1,721,016 research outputs found
Molecular characterization of Pseudomonas syringae pv. tomato strains overcoming the resistance of Pto-bearing tomato plants
No full textLarge-scale cultivation of Pto-bearing tomato genotypes, resistant to bacterial speck disease caused by the race 0 of Pseudomonas syringae pv. tomato (Pst), is increasing the risk of Pst race 1 appearance, which overcomes this gene-for-gene resistance. The occurrence of race 1 in field was reported in Canada, Bulgaria, USA and Italy. In Italy, it was recorded in 1996, when Pto-tomato plants were rarely cultivated, albeit it did not cause significant damage. In 2008, a severe outbreak of bacterial speck disease was observed on Pto-bearing tomato plants in Cremona Province (northern Italy), from which we obtained 3 bacterial isolates. LOPAT tests, rep-PCR, PCR amplification of hrpZPst and pathogenicity tests on susceptible Rio Grande and resistant Ontario 7710 tomato plants confirmed that they belong to race 1 of Pst. By using PCR and suitable primer we further characterize these isolates as well as 5 race 1 and 9 race 0 Pst strains collected in Italy and California for the presence of the avrPto effector gene, whose product was found to interact with the Pto protein. All race 1 strains were lacking avrPto gene, while all race 0 strain contain it, except for 2 strain. We can therefore suppose a complete deletion of avrPto gene in race 1 strains.
Since also avrPtoB was found to interact with Pto, further investigations are in progress to determine the presence of the avrPtoB gene in all strains studied
Nitric oxide releasing compounds systemically protect Arabidopsis thaliana plants from Tobacco Mosaic
No full textThe ability of nitric oxide releasing compounds, sodium nitroprusside (SNP) and S-nitrosocysteine (CysNO), to induce resistance in Arabidopsis thaliana plants (Col-0) against tobacco necrosis virus (TNV) was evaluated. SNP and CysNO were able to systemically and significantly (P≤0.05) protect Arabidopsis plants against TNV, with protection levels of 63 and 71%, respectively. A protection level of 66% was obtained with the SAR inducer acibenzolar-S-methyl as comparison. To verify whether the protection exerted by SNP and CysNO is mediated by salicylic acid, transgenic A. thaliana plants expressing the nahG gene were used. Reduced protection levels (38%) were observed in NahG Arabidopsis plants treated with SNP or CysNO in comparison with the wild-type plants. It is noteworthy that untreated NahG plants are less susceptible to TNV infection than wild-type plants. Our results suggest that the protection induced by the nitric oxide releasing compounds used are in part mediated by salicylic acid
Alternative control approaches against gray mold of Pelargonium zonale.
No full textIn collaboration with a nursery located near Aprilia (central
Italy), we started to investigate the use of antagonistic fungi of the genus Trichoderma (T. atroviridae P1, T. harzianum T22 and T67, T. reseii T34, Trichoderma spp. 8009, T. hamatum T382 and a commercial product containing the isolates ICC012 of T. harzianum and ICC080 of T. viride) and resistance inducers in the control of Pelargonium gray mold. In dual-culture tests, each Trichoderma isolate caused a significant reduction in the growth of an isolate of Botrytis cinerea collected in the nursery, which was iprodione-resistant as confirmed by in vitro assays. The effect was significantly higher when Trichoderma isolates were inoculated two days before the pathogen rather than simultaneously. Moreover, the isolates P1, T22, T34 and ICC012+ICC080 caused an abnormal hyphal branching of the pathogen, while T67 formed coiling around them.
Preliminary in vivo assays seemed to confirm the effectiveness of all the antagonists with the exception of T22, as they reduced significantly the severity of gray mold. Among the resistance inducers, Biochikol, which contains chitosan, reduced the disease severity, while treatments with pure chitosan dissolved in 1% acetic acid (0.04%, w/v) or 0.3 mM acibenzolar-S-methyl were ineffective and phytotoxic. As expected, pelargonium plants treated with iprodione (34 ppm) were not completely protected from gray mold, confirming the necessity for alternative control approaches
Diagnostic tools for the identification of Brenneria nigrifluens, the causal agent of persian walnut bark canker
No full textAfter the first report in 1998 in North Italy (Veneto and Piemonte), bark canker of persian walnut (Juglans regia L.), caused by Brenneria nigrifluens, has later been described in other italian regions (Lazio and Campania). In 2002, we found the symptoms of the disease in walnut plantations for timber production located in 13 farms of Central Italy (Umbria and Marche). All of the 44 isolates obtained from diseased plants were Gram-negative and had oxidative and fermentative metabolism. Twenty of them were submitted to API 20E system (bioMérieux) for the identification because they were oxidase negative and therefore belonged to the Enterobacteriaceae. Four isolates (1 from Umbria and 3 from Marche) gave the 7-digit code0005773, which is identical to those observed for the type strain LMG 2694T and the two reference strains LMG 5107 and LMG 5953 of B. nigrifluens. When trunks of young walnut plants were inoculated with these 4 isolates, they caused typical symptoms of the disease 3 months after the inoculation. A number of isolates associated with bark cankers and not pathogenic on walnut plants were identified as Erwinia rhapontici by API 20E system. Rep-PCR performed with the primers REP showed that the pathogenic isoaltes had high similarity (89%) with the type and reference strains of B. nigrifluens. At present, we intend to develop a diagnostic molecular assay exploiting a 905 bp fragment amplified during REP-PCR, which seems to be characteristic of B. nigrifluens
First report of leaf spot caused by Pseudomonas cichorii on Coreopsis lanceolata in Italy.
No full textCoreopsis lanceolata L. (Compositae), an ornamental species grown in parks and gardens, is very much appreciated
for its long-lasting flowering period. In August of 2008, pot-grown plants with necrotic leaf lesions were observed in a
commercial nursery located near Biella (northern Italy). Lesions were present, especially along the margin of basal
leaves, and sometimes had a chlorotic halo. On infected leaves, dark brown necrosis developed. Leaf stalks were
sometimes affected. In many cases, the leaves, especially those at collar level, were withered. Of 1,500 plants, 15%
were infected by the disease. Microscopic examination did not reveal any fungal structures within the lesions. Small
fragments of tissue from 30 affected leaves were macerated for 15 min in casein hydrolysate and 0.1-ml aliquots of
the resulting suspension were spread onto Luria Bertani agar (LB) and potato dextrose agar (PDA). Plates were
maintained at 22 ± 1°C for 48 h. No fungi were isolated from the leaf spots on LB or PDA. Colonies similar to those of
Pseudomonas spp. were consistently isolated on LB. Colonies were fluorescent on King's medium B, levan negative,
oxidase positive, potato soft rot negative, arginine dihydrolase negative, and tobacco hypersensitivity positive (LOPAT
test). The bacterial colonies were identified as Pseudomonas cichorii (2). The internal transcribed spacer (ITS) region
of rDNA was amplified using primers 27F and 1492R and sequenced (GenBank Accession No. FJ534557). BLAST
analysis (1) of the 998-bp segment showed a 98% homology with the sequence of P. cichorii. The pathogenicity of one
isolate was tested twice by growing the bacterium in nutrient broth shake cultures for 48 h at 20 ± 1°C. The
suspension was centrifuged, the cell pellet resuspended in sterile water to a concentration of 107CFU/ml, and 30 4-
month-old healthy coreopsis plants were sprayed with the inoculum. The same number of plants was sprayed with
sterile nutrient broth as a control. After inoculation, plants were covered with plastic bags for 48 h and placed in a
growth chamber at 20 ± 1°C. Five days after inoculation, lesions similar to those seen in the field were observed on all
plants inoculated with the bacterium, but not on the controls. Ten days later, 40% of the leaves were withered.
Isolations were made from the lesion margins on LB and the resulting bacterial colonies were again identified as P.
cichorii. The pathogen caused the same symptoms also on plants of Dendranthema frutescens (cv. Camilla),
Chrysanthemum morifolium (cvs. Eleonora and Captiva), and an Osteospermum sp. (cv. Wild side) when artificially
inoculated with the pathogen with the same methodology. The same bacterial leaf spot caused by P. cichorii was
observed in 2005 in other nurseries in the same area on Phlox paniculata (3). To our knowledge, this is the first report
of bacterial leaf spot caused by P. cichorii on C. lanceolata in Italy
The new species Pectobacterium aroidearum does not preferentially attack monocotyledonous plants
No full textMolecular characterization of a Fusarium oxysporum f. sp. gladioli population from saffron
No full textCharacterization of a Plasmopara sp. detected on Smyrnium olusatrum in Italy.
No full textEach year since 2009, in April-May, downy mildew symptoms and signs on leaves of Smyrnium olusatrum L. plants were observed in Perugia (Central Italy). They were characterized by chlorotic- yellow angular spots and a white mat in correspondence of the diseased areas on the upper and lower leaf surface, respectively. The white mat was constituted by sporangiophores aggregated in 4-14 fascicles, stout with a straight or slightly curved trunk and with a noticeably bulbous base. On each sporangiophore alternate branches were present, showing monopodial branching in one order. Sporangia were ovoidal with base and tip round and with apical dehiscence. Globose to irregular oospores, with smooth, colourless to yellowish, thick wall were present in the infected leaves. Haustoria were pyriform to vesicular. Phylogenetic analysis performed on partial sequences of the large subunit of the nuclear ribosomal DNA revealed that the pathogen fell in a cluster with Plasmopara species attacking hosts belonging to the Apiaceae family. Molecular analyses on downy mildew-affected S. olusatrum herbarium specimens are in progress to establish to which species the pathogen we describe belongs
Transcript profiling on developing Petunia hybrida floral organs
No full textThe cDNA-AFLP transcript profiling technique was used to analyse gene expression during flower development in Petunia hybrida. Reproductive and vegetative floral organs were sampled at five developmental stages and gene expression profiles were compared. This allowed us to assemble an inventory of genes expressed mainly in anthers during microspore development and in ovaries during macrosporogenesis. About 6,000 transcript tags were generated, 354 of which showed a modulated and/or organ-specific expression pattern. Stamen-specific transcripts exhibiting an upregulation in gene expression were well represented in our screening. Ovary-specific transcripts were less frequently observed and often displayed a constant level of gene expression. Of 194 fragments characterised further by sequencing, 35% showed homology with known genes in a database search. They belong to a wide range of gene classes, such as proteases, transcription factors and genes involved in metabolism, cell cycle and disease resistance. The usefulness of cDNA-AFLP transcript profiling as a tool to unravel complex developmental processes at the molecular level is discussed
- …
