IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2016 | Volume:52 | Issue:2|Papers Count:12

Turnip mosaic virus(TuMV) is one of the most prevalent viruses of canola fields in Iran. Use of resistant varieties is the best recommended manner to control losses caused by TuMV. In this research, the reaction of 11 commercial varieties and two lines of canola (Brassica napus L.) was investigated against a Netherland TuMV isolate under greenhouse condition. The seedlings were inoculated using TuMV-infected tobacco (Nicotiana benthamiana) sap at 3-5 leaf stage and their reaction was evaluated based on symptom severity index and ELISA OD405 values at four and the mean values of fresh and dry weights of plants at seven weeks after inoculation. This study was performed in a factorial experiment and randomized complete block design with three replications and each repeat involved four experimental units for each group of inoculated and uninoculated plants. Virus-infection was confirmed by RT-PCR. In accordance with evaluated parameters, reaction of varieties to the virus was significantly different. At probability level of 5%, Karaj3 was tolerant while Karaj2 was the most susceptible, RGS003 and Karaj1 were susceptible and the rest of canola varieties/lines were moderately susceptible to TuMV. Difference of OD405 values in ELISA was meaningless among inoculated plants of canola varieties/lines. Among canola varieties/lines, only fresh and dry weights of Karaj2 line was reduced significantly in virus-infected plants. The scoring system (0 to 8) for the symptoms severity of TuMV in canola was introduced for the first time in this research.

Among plant-parasitic nematodes collected from fields, orchards, meadows and grasslands of the primarily seven southern provinces of the countryviz. Fars, Sistan and Baluchistan, Hormozgan, Khuzestan, Kohgiloyeh and Boyer-Ahmad, Kerman and Bushehr; 13 species of the subfamily Telotylenchinae of the genera Bitylenchus, Neodolichorhynchus, Paratrophurus, Trophurus and Tylenchorhynchus were identified morphologically. Three species, N. phaseoli, Trophurus impar and Tylenchorhynchus qasimii, are new records for Iranian nematofauna. Description, morphometric data and line drawings provided for the above three species, as well as three other poorly known telotylenchids in Iran. Furthermore, Tylenchorhynchus variannus considered as a junior synonym of T. clarus here.

In order to identify the plant parasitic nematodes of the families Dolichodoridae and Pratylenchidae (Nematoda: Tylenchomorpha) collected from green space and gardens in Shiraz, Iran, 67 soil and root samples were collected from different localities of the region during 2014-2015. The nematodes were extracted, fixed and transferred to glycerin according to the De Grisse method. The permanent slides were prepared from the extracted nematodes and studied by light microscope. In this study 15 species namely Amplimerlinius globigerus, Merlinius brevidens, Trophurus pakendorfi, Tylenchorhynchus clarus, T. dubius, T. iphilus, T. mashhoodi, T. teeni, Pratylenchus ekrami, P. thornei, P. unzenensis, Zygotylenchus guevarai, Helicotylenchus digonicus, H. pseudorobustus and Rotylenchus buxophilus were identified. The species T. pakendorfi, T. iphilus and P. ekrami as new records of Iranian nematode fauna, along with P. unzenensis are redescribed.

Canker is one of the most damaging diseases of stone fruit trees which incites depressed brown to black lesions, often accompanied by exudation of gum, on twigs, branches and trunk of affected trees. The disease has been reported from different areas of Iran and shown to becaused by Pseudomonas syringae pv. Syringaea few case by Xanthomonas arboricola pv. pruni. To assess the distribution of the causal organisms samples were taken from fruit orchards in these regions. The stem tissues with canker symptoms were surface-disinfected in sodium hypochlorite, washed with sterile distilled water minced in drops of SDW. The suspension was plated on sucrose nutrient agar. The predominant colonies appearing on SNA were grayish-white, round and pasty. Representative isolates were tested for pathogenicity on peach seedling. Genomic DNA was extracted and a fragment of the 26S rRNA of the representative isolates was amplified by PCR and sequenced. The nucleotide sequence of 26S rRNA gene of the representative isolates showed high homology with sequences of Cryptococcus species. Comparison of their sequences with those deposited in GenBank. Also 27 isolates along with reference strains of Cryptococcus adeliensis and C. magnus were genetically characterized by using ERIC, REP, and BOXAIR primers in PCR. Cluster analysis was performed using NTSYS program. The isolates were separated into 11 genotypic groups by the concatenated data of rep-PCR at 33 % similarity level. The results demonstrated the existence of a considerable genetic diversity among isolates causing canker of stone fruit trees in the central provinces of Iran.

The new emergining charcol rot disease of oak is a seirous threat for oak forestes in Iran. Biscogniauxia mediterranea has been determind as the cause of charcoal rot disease on oak, in Zagros region. However, there is no data available on the incidence of this disease in Arasbaran forests. With this research, we aimed to detect the causal agent of charcoal disease in the Hatam-Baig and Kaleibar regions in Arasbaran forests, Iran. Towards this aim, samples were collected from truck and branches of oak trees with dieback and decline symptoms as well as healthy oak trees in the region during June and September 2014. In total 14 isolates belonging to the genus Biscogniauxia were recovered from symptomatic and healthy oak trees. The isolates were identified as B. mediterranea using previously designed species-specific primer set for the ITS-rDNA region. Asexual morph of the species was developed on MEA culture medium. Sexual structures were not observed under natural conditions and efforts made to induce the sexual structures of the species in laboratory conditions were unsuccessful. The results of pathogenicity assay on two-years oak trees (Quercus macranthera), revealed that all of the isolates tested in this study were pathogenic under greenhouse conditions. This is first report on the detection of charcoal rot disease of oak trees and identification of the causal agent in Arasbaran forests.

Potato cyst nematode, Globodera rostochiensis was reported from potato fields of Bahar County in Hamadan Province in 2008. In order to determine the pathotype of potato cyst nematode, ten populations of potato cyst nematode were collected from different potato fields in Bahar regions. Species identification was based on the morphological and morphometric characters of second stage juveniles and cysts, and by using species-specific primers and nucleotide sequences of the D2-D3 expansion segments of the 28S rRNA gene. Four potato cultivars viz Désirée, Marfona, Sante and Agria were used for pathotype determination, in pot experiments. The plants were treated by 6±1 eggs and second stage juveniles and maintained in growth chambers at 18-22oC for three months. Based on the results of resistance assessment and relative susceptibility of the tested cultivars the pathotype of the populations was determined as Ro1. The obtained sequences were compared through BLAST search from the NCBI and the phylogenic tree was depicted. The impact of susceptible cultivars Marfona, Désirée, resistant cultivars sante, and Agria on egg hatching indicated that there is no significant difference among the cultivars in most pot experiments and all the cultivars were placed in the same statistical groups.

Wheat rusts including stripe and stem rusts are the most important fungal diseases in the world and Iran as frequently causes natural epidemics and significant yield loses due to rapid development of new races in life cycle resulted from mutation or sexual recombination. In this research, distribution and genetic diversity of aecial infection on barberry bushes and their relation to wheat yellow rust was studied. A total of 95 samples of infected leaves to aecial stage on barberry bushes were collected from Borujerd, Dorud, Azna and Aligudarz regions. To identify the rust species, in vivo and in vitro pathogenicity test were conducted by artificial inoculation of wheat seedlings using collected aeciospores from each region. The results showed the production of urediniospores of P. striiformis f. sp. tritici (yellow rust) as well as P. graminis f. sp. tritici (black rust) in inoculated wheat seedlings. Molecular detection and sequencing of the rDNA regions of representative aecial isolates on Barberry were done. Genetic diversity of 134 aecial isolates was also studied by amplification of IGS1-rDNA region. The Results also confirmed the pathogenicity test and showed that barberry could be the aecial host of yellow and black rusts in Lorestan province. The IGS-rDNA amplification of aecial isolates from Azna and Aligudarz showed most a production of three bands with a frequency of 15 and 21 isolates respectively. In Dorud samples was with five bands (26 isolates) as well as in Broujerd samples with two bands (10 isolates) in which showed a genetic variation among aecial isolates collected from sampling regions in Lorestan province.

To investigate the causes of the spot disorders on fruits, random sampling was performed on trees of Red Delicious and Golden Delicious in two regions of Semirom and Padena, Iran. Concentration of minerals (calcium, potassium, magnesium and nitrogen) were determined in a compound sample for each garden and analyzed in an unbalanced complete randomized design. Results showed that fruits with symptoms for Red Delicious have only calcium deficiency, while for Golden Delicious both deficiency and excess calcium had found. Regarding erratic changes in the samplings, three orthogonal contrasts (including treatment groups: cultivars, regions and symptoms presence) were evaluated. The results showed that Red Delicious cultivar is more susceptible than Golden Delicious and Padena region is more favorable for occurrence of calcium disorders than Semirom region. Orthogonal contrasts between treatments with and without symptoms, showed significant differences for ratios of K+/Ca2+, (K++Mg2+) /Ca2+and (N+K++Mg2+) /Ca2+. Therefore, the disorder has negative relation with potassium content and K+/Ca2+ratio and positive relation with calcium content in the fruit. The research showed that occurance of calcium disorders in apple orchards of Semirom region were related to wheather changes and overuse of some minerals.

Field surveys were conducted to detect the incidence of viruses in major vegetable fruit growing areas in west and northwest of Iran. A total of 100 leaf samples from various vegetable fruit crops were analyzed for Cucumber mosaic virus(CMV), Cucumber green mottle mosaic virus (CGMMV), Watermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV) by RT-PCR using specific primers for each virus. Among the collected samples, the highest incidence was for CMV (46%), followed by ZYMV (35%), WMV (26%) and CGMMV (8%). Overall, 63.3%, 50%, 40%, 90%, 75% and 80% of green bean, cucumber, eggplant, squash, tomato and watermelon samples, respectively, were positive for at least one virus. CMV, ZYMV and WMV were identified in most regions, whereas CGMMV was found only in East Azerbaijan province. Mixed infections of two and three viruses in various combinations were detected in 30 and 8 samples, respectively. Restriction analysis with Msp I (Hpa II) on 13 PCR products of CMV coat protein revealed a previously described CMV subgroup I (S-I) specific profile (537 and 335 bp fragments) for the isolates. To the best of our knowledge, this is the first report of WMV and ZYMV from watermelon, tomato, eggplant and green bean in the West and Northwest regions of Iran and first report of ZYMV infecting green bean (Phaseolus vulgaris L.) in Iran.

Phytophthora root and crown rot caused by various species Phytophthora are the major threat to agricultural crops in Iran. Phytophthora melonis and P. capsici are reported on cucurbits in Iran but major species in cucurbits considered to be P.melonis and the importance of P.capsici in cucurbits has not been much investigated. In the present study the reactions of different cucurbits were compared to both species under greenhouse conditions. Two months old of 36 cucurbit species and cultivars were inoculated with vermiculite hempseed extract inoculums. The production of zoospore in drained water and reactions of cultivars were monitored during two months after inoculation. The results showed that cantaloupe and long melon were more susceptible to P. melonis and reacted differently to P.capsici. Pumpkin was resistant to both species but squash and water melon were more susceptible to P.capsici than P. melonis.

The root lesion nematode tea, Pratylenchus loosi, is currently the most important damage-causing factor of tea in Iran and all over the world. This nematode is considered as the most damage-causing factor of tea in many tea-producing countries including Sri Lanka, China, India, Japan and Bngladesh. In recent years, it’s also considered as a key disease and damage-causing of tea that cause to severe damage to tea shrubs, so that the growth of infected plants has been decreased and because of inability in creating the new branches and leaves, yield loss is severe. Tea plant is the host of this nematode and in addition to tea, it has been reported in the weed of forest millet, citrus and cherry in Iran, while citrus, apple, pear, grass and several species of weed are considered as its host in the world. This nematode has been reported from strawberry in Sri Lanka and this plant has been introduced as weak host. In order to investigation of host range of this nematode, a study is conducted in Iranian tea Research Institute in 2013. Tree Tonka (Dipteryx odorata), has been imported as shade tree and cultivated in tea farm margins in some areas. In second half of 2013, symptoms of nematode infection on shade trees were observed in Shahid-Eslami tea farm placed in Iranian tea research institute. After sampling the soil and root of this tree, extraction of nematodes from root was done using conventional methods. After investigation of morphological and morphometric characters using scientific authorized references, isolated nematode species from root was diagnosed as Pratylenchus loosi. Loof, 1960.The mentioned nematode population was counted in average of one hundred grams of soil as 30 nematodes and in 30 grams of root as 210 nematodes in February 2014. It is the first report of Tonka plant as a host (D. odorata) to P. loosi in the world. Considering the permanent Tonka tree, its role is crucial in survival of root lesion nematode P.loosi in tea farms.