IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2007 | Volume:43 | Issue:3 (171)|Papers Count:13

During 2004 to 2005 date palm regions in Fars province were surveyed and samples with symptoms of decline and spear, rachis, pinnea and bud rot, discoloration of leaves, vascular browning, and accumulation of bacterial slime in stalk were collected. A total of 40 strains were isolated from infected samples using EMB, CPG and YDC media. Strains were gram and oxidase negative, catalase positive and facultative anaerobs with green metallic colonies on EMB and cream-white colonies on CPG medium. The strains were identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) and Dicheya chrysanthemi on the basis of standard physiological, biochemical and nutritional properties. Representative strains were compared by physiological and biochemical characters, pathogenicity test, protein electrophoretic pattern and polymerase chain reaction (PCR). Protein electrophoretic pattern of the strains identified as P. carotovorum subsp. carotovorum were similar to a reference strain of Pcc. In PCR assay, 19 representative strains identified as P. carotovorum subsp. carotovorum produced predicted 550bp PCR products with EXPCCF/ EXPCCR primers but no PCR products were obtained from 3 strains identified as D. chrysanthemi with the primers.Artificial inoculation of one Pcc and one D. chrysanthemi strain to palm trees led to the formation of rot, tissue browning and cholorosis of leaves, although tissue maceration of green pepper was obvious in the most strains.

During growing seasons 2004-2006 samples of grapevine with esca symptoms were collected from different vineyards in Fars province including Abadeh (Djavadieh & Jannatabad), Eghlid, Bavanat (Soorian & Bavanat), Kavar (Akbarabad & Dashtak) & Shiraz.In this study 51 isolates were recovered & identified as Phaeomoniella chlamydospora, Phaeoacremonium aleophilum, Fusarium sp., Phoma sp., Phaeoacremonium sp. & Nattrassia sp. from wich Phaeoacremonium with 27 & Fusarium with 2 isolates had highest & lowest numbers of isolates. Pathogenesity test of P. aleophilum & Pm. chlamydospora was done under field & greenhouse conditions. Cutting inoculated in greenhouse showed leaf symptoms including midvein chlorosis which turned red after 9 months & eveatually partly become necrotic and defoliated. Under field conditions, P. aleophilum & Pm. chlamydospora caused wood discoloration beyond the inoculated points on the shoots & the pathogen was reisolated.

In order to identify Monilinia species, the causal agents of fruit brown rot in Guilan province, the present study was carried out during 2005 and 2006. Diseased samples were collected from rotting and mummified fruits and symptomatic twig and blossoms. Infected tissues were surface disinfested and placed on PDA. The fungal anamorphic characters including color and size of sporodochia, color, growth rate and margin of colony, type of sporulation, size of conidia on fruits and culture, type of conidial germination, number of germ tube and the distance of first branch to conidium were recorded for each isolate.Monilinia laxa from Prunus cerasus, P. domestica and P. persica and M. fructigena from Prunus cerasus, P. domestica, P. persica, Cydonia oblonga, Pyrus communis, Eryobotrya japonica and Mespilus germanica were identified. According to available literatures, P. ceracus is reported as a new host of M. laxa and P. ceracus, P. domestica, native pear (Khoj), Eriobotrya japonica and Mespilus germanica are reported as new hosts of M. fructigena in Iran. Also M. laxa is reported as new species for Guilan mycoflora.

Two DNA fragments of a Potato leafroll virus full-length cDNA which comprised parts of the PLRV ORF2 sequence were amplified by PCR. Both fragments were exactly the same except that they had the restriction sites for the enzymes XbaI and KpnI at the opposite ends.Therefore insertion of the two fragments into the same binary plasmid transformation vector would take place in the opposite orientations (sense or antisense). Using an Agrobacterium tumefaciens-mediated plant transformation procedure, leaf discs of Nicotiana tabacum were transformed with either of the fragments and regenerated into whole plants. Using PCR and RT-PCR, the transgenic plants that expressed mRNA transcripts of the transgenes were identified. Six lines of the plants transformed with sense and six lines of those transformed with antisense were crossed and the remaining was allowed to self-fertilise. The seeds obtained from these were grown to produce seedlings used in resistance tests. The resistance tests were done by aphid inoculation of seedlings with PLRV. Two weeks later the inoculated seedlings were tested for infection with PLRV by ELISA. Of the lines transgenic for sense and antisense only 28.5% and 23% were resistant to PLRV accumulation, respectively, whereas 50% of the lines obtained from crosses between sense and antisense plants were resistant. It seems that the simultaneous expression of sense plus antisense mRNA could have triggered post transcriptional gene silencing more effectively than expression of either sense or antisense mRNA alone.

Comparisons of nucleotide sequences of genes cloned from diverse plants for resistance to different pathogens indicate presence of conserved domains called resistance gene analogs (RGA) in these genes. Based on these conserved regions, degenerate primers have been designed and used to study defense mechanisms and to clone resistance genes. In this study, five pairs of degenerate RGA primers were used to detect genetic and resistance gene diversities in 30 local and foreign wheat cultivars. Results indicated sharp banding of PCR products in denaturing polyacrylamide gels electroforesed for 2-2.5 hrs at 1600 Volts in 400x400x0.4 mm apparatus. Totally 1486 bands with 33-42% polymorphism were detected.The local cultivars were clustered in a separate cluster. In the cluster of local cultivars, the position of each cultivar was related to its pedigree. Within the dendrogram, the most susceptible cultivars to yellow rust clustered together. The results indicate efficiency of RGA approach to study combined diversity of genetic candidate resistance genes. The analysis of the data is however somewhat complicated, due to the participation of two different properties in the clustering.

The simple, rapid and highly sensitive diagnosis of plant viruses using minimum plant material is a key element of virus free nuclear seed production in potato. Here we report a comparison of the efficiency of double antibody sandwich ELISA(DAS-ELISA) and nitrocellulose membrane ELISA (NCM-ELISA) methods for diagnosis of single and multiple infections of four important potato viruses (PLRV, PVY, PVA and PVS) in samples suspected of being virus infected. Out of 150 samples tested by DAS-ELISA method, PLRV, PVY, PVA and PVS were detected in 14, 56, 61 and 38 samples, respectively, while with NCM-ELISA these numbers were 8, 49, 59 and 33 respectively. In general 46% of infected plants had only one virus and 54% showed multiple infection from which 88% were infected with two viruses. Number of plants tested positive in the leaf tissue using DAS-ELISA was higher than that by NCM-ELISA. DAS-ELISA required 0.2 gram of leaf tissue, while NCMELISA required less than 0.1 garm of tissue .Therefore NCM-ELISA test was more suitable for virus diagnosis of small plantlets in the tissue culture and DAS-ELISA technique was suitable for diagnosis of virus infection in the greenhouse and field grown plants.

Root rots are important diseases in bean growing regions of the world including Iran. In 2007, prevalence of root rot pathogens and yield losses to the disease on common bean were studied under environmental conditions in Zanjan province. In general, the mean disease incidence (DI) and mean frequency of root rot pathogens isolated from root samples increased over the sampling time, from V3 to R9 growth stage, regardless of field location.Fusarium solani was the predominant fungus isolated from 54.2% of samples over the sampling time in 13 fields followed by Rhizoctonia solani (45.9%), Macrophomina phaseolina (26.5%) and F. oxysporum (9.4%). At the last sampling time, DI ranged from 4.7 to 95.3%, whereas the greatest mean values for disease index (DX) and severity (DS) were 29.2 and 2, respectively. Regression analyses demonstrated that each unites increase in DI, DS and DX reduced the number of pods by 0.1, 3.5 and 0.2, and seeds by 0.3, 12.4 and 0.7 per bean plant, respectively. Despite the weak correlation between DX and yield (g/m2), seed yield reduced by 5.8 (0.6%) and 275 (26.7%) g/m2 per DI and DS unite increase, respectively.Seed yield decreased by 30.5 (0.8%), 1241 (32.3%) and 68.7 (2%) no/m2 for each unite increase in DI, DS and DX, respectively. In general, yield loss averaged 10.8% pod no/plant and 12.1% seed no/plant or yield (no/m2) due to mean DX in the fields. DX was positively correlated with 100-seed weight irrespective of cultivar. Relations obtained between DX and yield components, particularly Pod no/Plant = 11.263 – 0.2021 DX and Yield (seed no/m2) = 3407 – 68.7 DX, may contribute to the future estimation of bean yield losses to root rots and selection for resistant cultivars.

In 2004, an unknown disease was found in a number of canola fields in South Australia. Symptoms, light brown spots with a yellow halo and a diffuse dark brown border, appeared on leaves, stems and pods but were more common on older leaves. On potato dextrose agar, the fungus produced dark green-brown mycelium, conidiophores 5 mm wide, conidia with 3 transverse septa and 1-3 vertical septa, 33-42×24-27 mm, and ascospores yellow brown, 7-septate, 33-36×13-15 mm. The morphology of the fungus isolated from spots on leaves, stems and pods was consistent with Stemphylium botryosum (Booth and Pirozynski, CMI no. 150, 1967) associated with the sexual state of Pleospora herbarum. The identification was confirmed by the Orange Agricultural Institute, NSW, Australia (accession number DAR 77420). For pathogenicity testing, conidial suspension (104 conidia/mL) of S. botryosum cultured on PDA was sprayed onto potted seedlings of canola until run off.After 6 days, leaf spots were evident and S. botryosum was re-isolated from the inoculated plants. Although S. botryosum is known to infect numerous crops worldwide, this is the first report of S. botryosum infecting Brassica napus.

During the 2006-2007 growing seasons, several cultivated plants infected by powdery mildews were collected from Yazd Province, Central Iran. The following references were used for identification of fungal specimens (Branu 1987, A monograph of the Erysiphales; Braun & Takamatsu, Schlectendalia 4: 1-33). This report documents the following noteworthy species which are new findings for Iranian funga.- Golovinomyces orontii (Castagne) V.P. Heluta, on Helianthus annuus L., Ardakan, October 2006. The fungus formed the following anamorphic features on the host: hyphae were ectophytic on the whole parts of flower heads specially, lower part. Conidiophores were long, often curved in the basal part. Conidia formed short chains and measured 27.5-42.5x10-17.5 mm. The teleomorph was lacking. This is the first report of G. orontii on H. annuus in Iran.- Phyllactinia babayanii Simonyan, on Prunus dulcis (Mill.) D.A. Web., Taft, autumn of 2004 and Abrkuh, 19 November 2006. In the specimen collected from Taft, only the anamorph was present. Dense and persistent vegetative hyphae grew superficially on the lower surface of the infected leaves. Conidia were clavate and measured 55-80x17.5-22.5 mm. In the specimen collected from Abrkuh mature ascocarps were found. Chasmothecia 256-324 mm in diameter, with equatorial appendages up to 450 mm long, which were stiff and apically pointed and had bulbous base. Asci numerous, 82.5-97.5x35-42.5 mm, and each containing 2 acospores.Ascospores were ellipsoidal or ovoid and 30-42.5x17.5-25 mm.- Podosphaera xanthii (Castagne) U. Braun & Shishkoff, on Cucumis sativus, Agricultural Research campus of Yazd province, 13 November 2006. Disease symptom and signs included chlorotic and necrotic areas on both sides of affected leaves with conspicuous white to gray masses of conidia and mycelia. Conidia with fibrosin bodies, measured 25-35 x 12.5-17.5 mm and formed in chains. The teleomorph was absent. Fungal morphological features and the host matched the features characteristics of P. xanthii (Braun et al. 2001. Schlechtendalia 7: 50).- Podosphaera pannosa (Wallr.) de Bary, on Eucalyptus sp., around the Yazd, spring of 2007; on Prunus dulcis, Taft, Aliabad, 16 February 2007. Diseased leaves of Eucalyptus displayed localized, chlorotic to violet regions with typical powdery mildew signs consisting of whitish masses of conidia and conidiophores. Conidiophores with conidial chains and ellipsoid-ovoid to doliiform conidia. Conidia had fibrosin bodies and measured 20-30x12-18 mm. Pannose mycelium was not observed on the Eucalyptus leaves however, other anamorphic features fitted well with those of P. pannosa (Branu 1987, A monograph of the Erysiphales). This is the first report of P. pannosa on Eucalyptus in Iran. In addition to Eucalyptus we also found P. pannosa on P. dulcis at investigated area. Primary and secondary mycelia were present on leaves and stems of infected plant. Mature ascocarps were found on plant stems. Chasmotecia were 80-94x60-72 mm in diameter. There was a single ascus per ascocarp with 8 ellipsoidal ascospore measured 20-27.5x12.5-15 mm. This is also the first report of P. pannosa on P. dulcis in Iran.- Erysiphe cruciferarum Opiz ex L. Junell, on Brassica napus L., Mohammad Abad and Sanij area, June 2007. Sign of the fungus included white mycelium consisting of hyphae and conidiophores bearing single conidia on both sides of the leaves, stems and on pods. Conidia were cylindrical to cylindric-doliiform, 25-45x10-17 mm. The teleomorph was absent. It seems this is the first report of E. cruciferarum on B. napus in Iran. Voucher specimens of all above mentioned fungi were deposited in the Fungus Collection of the Ministry of Jihad-e Agriculture (IRAN).

A destructive disease was observed in 2003 on Mazafati date palms in Golgeh-e-Chah Hashem (Iranshahr, Bluchestan). Affected plant tissues the from heart and rachis sectors were suspended in distilled water and streaked onto PDA and NA media. Plates were incubated at 28oC for 48 h. Milky color colonies were consistently isolated on PDA. Discrete colonies characterization tests. Eleven isolates were used in the identifying experiments, 7 from rotten heart and 4 from leaf rachis end were used for identification tests. Cultures on PDA were subjected to morphological and biochemical tests. Colonies were umbonate with undulate margins (fried-egg shape). The bacterium grew at 36oC and in 6% NaCl and YDC media.The bacterium was negative for urease and oxydase activity. Glucose, trehalose, celobiose, maltose and lactose were used. Tests for indol production, H2S from cystein, acetoin, pectat degradation and production of gas from glucose, gelatin liquefaction, nitrate production and phosphatase were positive. Hypersensitivite reaction on tobacco was positive. The bacterial isolates from date palm were identified as Erwinia chrysanthemi. This is the first report of this bacterium in Iran. This bacterium has been reported as the causal agent of sudden decline disease on date palm in Saudi Arabia by M.Y. abdallah in 2001 (Plant Dis. 85: 24-26).