Antifungal activity of Cymbopogon parkeri stapf. essential oil on some important phytopathogenic fungi.

The genus Cymbopogon that belongs to the Poaceae (Graminae) has some important aromatic species whit remarkable commercial value. Essential oils from different species of the Cymbopogon are used in the perfumery, cosmetic and soap industries and some of them have antifungal and insecticide activity. In this study, antifungal activity of C. parkeri essential oil on the growth of Rhizoctonia solani, Pyricularia orizea and Fusarium oxysporum, three important phytopathogenic fungi, was investigated. The essential oil was extracted from the air-dried parts in flowering stage by hydrodistillation in a Clevenger type apparatus, and Growth inhibition of Rhizoctonia solani, Pyricularia orizea, Fusarium oxysporum for 15, 30, 75,150, 300 and 600 microl L(-1) dosage of the essential oil in PDA was examined in vitro by media mixed method and was compared with control. Antifungal activity was determined in terms of growth inhibitory concentration for 50% growth inhibitory (EC50 microI L(-1)) and inhibition percentage of some dosages was obtained. The results showed that concentration of 600 microl L(-1) of the essential oil completely inhibits the growth of all tested fungi. EC50 for Rhizoctonia solani, Pyricularia orizea, Fusarium oxysporum were counted 39.82, 72.00 and 43.63 microl L(-1) respectively. The results indicated that the essential oil has strong fungi state activity.

Wheat Fusarium head blight and identification of dominant species in Moghan area, Iran.

In order to identify of head blight agents in Moghan area and determine predominant species, totally 60 samples from affected wheat heads of Atila 4, Zagros, Goadloop, Izen green and Gasquine cultivars that cultivated during 2004-2005, were collected from randomly selected commercial wheat fields in Moghan. Twenty randomly selected kernels and glumes from each sample were surface sterilized and were planted on synthesized nutrient agar medium (SNA), potato dextrose agar (PDA) and Nash-Snyder medium (NA) plates. Culture plates were incubated at 22 to 25 C with a 12-h photoperiod provided by fluorescent and ultra violet lights. For the species identification, cultures were incubated for 5 to 15 days on PDA plates to induce sporulation under light and temperature previously described. Single conidial isolates were obtained by spreading a conidial suspension across a water agar culture plate and transferring a single germinated conidium to a new PDA culture plates. Single spore cultures were grown on Carnation leaf agar (CLA) for spore morphology assessment and on PDA for color assessment. All species were identified based on descriptions given in Burgess et. al. and Nelson et al. The results indicated that in addition Fusarium graminearum and F. culmorum were identified as wheat FHB agents in Moghan area and F. graminearum was dominant species in Moghan area. Also severe infection was determined in Atila 4 cultivar by F. graminearum.

Identification of prevalent potyvirus on maize and johnsongrass in corn fields of Tehran province of Iran and a study on some of its properties.

During a growing season in 2004, 231 leaf samples of virus infected and mosaic and dwarf mosaic symptoms showing maize (Zea mays L.) plants and 258 leaf samples of mosaic showing johnsongrass (Sorghum halepens L.) plants from various corn fields in Tehran province were collected. Serological tests of DAS-ELISA and DIBA were performed on samples using antisera of sugarcane mosaic virus (SCMV), maize dwarf mosaic virus (MDMV), sorghum mosaic virus (SrMV) and johnsongrasss mosaic virus (JGMV). In both tests performed on leaf samples extractions, all samples reacted strongly with SCMV antiserum and no reaction was seen with other 3 potyviruses antisera. 0.1 M potassium phosphate buffer (pH = 7) containing 2% polyvinyl pyrrolidon (PVP) was used for mechanical inoculation and all isolates were inoculated and propagated on sweet corn cv. Pars 403 and grain sorghum cv. Kimia. In serological tests on the inoculated plants samples also only SCMV was detected. Purification of virus was done using a modified "minipurification" method and the concentration of purified virus was 11.45 mg/ml and ratio of A260/280 = 1.2 was calculated for it. Electron microscopic study using ISEM and decoration method with SCMV antiserum revealed filamentous flexuous particles of SCMV. In SDS-polyachrylamide gel electrophoresis and Western blot test using SCMV antiserum that were performed on infected samples and purified viruses, the molecular weight of the virus coat protein was approximately 37-38 KDa and a difference among the CP weights of various SCMV isolates was not found. Reverse transcription-polymerase chain reaction (RT-PCR) was done using SCMV F3 and SCMV R3 primers and amplified fragments of approximately 900 bp in size were as in expected. The host range study with selected isolates of SCMV showed that the virus isolates were not transmitted by mechanical inoculation on Avena sativa, Panicum miliaceum, Setaria italica, Pennisetum americanum, Hordeum vulgare and Triticum aestivum. The isolates produced red-brown necrotic streaks on sudangrass (Sorghum sudanense) that lately changed in systemic necrosis. In host reaction studies on sorghum (Sorghum bicolor) cultivars, the virus isolates caused severe necrotic and killer reaction on sorghum cultivars Payam, Sepideh and Speed feed, but caused systemic mosaic and non-killer reaction on sorghum cultivars Kimia, KFS2, KFS3 and Jumbo. The present study showed that SCMV is the prevalent potyvirus and the main causal agent of mosaic and dwarf mosaic on maize plants in province. Since the virus is prevalent on johnsongrass plants in marginal areas of corn fields too, it seems that the origin of the virus on corn is from johnsongrass and the virus is a special strain of sugarcane mosaic virus that infects johnsongrass too.

A study about geographical distribution of root lesion nematode (Pratylenchus loosi, Loof 1960) in tea gardens at Guilan Province, Iran.

Root lesion nematode of tea (Pratylenchus loosi) is one of the most dangerous and distractive pests in all over areas in the world where tea grows. In Iran, this species was one of the quarantine pests that for first time it were separated from the Japan imported tea slips and reported by Maafi (1993). Nowadays it has been distributed in some tea growth areas of Guilan and Mazandaran provinces (North of Iran). In this study, geographical distribution of this pest is reported on some tea growth areas of Guilan province. In order to, 147 samples from root and soil around them were investigated. These samples were gathered from various gardens of Guilan province. They were transferred to nematology lab with suitable temperature and moisture conditions and were stored at 5-10 degrees C until extraction time. Centrifugal methods for nematode extraction from soil (Jenkins, 1964) and from root (Coolen & D'Herde, 1972) were used. The nematode was identified by Handoo & Golden (1989) and Frederick & Tarjan (1989) diagnostic keys. According to this study different infested areas and geographical distribution were detected in Guilan province. Results indicated that many important tea growth areas in Guilan were infested by this nematode. In addition, it seems that it has been distributed during short time.

Effects of inoculum density and substrate type on saprophytic survival of Phytophthora drechsleri, the causal agent of gummosis (crown and root rot) on pistachio in Rafsanjan, Iran.

In this study, sampling was carrid out on soils around pistachio trees in various regions of Rafsanjan, Iran. Following isolation and identification of Phytophthora isolates, the predominant species was found to be P. drechsleri and used for further investigation. For studying saprophytic survival of the fungus, soils collected from different areas were combined and autoclaved. Sterile soil was divided into 10 parts and mixed with fungal inoculum at various concentrations of 0-9% (w/w) separately. Each soil part (100g) was placed in 15cm diameter plastic pot. Some soils in pots were supplemented with sterile wheat straw whereas others were mixed with pistachio leaves surface sterilized with 5% (v/v) sodium hypochlorite. After 3, 6 and 9 weeks of incubation, five leaves or straws samples were taken from each replicate and cultured on CMA-PARPH medium and the fungal colony formation was monitored. The experiment was performed using completely randomized design with factorial experiments including three factors (substrate type, inoculum density and time), 10 treatments (0-9 g inoculum levels) and nine replicates. The results showed that the type of substrate (wheat straw and pistachio leaf) was very important for the fungal saprophytic survival in that this was significantly greater for the pistachio leaves. Time was also considered another critical factor for the fungal survival. With passing incubation time, saprophytic survival of the fungus declined. Further, it was demonstrated that increasing inoculum density would result in longer survivability of P. drechsleri and maximum fungal survival on substrate was obtained when inoculum density was at 9% (w/w).