IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2005 | Volume:41 | Issue:2|Papers Count:13

Yellows are a prevalent disease of longmelon, snakemelon, squash and other cucurbits in the Boushehr Province of Iran. The disease begins as yellow spots which may spread and cover the whole leaf surface. Yellowing is more severe in older leaves. This paper reports the results of studies on the etiology of the disease. In a preliminary serological study, extracts of diseased leaves did not react with antisera to viruses reported from the area, namely, Watermelon mosaic virus, Cucumber mosaic virus and Squash mosaic virus. Electron microscopy showed presence of filamentous viruslike particles in concentrated extracts of diseased plants. The disease agent was not transmitted to cucurbit seedlings by mechanical inoculation (rubbings on leaves or stem injection) of diseased extracts. Typical disease symptoms, however, were produced under greenhouse conditions when cucurbit seedlings were inoculated with two (a local and a non-local) populations of whitefly (Bemisia tabaci) previously fed on diseased plants.Reverse transcription -polymerase chain reaction with a pair of primers corresponding to the coat protein region of Cucurbit yellow stunting disorder virus (CYSDV) resulted in the expected product.The type of symptoms, morphology of the associated particles, failure to be transmitted by mechanical inoculation, successful transmission with B. tabaci and RT-PCR results indicate that cucurbit yellows in Boushehr Province is caused by CYSDV, a member of the genus Crinivirus (Family Closteroviridae).

Almond red leaf blotch caused by Polystigma amygdalinum, is one of the most important leaf disease of almond. In order to evaluate relative resistance of commercial almond cultivars to P. amygdalinum, 20 cultivars of 2 year-old- almond seedlings were planted in a randomized block design with 3 replication (3 plants in each replicate) in Chahar-Takhteh Station in Shahr-e-Kord. Overwintered infected almond leaves were used as inucula in each plot. In order to maintain proper moisture for the release of ascospores, all planted trees irrigated daily with sprinking system for 0.5-1 hour, from the time of leaf emergence to complete leaf maturity.Sampling was carried out at the time of maximum lesion expanded. Relative resistance was assessed based on disease intensity and percent of leaf infection. The results showed that there is significant difference among cultivars. Cultivars of Frragness, Shekofeh, Shahrud-12 and Shahrud-6 were highly resistance; whereas, Emamieh 1, Shahrud-16, Shahrud-7 and Shahrud-19 cultivars were susceptible.

Eighty-eight Fusarium isolates morphologically identified as Fusarium graminearum and collected from northern, southern and northeastern parts of Iran, were studied using species-specific (Schilling's) primers. The results indicated that a specific band of 332 bp was amplified, when species-specific primers of F. graminearum was used Of 88 isolates examined, 72 were molecularly identified as F. graminearum. The remaining 12 belonged to other species of Fusarium. The primers failed to amplify any band in negative controls including F. pseudograminearum and F. culmorum. To determine the extent of genetic diversity among Iranian populations of F. graminearum, eight random primers were tested for RAPD analysis. Of these, two primers (OPA07 and OPA10) were reproducibly polymorphic. The results of cluster analysis of OPA07 showed that at 85% similarity, isolates were categorized into IS groups. The 1st, 4th, 5th, 6th, 9th, 11th, groups contained 18, 4, 18, 20, 5 and 10% of isolates, respectively. The remaining groups had only one member. At 90% similarity, 29 groups were recognized. The cluster analysis for OPAIO categorized isolates into 9 groups at 85% similarity. The 1st, 2nd, 3rd, 6th and 7th contained 24, 26, 22, 14, 3 and 3% of isolates, respectively. Other groups had only one member. At 90% similarity, the isolates were divided into 19 groups. Using these two primers, the isolates from northwestern parts of Iran were delineated from others. The isolates belonged to northern and southern parts of the country were distributed among various sub-clusters. This is the first report of molecular identification of F. graminearum using species-specific primers and the extent of its genetic diversity among Iranian populations of the species.

Potato pink rot criterion was applied to laboratory differentiation of Phytophthora melonis trom P. drechsleri which are morphologically similar and urecognizable. All P. drechsleri isolates trom different parts of the world and various hosts and also its sister phylogenetic taxa P. cryptogea and P. erythroseptica isolates incited pink rot in potato tubers, whereas none of the P. melonis isolates did. Application of pink rot symptoms as a reliable taxonomic character for differentiation of these two morphologically convergent taxa is discussed.

Foliage blight symptoms have been observed on cucunber (Cucumis sativus), cantaloupe (Cucumis melo) and squash (Cucurbita pepo) plants in Varamin since 1996. Symptoms consist of marginal mecrosis surrounded by chlorotic halos that expand as V-shaped blotches along and between the major leaf veins. The blight has been severe during and following periods of wet and rainy weather when the day-time temperature averaged 27-30°C. A rod-shaped, Gram-negative, oxidase positive, fluorescent Pseudomonas was consistently isolated from the diseased leaves on medium B of King.On the basis of the phenotypic features, the strains were identified as Pseudomonas marginalis pv. marginalis. The electrophoretic profiles of cell proteins of the strains were similar to each other and to a reference strain of Pseudomonas marginalia pv. Marginalis ICMP 3553. Pathogenecity of the strains was confined on cucumber (cv. Soltan and line RS- 410332) under greenhouse conditions, and strains were isolated from the inoculated plants. To evaluate the resistance of cucumber cultivars to the pathogen, an experiment using 77 cultivars and lines was performed under greenhouse conditions (22-30°C). The majority of cucumber cultivars and lines were rated as susceptible and a few rated tolerant to P. m. pv. marginalis. cultivars and lines Kozakloo, GH4,.KC 361106, KC 361065, TN 94162, TN 94139, TN 94190 and Super shoal appeared to be tolerant.

Ralstonia solanacearum, the causal agent of bacterial wilt, is an important pathogen of potato reducing yield in tropical and sub tropical regions. This pathogen is easily transmitted from one field to another by planting healthy looking seed tubers with latent infection.Development of a sensitive and rapid technique for diagnosis of R. solanacearum is crucial for efficient control of this disease. Therefore, PCR-based molecular diagnosis of R. solanacearum was studied. Application of this technique using specific primers, 759 and 760, amplified a DNA fragment of 281bp. The ordinary PCR technique could only detect 104 CFU/ml of R. solanacearum, while after an enrichment stage of 48 hours bacterial concentration of 10CFU/ml was detectable. Detection was accomplished using both stem and tuber tissues in three commercial potato cultivars Herta, Nicola and Fiana. PCR detection of R. solanacearm in soil samples was also successful post-enrichment of bacterial concentration in the sample. Enrichment of pathogen population in the sample leads to extraction of high quality DNA and dilution of soil inhibitors in the DNA solution and consequently enhances the fidelity and reliability of PCR detection in soil samples.

In this investigation, a rapid zearalenone (ZON) extraction method from fungal culture (a 5 mm disk) was developed using 50010ethanol and freezing-thawing procedure. In addition, a rapid and inexpensive bioassay method for evaluation of zearalenone production in fungi was calibrated and used to screen for ZON production in Iranian isolates of Fusarium graminearum, the causal agent of wheat headblight. This bioassay, which is based on b-galactosidase induction in a genetically engineered Saccharomyces cerevisiae in response to an estrogenic substance like ZON, was calibrated using seven fungal species as negative and positive controls and pure ZON (Sigma) as standard. Gibberella fujikuroi, F. sporotrichoides, F. oxysporum, F. o. cucumerinum, F. solani and F. subglutinans as negative controls showed no difference from mock preparation (50% ethanol). An isolate of F. graminearum and a pure sanlple of ZON effectively induced b-galactosidase and considered as positive control. Eighty-eight Iranian isolates of F. graminearum collected from various parts of the country were screened using this bioassay method. The results showed that 32% of isolates tested produced ZON in various degrees. This is the first report of application of this bioassay method for evaluating ZON production in fungi. This method can potentially be used in rapid screening of many fungal mutants as an attractive low-cost tool for monitoring ZON production. Since ZON producer isolates were presented in all area of Hill distribution, monitoring of contamination of agrifoods and determining of acceptable daily intake (ADI) are mandatory.

One hundred and twenty eight isolates of Fusarium oxysporum f.sp. sesami (Fos) were isolated from sesame plant during 2001-2002 growing season in major sesame growing areas in Fars province. Nit mutants were synthesized on minimal medium (MM) containing 3% potassium chlorate. Based on colony growth on basal medium containing nitrogen sources such as sodium nitrate, sodium nitrite, hypoxanthine, anunonium tartrate and uric acid the nit mutants were grouped. To obtain heterokaryon, nit mutants were crossed on MM. Formation of mycelial tufts at the junction was considered as compatible and no growth as non-compatible reaction. Nit mutants were generated from all isolates. Based on the ability to use different nitrogen sources the mutants were grouped in to three phenotypic classes nit 1 (77.3%), nit 3(12.9%) and nitM (9.8%). Ten compatible groups were recognized among nit mutants. The results are indicative of relationship between vegetative compatibility groups (VCGs) and geographic origin of the isolates. Since there was no sesame seeds exchange in the areas and farmers usually used their own seeds, the pathogen had limited distribution resulted in local VCGs group.

In order to investigate the role of ribosomal protein L3 (RPL3) in inducing resistance against the mycotoxin of Fusarium graminearum, deoxynivalenol (DON) in wheat, different alleles of RPL3 gene were identified and sequenced The RPL3 gene family in wheat consists of six genes, RPL3 A and RPL3 B loci, each having three homologs. Wheat RPL3 ESTs were obtained using yeast and rice RPU sequence information. We developed gene-specific primers and cloned genomic and cDNA fragments of RPL3 homologs from sensitive and resistant wheat genotypes. Sequence analysis showed a very high similarity among the homologs, while none of the expected amino acid differences related to DON-resistance were found in naturally existing alleles among the genotypes. SNP-based markers were developed which can be exploited in gene mapping and back cross selection programs. The available sequences will provide more in-depth knowledge and understanding for developing effective and durable resistance against Fusarium head blight in wheat, which is not easily overcome by the pathogen.

This study is aimed to evaluate the phenotypic and electerophoretic characteristics of pectobacterium strains infecting corn in Mazandaran province during 1998-1999. Infected corn samples were collected from different fields. Twenty pectobacterium strains were isolated and purified. The strains were heterogeneous based on the result of one hundred phenotypic tests. In numerical analysis of the phenotypic characteristics, two main clusters were identified.Strains of the first phenon (12 strains) with characters in common with those of Pectobacterium chrysanthemi, P. atrosepticum. P. betavascularum and P. c. subsp. atrosepticum did not match with any of the named species and subspecies. Strains of the second phenon (8 strains) were identified as P.ehrysanthemi, and resembled more closely the biovar 3 of the species.The electrophoretic patterns of cell proteins of the representative strains from each phenon were compared with those of the reference strains of Pcc UPB 066 and Pch SCRI#4064.Heterogenecity in protein profiles was also noted. Therefore, atypical strains are probably members potentially new species or subspecies.

In order to mass reproduce P.betae, Agrobactrium rhizogenes was used to produce hairy roots from sugar beet petals. Root segments cut from sugar beet plants grown in soil containing resting spores were surface sterilized and placed next to hairy roots. One day after co-culturing hairy roots was transferred into hydroponics culture. Two weeks later, the presence of resting spores in hairy roots using inverted microscope was shown. Polymerase chain reaction using P.betae specific primers proved the presence of P. betae in the infected hairy roots. The ability of the newly formed resting spores to infect fresh hairy root was examined by co-culturing of the healthy and infected hairy root segments using the liquid media surrounding the infected hairy roots. PCR and microscopic observations were indicative of reinfecting ability.