IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2015 | Volume:51 | Issue:3|Papers Count:13

Beet necrotic yellow vein virus (BNYVV, Benyvirus) is an economically important soil borne pathogen of sugar beet throughout the world. It is a multipartite virus in which RNA-3 encoded p25 protein controls disease symptoms in sugar beet. Under certain conditions, resistance-breaking variants are generated by amino acid changes at positions 67 and 68 in p25. In the present study p25 protein in three populations of the virus from Moghan, Lorestan and Fars were analyzed in susceptible and resistant sugar beet cultivars. Lorestan and Fars populations were serially passaged through resistant or susceptible sugar beet cultivars for 4 generations and p25 was monitored for possible amino acid changes. No significant amino acid changes were observed when the populations were passaged through susceptible cultivars. However, passage of the populations through resistant cultivars resulted in changes of amino acids at positions 30, 49, 67, 68, 129, 163 and 198. Changes were more frequent in position 67 in the tetrad amino acids. Biotype P of BNYVV which was found in Moghan and Lorestan may have appeared as a result of selection under pressure of resistant cultivars. Information on certain evolutionary parameters and motifs of p25 is included.

Fungi belonging to the genus Trichoderma are one of the most effective biocontrol agents of plant diseases. Because of importance of Trichoderma strains in agriculture and lack of information about their ecology and population dynamics in natural habitats in Iran, we studied seasonal changes of Trichoderma spp. populations and its relation to microbial competition and environmental factors (soil moisture, pH, EC, organic matter as well as precipitation and temperature). Three rice fields in North of Iran (Amol, Mazandaran province) were selected and sampling was performed monthly for one year at 15 cm soil depth. All microorganisms were isolated with dilution plate method, using general and selective media. Trichoderma, total fungi and bacterial populations in paddy soils ranged 1.1´101-11´103, 1.7´103-3.1´104 and 2.2´104-6.5´105 cfu/g soil, respectively. Highest Trichoderma population was recorded in late spring and during autumn for all fields, while, population was decreased in winter. According to the multiple linear regression analysis results, there was positive correlation between Trichoderma populations and soil moisture and electrical conductivity, and negative correlation with total fungal count (P=0.01). There was no significant correlation between Trichoderma populations and other factors.

In nature, plants are exploited by a plethora of microbes species that can cause severe diseases or establish beneficial relationships with them and improve plant growth or help the plant to overcome biotic or abiotic stresses. Trichoderma and fluorescent pseudomonads are the most useful beneficial microbes. In this study, the effects of Trichoderma harzianum Tr6, Pseudomonas sp. Ps14 and their combination, which isolated from cucumber rhizosphere and were able to induce resistance on cucumber, were evaluated on cucumber immune system by evaluation of defense gene expression. The results showed that expression of b-1, 3- glucanase and chitinase transiently increased after inoculation with both microbes. The transient increase of expression of PR1 and LOX1 was observed after inoculation with Tr6 and its combination with Ps14, whereas only LOX1 was increased after inoculation with Ps14. These findings indicate that the plant defense system was activated against beneficial microbes but later these microbes actively suppress the immune system of plants to establish a mutualistic interaction.

In order to taxonomic investigation on Valsa sordida, the causal agent of canker disease on trees, 125 infected plant specimens were collected from Golestan Province. Based on morphological features, among obtained 49 fungal isolates, 35 isolates were identified as V. sordida. Moreover, asexual morphological characteristics of 12 isolates were nearly similar to C. chrysosperma and named as Cytospora sp.1. Also, morphological characteristics of an isolate (from Populus deltoides) was almost similar to V. sordida and named as Valsa sp.1. Finally, morphological characteristics of an isolate (from Ficus elastica) was different from C. chrysosperma and was near to Cytospora ribis and considered as Cytospora sp.2. To investigate the phylogeny of selected isolates, nucleotide sequence of ITS1-5.8S-ITS2 regions from nuclear ribosomal DNA (rDNA) were determined in 14 isolates (five isolates of C. chrysosperma, seven isolates of Cytospora sp.1, one isolate of Valsa sp.1 and one isolate of Cytospora sp.2), and were used along with 32 related sequences from GenBank (NCBI). The results of molecular grouping confirmed the morphological diversity in the isolates.

Root knot nematodes are one of the most important plant parasitic nematodes with worldwide distribution and wide host range. Regarding to the hazards of synthetic chemicals, this is necessary to use other measures, such as biological control. In some studies, the separate, as well as the combined effects of two biocontrol agents, Metarhizium anisopliae and Pseudomonas fluorescens CHA0, on Meloidogyne incognita were studied. In a laboratory test, it has been showed that there is no non-volatile inhibitory effect of P. fluorescens CHA0 on M. anisopliae. In case of In vitro assay of culture filtrate and suspension of both biocontrol agents, the mixture of culture filtrates and culture filtrate of the bacterium caused about 95% and 80% larval mortality, respectively. Maximum inhibitory in egg hatch (93-98%) observed in those treatments in which culture filtrate of one or two agents were included. In the experiment that was designed to compare the application methods, the growth factors of tomato plants considerably increased and the nematoderelated factors considerably decreased, in those M. anisopliae spore suspension were applied as soil drench. Soil drench of the trade formulation of M. anisopliae to the soil and foliar spray of P. fluorescens CHA0, improved the plant-related factors and decreased up to 30% of gall formation and up to 75% of reproduction factor. This is the first report of nematicidal effect of M. anisopliae on M. incognita.

Species belonging to the genus Populus are widely used for log production, landscape design, and windbreak plantations. Septoria spp. are the most prevalent fungi causing leaf spot on poplars, which is one of the most damaging foliar diseases of these trees. However, identification of species belonging to this genus through morphological analysis is often problematic. The present work aimed to identify Septoria spp. causing leaf spot disease on poplars in East Azarbaijan, West Azerbaijan and Ardabil Provinces by using species specific primers as well as morphological features. Primers have been designed based on nr ITS rDNA sequences of S. populi and S. populicola. For this purpose, during summer 2013 symptomatic leaves were sampled from poplars in these regions, and pure cultures of isolates belonging to the genus Septoria were established. Genomic DNA of the isolates was extracted using CTAB method, and efficacy of the primers in identification of causative agent (s) of the disease was evaluated. With species-specific primer set of S. populicola we failed to obtain specific amplification products (329 bp). Species-specific primer set of S. populi, however, amplified a 439 bp fragment of all Septoria isolates. Hence, the results revealed S. populi as the only causal agent of Septoria leaf spot disease of poplars in these regions. Finally, on the basis of pathogenicity test all chosen strain caused disease on popular leaves.

Bean common mosaic virus (BCMV), Bean common mosaic necrosis virus (BCMNV) and Cucumber mosaic virus (CMV) are seed-borne viruses in beans causing severe damage and reduction of yield and quality of this crop. Since there are lots of reports on the occurrence of mixed infection of BCMV, BCMNV and CMV, thus setting up an accurate, reliable and rapid method for detecting of these viruses in bean crops could play an important role in prevention of their spread and damages and also screening of healthy plants. For this purpose, in the present study, we tried to set up a multiplex RT-PCR for simultaneous detection of BCMV, BCMNV and CMV as well as an internal control gene, 18S rRNA. To do this end, the infection of bean plants to above mentioned viruses was confirmed by DAC-ELISA. Following total RNA extraction, cDNA was synthesized using random hexamer primers. cDNA fragments were successfully amplified using specific primers in expected sizes as almost 470 bp for BCMV, 500bp for internal control, 704 bp for BCMNV and 870 bp for CMV, respectively. The results of this study showed that this method is capable of detecting BCMV, BCMNV and CMV in 100 ng of total RNA.

Phytophthora drechsleri Tucker which earlier was considered to be responsible for cucurbit root rot in various parts of the world including Iran is similar to P. melonis Katsura in terms of morphology and and temperature requirement. The objective of the present study was to compare pathogenicity and reaction of both species on 87 species and vareties of cucurbits including cantaloupe, long melon, cucumber, watermelon, squashes and pumpkin. Two month old cucurbit seedlings were inoculated with 4-6 week old inoculum of both species grown on vermiculate supplemented with hemp seed extract and evaluated after two months under green house conditions. The result showed that none of the cucurbit species infected with P. drechsleri and indicated that P. melonis is one of the major cucurbit root rot in Iran. The reaction of cucurbit species and cultivars showed that cantaloupeis the most susceptible host to P. melonis. Long melon and cucumber were less susceptible cucurbita species and watermelon was more resistant than other cucurbits used.

Powdery mildew is an important disease in the fields and greenhouse-grown tomatoes in the world. Leveillula taurica has been reported as only tomato powdery mildew causal agent in Iran. During study on Erysiphaceae in Ardabil province, tomato leaves with powdery mildew symptoms in one greenhouse in Ardabil city were collected and isolates were identified based on morphological characteristics. Moreover, total DNA was extracted with Chelex 5% method and the ITS region of rDNA were amplified and sequenced using ITS1 and ITS4 primers. According to morphological and molecular characteristics, the fungus identified as Pseudoidium neolycopersici. Thus, this species reported for the first time as powdery mildew on Lycopersicon esculentum in Iran. P. neolycopersici is one of important causal agents of tomato powdery mildew in the world and its occurrence is a new treat on tomato culture in Iran.

Traditionally, in suburbs of Tabriz city, northwest Iran (GPS 38o 06’N, 46o 15’E, mean temperature of 6.6-20.0o C, sandy loam soil type), different types of vegetables including cabbages have been cultivated for many years. The cabbage cyst nematode, Heterodera cruciferae was reported as one of the plant parasitic nematodes infecting kohlrabi (Brassica oleracea L. var. gongylodes) and white cabbage (Brassica oleracea L. var. captita alba) in the region. Besides these plants, brussels sprouts, cauliflower, broccoli, radish and Alyssum maritimum, Crambe maritime, Cheiranthus allionii, C. cheiri, Iberis umbellate, Lepidium sativum, Raphanus sativus, Sinapis alba, Lamium album, L. purpureum, Stachysannua, Alyssum montanum, Lunaria annua, Moricandia arvensis and M. sonchifolia, carrot, pea, potato, sweet sop (Annonas quamosa), sugar beet and garden beet, are known as hosts of the H. cruciferae worldwide.During a study on the life cycle of cabbage cyst nematode on its main hosts in the region, 2012-2013, several vegetable crops and different weeds were sampled and checked for the possibility of infection with the cyst nematode. The roots of the plants were stained using lactoglycerin-acid fuchsin solution, examined under stereomicroscope and different developmental stages of the nematode monitored. The morphological and morphometric characters of cysts were determined. As a result, the plants Coriander (Coriandrum sativum L., Umbelliferae), Sonchus (Sonchus asper (L.) Hill., Asteraceae) and Sisymbrium loeselii L. Brassicaceae were found as naturally infected hosts of the cabbage cyst nematode (Fig 1) and herein are reported as new hosts of H. cruciferae. According to available literature, there is no previous documentation of these plants as hosts of the nematode. Other plants such as Chenopodium album, Raphanus sativus and Lepidium sativum found that are infected by the cabbage cyst nematode in the area, too.

Septoriosis is one of the most important disease in pistachio tree worldwide and is incited by several species of Septoria among which S. pistacina islimited to Mediterranea regions and recently reported on Pistacia vera in Golestan province of Iran (Aghajani et al. 2009. Austr. Plant Dis. Notes 4: 29-31). Leaf samples of P. vera from Ghazvin (Fig. 1) collected in October 2013, and samples from P. mutica (Baneh) (Fig. 2) collected also in October 2009 from Darab in Fars province showed various sizes of discolored leaf spots with many pycnidia embedded in leaf tissue extruding dark cirri. Pycnidiospores were filiform, curved, hyaline with one septum measuring 2.5´30 mm in Ghazvin and 2.5´31.6 mm from Darab samples. Single spore conidia from both locations exhibited yeast like growth on PDA. Based on morphological and growth pattern and host the fungus was identified as Septoria pistacina (Chitzandis 1956. Anna. Inst.Phyto. Ben. 10: 29-44). The species has recently been proposed to be transferred to Pseudocercospora pistacina (Crous et al. 2013. IMA Fungus 4: 187-199) which needs further support. Pycnidiospores from P. mutica samples maintained low germination after 4 years in dry leaf under laboratory conditions. This is the first report on the presence of the fungus in Ghazvin on P. vera and based on available information for the first time on P. mutica in world.