight samples of barbadosnut collected from Luodian Plantation in Guizhou Province. The strain PE06 was investigated to be the pathogen based on pathogenic test and identified as Pestalotiopsis microspora according to the
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Jatropha curcas
Pestalotiopsis
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A study was carried out on the fruit rot of watermelon (Citrullus lanatus (Thunb.) Matsum. Nakai) in Ilorin, Nigeria between February and May, 2008. A large area planted to watermelon in Obbo-ille, a town near Ilorin, Kwara State was severely infected with both leaf and fruit blotches. Both diseases occurred together in all infected watermelon stands. Leaf and fruit samples were taken to the laboratory at the University of Ilorin, for investigation. A bacterial isolate identified asPseudomonas pseudoalcaligenes Stanier (= Acidovorax avenae) was recovered from both infected leaf and fruit samples. Koch’s postulates were performed on both samples using a suspension of the culture isolate. Symptoms were produced on artificially inoculated leaves and fruits and P. pseudoalcaligenes was also re-isolated. This organism was, therefore, identified as the causal organism of bacterial fruit and leaf blotch in watermelon in Ilorin, Kwara State of Nigeria.
Key words: Watermelon, fruit, leaf, blotch, Pseudomonas sp.
Citrullus lanatus
Citrullus
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Twenty-three isolates of Botrytis cinerea Pers. were obtained from the diseased tissue collected in Hefei,Bengbu,Changfeng and Hexian,by means of tissue isolating method. The pathogenicity of the isolates of B. cinerea from different hosts to the fruits and leaves of strawberry were investigated by applying mycelial block wound inoculation,respectively. The preliminary results showed that all of the tested isolates caused occurrence of grey mould on strawberry fruits and leaves,but there be significant difference in the average diameters of the lesions caused by different isolates and there was difference in the different strawberry varieties,suggesting that there was significant differentiation in pathogenicity of B. cinerea to strawberry fruits and leaves among isolates. According to the average diameters of the lesions caused to strawberry fruits and leaves,the pathogenicity of the all isolates was classified into three categories:strong,intermediate and weak. In general,the isolates from strawberry and tomato were more strongly pathogenic to the fruits and leaves of strawberry,and the isolate from capsicum was weakly pathogenic to strawberry fruits and leaves. However,there was difference in pathogenicity among the different isolates from the same host,and the pathogenicity difference was not obviously related to the localities of isolates.
Fragaria
Botrytis
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Fruit rot
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Pomegranate (Punica granatum L.) is an increasingly important fruit crop that is widely cultivated in Turkey. Typical bacterial blight symptoms were observed since spring of 2011 in pomegranate orchards located in Antalya Province. Symptoms were characterized by dark brown, angular to irregularly shaped spots on leaves and fruit; cankers on stems, branches, and trunks; and split trunks. The pathogen was isolated from leaf spots on naturally infected plants showing typical symptoms onto yeast dextrose chalk agar. Bright yellow bacterial colonies were consistently isolated. Bacterial strains were characterized as gram negative, oxidase negative, catalase positive, tobacco hypersensitivity positive, and able to produce acid from L-arabinose, D-galactose, D-glucose, and D-mannitol but not from D-xylose. Pathogenicity of the representative bacterial strain Serik-4 was performed on 2-year-old pomegranate plants cv. Hicaz. Leaves were sprayed until runoff with bacterial cell suspensions containing 107 CFU/ml. Inoculated plants were covered with transparent plastic bags to maintain moisture for 48 h. Negative control plants were inoculated with sterile distilled water. Plants were then incubated in a greenhouse at 30°C for 14 days. Symptoms on leaves included dark brown, angular to irregularly shaped water soaked lesions along the veins of the inoculated plants 10 days after inoculation. No lesions developed on the control plants. The symptoms on inoculated plants were similar to those on naturally infected plants. Yellow bacterial colonies were re-isolated from the inoculated plants and identified as the same as the original strain by conventional tests and FAME analysis, thus fulfilling Koch's postulates. Fatty acid methyl ester profiling of the representative strain Serik-4 using GC-MIDI (Microbial Identification Inc, Newark, DE) identified the genus of the bacterium as Xanthomonas. The identity of Serik-4 was further confirmed by amplifying the 16S rRNA gene with the universal primers 27F and 1492R (3) and sequence analysis (GenBank Accession No. KM007073). The 16S rRNA gene sequences of Serik-4 was 99% identical to the corresponding gene sequences of the Xanthomonas axonopodis pv. punicae strain present in the NCBI database (JQ067629.1). High incidence of bacterial blight caused by X. axonopodis pv. punicae on pomegranate has been previously reported in India (2), Pakistan (1), and South Africa (4). To our knowledge, this is the first report of bacterial blight on pomegranate caused by X. axonopodis pv. punicae in Turkey. References: (1) M. A. Akhtar and M. H. R. Bhatti. Pakistan J. Agric. Res. 13:95, 1992. (2) R. Chand and R. Kishun. Indian Phytopathol. 44:370, 1991. (3) D. J. Lane. Page 115 in: Nucleic Acid Techniques in Bacterial Systematics, 1991. (4) Y. Petersen et al. Australas. Plant Pathol. 39:544, 2010.
Xanthomonas
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