IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2007 | Volume:43 | Issue:4 (172)|Papers Count:15

Roselle (Hibiscus sabdariffa) is an annual shrub belonging to the malvaceae, widely cultivated in Asia, Australia and central Africa. as an industrial and medicinal plant. In the fall of 2007, at least 30% of 5-month-old roselle plants grown from seed near Birjand, southern Khorasan province, were found to be infected with powdery mildew. Typical symptoms of the disease included extensive growth of white, superficial mycelium and angular patches on the lower and upper surfaces of infected leaves, followed by partial defoliation. Newly infected leaves had a sparse covering of powdery mildew. Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica [Lév.] Salmon) was subsequently identified by the presence of endophytic mycelia through stomata, often branched conidiophores, hyaline, single-celled and dimorphic conidia borne singly. In 100 measurements of each type, primary conidia (lanceolate with distinct apical points) averaged 60 × 18.8 mm (55 - 62.5 × 17.5 -22.5 mm) and secondary conidia (cylindrical to oblong) averaged 59.25 × 18.3 mm (50 - 67.5 ×17.5 – 20 mm). The teleomorph was not observed. To confirm pathogenicity, diseased leaves were pressed against lower sides of leaves of 6-month-old roselle plants grown in field. After three weeks, powdery mildew developed on all inoculated plants and symptoms were similar to those of diseased plants collected from fields. No symptoms developed on control plants. Although L. taurica has been reported from Hibiscus sabdariffa in Pakistan and Thailand (AMANO, K. 1986. Host Range and Geographical Distribution of the Powdery Mildew Fungi, to our knowledge this is the first report of the pathogen occurring on Hibiscussabdariffa in Iran. Leveillula taurica, the causal agent of powdery mildew, was reported as a pathogen of kenaf (Hibiscus cannabinus) belonging to the malvaceae, in USA, Italy and Egypt. A voucher specimen was deposited with the Fungus Collection of the Ministry of Jihad -Agriculture, Tehran (Iran 12821F).

Stunting and declining symptoms on 3-5 year old apple trees grafted on Maling rootstocks were associated with uneven growth of root and presence of numerous thin and tender roots, similar to hairy root symptoms, on the main and lateral roots of the trees. The growth of the main root appeared to be arrested. Symptoms were observed on trees grown in two orchards in Semirom in Isfahan province and on apples grafted on Maling-Morton (MM) rootstocks in a nursery in Mashhad, Khorasan province. Segments of roots with hairyroot symptoms were thoroughly washed under tap water, rinsed in sterile distilled water (sDw), and then minced with a sterile razor blade in a few drops of SDW in a Petri plate. The suspension, following a 20-30 min standing at room temperature, was streaked onto plates of 2E and potato dextrose agar + calcium carbonate media and incubated at 25-27°C. White mucoid colonies appearing on both media after 4-5 days of incubation were isolated and used in phenotypic and genotypic characterization and identification. All isolates induced formation of copious amounts of callus on carrot root slices, but none produced any noticeable number of roots on the slices, up to one month post-inoculation. Twenty five of the 60 strains isolated were used as representatives in further characterization tests. The strains were motile, oxidase positive, and catalase positive, could grow on media containing 2% sodium chloride and at 33°C. They formed pellicle on ferric ammonium citrate and used sucrose and citrate as the sole carbon sources for growth. None produced 3-ketolactose nor utilized melezitose or malonate. In polymerase chain reaction (PCR) assays, with ipt and vir D primers, the species-specific fragments of 427 bp and 224 bp long were amplified, respectively, using from DNAs of all strains as templates. Based on the results of phenotypic tests and PCR assays, the strains belong to Agrobacterium tumefaciens (Rhizobium radiobacter). Similar root-inducing strain of A. tumefaciens have also been isolated from cucumber roots in England and named rhizogenic A. tumefaciens .

Despite the widespread occurrence of Citrus tristeza virus (CTV) in some regions of southern and northern Iran, there is no information about the distribution and genetic variation of CTV isolates in Kerman province. In this study the prevalence and the molecular variability of CTV isolates from four citrus growing regions of this province, including Bam, Jiroft, Orzuieh and Hossein Abad, were investigated. Total RNA from CTV infected bark and midrib of different citrus trees was extracted and used for amplification of CP and K17 region of the polymerase genes of the CTV genome, by RT-PCR. The results of ELISA showed that out of 203 random citrus samples collected from the four regions in Kerman province; about 50% were infected with CTV. The rate of CTV infection in samples of Jiroft, Bam, Hossein Abad and Orzuieh, was 60%, 56%, 50% and 45%, respectively. PCR results showed the presence of expected 672 and 409 bp fragments for CP in 9 samples and K17 region of polymerase genes in 9 samples of the CTV genome respectively in 9 samples of Kerman province isolates. The resulted PCR products were inserted into pTZ57R/T plasmid, cloned in E.coli strain DH5a, sequenced, and compared with the related sequences from the GenBank by BLAST search program. The results revealed that on the basis of CP and a part of the polymerase genes, CTV isolates of Kerman province have a higher homology with the California stem pitting (SY568) and Japanese seedling yellows (NUagA) isolates. However, six isolates of Kerman province (KBA, KG-9, KG-10, KG-11, KH-10, KS-7), showed distinct differences with other CTV isolates in four amino acids in CP gene and formed a separate branch in dendrogram. 

In order to identify plant parasitic nematodes (Criconematoidea and Longidoridae) in Kerman Province, 94 samples of soil and root were collected from Kerman province during 2004 and 2005. The samples were washed and nematodes were extracted by centnifugal floatation technique. They were fixed and transferred to glycerin according to the De Grisse method. Permanent slides were prepared. Morphological and morphometrical features were studied by a light microscope attached to a drawing tube. In this study three species of Longidoridae and eight of Criconematoidea were identified. The genus of Trophotylenchulus Raski 1957 and species of T. asoensis Mingawa 1983 are reported from Iran for the first time, Cacopaurus pestis Thorne 1943 and Longidorus orientalis Loof 1983 is reproted for the first time from Kerman province, respectively. 

From 2004 to 2005, cypress samples with gall symptoms on roots were collected from the Phin orchard of Kashan. Galls were crushed in a few drops of water and the suspension was plated on IA, SC and LB agar media containing cyclohexamid (50 mg mL). The isolated bacteria were rod-shaped, gram negative and aerobic. All of the isolates were pectinase, levan, nitrate reduction, starch and esculin hydrolysis, urease and DNase negative but positive in production of oxidase, catalase, arginine dihydrolase, and gelatinase. All of the isolates could use melezitol, arabinose, mannitol, galactose and lactose as carbon sources but none of them could utilize erythritol, L-tartrate, inositol, xylose, sucrose, sorbitol and trehalose. They produced slime on media containing carbohydrates. Pathogenicity test. was done on tomato and carrot and gall formation observed on these plants. On the basis of the biochemical, physiological and pathogenicity properties and the PCR test with sepcefic primers, the causal bacterium was identified as Agrobacterium tumefaciens biovar 1. This is the first report of crown gall disease of cypress in Iran.

In order to isolation of grape crown gall agent and study on effect of hot water and chemical treatments on reducing of bacterium from infected cuttings and some characteristics of rooted cuttings cvs. Sefid Bedaneh and Hossaini, an experiment was conducted in Grape Research Station of Takestan (3 years). Experiment was done as Split-Split plot (based on CRBD, 4 replications, 40 samples in plot). Isolation and identification of bacteria isolates was done by using common methods such as selective media and test on indicator plants. Treatments were cultivars (Main Factor), Hot-Water (sub-plot) and chemical treatments (subsub plot). Cuttings were rooted in disinfected mixed of Perlite, sand and compost soil (isolated nursery). 3 years duration, effects of treatments on deleting of infection were studied by observation of gall formation and bacterium growing on selective media. Analysis of variance was done by MSTAT-C program and mean comparison done by LSD method. 17 strains of 20 isolates were had Agrobacterium tumefaciens characteristics and 3 of them were A. vitis. Effect of combined treatments on vitality and growth characteristics varied with different cultivars and treatments. The number of healthy rooted cuttings, cuttings survival, roots fresh weight and weight of shoots were varied. Also, flower initiation was affected by treatments in two cultivars. Results showed that agent of crown gall was eradicated or reduced below the level of detection in dormant cuttings of two cvs of grapes by combined Hot water treatment (50°C/30 min)× chemical treatment (Streptomycin Sulfate 1000 ppm). Although, 60°C/15 min treatment was more effective treatment, but it killed high number of cuttings. Rooting of cuttings, fruit production and other characteristics were better by combined (50°C/30 min) × chemical treatment (Streptomycin Sulfate 1000 ppm).

Occurrence and identification of symbiotic endobacteria associated with some in vitro cultured plates of Gigaspora margarita were studied using morphological as well as molecular methods. Different fungal structures including spores, mycelia, auxiliary cells and mycorrhizal roots were separated from different in vitro cultured fungal isolates. To decontaminate surfaces of fungal structures such as mycelia, spores and auxiliary cells, the materials were surface sterilized and checked for decontamination using the viability staining procedure kit. Fungal structures were crushed, the cytoplasmic contents were stained, and then the living bacteria fluoresced yellow to bright green under blue light and appeared as rod shaped spots, while the dead bacteria fluoresced red. These bacteria were observed in different fungal structures including spores, germinating hyphae, extraradical mycelia as well as auxiliary cells. Also, bacterial cells in the process of fission were observed in fungal structures especially in germinating spores. Molecular studies using different specific primers showed the presence of symbiotic endobacteria in different structures in some of the fungal in vitro cultured plates: including spores, mycelia, auxiliary cells and mycorrhizal roots. At the same time, there were no symbiotic bacteria in some other plates indicating differences between the fungal samples in presence or absence of the bacterium.

A survey was carried out to reexamine Phyllactinia species in Iran during 2004- 2005. Seven taxa namely Phyllactinia babayanii on Prunus dulcis, P. fraxini on Fraxinus excelsior, P. guttata on Alnus glutinosa,, Carpinus betulus, Cornus sanguinea, Cornus sp., Corylus avellana, Cydonia oblonga, Paliurus spina-christi, Parietaria officinalis, Prunus armeniaca, and Pyrus communis, P. mali on Crataegus spp. and Mespilus germanica, P. moricola on Morus sp., P. roboris on Quercus macranthera and Lonicera iberrica and Phyllactinia sp. on Salix eagiptiaca were identified. Phyllactinia babayanii is newly reported from Iran. Phyllactinia sp. on S. aegiptiaca showed 3-spored asci which is same as shown in P. fraxini. However, conidial state was not seen, which is critical for exact identification of above specimen. Conidiophores in P. fraxini are markedly different from allied taxa by having curved and twisted foot cells. Based on morphological characteristics Phyllactinia on Cornus spp. were identified as P. guttata. Lonicera powdery mildew showed ascoma and conidial morphology as described for P. roboris, thus L. iberrica is matrix nova. Examination of powdery mildew infected leaves on Alnus glutinosa showed this plant could be infected by Phyllactinia guttata in Iran and P. alni, which have already been described on Alnus spp., could not occur in Iran.

In this study the optimum temperature for urediniospore germination was in the range of 15-25°C in an isolate from Khuzestan, Iran. Twenty four hours incubation of urediniospores at 32°C caused their mortality. Continuous fluorescent light (3600 Lux) significantly decreased urediniospore germination. The cardinal temperatures for teliospore germination were 12, 18 and 23°C. Continuous darkness resulted in decreased numbers of basidium and basidiospore formation. Results showed that teliospores germinated best under long day and exposure to continuous fluorescent light (3600 lux). Also optimum basidiospore formation occurred under long day condition (16 hrs light exposure). Results showed that teliospores were able to germinate without any pre-treatment; however, moisture and heat pre-treatments of teliospores improved their germination and basidiospore differentiation. Moisture pretreatments (floating teliospores on distilled H2O for 24 hrs) resulted in better germination and basidiospore formation.

Root rots are important diseases in major bean growing regions of the world including Iran. In 2007, root rot pathogens were detected in root, seed and soil samples collected from bean fields in Zanjan. Regression analysis demonstrated that the incidence of root rot disease in the fields was positively correlated with frequency of each predominant pathogen isolated Short 160 communications from root samples collected from V3 to R9 growth stage in the fields. Therefore, for each unit increase in the disease incidence, isolation frequencies of Fusarium oxysporum, F. solani, Macrophomina phaseolina and Rhizoctonia solani increased by 0.16, 0.41, 0.22 and 0.44%, respectively. The mean CFU of the pathogens per gram soil sampled from bean fields at V3 and R9 varied by field location, pathogen species, and sampling time. F. solani showed the greatest mean CFU per gram soil at V3 (1212) and R9 (3077) in the fields, followed by F. oxysporum, R. solani and M. phaseolina. The mean CFU of each pathogen and total mean CFU of the pathogens per gram soil at R9 were significantly greater than those at V3. Seed yield variables were significantly correlated with CFU of F. solani per gram soil at R9. The major root rot pathogens, F. oxysporum, F. solani, M. phaseolina and R. solani, were also isolated from seed samples collected from the fields surveyed. The mean frequency of the pathogens isolated from seeds varied by pathogen species and field location. At R9, the disease incidence, severity and index were positively correlated with frequency of M. phaseolina isolated from seeds. Findings provide useful information for developing improved management strategies and selecting for resistance.

Root rots are important diseases in major bean growing regions of the world including Iran. In 2007, root rot pathogens were detected in root, seed and soil samples collected from bean fields in Zanjan. Regression analysis demonstrated that the incidence of root rot disease in the fields was positively correlated with frequency of each predominant pathogen isolated Short 160 communications from root samples collected from V3 to R9 growth stage in the fields. Therefore, for each unit increase in the disease incidence, isolation frequencies of Fusarium oxysporum, F. solani, Macrophomina phaseolina and Rhizoctonia solani increased by 0.16, 0.41, 0.22 and 0.44%, respectively. The mean CFU of the pathogens per gram soil sampled from bean fields at V3 and R9 varied by field location, pathogen species, and sampling time. F. solani showed the greatest mean CFU per gram soil at V3 (1212) and R9 (3077) in the fields, followed by F. oxysporum, R. solani and M. phaseolina. The mean CFU of each pathogen and total mean CFU of the pathogens per gram soil at R9 were significantly greater than those at V3. Seed yield variables were significantly correlated with CFU of F. solani per gram soil at R9. The major root rot pathogens, F. oxysporum, F. solani, M. phaseolina and R. solani, were also isolated from seed samples collected from the fields surveyed. The mean frequency of the pathogens isolated from seeds varied by pathogen species and field location. At R9, the disease incidence, severity and index were positively correlated with frequency of M. phaseolina isolated from seeds. Findings provide useful information for developing improved management strategies and selecting for resistance.