IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2006 | Volume:42 | Issue:1|Papers Count:13

In order to identify the plant-parasitic nematodes (Tylenchida) of fruit trees in Zanjan region, 100 soil and root samples were collected from orchards during 2001 and 2002. The samples were washed and the nematodes were extracted by centrifugal flotation technique. They were fixed and transferred to glycerin according to the De Grisse method (1969). The permanent slides were prepared from the extracted nematodes and some cross sections were made from different parts of the body. Morphological and morphometrical characters were studied by a light microscope attached to a drawing tube. In this study 17 species belonging to 15 genera of order Tylenchida were identified.Coslenchus assamensis (phukan & Sanwal 1980) Andrassy, 1981 and Paratylenchus nanus Cobb, 1923 are reported from Iran for the first time.

In this survey, the effect of temperature on the rate and trend of macroconidium germination of Fusarium graminearum on water agar was studied and as a result, suitable models for describing this phenomenon were obtained. Germination rate was studied using 12 models. Among these models the linear model, as the simplest one, with Logarithmic transformation of the percentage of spore germination with equation Log (g)=Log (go)+rgt selected for further modeling procedure. In this model g is the percentage of spore germination, t, time, g0, y-intercept and rg, the germination rate. The parameters of this model were estimated using linear regression analysis. Accordingly, the germination rate (rg) at 5, 10, 15, 20, 25 and 30 C were 0.082, 0.94, 0.95, 0.59, 0.35 and 0.35, respectively. The calculated R2 for above mentioned parameters were 44.31, 52.42, 56.29, 45.17, 44.82 and 40.22, respectively. Regression analysis was performed to estimate correlation between rate of germination as dependent variable and temperature variable (T) as independent variable. On the basis of these analysis a quadratic function (rg=b0+b1T+b2T2) and a polynomial function (rg=b0+b1T+b2T2+b3 (T-15)+b4 (T-15)2) were selected. The estimated parameters of quadratic function were as follow: b0=0.085, b1=0.001 and b2=-0.0001. Using nonlinear regression these parameters for polynomial function were estimated as b0=-7.308, b1=-0.530, b2=0.068, b3=0.66271 and b4=-1.518. The coefficients of determination for quadratic and polynomial function were 82.61% and 82.60%, respectively. The Durbin-Watson Statistic was about 2 for both models, which showed a good fitness in describing the trend of germination rate of macroconedia. In addition, comparison of observed and predicted germination curves supported this analysis. This marks the first finding on modling germination rate as influenced by temperature in this species.

During 1998-1999 samples from root of winter wheat in different region of Fars province were collected and rhizosphere fluorescent Pseudomonads were isolated. The isolates were identified as P. sedomonas fluorescens biotype I. P. fluorescens biotype II,P. fluorescens biotype III, P. fluorescens biotype IV, P. fluorescens biotype V, P. aerofacians, P. aeroginosa, P. cichorii, P. putida, P. syringae and P. viridiflava. Bacterial strains which exhibited high activities in the preliminary antagonistic tests against -Geotrichum sp. Were used for further antagonistic studies against wheat root pathogenic Fusarium species isolated from wheat rhizosphere in Fars province. Successful isolates in the later antagonistic tests were used against Fusarium culmorum in antagonistic in situ tests in rhizosphere. The results showed that 75% of the strains had antagonistic activities against Geotrichum sp. Index isolate. All the antagonistic strains produced siderophore while only 33% produced antibiotics. All the antagonistic strains caused inhibition zone in vitro against root rot Fusaria, although the rates of antagonistic activities were different among various strains. Strains E50 of P. fluorescens biotype V, K172 of P. aeroginosa and S200 of P. syringae were the most promising strains against wheat root rot Fusaria. The reasons, none of the bacterial isolates achieved in in situ tests against F. culmorum, were discussed.

Curly top disease (CID) is one of the most economically important diseases of sugar beet (Beta vulgaris L.) in Iran. Resistant varieties have been used effectively for controlling CTD. In the present study, 50 accessions of sugar beet germplasm were evaluated for curly top resistance. A sugar beet plant with typical symptoms of CTD was selected in Zarghan (Fars Province) and used as a source of beet curly top virus (BCTV) in inoculation experiments. Twenty one seedlings of each accsession were tested. Two young viruliferous leafhoppers (Circulifer haematoceps) were caged on each plant at two-leaf stage and allowed to feed for 5 days. The plants were rated for severity of curly top symptoms four and eight weeks after inoculation. Each inoculated plant was graded using a 0-5 scale (0, plants free of symptoms; 5, plants dying). Mean value of disease severity index (DSI) was computed for each accession tested. DSI values varied from 1.25 to 3.8. DSI range in 21, 22 and 7 accessions was 3 - 3.8, 2 - 3 and less than 2, respectively. F-20511, 16402-66, 13687-62, F-20510 and 13691-62 with DSI 1.25, 1.35, 1.5, 1.55 and 1.65, respectively, were considered the most resistant accessions and are recommended for further research in the field and incorporation in breeding programs. In most cases, DSI recorded after eight weeks was less than that recorded after four weeks, indicating general recovery tendency in some genetic materials. The rate of recovery varied among accessions and its possibility for selection program must be studied further.

The life cycle of Pileolaria terebinthi the causal agent of Beneh (Pistada mutica) rust was investigated under Fars natural conditions and greenhouse. In both conditions the basidiospores caused infection on Pistacia species and formed all developmental stages including spormogonium, uredinoid aecium, uredium and telium. Teliospores on leaves on forest floor considered to be the main survival propagules under natural conditions. Uredinospores and dikaryotic hyphae in infected branches could not overwinter. Overwintered teliospores germinated and released basidiospores in late winter or early spring. The first disease symptom was observed in late March forming numerous spormogonia on deformed leavers and petiols followed by the formation of uredinoid aecium and uredium. Telium was found in late season. In Fars condition, secondary infection by urediospores occurred infrequently, and most infection were due to basidiospores in early spring. All Pistada species and commercial P. vera cultivars were susceptible to the pathogen.

During 2002- 2004 and early 2004 samples of potato tubers showing common scab symptoms and the related soils were collected from fields at different area from Fars province. A total of70 Streptomyces strains were isolated from potato scab lesions and soil. Strains were identified based on morphological, physiological and biochemical characteristics and were classified into six distinct groups. Thirty five representative strains were tested for pathogenicity on potato tubers and radish seedlings. Strains of group 1 were identical to the reference strain of S. scabies. Strains of group 2 were similar to S. scabies in respect to some morphological characteristics and differed in several biochemical characters. Most of the strains of group 3 were similar to S. acidiscabies and a small number of strains were similar to S. griseus in some morphological and biochemical characteristics. Characteristics of the strains of group 4 were similar to S. turgidiscabies, but differed in some physiological and biochemical characteristics. The morphological and physiological characteristics of the strains of group 5 that were isolated from superficial scab symptoms (russet and netted scab) were similar to S. aureofaciens and S. reticuliscabies and differed from those of described scab pathogens, such as S. scabies, S. turgidiscabies and S. acidiscabies Strains of group 6 in morphological and some biochemical characters were similar to S. acidiscabies, but differed in several biochemical tests. Also polymerase chain reaction (PCR) were used for detection of necl gene that is present in most pathogenic strains of S. scabies, S. acidiscabies and S. turgidiscabies. The predicted 700bp PCR products for the coding sequences of necl gene were obtained from reference strain of S. scabies (positive control) and some strains of group 1, 3, and 4 that were induced lesions of common scab on potato tubers in greenhouse conditions. No PCR products were obtained from the non-pathogenic strains and pathogenic strains of group 2, 5, and 6. Therefore, necl gene was not found in non-pathogenic and some of pathogenic strains, but each of strains that had nee] gene, was shown to be pathogenic on potato tubers and radish seedlings. In electrophoresis patterns of the whole cell proteins differences and similarities were observed among strains of these six distinct groups which in some cases did not correspond with the phenotypic grouping.

During growing season 2002-2003 sesamum seeds were collected from plants showing yellowing and one side wilting in different parts of Fars province. The amount of seed transmission by Fusarium oxyporum f.sp. sesami was determined using direct seeding or culture media. One hundred seeds were randomly selected and surface sterilized for 1.5 and 3 minutes in 0.5% sodium hypochlorite, blotted, cultured on PDA medium and incubated at 25˚C with 12h photoperiod. Growing colonies originated from seeds were purified, identified and proved pathogenicity on sesame seedlings. Seed samples from different locations were also used for bioassays. Seeds were surface sterilized for l.5min with 0.5% sodium hypochlorite and grown in sterilized sand and incubated at 29˚C with 16h photo period. The pathogen was recovered from wilted or dead plants. The amount of seed transmission by F. oxysporum f. sp. sesame was found to be 1.25-12.1 and 14.3-23.47% respectively in agar and sand method. The results indicated that systemically infected sesame plants could transmit the pathogen through seeds. This is believed to be the main source of distribution of the pathogen in the country. Use of certified seeds is considered to be an important method to manage the disease.

Antibiotic production by fluorescent pseudomonad isolates used against Sclerotinia sclerotiorum, the causal agent of sunflower root rot was examined using HPLC method. Of 25 isolates tested three isolates, B111, B112 and B119 produced antibiotics. B112 and Bl19 produced diacetylphloroglucinol (DAPG), monoacetylphloroglucinol (MAPG) and pyoluteorin (P1t). B111 produced phenazine (PCN). Also B112 and B119 produced salicylic acid (SA) in KB and MA media.Effect of environmental factors on antibiotic production showed that B112 and B119 produced DAPG only in YMP medium increasing until 96 hours after incubation. Also B112, and B119 produced monoacetylphloroglucinol only in YMP, but the production level decreased as time progressed. B112 and B119 produced pyoluteorin (p1t), only in KB medium. The production of P1t increased until 76 hours and then decreased. B111 produced phenazine (PCN) in KB and YMP. The level of PCN in YMP was higher compared with that on KB medium. The level of PCN increased up to 96 hours post-incubation.

Despite severe damage of witches' broom disease of lime (WBDL) and its apparent natural spread in affected groves, vector of its associated phytoplasma has remained undetermined. The aim of the present investigation was to study various insects for their possible involvement in transmission of this phytoplasma. Piercing-sucking insects were collected by sweep net in infected lime groves in different seasons in 2003 and 2004. Samplings were carried out in affected lime groves in Hormozgan and Kerman Provinces. Nested PCR followed by RFLP or cloning and sequencing were used for detection and identification of phytoplasmas in insect bodies. Results of this study revealed that the 16s rRNA gene of WBDL phytoplasma is detectable in leafhopper species Hishimonus phycitis, Recilia schmidtgeni and Idioscopus clypealis and in citrus psylla, Diaphorina citri. Further studies indicated that Candidatus Phytoplasma aurantifolia persists in the body of H. phycitis and D. citri for several weeks after feeding on healthy lime seedlings. Partial sequence of a phytoplasmal 16s rRNA gene similar to that of WBDL phytoplasma was detectable in the head and salivary glands and in the sucrose solution used as feeding medium for Hishimonus phycitis. H. phycitis and D. citri were the only piercing-sucking insects collected on lime trees.

In order to identify the plant parasitic nematodes associated with sugar beet fields in Hamadan province and determining their distribution, 83 soil samples collected Horn different locations, during summer and autumn of 1999. Nematodes were extracted by the centrifugal-flotation method, killed, fixed, and processed to anhydrous glycerin. The nematodes were mounted on slides and studied by light microscope. In this survey, 37 known species belonging to 19 genera of order Tylenchida were identified and their distributions were determined. Results of this survey showed that the most of these species belong to the family of Tylenchidae, which are not economically important. Pratylenchus neglectus, Filenchus vulgaris and Aphelenchus avenae were found in 54.8, 51.2 and 42.9 percent of samples, respectively, and they were the most abundant species in the sugar beet fields of the province.

During growing seasons 2001 and 2002, 53 isolates of Fusarium solani f. sp. pisi wer collected from chickpea and weeds growing in chickpea fields in Fars province ( Shiraz, Ghir and Karsin, Mamasani, Fasa, Khafr, Neyriz, Estahban, Zafarabad, Sepidan, Firouzabad, Kavar, Bavanat, Abadeh and Eghlid). Vegatative compatibility groups (VCGs) of the isolates were determined using nitrate non utilizing mutants method Nit mutants were generated using Czapek Dox Agar (CDA), Potato Dextrose Agar (PDA) and Minimal Medium (MM) supplemented with %7 KCLO3 which resulted in nit mutant formation 84.21, 73.53 and 68.57% respectively. Finally 476 nit mutants recovered from CDA supplemented with 7% KCL03. Nit mutants subcaltured on Basal Medium (BS) supplemented with one of the sodium nitrate, sodium nitrite, hypoxantine and amonium tartarate and classified as nit1, nit3 and NitM with the frequencies of 60.71, 24.79, and 14.5% respectively. Complementation tests with nit mutants divided 53 isolates of Fsp, in to 11 VCGs. VCGl with 25 isolates was the largest and VCG11 with one isolate was the smallest group. In VCG5 (isolates of Bavanat) there was a positive relationship in respect to geographical distribution, disease severity and VCGs. While in VCG7 (isolates of Zafarabad) there was a positive relationship between VCGs and geographical distribution. There was no relationship among VCGs, geographical distribution and disease severity of the other isolates.