IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2007 | Volume:43 | Issue:2 (170)|Papers Count:12

  Stem and tubers of potato (Solanum tuberosum.L) whith black leg or soft rot symptoms were collected from differnet areas in Fars province in 1995 and 1996. Pectolyic Erwinias were isolated from the samples and their phenotypic charateristics in 100 biochemical and physiological tests, were determined. Strains were placed into four phenotypically heterogeneous groups. Members of two groups were identified as Pectobacterium carotovorum subsp. carotovorum(Pcc),and P.atrosepticum(Pa). Strains forming the other phenotypic groups had features not common to any known species or subspecies. These strains appeared to be unique for their reaction in some key tests and were among the key features on which basis differentiation into four phena was laid. Pair - wise comparison of the strains were performed through calculation of simple matching coefficient. The third and the fourth phena were closer to Pcc and Pa. at 84% and 74% similaity levels, respectively. The protein electrophoretic patterns in phena were not similar, and showed some variations. The patterns were not similar to known strains of Pcc (from Iris) and Dc ( a strain form maize).

For detection and identification of the causal agents of potato blackleg in Isfahan, the potato fields were surveyed during 2003-2004 growing seasons. Fifty four strains of Pectobacterium and Dickeya were isolated from the diseased stems and tubers. According to their biochemical and physiological test results, 43 isolates were identified as D. chrysanthemi. The remaining 11 isolates were placed in the second group which were identical with P. carotovorum subsp. carotovorum in biochemical characteristics. None of the isolates appeared to be P. atrosepticum. The results were confirmed by polymerase chain reaction technique using the recommended specific primer sets. Use of G1/L1 primer pair made it possible to detect Pa, Pcc and Dch in one PCR reaction. By using this primer set, the ITS regions of the bacteria were amplified. On the basis of the banding patterns obtained with G1/L1 the isolates were placed in three groups. The first group of ITS- PCR comprised only the standard isolate Eca SCRI1043. Isolates which were identified as Pcc by biochemical tests were placed in the second group and the third group included isolates that were identified as Dch on the basis of their biochemical and physiological characteristics. Results of the present study indicate that Pcc and Dch are the predominant causal agents of potato blackleg and soft rot in Isfahan.

Distribution of Phytophthora species the casual agents of walnut root and crown rot was investigated in Kerman, Kohgilueh -and- Boyrahmad and Fars Provinces. Of 33 isolates of Phytophthora recovered 18 were identified as P. citicola that were isolated from crown, basal stem and root in Eghleed, Khaneh Zenyan, Yasuj and from crown in Sepidan. The sporangia were ovoid to spherical, pyriform, with 1 , 2 or occasionally with 3 prominent papilla, noncaducous with average dimension of 51.69 31.59 μm. The optimum temperature for growth was 25 °C. Twelve isolates were identified as P. citrophthora which were isolated from crown and basal stem in Bafte Kerman, Khabr. Rabor and Goohar (Kerman Province), Gian, Sorian, Seamakan and Asemi (Bavanat) and from crown and root in Shiraz. Sporangia were ovoid to spherical, pyriform, with 1 or 2 prominent papilla, noncaducous with average dimension of 55.18 × 29.6μm. The optimum temperature for growth was 25°C. Three isolates were identified as P. cactorum that were isolated from soil around declining walnut trees in Marvdasht by safflower seedlings method. The sporangia were ovoid to spherical, pyriform with one prominent papilla, caducous with average dimensions of 27.13 × 23.66μm. The optimum temperature for growth was 25 °C. Pathogenicity test of the isolates was carried out on detached walnut branches. In all cases P. citricola was more pathogenic and aggressive than P. citrophthora and P. cactorum.The reaction of crown and root of 8-month-old Juglans regia cultivars Sayed Hosseini, Ghlami, Sultan Ebrahim, Klaghi, Khooshaee, Reez Yasuj, B6SH10, OR33 T2. Hajmirza Khan, poost kaghazi, G4, G7, G2 and wingnut (Pterocarya fraxinifolia) to a more virulent isolats of P. citricola, P. citrophthora and P. cactorum was evaluated under greenhouse conditions. The inoculum was obtained on vermiculite-hemp seed extract and positioned around either crown or root systems. Percent dead seedlings and crown and root colonization, disease progress, plant height and dry weight of root and foliage were evaluated. Comparative percent dead seedlings and crown and root colonization and disease progress showed that all J.regia cultivars were infected with the pathogen but Sayed Hosseini was the most susceptible cultivar. Pterocarya fraxinifolia showed immune response to Phytophthora species.

Seven clones of Rhopalosiphum padi from different regions in Iran were tested for their efficiency of transmitting four isolates of barley yellow dwarf virus-PAV (BYDV-PAV). After acquiring the virus, aphids of each clone- virus isolate combination were caged on 35 oat seedlings using 3 fourth instar larvae per seedling. The inoculated and control plants were assayed by ELISA and assessed visually to determine the rate of transmission and the mean ELISA value for each treatment. It was found that all clones of R. padi were able to transmit various BYDV-PAV isolates, though with different efficiencies. A positive correlation was found between the rate of transmission and the mean absorbance value. Aphid clones differed in their efficiency of transmission of virus isolates. On the other hand, any single clone transmitted different virus isolates with varying efficiencies. Each aphid clone transmitted its sympatric virus isolate at highest rate. In general Shahre Kord and Dashtak clones of aphids showed highest efficiency of transmission and Dashtak isolate of virus was transmitted more than other isolates.

In order to study taxonomy of the genus Mesocriconema in Iran, 250 soil and root samples were collected from different field crops, orchards, forests and pastures in Iran, during 2004-2005 years. The nematode specimens were extracted from the soil by using the centrifugal-flotation technique and were processed to glycerin by modified Se inhorst method. The extracted nematodes were mounted in permanent slides. In this study nine species of this genus, M. ornatum, M. curvatum, M. dherdei, M. antipolitanum, M. solivagum, M. sphaerocephalum, M. pseudosolivagum,M. rusticum and M. xenoplax were identified. M. dherdei, M. pseudosolivagum and M. rusticum are new records for Iran. The first two species were isolated from soil samples around the root of ash tree in Garedagh forest (Kaleibar) and the latter species was isolated from soil samples collected from rhizospheres of grass in Saee park (Tehran). A key for identification of species of the genus Mesocriconema in Iran is also provided.

During 2005-2006 effect of environmental conditions on ascospores discharge of Polystigma amygdalinum ,the causal agent of almond leaf blotch, and time of spraying to manage the disease was investigated in Chahar Mahal va Bakhtiari province. Two infected almond orchards of cultivar Mamaee were selected along Zayande-Rood (Emamea) and Ardal (Rostam-Abad). Ascospore discharge was monitored using slide traps and 2-year-old Mamaee almond seedlings a cultivar susceptible to the pathogen. Bordeaux mixture at the rate of 1.5% was used at different intervals (twelve treatments) based on phenology of the host (time after petal fall). The results of two years of experiment showed that the earliest disease symptoms appeared as small pale leaf spots five to six weeks after ascospore discharge. Based on the appearance of disease symptoms under natural and greenhouse conditions the incubation period was estimated about to be 40-45 and 35-40 days respectively. The peak of ascospore discharge was 2-3 weeks after petal fall and was dependent on rain fall. Two applications of Bordeaux mixture at 2 and 4 weeks after petal fall was found to be the most efficient control treatment in both years and both locations. A single spray two weeks after petal fall also reduced the disease significantly.

Lettuce virus X (LeVX) was recently described as a new potexvirus infecting lettuce plants in Iran. The response of five lettuce cultivars, differing in their reaction to Lettuce mosaic virus (LMV) to single and double infection with LeVX and LMV was investigated. No resistance was observed against LeVX in tested cultivars while infection was without significant symptoms. Mixed inoculation of LMV-resistant cultivars (Floribibb, Salinas 88 and Mantilia) resulted in LeVX infection but did not affect their resistance status to LMV. Double infection with LMV and LeVX was established by mechanical inoculation in some of inoculated Trocadéro and Salinas (LMV susceptible cultivars) plants. In all doubly infected plants of both cultivars, more severe symptoms were developed in comparison to singly infected plants, with Trocadéro being more severely affected than Salinas. While LeVX concentration increased in doubly infected plants of both cultivars, LMV concentration showed a decrease in doubly infected compared to singly infected Trocadéro cultivar as determined by ELISA. The accumulation of LeVX (+) RNA level enhanced slightly in doubly infected Trocadéro, but did not vary in doubly infected Salinas plants compared with singly infected ones. Interestingly, LeVX CP accumulated in the same level in doubly and singly infected plants of both cultivars, LMV CP level showed a decrease in doubly infected plants of both cultivars as determined by western blot. These results suggest a synergic relationship between LMV and LeVX only in Trocadéro but not Salinas cultivar of lettuce.

Fusarium wilt of tomato (Lycopersicum esculentum Mill.) is caused by Fusarium oxysporum f.sp. lycopersici is an economically important disease in tomato both in fields and commercial glasshouse. The causal agent is a soil-borne pathogen, and the management of Fusarium wilt is mainly through chemical soil fumigation. In this research the effect of Basamid granulate (Dazomet 98%) at different concentrations (200, 266, 333 gr/m3) were tested In vitro and In vivo for their ability in order to control Fusarium wilt of tomato. Treatments were analyzed by program of MSTATC. The results indicate that if granulate basamid is used at the rate of 333 g/m3, complete death of pathogen in soil and in plant is observed. Also results show that fumigation and application of Dazomet is cheaper, easier, and safe. It is an acceptable alternative for the replacement of methyl bromide fumigation to control Fusarium wilt of tomato.

Brown to brownish purple spots and blotches were observed on the foliage of narcissus in an ancient narcissus orchard in Behbahan, KHUZISTAN province. Surveys during 2002- 2004 showed that disease symptoms first appeared as small pale yellow spots at the end of fall, late Nov. & early December. Maximum infection and disease symptoms occurred by mid-winter(Table 1), when the foliage and specially stem bases showed large purplish, irregular spots. Microscopic observation of cross sections made from symptomatic tissues revealed the presence of yellowish brown masses of resting sporangia and fine rhizomycelium embedded in the diseased tissue. The sporangia were spherical to sub-spherical smoothwalled with small depressions on the surface as if pitted and measured 16-24 μm in diameter. Attempts to germinate freshly collected current season`s resting sporangia failed, indicating that the fungus requires overwintering or rather a period of maturation. Good germination of resting spores was obtained when spore suspensions prepared by blending of previous year,s diseased tissue were kept in refrigerator (6-9 C°) for a few days or up to one month and then transferred to room temperature and exposed to illumination. The sporangia have circular cap (operculum) that was discharged to release zoospores after exposure to low temperature. Based on the morphological features of the resting sporangia and the rhizomycelium with turbinate cells, the causal agent of the disease was identified as Physoderma narcissi (G. Poirrault) Sacc. & Trotter (Chytridiomycota). According to the literature this disease has been reported previously only once from France in 1915 (Poirrault, 1915). Specimens of diseased plants are kept under accession No. of "IRAN 2031 F" at the herbarium of Ministry of Agriculture (Jehad e Keshavarzi) Iranian Research Institute of Plant Protection.