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Samples of leaf, twig and fruit from ‘Mexican’ lime (Citrus aurantifolia) and grapefruit (Citrus paradisi) with symptoms of bacterial canker were collected from different provinces throughout Iran during spring and summers of 2010 and 2011. Yellow, gram-negative colonies were isolated from infected tissue samples. Results of pathogenicity assays indicated that some isolates incited tissue hyperplasia, hypertrophy and raised callus-like lesions typical of canker in hosts while other isolates stimulated flat necrotic and water-soaked lesions on leaves. Candidate samples of each group were identified according to morphological and physiological characteristics. Detections were also made using specific primers and partial sequencing of 16SrDNA for Pantoea group and gyrB for Xanthomonas group. Results showed that one group was characterized as the typical Xanthomonas citri subsp. citri strain while the other group containing most of the isolates was identified as Pantoea agglomerans. Samplings done frequently in different seasons revealed the presence of high populations of P. agglomerans with bacterial canker, especially in warmer and drier regions. These bacteria were able to incite canker-like symptoms on grapefruit seedlings and could be reisolated after two months.

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A total of ten isolates of fungi with Rhizoctonia-like mycelia were obtained from infected roots and stems of Pistachio Pistacia vera grown in a commercial nursery in Rafsanjan, Iran, during the autumn of 2011. The infected seedlings showed symptoms of chlorosis that later turned to necrosis. All of the isolates were identified as binucleate Rhizoctonia on the basis of hyphal characteristics and nuclear number. They were tested for detection of the anastomosis group, optimum growth temperature, rDNA-ITS region traits and pathogenicity on pistachio seedlings in vitro and in vivo. The analysis of hyphal anastomosis reaction was carried out with the tester isolates of binucleate Rhizoctonia AG-A, AG-Ba, AG-G and AG-F as well as multinucleate Rhizoctonia AG4 as already detected on pistachio seedlings. The optimum temperature for growth of binucleate Rhizoctonia sp.was 35 °C. In in vivo test, the symptoms of root rot were observed 30 days after inoculation and mortality happened two weeks thereafter. According to molecular characteristics and anastomosis test groups, all isolates showed greatest similarity to anastomosis group AG-F. This finding is the first report of anastomosis group F (AG-F) of binucleate Rhizoctonia, as causal agent of root and stem rot disease of pistachio in the world and Iran.

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Fusarium crown and root rot of cucumber caused by Fusarium oxysporum is one of the most important diseases in cucumber. Although various methods have been recommended to manage this disease, biological control is considered as an environmentally friendly method. In the present study, antagonistic effects of six Pseudomonas and Bacillus genera strains were investigated against F. oxysporum, where in vitro and in vivo assays were performed under drought stress. All of the strains were capable to inhibit the growth of F. oxysporum. The results of drought stress also indicated that the bacterial strains were able to tolerate different levels of drought stress. In general, Pseudomonas fluorescens VUPF5 caused the best inhibitory effect in all of the assays in vitro and under greenhouse conditions.

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Five fungicides, with active ingredients azoxystrobin, imazalil, thiabendazole, azoxystrobin + difenoconazole and fludioxonil + difenoconazole, were tested against two isolates of Fusarium solani and two isolates of F. oxysporum, causing potato dry rot in Mashhad region. PDA media amended with the fungicides significantly inhibited the mycelia growth of all Fusarium isolates incubated at 25 °C for 7 days; however only Imazalil and Thiabendazole completely stopped the mycelia growth of all fungal isolates even at their lower concentration (40 and 5ppm respectively). The mean penetration of F. solani FPO-67 and F. oxysporum FPO-39, the more virulent of the four isolates, after 21 days of incubation at 25-27 °C indicated that imazalil and thiabendazole at concentrations of 1.5 and 2/1000, completely inhibited the penetration of F. oxysporum FPO-39 into potato tubers, but in the case of F. solani FPO-67 all treatments (1, 1.5 and 2/1000) significantly reduced the development of dry rot compared to untreated control. In natural condition, tuber treatment with Imazalil and Thiabendazole (2/1000), prior storage, reduced F. solani FPO-67 development by 68 and 71.69% respectively. According to the results, these fungicides could play a role in integrated pest management against tuber-borne fungal pathogens.
 
 

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One critical environmental stress that limits plant production and development is salinity stress. Recently it has been shown that application of plant growth-promoting rhizobacteria (PGPR) can alleviate the deleterious effects of environmental stresses. Present study aimed to evaluate the effects of some bacterial strains on proline, sugar, total phenolic compounds (TPC), Phenylalanine ammonia lyase (PAL), photosynthetic pigments and antioxidant activities (guaiacol peroxidase, polyphenol oxidase and superoxide dismutase) of cucumber plants under salinity stress. A completely randomized design was applied with a factorial arrangement of two factors: salinity at three levels (0, 50 and 100 mM) and Pseudomonas fluorescens and Bacillus subtilis strains, with three replications. The results showed that cucumber plants that were inoculated with Pseudomonas and Bacillus strains possessed noticeable variations in proline, sugar, TPC, PAL and enzymes activity compared to un-inoculated control. These results suggest that use of these bacterial strains overcame harmful effect of salinity by accumulation of proline, TPC, sugar, PAL activity and enzymes activity that can be considered as a suitable method to manage salinity stress.

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 Identifying resistant genotypes is necessary to control wheat take-all disease Gaeumannomyces graminis var. tritici. In this study, 30 bread wheat genotypes were evaluated under greenhouse and field conditions. The genotypes were evaluated with fifteen molecular markers (SSR and specific primers for translocation wheat-rye). The genotypes were divided into four groups based on disease severity (the greenhouse) and agronomic traits (the field). Chi-square results showed the interactions for these groupings. The correlation between disease severity and agronomic traits indicated that plant resistance is strongly dependent on plant yield. Based on cluster analysis for molecular data (based on simple matching similarity coefficient and UPGMA method), genotypes were separated into resistant and susceptible ones. The correlation between disease severity and amplified loci showed that disease resistance is interactive with xbarc232, xbarc124, and gpw95001 markers. Resistance to take-all disease is probably associated with the interaction of several genes. These results add significant information to our knowledge of the chromosomal location of genes for the take-all disease.

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Root-knot nematodes are the most economically important plant pathogens in pistachio. The ability of Pseudomonas fluorescens strains VUPF5, VUPF52, Bacillus cereus strain PRC95 and Bacillus subtilis strain PRC96 were tested as biocontrol agents for Meloidogyne incognita on the pistachio cultivars Sarakhs and Badami. The effect of these bacterial strains on defense-related enzymes activity in pistachio was also investigated. Pistachio seedlings of both cultivars were treated with bacterial strains and then were inoculated with 2000 second-stage juveniles of nematode after two days. Evaluations were made for changes of Peroxidase (POX), PolyPhenolOxidase (PPO), Phenylalanine Ammonia lyase (PAL) and Total Phenolic Content (TPC) determined at 2, 4, 7, and 10 Days After nematode Inoculation (DAI). Results showed improved activity of POX, PAL and PPO in both cultivars. The most significant result for POX activity in the treated seedlings belonged to Pseudomonas strain VUPF5 at 7 DAI for Sarakhs and 10 DAI for Badami. However, this strain displayed an increase in PAL activity at 2 and 4 DAI in Badami and Sarakhs, respectively. Seedlings treated by the Pseudomonas strain VUPF52 at 10 DAI had the highest PPO activity among cultivars. TPC concentration was slightly higher, by 8.4% at 4 DAI, in Sarakhs seedlings treated with VUPF5, but no significant increase could be seen in the Badami cultivar compared with the control. In another experiment, 4 months after nematode inoculation in seedlings of both cultivars treated by bacterial strains, numbers of galls, egg masses, and second juveniles decreased compared with the non-treated seedlings.

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Biofilm formation and rhizosphere colonization of the plants are the main infrastructures for the biological control of the plant diseases. Bacteria accumulation in the protective layer, which results from their self-production of Exopolysaccharides (EPS), is called the biofilm. The formation of these complex structures originates from the multicellular behaviors of bacteria. Various elements can play a role in these mechanisms. In this study, we examined biofilm formation, root colonization, and salt tolerance to four concentrations of NaCl in the strains of Bacillus velezensis (Q12, US1, and UR1). The results showed that the biofilm strength plays an important role in the efficiency of tomato root colonization. Furthermore, UR1 that had defects in producing the surfactin, iturin, and fengycin using Ultrahigh-Performance Liquid Chromatography-High Resolution Electrospray Ionization Mass Spectrometry (UHPLC-HRESIMS), was incapable of tolerance to salinity, biofilm formation, competition, and rhizosphere colonization. Confocal Laser Scanning Microscopy (CLSM) studies showed that strains US1 and Q12 differed in the biofilm strength, the position of the bacteria that are located laterally, polar, or both, and root colonization. Q12 was introduced as the best strain in all these experiments. Also, based on the findings of this and previous studies, the possibility to create the subpopulations influenced by genetic diversity in Bacillus velezensis strains during biofilm formation is suggested.