IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2002 | Volume:38 | Issue:1-2|Papers Count:14

Brown blotch of cultivated mushroom (Agaricus bispoms) has become a major and widespread disease of the crop in mushroom growing facilities throughout Iran. Disease symptoms, as brown, sunken lesions and blotches appear on pilei and stipes in all stages of mushroom growth, during shipment and in the retail market. In severely affected mushrooms and under favorable conditions, the lesions enlarge coalesce and encompass the entire surface of the caps. The rotted mushrooms assume a slimy appearance. A fluorescent oxidase and arginine dihyolrdase positive pseudomonad was isolated from the diseased mushrooms. The identity of the strains as Pseudomonas tolaasii was verified through phenotypic characterization, proof of pathogen city and the white-line reaction with pseudomonas reactans. The strains differed in virulence and were placed in four virulence groups.

Bacterial blight of walnut caused of Xantomonas arbor cola pv. Jug landis is widespread throughout the central and northern provinces of Iran. To evaluate the heterogeneity of the strains in various regions of the country, 48 strains of the causal bacterium were isolated from diseased leaves, twigs and shells collected form Qazvin, Hamadan, Tehran, Markazi, Aradabil, Guilan, Mazandaran and Golestan provinces and were characterized. Strains appeared to be very similar in phenotypic features and in pathogen city. They reacted differently in tests for hydrolysis of starch, gelatin and casein, tolerance to NaCl and utilization of sorbitol and L-alanine. The electrophoretic profiles of cell proteins of the strains were very similar to each other and to that of a reference strains of X a. pv. juglandis. The results indicate that the strains causing bacterial blight of walnut in various regions of the country are fairly homogeneous and differ from each other in only a few phenotypic features.

The aim of the present study was to identify Trichoderma species isolated from Iran. Soil samples were collected from different parts of Iran focusing on the agricultural fields. Trichoderma selective media and malt extract agar (MEA) were used to isolate Trichoderma species from the soil samples. Petri plates were incubated at 25°C in the dark for the first 24 hours and then 12/12 (dark/flourescent light) at the same temperature. All the cultures were purified on 2% water agar by hyphal tip method prior to morphological examination. Morphological observations were carried out on the cultures grown on 2% MEA at 20oC under ambient laboratory conditions. Microscopic features of conidiophores and shape and size of conidia were studied and recorded 3-5 days after inoculation. Out of 350 obtained isolates, using morphological features ten species (T. citrinoviride Fig.1, T. longibrachiatum, Fig. 2, T. satumisporum Fig. 3, T. hamatum, Fig. 4, T. harzianum, Fig. 5, T. inhamatum, Fig. 6, T. tomentosum, Fig. 7. T. virens, Fig. 8, T. asperellum, Fig. 9 & T. koningii, Fig. 10) were identified. Among the species T. harzianum with 150 and T. virens with 57 isolates were the most frequent species.

During 1996-99 wheat spikes with symptoms of gummy spike blight were collected from several wheat growing provinces of Iran. Kernels were triturated in distilled water and the suspensions were streaked onto plates of yeast extract and sucrose nutrient agar. Yellow-pigmented strains were selected and their phenotypic characteristics and electrophoretic profiles of cell proteins were determined. Results indicated that Rathayibacter iranicus was distributed in East Azarbayejan, Ealam and Kuhkilouyeh and Boyer-Ahmad and R. tritid was prevalent in Golestan, Khuzistan and Sistan and Bluchistan provinces. Both species were present in Isfahan but in separate wheat growing areas. Some heterogeneities in phenotypic features and electrophoretic profile of cell proteins among R. iranicus strains were observed.

To study the role of Pythium species associated with wheat root and crown rot during two growing seasons 1995-1996 diseased samples were collected from different irrigated wheat fields in Fars province including Maharloo, Marvdasht, Firoozabad, Kavar, Estahban, Neiriz, Fassa, Darab, Borazjan, Kazeroon and Badjgah. Decaying root and crown segments (5mm) were washed and plated on CMA containing Delvocid (50% pimaricin), ampicillin, rifampicin, benomyl and PCNB. Of 17 isolates recoverd from various parts of the province, based on morphological characters, the following Pythium species were identifield: P. aristospornm, P. ultimum var. ultium P. ultimum var. ultimum, P. periplocum, P. heterothallicum, Pythium G. "F".Pathogenicity tests were carried out under greenhouse conditions using sterlized soil artificially infested with corn seed inoculum. Pre-and post-emergence damping-off and root and crown rot were evaluated. None of the isolates caused mortality of wheat seedlings and seed dacay was low in some isolates of Pythium G. "F". P. aristospornm and P. ultimum var. ultimum caused root and crown dacay. Isolates which caused root and crown rot in ascending order of pathogenicity were: Pythium G. "F", P. aristospornmand P. u. var. ultimum.

In recent years seeds, bulls, rhizomes and seedlings of ornamental plants have been imported accompanied by some important phytopathogenic agents. Phytophthora nicotianae van Breda de Hann was the causal agent of root, stem, bulb and, rhizome-like tuber rot of imported and home products of Rose, Lilium longiflorum, Dieffenbachia amonea, Peperomia obtusifolia, Alstroemeria hookeri. Mentioned above isolates of P. nicotianae were compared morphologically, physiologically, and isozymicaly. Colony morphology of the isolates on CMAwas dense or loose rosette, lanose, and intermediate between rosette or stellate and lanose. Chlamidospores were formed abundantly in Peperomia and Dieffenbachia isolates, spherical, 27.4-34.3 µm in diameter. Sporangia were produced abundantly in liquidand solid cultures singlyor in a loose sympodium on long stalk predominantly sphaerical and ovoid with a prominent papilla, 34.5-54.04 longx27.2-38.2µm wide (average), with length, breadth ration 1.24-1.43, noncaducous, Diffenbachia isolates produced sporangia often attached to sporangiophore laterally and a few sphaerical sporangia had two papillae. Most isolates were heterothallic but Peperomia isolates produced oogonia and oospores when paired with either Al or A2 mating type of P. nicotianae. Antheridia were amphigynous and sphaerical, 13.3xI1.6µmin diameter. Oogonia were smoth and sphaerical,29.2µ,m in diameter. Oospores were sphaerical, aplerotic, pale yellow when matured, 23.6µm in diameter. The minimumtemperature for growthwas less than 10"C,the optimum was 29-33°C,most isolatesexcept Diffenbachiaones grownwellat 35°C. The electrophoretic estrase patterns for all isolates were similar using protein polyacrilamid gel electrophoresis. In pathogenicity tests allP. nicotianae isolates were founded to be pathogenic on their hosts. The isolates were reisolated from infected plants.

In order to evaluate competitive ability of soybean with weeds, in 1999-2000 an experiment was conducted in Karaj weed experimental station in a randomized complet block design with 5 treatments [Red root pigweed, Velvetleaf, barnyargrass and common lambs quarters] plus control (soybean without weed) and 4 replications per treatment. Results of analysis of variance indicated significant difference between weed treatments. So that soybean yield, number of pods per plant, number of branches, chlorophyll content in soybean leaves and percentage of radiation interpenetration within soybean canopy varied under different treatments. Velvetleaf, red root pigweed, barnyard grass and common lambs quarters had respectively the most negative effects on soybean yield.

Pistachio nut (Pistacia vera) is a major nut crop in Iran and gummosis is one of the crps most serious diseases, diseased trees exuding gum from the crown and lower parts of the trunks of affected trees often die irom root and crown rot. Several species of Phytophthora have been isolated from affected trees, but the principal causes of gummosis in Kerman province, the mjor pistachio-producing region in Iran, are two non-papilIate species. To date one has been described as P. megasperma and the other asP. drechsleri based on their morphological and physiologicalfactros. A technique based on the polymerase chain reaction(PCR) for the specificdetectionof the two main gummosis-causing Phytophthoraspecieswas developedusingthe nucleotide sequence of ITS I and ITS2 (internally transcribed spacer regions) of their genomic ribosomal RNA gene repeat (rDNA). DNA sequence from the ITS regions of the pistachio P. megasperma isolates were used to develop a pair of oligonucleotide primers, pisl fwd and pisl rev. These amplified a specific fragment within ITS I and ITS2 of the all 24 isolates of P. megasperma from pistachio. In further tests of specificity, the primers also generated an amplicon of the same size wiht DNA of Phytophthora sojae, P. melonis, P. sinensis, P. cajani, as well as P. drechsleri isolates from pistachio. In fact the isolates. from pistachion ascribed to P. megasperma and P. drechsleri siolates, have been shown to belong to a previously undescribed species and to P. melonis, respectively. Together with all the aforementioned species, they form a tight clade within Phytophthora. No other Phytphthora species outside this ciade was amplified with pisl fwd and pisl rev. Amplification was highly sensitive with as little as 4 ng template DNA being detected in each case. PCR amplification also detected both Phytophthora species, that cause gummosis in in feted roots of greenhouse-grown pistachio plants. Nested PCR with primers DC6 and ITS4, followed by the PIS 1 fwd and PIS 1 rev primers, gave clear products in every case with roots giving positive signals, in both symptomatic and asymptomatic infected plants. Digestion with Bsli of ITS amplicons (710bp) from the pistachio P. megasperma isolates, created two fragments 370 and 310 bp long. These matched the two unique restriction sites within the sequence of the amplicon but were different from RFLPs generated by the same enzyme in the amplicon of P. sojae, P. melonis, P. sinensis, P. cajani. Use of the Bsl/ restriction enzyme discriminated between the two major gummosis inciting agents and distinguished them from the closely related P. sojae, P. melonis, P. sinensis, P. cajani.

Wheat Eqlid mosaic virus (WEqMV) induces mosaic, streaks, and stripes on leaves and reduction of growth in wheat in the Eqlid region of Fars. About 30% of mosaic symptoms in wheat in this region is due to WEqMV. Setaria viridis, Secale cereale, Bromus sterlis and Echinochloa colona were found to be other natural hosts of WEqMV in the area and showed mosaic symptoms.Barley, rye, maize, sorghum, oat, 30 other gramineous species and seven dicotyledonous plants were mechanically inoculated with the virus under greenhouse conditions. Only barley and rye showed mosaic symptoms and together with symptom less Hordeum morinum were ELISA positivefor WEqMV. Eleven varieties of common wheat, a durum wheat and Triticum turgidum were evaluated for their sensitivity to. Mechanical inoculation with WEqMV. There were significant differences among varieties of common wheat in the rate of infection and ELISA values of their crude sap. Darab variety of bread wheat and T. turgidum showed maximum and minimum infection rates, while Marvdasht and Omid varieties had maximum and minimum ELlS A values, respectively. In a search for WEqMV vector, no indication of Polymyxa graminis was found when 221 roots of field collected wheat with mosaic symptoms (including 67 samples of ELlSA positive for WEqMV) were examined under microscope. Wheat seeds planted adjacent to infected plants or soil samples from infected field did not develop into diseased plants. A ceria tulipae (wheat curl mite), A ceria sp. (Eriophyes sp.) (Bermuda grass mite), and the aphids Sitobion avenae, Sipha maydis, Schizaphis graminum, Metopolophium dirhodum, Rhopalosiphum padi and Diuraphis noxia failed to transmit the virus under greenhouse conditions. Only the wheat root aphid Forda marginata was able to transmit the virus.

In peppers, inhibition of hrp mutant cells of Xanthomonas campestr is pv. vesicatoria (Xcv) within leaf intercellular spaces is associated with alterations of mesophyll cell wall and papilla deposition. Immunocytochemical and histochemical tests on the responding cells indicated that lignification occurred in the altered walls. The papillae also contained substantial amounts of lignin in addition to auto fluorescent phenolics and callose. Their progressive enlargement was associated with accumulation of hydrogen peroxide. Data on recovery of hrp mutant cells from inoculated leaves indicated that the bacteria not only failed to multiply, in planta but they also induced a bactericidal status in which the virulent Xcv cells failed to multiply. As a result, water-soaking symptom was prevented. The inhibition of the virulent cells was neither related to a secreted compound nor nutrient shortage. Observations on mesophyll cell reactions to a number of saprophytic and non-pathogenic bacteria showed the occurrence of similar structural alterations at interaction sites. It is suggested that the prime cause for non-pathogenicity of the examined bacteria was activation of non-specificdefensivestructures rather than their disability to survive within leaf intercellular spaces.

Use of crops of allelopathic potential for weed control is one of the important goals of integrated weed management and can reduce pesticide usage, protect environment, reduce crop production costs, and provide a sustainable agriculture system. Newly germinated seeds of ten Northern Iranian rice varieties were allowed to grow for a week and then mix-cultured with barnyard grass (Echinochloa crus-galli L.) P. Beauv. and umbrella sedge (Cyperus difformis L.) seedlings in pots containing sterilized paddy soil. The tested rice varieties included native Tarom-atri, Binam, Bejar, Dasht, Unda, Haraz, Neamat, and Lines 424 and 7165. The potted plants were allowed to grow under field conditions, weeds were harvested 10 days after being transplanted, and compared with control". The results indicatied a growth reduction of mix-cultured weeds with most of the rice varieties. The barnyard grass fresh weight reduction ranged from 42 to 72% compared with both control and barnyard grass mixed cultured with non-allelopathic rice (parallel control). The seedling lenght reduction of barnyard grass ranged from 31 to 55% and 23% compared with control and non allelopathic control, respectively. The umbrella sedge fresh weight reduction ranged from 30 to 52% compared with control and 47 to 63% compared with umbrella sedge mix-culturednon-allelopathicrice control and its seedling length reduction ranged from 31 to 55% and 25-52% compared with control and non-allelopathic control, respectively. In general, Tarom-atri, Neamat and Dasht cultivars are recognized as the cultivars which have the highest allelopathic